Availableonlineatwww.sciencedirect.com SCIENGE DIRECT PROGRESS IN ENERGYAND COMBUSTION SCIENC ELSEVIER rogress in Energy and Combustion Science 30(2004)545-672 www.elsevier.com/locate/pecs Pulse detonation propulsion: challenges, current status and future perspective G.D. Roy. S.M. Frolov, A.A. Borisov, D W. Netzer Ofice of Naval Research, Ballston Centre Tower 1, Arlington, VA 22217, US N.N. Semenov Institute of Chemical Physics, Moscow, Russia Naval Postgraduate School, Monterey, CA, USA Received I April 2003: accepted 11 May 2004 Available online 27 September 2004 Abstract The paper is focused on recent accomplishments in basic and applied research on pulse detonation engines(PDE)and various PDE design concepts. Current understanding of gas and spray detonations, thermodynamic grounds for detonation-based propulsion, principles of practical implementation of the detonation-based thermodynamic cycle, and various operational constraints of PDEs are discussed c 2004 Published by Elsevier Ltd Keywords: Gaseous and heterogeneous detonation; Pulse detonation engine; Design concepts; Propulsion: Thrust performance Contents 2. Fundam 2.1. Historical review ...549 2.2. Gaseous detonations 552 2. 1. General propertie 2. 2. Detonability limits 559 2. 23. Direct initiation 2.2.5. Nonideal detonations 2.2.6. Transient deflagration and ddt 2.3. Heterogeneous detonations 2.3.1. General properties 2.3. 2. Detonability limits 2.3.3. Direct initiation 594 2.3. 4. Detonation transition 3.5. Nonideal detonations 2.3.6. Transient deflagration and dDt Abbreviations: Al, air inlet; BR, blockage ratio: CJ, Cha cross-section; DC, detonation chamber; dDt, deflagration to detonation transition; FAM, fuel-air mixture(-); HE, hi drogen peroxide; IPN, isopropyl nitrate: IR, infra red; NM Orescence: RFBR. Russian Foundation for Basic researc ean diameter: SwACER, shock wave amplification through coherent release: TEP, thermochemical equilibriu turbojet engine: TNT, trinitrotoluene: ZND, Zel'dovich- Neumann-Doering: 1D, one-dimensional: 2D, two-dimens 0360-1285/S- see front matter o 2004 Published by Elsevier Ltd. doi:10.1016 -pecs.2004.05001
Pulse detonation propulsion: challenges, current status, and future perspective G.D. Roya,*, S.M. Frolovb , A.A. Borisovb , D.W. Netzerc a Office of Naval Research, Ballston Centre Tower 1, Arlington, VA 22217, USA b N.N. Semenov Institute of Chemical Physics, Moscow, Russia c Naval Postgraduate School, Monterey, CA, USA Received 1 April 2003; accepted 11 May 2004 Available online 27 September 2004 Abstract The paper is focused on recent accomplishments in basic and applied research on pulse detonation engines (PDE) and various PDE design concepts. Current understanding of gas and sprary detonations, thermodynamic grounds for detonation-based propulsion, principles of practical implementation of the detonation-based thermodynamic cycle, and various operational constraints of PDEs are discussed. q 2004 Published by Elsevier Ltd. Keywords: Gaseous and heterogeneous detonation; Pulse detonation engine; Design concepts; Propulsion; Thrust performance Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 546 2. Fundamentals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 549 2.1. Historical review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 549 2.2. Gaseous detonations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 552 2.2.1. General properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 552 2.2.2. Detonability limits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 559 2.2.3. Direct initiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 567 2.2.4. Detonation transition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 573 2.2.5. Nonideal detonations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 580 2.2.6. Transient deflagration and DDT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 584 2.3. Heterogeneous detonations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 588 2.3.1. General properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 588 2.3.2. Detonability limits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 591 2.3.3. Direct initiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 594 2.3.4. Detonation transition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 598 2.3.5. Nonideal detonations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 599 2.3.6. Transient deflagration and DDT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 600 0360-1285/$ - see front matter q 2004 Published by Elsevier Ltd. doi:10.1016/j.pecs.2004.05.001 Progress in Energy and Combustion Science 30 (2004) 545–672 www.elsevier.com/locate/pecs * Corresponding author. Tel.: þ1-703-696-4406. Abbreviations: AI, air inlet; BR, blockage ratio; CJ, Chapman-Jouguet; CS, cross-section; DC, detonation chamber; DDT, deflagration to detonation transition; FAM, fuel—air mixture (2); HE, high explosive; HP, hydrogen peroxide; IPN, isopropyl nitrate; IR, infra red; NM, nitromethane; ON, octane number; PDE, pulse detonation engine; PDRE, pulse detonation rocket engine; PLIF, particle laser induced fluorescence; RFBR, Russian Foundation for Basic Research; SMD, sauter mean diameter; SWACER, shock wave amplification through coherent energy release; TEP, thermochemical equilibrium program; TJE, turbojet engine; TNT, trinitrotoluene; ZND, Zel’dovich— Neumann—Doering; 1D, one-dimensional; 2D, two-dimensional; 3D, three-dimensional
546 G.D. Roy et al. Progress in Energy and Combustion Science 30(2004)545-672 2.4. Thermodynamic grounds for detonation cycle 2.5. Implementation of the detonation cycle 2.6. Detonation impulse 2.7. Operational constraints of pulse detonation e 3. 1. Preliminary remarks 3.2. Valved concepts 3.3. Valveless concepts 3. 4. Predetonator concept 3.5. Enchanced DDT concept 3.6. Stratified-charge concept 3.7. Dual-fuel concept 3.8. Shock-booster concept 3.9. Shock-implosion concept 3.10. Pulse-reinitiation concept 3. 11. Pulse-blasting concept 3. 12. Multitube schemes 3. 13. Resonator concept 3. 14. Inlets 3. 15. nozzles 16. Active control 3. 17. Rocket pulse detonation propulsic 4. Concluding remarks References the chamber resulting in a nearly constant-volume heat addition process that produces a high pressure in the The current focus in utilizing detonation for air -breathin combustor and provides the thrust. The operation of multitube propulsion has moved from the long-term studies of the PDE configurations at high detonation-initiation frequency possibility of fuel energy transformation in stabilized oblique(about 100 Hz and over)can produce a near-constant thrust. In detonation waves to investigations and practical development general, the near-constant-volume operational cycle of PDE of propulsion engines operating on propagating detonations in provides a higher thermodynamic efficiency as compared to a pulse mode. Contrary to the oblique-detonation concept that the conventional constant-pressure(Brayton) cycle used in gas is applicable to hypersonic flight at velocities comparable or turbines and ramjets. The advantages of PDE for air-breathing higher than the Chapman-Jouguet(C]) detonation velocity of propulsion are simplicity and easy scaling, reduced fuel the fuel-air mixture(FAM), the concept of pulse detonation consumption, and intrinsic capability of operation from zero engine(PDE) is attractive for both subsonic and supersonic approach stream velocity to high supersonic flight speeds flight with PDE as a main propulsion unit or as an afterburner The global interest in the development of PDE for in turbojet or turbofan propulsion system. In particular, PDE- propulsion has led to numerous studies on detonations, based propulsion is attractive for flight Mach number up to particularly pertaining to its control and confinement. This is about 3-4(see Section 2.4). Within this range of Mach evident from the formation of collaborative teams by number, solid rocket motors are known to be very efficient in iversities and industry worldwide. Dedicated technical terms of simplicity and high-speed capability, but they have a meetings and special minisymposia and sessions on PDE limited powered range. Turbojet and turbofan engines, due to in combustion-related conferences are becoming very popular their high specific impulse, provide longer range and heavie Several reviews have been already presented at various payloads, but at flight Mach number exceeding 2-3 they are meetings [1-10] and published in archival journals [11-13l getting too expensive. Ramjets and ducted rockets designed During the period from 1998 to 2002, the US Office of for flight Mach number up to 4 require solid rocket boosters to Naval Research(ONR)and the Russian Foundation for Basic accelerate them to the ramjet take over speed, which increases Research(rFBR) have jointly sponsored three International the complexity and volume of a propulsion system. Com olloquia on detonations, in particular, those aspects of bined-cycle engines, such as turborockets or turboramjet, are detonations that are directly relevant to the development of also very complex and expensive for similar applications. PDEs. In 1998, the International Colloquium on Advances in In a pde, detonation is initiated in a tube that serves as Experimentation and Computation of Detonations was held the combustor. The detonation wave rapidly traverses in St Petersburg with the participation of more than 60
2.4. Thermodynamic grounds for detonation cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 603 2.5. Implementation of the detonation cycle. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 609 2.6. Detonation impulse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 614 2.7. Operational constraints of pulse detonation engine. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 622 3. Design concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 625 3.1. Preliminary remarks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 625 3.2. Valved concepts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 625 3.3. Valveless concepts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 633 3.4. Predetonator concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 637 3.5. Enchanced DDT concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 639 3.6. Stratified-charge concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 643 3.7. Dual-fuel concept. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 644 3.8. Shock-booster concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 646 3.9. Shock-implosion concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 650 3.10. Pulse-reinitiation concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 651 3.11. Pulse-blasting concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 653 3.12. Multitube schemes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 655 3.13. Resonator concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 657 3.14. Inlets. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 658 3.15. Nozzles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 659 3.16. Active control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 661 3.17. Rocket pulse detonation propulsion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 661 4. Concluding remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 663 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 665 1. Introduction The current focus in utilizing detonation for air-breathing propulsion has moved from the long-term studies of the possibility of fuel energy transformation in stabilized oblique detonation waves to investigations and practical development of propulsion engines operating on propagating detonations in a pulse mode. Contrary to the oblique-detonation concept that is applicable to hypersonic flight at velocities comparable or higher than the Chapman-Jouguet (CJ) detonation velocity of the fuel–air mixture (FAM), the concept of pulse detonation engine (PDE) is attractive for both subsonic and supersonic flight with PDE as a main propulsion unit or as an afterburner in turbojet or turbofan propulsion system. In particular, PDEbased propulsion is attractive for flight Mach number up to about 3–4 (see Section 2.4). Within this range of Mach number, solid rocket motors are known to be very efficient in terms of simplicity and high-speed capability, but they have a limited powered range. Turbojet and turbofan engines, due to their high specific impulse, provide longer range and heavier payloads, but at flight Mach number exceeding 2–3 they are getting too expensive. Ramjets and ducted rockets designed for flight Mach number up to 4 require solid rocket boosters to accelerate them to the ramjet take over speed, which increases the complexity and volume of a propulsion system. Combined-cycle engines, such as turborockets or turboramjets, are also very complex and expensive for similar applications. In a PDE, detonation is initiated in a tube that serves as the combustor. The detonation wave rapidly traverses the chamber resulting in a nearly constant-volume heat addition process that produces a high pressure in the combustor and provides the thrust. The operation of multitube PDE configurations at high detonation-initiation frequency (about 100 Hz and over) can produce a near-constant thrust. In general, the near-constant-volume operational cycle of PDE provides a higher thermodynamic efficiency as compared to the conventional constant-pressure (Brayton) cycle used in gas turbines and ramjets. The advantages of PDE for air-breathing propulsion are simplicity and easy scaling, reduced fuel consumption, and intrinsic capability of operation from zero approach stream velocity to high supersonic flight speeds. The global interest in the development of PDE for propulsion has led to numerous studies on detonations, particularly pertaining to its control and confinement. This is evident from the formation of collaborative teams by universities and industry worldwide. Dedicated technical meetings and special minisymposia and sessions on PDE in combustion-related conferences are becoming very popular. Several reviews have been already presented at various meetings [1–10] and published in archival journals [11–13]. During the period from 1998 to 2002, the US Office of Naval Research (ONR) and the Russian Foundation for Basic Research (RFBR) have jointly sponsored three International colloquia on detonations, in particular, those aspects of detonations that are directly relevant to the development of PDEs. In 1998, the International Colloquium on Advances in Experimentation and Computation of Detonations was held in St Petersburg with the participation of more than 60 546 G.D. Roy et al. / Progress in Energy and Combustion Science 30 (2004) 545–672
G D. Roy et al. Progress in Energy and Combustion Science 30(2004)545-672 universal gas constant aaaA transverse detonation cell size Reynolds number ransverse size of primary detonation cell S entropy ansverse size of secondary detonation cell specific volume mplitude or coefficient tIme T Al, A2, A3 constants emperature b longitudinal detonation cell size U b, longitudinal size of secondary detonation cell voltage velocity speed of sound We Weber number specific heat at constant pressure specific heat at constant volume velocity fluctuation diamete coordinate shock wave, detonation, or flame front velocity P igh nonideal detonation velocity oordinate internal energy Es energy flux oxidizer-to-fuel ratio nergy or activation energy In explosive cross-section area B reaction progress variable specific heat ratio h formation enthalpy interval H flight altitude or total enthalpy function or width/height H mensionless fluctuation of enthalpy dimensionless velocity deficit acceleration of gravity parameter in detonation cell model coefficient momentum flux dimensionless energy loss cycle-averaged specific impulse temperature ratio function mpule at fully filled conditions ecific impulse at fully filled conditions rotation angle umber or dimensionless heat release coefficient of pressure loss in shock wave constants dimensionless distance k kinetic energy dissipation molecular weight dimensionless fluctuation of internal energy geometrical factor stoichiometric coefficient distance s number or nitrogen dilution coefficient nass or temperature exponent hE charge mas cycle-averaged specific thrust n density flow eo liquid density density ratio or normalized deficit of detonation mass flu M velocity Mach number time or dimensionless time reaction order shear stress t dimensionless duration of positive overpressure pressure equivalence ratio P function or cone/wedge angle mass flow rate X thermodynamic efficiency radius cone half-angle dynamic radius molar fraction 2 adius or gas constant transmissibility parameter R
Nomenclature a transverse detonation cell size a1 transverse size of primary detonation cell a2 transverse size of secondary detonation cell A amplitude or coefficient A1; A2; A3 constants b longitudinal detonation cell size b2 longitudinal size of secondary detonation cell B coefficient c speed of sound cp specific heat at constant pressure cv specific heat at constant volume C capacitance d diameter D shock wave, detonation, or flame front velocity D0 nonideal detonation velocity e internal energy Es energy flux E energy or activation energy f frequency F cross-section area h enthalpy h8 formation enthalpy H flight altitude or total enthalpy H0 dimensionless fluctuation of enthalpy g acceleration of gravity Is momentum flux I impulse ~Isp cycle-averaged specific impulse I 0 impulse at fully filled conditions ~I 0 sp specific impulse at fully filled conditions J number or dimensionless heat release k; K constants k0 kinetic energy dissipation K0 dimensionless fluctuation of internal energy L length l distance m mass or temperature exponent mc HE charge mass m_ mass flow ~m_ cycle-averaged mass flow Ms mass flux M Mach number n reaction order N power p pressure P thrust P~ cycle-averaged thrust q heat release Q mass flow rate r radius r dynamic radius R radius or gas constant R8 universal gas constant Re Reynolds number S entropy v specific volume t time T temperature u velocity U voltage w velocity W work We Weber number u0 velocity fluctuation X distance x coordinate Y height y coordinate Greek Symbols a oxidizer-to-fuel ratio an parameter in strong explosion theory b reaction progress variable g specific heat ratio D interval d function or width/height dD dimensionless velocity deficit 1 parameter in detonation cell model z coefficient h dimensionless energy loss q temperature ratio u function urot rotation angle k0 coefficient of pressure loss in shock wave l dimensionless distance m molecular weight n geometrical factor ni stoichiometric coefficient j number or nitrogen dilution coefficient p compression ratio P~ cycle-averaged specific thrust r density r0 l liquid density s density ratio or normalized deficit of detonation velocity t time or dimensionless time tw shear stress t þ dimensionless duration of positive overpressure F equivalence ratio w function or cone/wedge angle f dimensionless kinetic energy dissipation x thermodynamic efficiency y cone half-angle c molar fraction V transmissibility parameter G.D. Roy et al. / Progress in Energy and Combustion Science 30 (2004) 545–672 547
548 G.D. Roy et al. Progress in Energy and Combustion Science 30(2004)545-672 Inaxlmu b back N nitrogen without additive nozzle cell disappearance oxygen cl closed oD overdriven detonation combustion products plateau critical purging D detonation pressure recovery detonation chamber DDT deflagration-to-detonation transition reaction di diffuser inlet reinitiation diffuser exit shock wave stoichiometric nergy release traversing unit area measured wall flame or fuel along z-axis symmetry (1, 2, or 3) A fr fresh reactants turbed ignitin planar induction :98 standard temperature limit 3 spherical experts. In 2000, the International Colloquium on Control of the components in the detonation chamber (DC); (2)low- Detonation Processes was organized in Moscow with more energy source for detonation initiation to provide fast and than 100 participants. The International Colloquium on reliable detonation onset; (3)cooling technique for rapid, Advances in Confined Detonations was held in Moscow in preferably recuperative, heat removal from the walls of 2002 with more than 120 participants. As a result of these to ensure stable operation and avoid premature ignition of meetings, a number of books have been published containing FAM leading to detonation failure; (4) geometry of the extended abstracts of all presentations [14-16] and full combustion chamber to promote detonation initiation and f selected propagation at lowest possible pressure loss and to ensure colloquia [17-19]. The goal of this review paper is to high operation frequency; and (5)control methodology that provide, based primarily on the materials presented at the allows for adaptive, active control of the operation process eetings mentioned above, a text or reference for those who to ensure optimal performance at variable flight conditions, are interested in recent accomplishments in basic and applie while maintaining margin of stability. In addition to the research on PDE and numerous Pde design concepts fundamental issues dealing with the processes in the dC. ented in review meetings and discussed in the literature. there are other issues such as(6)efficient integration of pde In order to use propagating detonations for propulsion with inlets and nozzles to provide high performance; and and realize the pde advantages mentioned above. a number of challenging fundamental and engineering problems has configuration. Among the most challenging engineering yet to be solved. These problems deal basically with low- issues, is the problem of durability of the propulsion system. cost achievement and control of successive detonations in a As the structural components of PdE are subject to repeated propulsion device. To ensure rapid development of a high-frequency shock loading and thermal deformations, a detonation wave within a short cycle time, one needs to considerable wear and tear can be expected within a apply (1)efficient liquid fuel injection and air supply relatively short period of operation. The other problems ystems to provide fast and nearly homogeneous mixing of are noise and vibration
experts. In 2000, the International Colloquium on Control of Detonation Processes was organized in Moscow with more than 100 participants. The International Colloquium on Advances in Confined Detonations was held in Moscow in 2002 with more than 120 participants. As a result of these meetings, a number of books have been published containing extended abstracts of all presentations [14–16] and full edited manuscripts of selected papers presented at the colloquia [17–19]. The goal of this review paper is to provide, based primarily on the materials presented at the meetings mentioned above, a text or reference for those who are interested in recent accomplishments in basic and applied research on PDE and numerous PDE design concepts presented in review meetings and discussed in the literature. In order to use propagating detonations for propulsion and realize the PDE advantages mentioned above, a number of challenging fundamental and engineering problems has yet to be solved. These problems deal basically with lowcost achievement and control of successive detonations in a propulsion device. To ensure rapid development of a detonation wave within a short cycle time, one needs to apply (1) efficient liquid fuel injection and air supply systems to provide fast and nearly homogeneous mixing of the components in the detonation chamber (DC); (2) lowenergy source for detonation initiation to provide fast and reliable detonation onset; (3) cooling technique for rapid, preferably recuperative, heat removal from the walls of DC to ensure stable operation and avoid premature ignition of FAM leading to detonation failure; (4) geometry of the combustion chamber to promote detonation initiation and propagation at lowest possible pressure loss and to ensure high operation frequency; and (5) control methodology that allows for adaptive, active control of the operation process to ensure optimal performance at variable flight conditions, while maintaining margin of stability. In addition to the fundamental issues dealing with the processes in the DC, there are other issues such as (6) efficient integration of PDE with inlets and nozzles to provide high performance; and (7) efficient coupling of DCs in a multitube PDE configuration. Among the most challenging engineering issues, is the problem of durability of the propulsion system. As the structural components of PDE are subject to repeated high-frequency shock loading and thermal deformations, a considerable wear and tear can be expected within a relatively short period of operation. The other problems are noise and vibration. Indices A additive av average b back CJ Chapman-Jouguet c cycle cd cell disappearance cl closed cp combustion products cr critical D detonation DC detonation chamber DDT deflagration-to-detonation transition di diffuser inlet de diffuser exit d droplet e expansion eff effective er energy release ex exhaust exp measured f flame or fuel fd feed fl filling fr fresh reactants hs hot spot i ignition in initiation ind induction l limit m mechanical max maximum min minimum N2 nitrogen na without additive nz nozzle O2 oxygen OD overdriven detonation p plateau pg purging pr pressure recovery R ram r reaction ri reinitiation rz reaction zone s shock wave sp specific st stoichiometric tr traversing ua unit area w wall z along z-axis n symmetry (1, 2, or 3) S total 1 undisturbed 0 initial conditions 1 planar 2 cylindrical 298 standard temperature 3 spherical 548 G.D. Roy et al. / Progress in Energy and Combustion Science 30 (2004) 545–672
G D. Roy et al. / Progress in Energy and Combustion Science 30(2004)545-672 The paper is organized in such a way that the reader first th-explosive charge. Later on it was observed in long tubes gets acquainted with a brief history of detonation research even when gas was ignited by nonexplosive means(spark or Section 2. 1)and with the ci understanding of gas and open flame). In this case, flame acceleration along the tube, spray detonation properties and dynamics(Sections 2.2 and often accompanied with flame speed oscillations, was 2.3). Then, based on this material, thermodynamic grounds detected prior to onset of detonation. The most impressive detonation-based propulsion are discussed in Section findings of those times indicated that the detected detonation 2.4, followed by the principles of practical implementation velocity was independent of the ignition source and tub of the detonation-based thermodynamic cycle in Section 2.5. diameter and was primarily a function of the explosive As the main focus of this paper is the utilization of PDE for mixture composition. The main distinctive feature of propulsion, various performance parameters of PDEs(e.g. detonation was a severe mechanical effect implying the specific impulse, thrust, etc )are discussed in Section 2.6 development of a high pressure in the propagating wave. The Based on the analysis of detonation properties mechanism of detonation propagation has been identified as dynamics, and on the requirements for practical implemen- governed by adiabatic compression of the explosive mixture tation of the pulse-detonation cycle, various operational rather than by molecular diffusion of heat. During those constraints of PDEs are described in Section 2 times, the interest in detonation was basically associated Section 3 provides the reader with a detailed description with explosion prevention in coal mines of various PDe design concepts, including valved and a few years later, based on the shock wave theory of valveless approaches(Sections 3. 2 and 3.3), predetonator Rankine[28]and Hugoniot [29], Mikhelson in 1890[30, 311 concept(Section 3.4), design solutions utilizing enhanced Chapman in 1899[32], and Jouguet in 1904 [33, 34] provided deflagration-to-detonation transition (DDT)(Section 3.5), theoretical estimates for the detonation parameters based on concepts applying stratified fuel distribution in the PDe one-dimensional(ID)flow considerations and mass, momen- combustion chamber(Section 3.6), or using two fuels of tum and energy conservation laws. In their theory, the different detonability (Section 3.7), several novel PDE detonation wave was considered as a pressure discontinuity coupled with the reaction front (instantaneous reaction) (Sections 3.8-3. 10), and the pde concept applying stron ccording to the theory, the detonation products possess eactive shocks rather than detonations(Section 3.11). The density that is almost two-fold higher than the initial mixture PDE concepts described in Sections 3.2-3.10 imply the use density; temperature and pressure that are, respectively, of ducted combustors, either in single-tube or multitube 10-20% and two-fold higher than the corresponding values configuration. Some specific features of multitube PDE of constant-volume explosion; particle velocity that attains a design are discussed in Section 3. 12. Resonator concept of value close to one half of the detonation velocity. Comparison Section 3. 13 is somewhat different as it utilizes the cavity of the theoretical predictions with experimentally observed induced resonant flow oscillations in the combustion detonation velocities showed fairly good agreement. chamber. Problems of integrating inlets and nozzles to the Since the end of the 19uh-the beginning of the 20th century, PDE design are discussed in Sections 3 14 and 3. 15. Some significant progress has been made both in experimentation and ues dealing with control of repeated detonations in a PDE analysis of detonations. In addition to explosion safety issues in are considered in Section 3. 16. The last Section 3. 17 briefly coal mines and pits, other applications surfaced. in particular, describes application of PDEs for rocket propulsion those dealing with new technologies, balloon transportation d reciprocating intermal combustion engines. After the World War l, there was a considerable growth of interest to combustion 2. Fundamentals notive and aircraft engines worth mentioning are the early contributions of Dixon, Nernst, Crussard, Woodbury 2. Historical review Campbell, Bone, Frazer, Egerton, Payman, Laffite, Townsend, and lewis in understanding the mechanism of detonation onset Early attempts to utilize the power obtained from and propagation(see corresponding references in Refs. [35, 36D explosions for propulsion applications date back to late Two principal conditions required for detonation 17th-early 18th centuries and the contributions of Huygens ere observed, namely, (i)formation of a shock wave and Allen are noteworthy. In 1729, Allen proposed a jet tensity sufficient for explosive mixture to autoignite, and propelled ship [20]whose operation is owing to the (i)increase in the local rate of energy release up to the level explosion of gunpowder'in a proper engine placed within a sufficient for shock wave reproduction in the adjacent layer ship. Before this archival contribution, gunpowder was of the explosive mixture Mixture autoignition was often predominantly used in artillery for destructive purposes detected ahead of the accelerating flame giving rise to blast First exposure of gaseous detonations dates back to waves propagating downstream and upstream. The former 1870-1883 period when Berthelot and Vieille [21-251, and blast wave was attributed to detonation and the latter was Mallard and Le Chatelier [26, 27] discovered a combustion called retonation. Apart from gasdynamic models of mode propagating at a velocity ranging from 1. 5 to 2.5 km/s. detonation, there were attempts to develop models based This combustion mode arose when gas was ignited with on the molecular mechanism of energy transfer in
The paper is organized in such a way that the reader first gets acquainted with a brief history of detonation research (Section 2.1) and with the current understanding of gas and spray detonation properties and dynamics (Sections 2.2 and 2.3). Then, based on this material, thermodynamic grounds for detonation-based propulsion are discussed in Section 2.4, followed by the principles of practical implementation of the detonation-based thermodynamic cycle in Section 2.5. As the main focus of this paper is the utilization of PDE for propulsion, various performance parameters of PDEs (e.g. specific impulse, thrust, etc.) are discussed in Section 2.6. Based on the analysis of detonation properties and dynamics, and on the requirements for practical implementation of the pulse-detonation cycle, various operational constraints of PDEs are described in Section 2.7. Section 3 provides the reader with a detailed description of various PDE design concepts, including valved and valveless approaches (Sections 3.2 and 3.3), predetonator concept (Section 3.4), design solutions utilizing enhanced deflagration-to-detonation transition (DDT) (Section 3.5), concepts applying stratified fuel distribution in the PDE combustion chamber (Section 3.6), or using two fuels of different detonability (Section 3.7), several novel PDE concepts emphasizing on detonation initiation issues (Sections 3.8–3.10), and the PDE concept applying strong reactive shocks rather than detonations (Section 3.11). The PDE concepts described in Sections 3.2–3.10 imply the use of ducted combustors, either in single-tube or multitube configuration. Some specific features of multitube PDE design are discussed in Section 3.12. Resonator concept of Section 3.13 is somewhat different as it utilizes the cavityinduced resonant flow oscillations in the combustion chamber. Problems of integrating inlets and nozzles to the PDE design are discussed in Sections 3.14 and 3.15. Some issues dealing with control of repeated detonations in a PDE are considered in Section 3.16. The last Section 3.17 briefly describes application of PDEs for rocket propulsion. 2. Fundamentals 2.1. Historical review Early attempts to utilize the power obtained from explosions for propulsion applications date back to late 17th–early 18th centuries and the contributions of Huygens and Allen are noteworthy. In 1729, Allen proposed a jet propelled ship [20] ‘whose operation is owing to the explosion of gunpowder’ in a proper engine placed within a ship. Before this archival contribution, gunpowder was predominantly used in artillery for destructive purposes. First exposure of gaseous detonations dates back to 1870–1883 period when Berthelot and Vieille [21–25], and Mallard and Le Chatelier [26,27] discovered a combustion mode propagating at a velocity ranging from 1.5 to 2.5 km/s. This combustion mode arose when gas was ignited with a high-explosive charge. Later on it was observed in long tubes even when gas was ignited by nonexplosive means (spark or open flame). In this case, flame acceleration along the tube, often accompanied with flame speed oscillations, was detected prior to onset of detonation. The most impressive findings of those times indicated that the detected detonation velocity was independent of the ignition source and tube diameter and was primarily a function of the explosive mixture composition. The main distinctive feature of detonation was a severe mechanical effect implying the development of a high pressure in the propagating wave. The mechanism of detonation propagation has been identified as governed by adiabatic compression of the explosive mixture rather than by molecular diffusion of heat. During those times, the interest in detonation was basically associated with explosion prevention in coal mines. A few years later, based on the shock wave theory of Rankine [28] and Hugoniot [29], Mikhelson in 1890 [30,31], Chapman in 1899 [32], and Jouguet in 1904 [33,34] provided theoretical estimates for the detonation parameters based on one-dimensional (1D) flow considerations and mass, momentum and energy conservation laws. In their theory, the detonation wave was considered as a pressure discontinuity coupled with the reaction front (instantaneous reaction). According to the theory, the detonation products possess density that is almost two-fold higher than the initial mixture density; temperature and pressure that are, respectively, 10–20% and two-fold higher than the corresponding values of constant-volume explosion; particle velocity that attains a value close to one half of the detonation velocity. Comparison of the theoretical predictions with experimentally observed detonation velocities showed fairly good agreement. Since the end of the 19th–the beginning of the 20th century, significant progress has been made both in experimentation and analysis of detonations. In addition to explosion safety issues in coal mines and pits, other applications surfaced, in particular, those dealing with new technologies, balloon transportation, and reciprocating internal combustion engines. After the World War I, there was a considerable growth of interest to combustion in automotive and aircraft engines. Worth mentioning are the early contributions of Dixon, Nernst, Crussard, Woodbury, Campbell, Bone, Frazer, Egerton, Payman, Laffite, Townsend, and Lewis in understanding the mechanism of detonation onset and propagation (see corresponding references in Refs.[35,36]). Two principal conditions required for detonation onset were observed, namely, (i) formation of a shock wave of intensity sufficient for explosive mixture to autoignite, and (ii) increase in the local rate of energy release up to the level sufficient for shock wave reproduction in the adjacent layer of the explosive mixture. Mixture autoignition was often detected ahead of the accelerating flame giving rise to blast waves propagating downstream and upstream. The former blast wave was attributed to detonation and the latter was called retonation. Apart from gasdynamic models of detonation, there were attempts to develop models based on the molecular mechanism of energy transfer in G.D. Roy et al. / Progress in Energy and Combustion Science 30 (2004) 545–672 549
550 G.D. Roy et al. Progress in Energy and Combustion Science 30(2004)545-672 the detonation wave. Lewis applied the theory of chain- Ferrie and Manson[47 Schelkin [48] reported pioneering branching reactions developed by Hinshelwood [371 and results on the effect of wall roughness on the ddt distance Semenov [38] to put forward the chemical mechanism of and time, as well as on the detonation propagation velocity. tonation propagation. within this model, the detonation By using various wire spirals inserted into the detonation wave propagates due to energy transfer from detonation tube he controlled the ddt distance and time within a wide products to the fresh mixture with active molecules inge. Of particular importance was Shchelkin's finding that possessing the energy sufficient for self-sustained reaction detonation can propagate at velocities considerably less than propagation. Detailed experimental studies of the effect of the thermodynamic CJ velocity initial mixture pressure and temperature, as well as tube In 1940, Zel'dovich [491 developed a theory of length and diameter on the run-up distance to detonation detonation wave structure and detonability limits. The were reported. The existence of concentration limits of keystone of his theory is the necessity of close coupling detonation was identified. In 1926, Campbell and between the lead shock wave and the finite-rate combustion Woodhead [39 have discovered the spinning detonation chemistry. The lead shock wave provides adiabatic propagating at oscillatory velocity. This discovery initiated compression and heating of the fresh explosive mixture. numerous studies of the detonation wave structure The compressed mixture autoignites after a certain induc- Campbell, Miga d, many researchers(Ricardo, Edgar, tion period and a part of the energy released is consumed to In this support constant-speed propagation of the lead shock Serruys, Schnauffer, Sokolik, Voinov and others, see corre- According to the theory, the structure and velocity of a sponding references in Ref. [40)) were involved in studies of detonation wave propagating along the tube is affected by combustion control in internal combustion engines it has been heat and momentum losses at the tube walls via variation of observed that at elevated compression ratios piston engines the chemical induction time and momentum and ener exhibited a sharp decrease in the effective pressure and, as a fluxes behind the lead shock. At a certain level of losses result-decrease in engine power. The term knocking in (governed by tube diameter, dilution ratio, etc. ) steady-state combustion comes from the fact that the mentioned decrease propagation of the detonation wave becomes impossible, as engine power is accompanied by a characteristic ringing noise. the lead shock and the reaction zone tend to decouple from As knocking combustion restricted the allowable compression each other. Later on, von Neumann [50] and Doering [511 ratio, there was mucheffort to study the mechanism of'knock have independently put forward similar models of a Ricardo [41] attributed this mode of combustion in the engine detonation wave comprising a lead shock followed by the to pre-flame autoignition of the end-gas in the cylinder. In his reaction front, taking into account the finite-rate chemistry. interpretation, autoignition of the end-gas results in a sharp At present, this model is known as Zel'dovich -Neumann pressure rise and formation of a blast wave that, similar to Doering(ZND)model of detonation hammer, hits cylinder walls. In 1930, Aubert and duchene Based on the theory, a number of important results have applied photographic method to study combustion phenomena been obtained in 1940-1950s. For example, it was proved in engines. In a knocking engine they detected high-speed theoretically in Refs. [52-54] that (i) there exist nonplanar luminous fronts propagating both into fresh mixture and into (cylindrical or spherical) detonation waves propagating at the combustion products-phenomena resembling detonation same constant velocity as planar detonations, (i)the critical onset in a tube with a characteristic retonation wave. In initiation energy of detonation is proportional to t;(where f; is 1934, Sokolik [40] substantiated the idea of Nernst[42 that the reaction induction time behind the lead shock front and vis detonation in tubes and knock in internal combustion the geometry index equal to 1, 2, and 3 for plane, cylindrical re essentially the same phenomena. His comparative analysis and spherical waves, respectively), (iii) there exists a critical of available evidence of detonation and knock onset revealed radius of the blast wave produced by the initiator at which its that physical conditions for these phenomena are completely amplitude drops to the value corresponding to the CJ similar. Experimental observations of autoignition in the detonation, and this critical radius depends on the reaction preflame zone [43] revealed the existence of exothermic rate and defines both the critical energy of the initiation centers that give rise to fast flames and shock waves resulting and the minimum size of a cloud which can support detonation. in flame flashback. Apparently due to technical reasons, most The ZND model allowed reasonable predictions of of studies dealing with knocking combustion in piston engines tration limits of detonations as well as dependencies of the vere aimed at searching for effective anti-knock chemicals to miting tube diameter on initial pressure, temperature and inhibit preflame autoignition[44] dilution ratio(see review articles [55, 56 ) A considerable progress in understanding detonation Although the ZND model is physically well-based and isa physics occurred during the 1940-1950s period. Exper very helpful idealization of a real detonation wave, later on it iments indicating a possibility of spherical flame accelera- has been clearly demonstrated both experimentally and tion and transition to detonation(i.e. DDT) were reported by theoretically that a detonation is essentially three-dimen- Rakipova et al. [45] and Zel'dovich and Roslovsky [46]. sional (3D) and steady-state only on average. Voinov [57 The first comprehensive publication in which observations based on detailed observations of spinning detonations, of spherical detonations were thoroughly discussed was by discovered transverse waves behind the lead shock front
the detonation wave. Lewis applied the theory of chainbranching reactions developed by Hinshelwood [37] and Semenov [38] to put forward the chemical mechanism of detonation propagation. Within this model, the detonation wave propagates due to energy transfer from detonation products to the fresh mixture with active molecules possessing the energy sufficient for self-sustained reaction propagation. Detailed experimental studies of the effect of initial mixture pressure and temperature, as well as tube length and diameter on the run-up distance to detonation were reported. The existence of concentration limits of detonation was identified. In 1926, Campbell and Woodhead [39] have discovered the spinning detonation propagating at oscillatory velocity. This discovery initiated numerous studies of the detonation wave structure. In this period, many researchers (Ricardo, Edgar, Campbell, Midgley, Boyd, Brown, Watkins, Dumanois, Pye, Serruys, Schnauffer, Sokolik, Voinov and others, see corresponding references in Ref. [40]) were involved in studies of combustion control in internal combustion engines. It has been observed that at elevated compression ratios piston engines exhibited a sharp decrease in the effective pressure and, as a result—decrease in engine power. The term ‘knocking’ in combustion comes from the fact that the mentioned decrease in engine power is accompanied by a characteristic ringing noise. As knocking combustion restricted the allowable compression ratio, there was much effort to study the mechanism of ‘knock’. Ricardo [41] attributed this mode of combustion in the engine to pre-flame autoignition of the end-gas in the cylinder. In his interpretation, autoignition of the end-gas results in a sharp pressure rise and formation of a blast wave that, similar to hammer, hits cylinder walls. In 1930, Aubert and Duchene applied photographic method to study combustion phenomena in engines. In a knocking engine they detected high-speed luminous fronts propagating both into fresh mixture and into combustion products—phenomena resembling detonation onset in a tube with a characteristic retonation wave. In 1934, Sokolik [40] substantiated the idea of Nernst [42] that detonation in tubes and knock in internal combustion engines are essentially the same phenomena. His comparative analysis of available evidence of detonation and knock onset revealed that physical conditions for these phenomena are completely similar. Experimental observations of autoignition in the preflame zone [43] revealed the existence of exothermic centers that give rise to fast flames and shock waves resulting in flame flashback. Apparently due to technical reasons, most of studies dealing with knocking combustion in piston engines were aimed at searching for effective anti-knock chemicals to inhibit preflame autoignition [44]. A considerable progress in understanding detonation physics occurred during the 1940–1950 s period. Experiments indicating a possibility of spherical flame acceleration and transition to detonation (i.e. DDT) were reported by Rakipova et al. [45] and Zel’dovich and Roslovsky [46]. The first comprehensive publication in which observations of spherical detonations were thoroughly discussed was by Ferrie and Manson [47]. Schelkin [48] reported pioneering results on the effect of wall roughness on the DDT distance and time, as well as on the detonation propagation velocity. By using various wire spirals inserted into the detonation tube, he controlled the DDT distance and time within a wide range. Of particular importance was Shchelkin’s finding that detonation can propagate at velocities considerably less than the thermodynamic CJ velocity. In 1940, Zel’dovich [49] developed a theory of detonation wave structure and detonability limits. The keystone of his theory is the necessity of close coupling between the lead shock wave and the finite-rate combustion chemistry. The lead shock wave provides adiabatic compression and heating of the fresh explosive mixture. The compressed mixture autoignites after a certain induction period and a part of the energy released is consumed to support constant-speed propagation of the lead shock. According to the theory, the structure and velocity of a detonation wave propagating along the tube is affected by heat and momentum losses at the tube walls via variation of the chemical induction time and momentum and energy fluxes behind the lead shock. At a certain level of losses (governed by tube diameter, dilution ratio, etc.) steady-state propagation of the detonation wave becomes impossible, as the lead shock and the reaction zone tend to decouple from each other. Later on, von Neumann [50] and Doering [51] have independently put forward similar models of a detonation wave comprising a lead shock followed by the reaction front, taking into account the finite-rate chemistry. At present, this model is known as Zel’dovich–Neumann– Doering (ZND) model of detonation. Based on the theory, a number of important results have been obtained in 1940–1950s. For example, it was proved theoretically in Refs. [52–54] that (i) there exist nonplanar (cylindrical or spherical) detonation waves propagating at the same constant velocity as planar detonations, (ii) the critical initiation energy of detonation is proportional to t n i (where ti is the reaction induction time behind the lead shock front and n is the geometry index equal to 1, 2, and 3 for plane, cylindrical, and spherical waves, respectively), (iii) there exists a critical radius of the blast wave produced by the initiator at which its amplitude drops to the value corresponding to the CJ detonation, and this critical radius depends on the reaction rate and defines both the critical energy of the initiation source and the minimum size of a cloud which can support detonation. The ZND model allowed reasonable predictions of concentration limits of detonations as well as dependencies of the limiting tube diameter on initial pressure, temperature and dilution ratio (see review articles [55,56]). Although the ZND model is physically well-based and is a very helpful idealization of a real detonation wave, later on it has been clearly demonstrated both experimentally and theoretically that a detonation is essentially three-dimensional (3D) and steady-state only on average. Voinov [57], based on detailed observations of spinning detonations, discovered transverse waves behind the lead shock front. 550 G.D. Roy et al. / Progress in Energy and Combustion Science 30 (2004) 545–672
G D. Roy et al. Progress in Energy and Combustion Science 30(2004)545-672 551 Voitsekhovsky [58 and Denisov and Troshin [59] have ven s a discovered the multihead detonation and analyzed the flow shock wave reflection at contact discontinuities patterns at the triple wave configurations with transverse walls were visualized shock waves and reaction fronts arising at the detonation Flame acceleration, DDT, and detonation propagation in front and changes in the flow patterns upon collisions of these ough-walled tubes were first visualized by babkin and figurations. Instability of realistic detonation waves and Kozatchenko [80, 81]. It has been shown that the structures their 3D structure raised serious questions concerning the of detonations in rough and smooth tubes can differ validity of the Arrhenius kinetics with an average tempera- considerably. In a tube with rough walls, mixture ignition ture in ID ZND modeling of detonation initiation and is facilitated by roughness elements due to high local propagation. Direct photographs and soot imprints [60-62] temperatures behind reflected shock waves. One-dimen- uivocally the fish-scales like cellular structure sional model predicts that due to this fact, detonations in not only of cj detonations but of the initial detonation kernel rough tubes should exhibit higher stability and wider which meant that the mixture was actually ignited behind the concentration limits [55, 56]. However, experimental obser shock front in hot spots where temperature is significantly vations [82,83] show somewhat narrower concentration higher than the average temperature limits of low-velocity regimes as compared to detonation in Based on this understanding numerous models of single smooth tubes and quite large wave velocity fluctuations and head (spinning) and multihead detonations have been recovery of a detonation wave upon its entry from a rough suggested since 1950s(see review articles [63, 641). tube into a smooth tube occurs within still narrower limits With the growing availability of diagnostics with This is evidently attributable to an essentially multidimen- mproved temporal and spatial resolutions and powerful sional nature of the reactive waves in rough tubes omputing resources, the progress in the detonation science One of the questions of practical importance is, how after the 1960s has been overwhelming First of all, it became detonation wave originated in a narrow tube behaves when it possible to visualize the ignition process behind a reflected enters a tube of a larger volume or unconfined mixture? The shock wave and discover two different modes of shock- answer to this question should provide information about induced ignition of a reactive gas, namely, 'strong'an al ways of detonation initiation in large volumes, mild ignition[65, 66]. violent volumetric ignition of shock because a mixture in a narrow duct can be initiated much compressed gas in which no local fluctuations of the ignition easier than in wide ones. Transition of detonation waves delays were resolved by the photographic technique was from narrow to wide ducts has been systematically studied termed strong ignition in contrast to mild ignition of the by a number of investigators, starting as early as in 1956 shock-compressed gas in clearly visible exothermic centers 1541. Visualization of detonation transmission from a (hot spots) giving rise to an accelerating flame fronts that run channel into an unconfined volume was probably first up to detonation in some cases. It has been unambiguously lade by mitrofanov and Soloukhin [84 in 1964. demonstrated that it is strong ignition mode that is relevant to Extensive experimental data on detonability of various detonation. However, the ignition process still remains fuels has been provided by research groups from all over the pendent on flow fluctuations even in this case. A world [64, 85-88. Based on well-documented experimental xperimental evidence shows [67 the ignition front behind data on detonation initiation, propagation and transition. the lead shock is quite irregular. This is supported by the well- several important empirical criteria have been extracted. The known nonuniform pattern of soot prints of multihead characteristic size in the fish-scales like structure of realistic detonations. An anal Ref [68] shows that the driving detonation waves, referred to as the detonation cell size, was mechanism of ignition delay fluctuations are gasdynamic found to be a representative parameter to qualitatively grade pulsations of the flow parameters due to collisions of weak detonability of the mixture: the larger the cell size the less coustic and quasi-acoustic waves traveling behind the shock sensitive is the mixture. The cell size was found to be a wave front and affecting it(because of the subsonic nature of function of the initial pressure, temperature, mixture the flow behind the shock wave). Interestingly, these composition and tube diameter. The cell size was proved fluctuations show up even in overdriven waves in which to be directly relevant to detonation transition from a channel the heat release is relatively very low(the temperature rise to an unconfined volume [64 to the limiting tube diameter due to the reaction not exceeding 400 K[691 1891, and to the critical energy of detonation initiation [90 Numerous theoretical works on ID and two-dimensional Detonations in heterogeneous media containing gaseous (2D) analysis of detonation wave instability predict the oxidizer and liquid fuel spray or film, or solid fuel virtually all waves with realistic reaction kinetics are unstable uspension is a topic of growing interest since the 1950s and develop a spinning or multihead structure [70-76] in view of industrial safety and military applications. In the series of elaborate photographic studies Detonations in such media were extensively studied bot Oppenheim et al. [62,77-79 revealed various scenarios experimentally [91] and theoretically [92]. It has been found of detonation onset during DDT in tubes with smooth walls. that detonability of heterogeneous mixtures depends Fast ejection of fame tongues and detonation kernel significantly on the fuel vapor concentration, in particular, formation near the accelerating flame brush, as a result of for heavy hydrocarbon fuels
Voitsekhovsky [58] and Denisov and Troshin [59] have discovered the multihead detonation and analyzed the flow patterns at the triple wave configurations with transverse shock waves and reaction fronts arising at the detonation front and changes in the flow patterns upon collisions of these configurations. Instability of realistic detonation waves and their 3D structure raised serious questions concerning the validity of the Arrhenius kinetics with an average temperature in 1D ZND modeling of detonation initiation and propagation. Direct photographs and soot imprints [60–62] showed unequivocally the fish-scales like cellular structure not only of CJ detonations but of the initial detonation kernel, which meant that the mixture was actually ignited behind the shock front in hot spots where temperature is significantly higher than the average temperature. Based on this understanding numerous models of singlehead (spinning) and multihead detonations have been suggested since 1950s (see review articles [63,64]). With the growing availability of diagnostics with improved temporal and spatial resolutions and powerful computing resources, the progress in the detonation science after the 1960s has been overwhelming. First of all, it became possible to visualize the ignition process behind a reflected shock wave and discover two different modes of shockinduced ignition of a reactive gas, namely, ‘strong’ and ‘mild’ ignition [65,66]. Violent volumetric ignition of shockcompressed gas in which no local fluctuations of the ignition delays were resolved by the photographic technique was termed strong ignition in contrast to mild ignition of the shock-compressed gas in clearly visible exothermic centers (hot spots) giving rise to an accelerating flame fronts that run up to detonation in some cases. It has been unambiguously demonstrated that it is strong ignition mode that is relevant to detonation. However, the ignition process still remains dependent on flow fluctuations even in this case. As experimental evidence shows [67] the ignition front behind the lead shock is quite irregular. This is supported by the wellknown nonuniform pattern of soot prints of multihead detonations. An analysis in Ref. [68] shows that the driving mechanism of ignition delay fluctuations are gasdynamic pulsations of the flow parameters due to collisions of weak acoustic and quasi-acoustic waves traveling behind the shock wave front and affecting it (because of the subsonic nature of the flow behind the shock wave). Interestingly, these fluctuations show up even in overdriven waves in which the heat release is relatively very low (the temperature rise due to the reaction not exceeding 400 K [69]. Numerous theoretical works on 1D and two-dimensional (2D) analysis of detonation wave instability predict that virtually all waves with realistic reaction kinetics are unstable and develop a spinning or multihead structure [70–76]. In the series of elaborate photographic studies, Oppenheim et al. [62,77–79] revealed various scenarios of detonation onset during DDT in tubes with smooth walls. Fast ejection of flame tongues and detonation kernel formation near the accelerating flame brush, as a result of collision of flame-driven shock waves, and as a result of shock wave reflection at contact discontinuities and tube walls were visualized. Flame acceleration, DDT, and detonation propagation in rough-walled tubes were first visualized by Babkin and Kozatchenko [80,81]. It has been shown that the structures of detonations in rough and smooth tubes can differ considerably. In a tube with rough walls, mixture ignition is facilitated by roughness elements due to high local temperatures behind reflected shock waves. One-dimensional model predicts that due to this fact, detonations in rough tubes should exhibit higher stability and wider concentration limits [55,56]. However, experimental observations [82,83] show somewhat narrower concentration limits of low-velocity regimes as compared to detonation in smooth tubes and quite large wave velocity fluctuations and recovery of a detonation wave upon its entry from a rough tube into a smooth tube occurs within still narrower limits. This is evidently attributable to an essentially multidimensional nature of the reactive waves in rough tubes. One of the questions of practical importance is, how a detonation wave originated in a narrow tube behaves when it enters a tube of a larger volume or unconfined mixture? The answer to this question should provide information about optimal ways of detonation initiation in large volumes, because a mixture in a narrow duct can be initiated much easier than in wide ones. Transition of detonation waves from narrow to wide ducts has been systematically studied by a number of investigators, starting as early as in 1956 [54]. Visualization of detonation transmission from a channel into an unconfined volume was probably first made by Mitrofanov and Soloukhin [84] in 1964. Extensive experimental data on detonability of various fuels has been provided by research groups from all over the world [64,85–88]. Based on well-documented experimental data on detonation initiation, propagation and transition, several important empirical criteria have been extracted. The characteristic size in the fish-scales like structure of realistic detonation waves, referred to as the detonation cell size, was found to be a representative parameter to qualitatively grade detonability of the mixture: the larger the cell size the less sensitive is the mixture. The cell size was found to be a function of the initial pressure, temperature, mixture composition and tube diameter. The cell size was proved to be directly relevant to detonation transition from a channel to an unconfined volume [64], to the limiting tube diameter [89], and to the critical energy of detonation initiation [90]. Detonations in heterogeneous media containing gaseous oxidizer and liquid fuel spray or film, or solid fuel suspension is a topic of growing interest since the 1950s in view of industrial safety and military applications. Detonations in such media were extensively studied both experimentally [91] and theoretically [92]. It has been found that detonability of heterogeneous mixtures depends significantly on the fuel vapor concentration, in particular, for heavy hydrocarbon fuels. G.D. Roy et al. / Progress in Energy and Combustion Science 30 (2004) 545–672 551
G.D. Roy et al. Progress in Energy and Combustion Science 30(2004)545-672 A considerable progress has been made in understanding advantage of detonation is capitalized properly, consid the mechanism of detonation initiation in the course of flame benefits are expected to be achieved in terms of development. Two principal concepts are worth mentioning: consumption, manufacturing and operational costs, pollutant Oppenheim's concept of predetonation point explosions emissions, etc. It is the authors'profound belief that the giving rise to detonation bubbles[62], and the Zel'dovich existing knowledge and the on-going research will lead to the gradient mechanism of detonation onset [93]. Somewhat of olutions of this challenging problem a mixed concept(shock wave amplification through coherent energy release(SWACER)) has been put forward by Lee and 2. 2. Gaseous detonations o-workers [94]. The Oppenheim's concept implies that, attaining the autoignition conditions, shock-compressed gas 2. 2. 1 General properties explodes in several exothermic centers resulting in gener In this section, steady reaction waves propagating at ation of spherical blast waves. Collision of the blast waves supersonic velocities are considered. This is necessary to he onset of detonation kernels that give rise to understand the kind of unsteady regimes that can be Zel'dovich's gradient mechanism implies that anticipated in combustible mixtures. Steady-state analysis of shock-compressed gas, of gasdynamic equations, which predicts only restricted with the minimum ignition delay, then moves towards the ranges of reaction wave velocities seems to be inconsistent locations with longer ignition delays (i.e. along the vector of with the experimental evidence of reactive waves propa- ignition delay gradient). As the apparent velocity of the 'self gation at any velocity between those of detonation and ignition wave'approaches the characteristic gasdynamic normal-flame. This contradiction is eliminated assuming velocity(e.g. local speed of sound), a shock wave is formed in that the observed waves that do not obey the steady the compressible reactive mixture followed by spontaneous equations are unsteady reactive waves (or quasi-detona- coupling of the shock with exothermic reaction and eventual tions). Interestingly, the reaction zone velocity relative to transition to detonation. SWACER concept implies that the fluid immediately ahead of it never exceeds(even in localized microexplosion in the shock-compressed mixture unsteady waves)the maximum found from the slope of the gives rise to a blast wave (like in the Oppenheim's concept) Rayleigh line(actually Rayleigh-Michelson line [35, 36],to that is further amplified according to the gradient mechanism give a tribute of respect to Michelson, who pioneered in the All these concepts differ only at first glance. Indeed detonation theory [30,31 tangent to the lower branch of the detonation onset in the detonation kernels should essentially Hugoniot curve plotted for the initial state corresponding to be based on Zel'dovich's mechanism of coupling between the gas compressed in the precursor shock wave the compression wave and exothermic reaction, otherwise For applications, the dependence of detonation para- fame would never accelerate to velocities sufficient to drive a meters on the initial conditions and their sensitiveness to the nock wave capable of self-igniting the mixture with delays mixture equivalence ratio are of importance. Normally, this inherent in detonation waves. On the other hand, as dependence is bell-shaped descending both towards lean experiment shows, incipience of detonation waves never and rich mixtures, except for hydrogen mixtures where the occurs throughout the whole mixture volume, thus support- detonation velocity keeps rising far into the region of rich ing the idea of hot spot self-ignition. Thus, all the concepts are mixtures. based on considering'microexplosion(s)in the exothermic In homogeneous hydrocarbon-air mixtures, the detona- center(s) formed in the shock-compressed gas. Zel'dovich's tion velocities peak in slightly rich mixtures. The maximum concept is less formal than the others because it includes the detonation velocity is attained in air mixtures with the evolution of reaction inside the exothermic center, provides a equivalence ratio ps 1. 2 for saturated hydrocarbons, and complete physical explanation of the hot spot development p= 1.3 for unsaturated hydrocarbons and clear criteria for detonation origination, thus avoiding Fig. I shows the predicted dependencies of the detonation speculations on the strength of the blast wave produced by velocity Dc(a), temperature of detonation products Tc(b), dimensionless pr of detonation products pc/po (c). Historically, the two fundamental modes of combustion, and molecular mass of detonation products uc(d)on molar amely flame and detonation, have found a wide variety of fraction of fuel in gaseous iso-octane-air(solid curve)and applications in human activities. It is a slow flame that has n-heptane-air(dashed curve)mixtures, calculated by using been extensively utilized in propulsion, power engineering, thermodynamic code SAFETY [95]. Here, indices 0 and CJ material science, and chemical technology, while detonations label quantities ahead of the detonation front and at the used basically for military purposes. As the knowledg CJ plane, respectively. The dependencies of detonation in detonation physics and chemistry is continuously advan- elocity, temperature and pressure exhibit a characteristic cing, one inevitably arrives at the time when this knowledge is bell shape, attaining detonability limits on both sides from to be used for constructive purposes as well to help humanity the stoichiometric composition. n-Heptane and iso-octane at large. Detonation is a very attractive phenomenon from the mixtures show very similar properties. viewpoint of the thermodynamic efficiency of chemical Fig. 2 shows the calculated dependencies of the detona- energy conversion into thermal and kinetic energy. Once this tion velocity Dc(a), temperature Ta (b), dimensionless
A considerable progress has been made in understanding the mechanism of detonation initiation in the course of flame development. Two principal concepts are worth mentioning: Oppenheim’s concept of predetonation point explosions giving rise to detonation ‘bubbles’ [62], and the Zel’dovich ‘gradient’ mechanism of detonation onset [93]. Somewhat of a mixed concept (shock wave amplification through coherent energy release (SWACER)) has been put forward by Lee and co-workers [94]. The Oppenheim’s concept implies that, at attaining the autoignition conditions, shock-compressed gas explodes in several exothermic centers resulting in generation of spherical blast waves. Collision of the blast waves results in the onset of detonation kernels that give rise to detonation. Zel’dovich’s gradient mechanism implies that self-ignition of shock-compressed gas, starting at location with the minimum ignition delay, then moves towards the locations with longer ignition delays (i.e. along the vector of ignition delay gradient). As the apparent velocity of the ‘selfignition wave’ approaches the characteristic gasdynamic velocity (e.g. local speed of sound), a shock wave is formed in the compressible reactive mixture followed by spontaneous coupling of the shock with exothermic reaction and eventual transition to detonation. SWACER concept implies that localized microexplosion in the shock-compressed mixture gives rise to a blast wave (like in the Oppenheim’s concept) that is further amplified according to the gradient mechanism. All these concepts differ only at first glance. Indeed, the detonation onset in the detonation kernels should essentially be based on Zel’dovich’s mechanism of coupling between the compression wave and exothermic reaction, otherwise flame would never accelerate to velocities sufficient to drive a shock wave capable of self-igniting the mixture with delays inherent in detonation waves. On the other hand, as experiment shows, incipience of detonation waves never occurs throughout the whole mixture volume, thus supporting the idea of hot spot self-ignition. Thus, all the concepts are based on considering ‘microexplosion(s)’ in the exothermic center(s) formed in the shock-compressed gas. Zel’dovich’s concept is less formal than the others because it includes the evolution of reaction inside the exothermic center, provides a complete physical explanation of the hot spot development and clear criteria for detonation origination, thus avoiding speculations on the strength of the blast wave produced by ‘microexplosion’. Historically, the two fundamental modes of combustion, namely flame and detonation, have found a wide variety of applications in human activities. It is a slow flame that has been extensively utilized in propulsion, power engineering, material science, and chemical technology, while detonations were used basically for military purposes. As the knowledge in detonation physics and chemistry is continuously advancing, one inevitably arrives at the time when this knowledge is to be used for constructive purposes as well to help humanity at large. Detonation is a very attractive phenomenon from the viewpoint of the thermodynamic efficiency of chemical energy conversion into thermal and kinetic energy. Once this advantage of detonation is capitalized properly, considerable benefits are expected to be achieved in terms of fuel consumption, manufacturing and operational costs, pollutant emissions, etc. It is the authors’ profound belief that the existing knowledge and the on-going research will lead to the solutions of this challenging problem. 2.2. Gaseous detonations 2.2.1. General properties In this section, steady reaction waves propagating at supersonic velocities are considered. This is necessary to understand the kind of unsteady regimes that can be anticipated in combustible mixtures. Steady-state analysis of gasdynamic equations, which predicts only restricted ranges of reaction wave velocities seems to be inconsistent with the experimental evidence of reactive waves propagation at any velocity between those of detonation and normal-flame. This contradiction is eliminated assuming that the observed waves that do not obey the steady equations are unsteady reactive waves (or quasi-detonations). Interestingly, the reaction zone velocity relative to the fluid immediately ahead of it never exceeds (even in unsteady waves) the maximum found from the slope of the Rayleigh line (actually Rayleigh–Michelson line [35,36], to give a tribute of respect to Michelson, who pioneered in the detonation theory [30,31]) tangent to the lower branch of the Hugoniot curve plotted for the initial state corresponding to the gas compressed in the precursor shock wave. For applications, the dependence of detonation parameters on the initial conditions and their sensitiveness to the mixture equivalence ratio are of importance. Normally, this dependence is bell-shaped descending both towards lean and rich mixtures, except for hydrogen mixtures where the detonation velocity keeps rising far into the region of rich mixtures. In homogeneous hydrocarbon–air mixtures, the detonation velocities peak in slightly rich mixtures. The maximum detonation velocity is attained in air mixtures with the equivalence ratio F < 1:2 for saturated hydrocarbons, and F < 1:3 for unsaturated hydrocarbons. Fig. 1 shows the predicted dependencies of the detonation velocity DCJ ðaÞ; temperature of detonation products TCJ ðbÞ; dimensionless pressure of detonation products pCJ=p0 ðcÞ; and molecular mass of detonation products mCJ ðdÞ on molar fraction of fuel in gaseous iso-octane–air (solid curve) and n-heptane-air (dashed curve) mixtures, calculated by using thermodynamic code SAFETY [95]. Here, indices 0 and CJ label quantities ahead of the detonation front and at the CJ plane, respectively. The dependencies of detonation velocity, temperature and pressure exhibit a characteristic bell shape, attaining detonability limits on both sides from the stoichiometric composition. n-Heptane and iso-octane mixtures show very similar properties. Fig. 2 shows the calculated dependencies of the detonation velocity DCJ ðaÞ; temperature TCJ ðbÞ; dimensionless 552 G.D. Roy et al. / Progress in Energy and Combustion Science 30 (2004) 545–672
G D. Roy et al. / Progress in Energy and Combustion Science 30 (2004)545-672 中f ig. 1. Predicted dependencies of (a) detonation velocity Dc, (b) temperature TcJ, (c) dimensionless pressure Pc/po, and(d) molecular I Ac of detonation products on fuel molar fraction in gaseous iso-octane-air(solid curves)and n-heptane-air(dashed curves) mixtures [95]- Vertical lines correspond to stoichiometric fuel molar fraction vf.st 2900 To/K T。/K Fig. 2. Calculated dependencies of (a)detonation velocity Dc. (b)temperature Tc, (c)dimensi sure pcpo detonation products Ac on the initial temperature and pressure for stoichiometric iso-octa ture95}:1-po=0.5atm,2-10 -20.4-5.0.and5-10.0atm
Fig. 1. Predicted dependencies of (a) detonation velocity DCJ; (b) temperature TCJ; (c) dimensionless pressure pCJ=p0; and (d) molecular mass mCJ of detonation products on fuel molar fraction in gaseous iso-octane–air (solid curves) and n-heptane–air (dashed curves) mixtures [95]. Vertical lines correspond to stoichiometric fuel molar fraction cf;st: Fig. 2. Calculated dependencies of (a) detonation velocity DCJ; (b) temperature TCJ; (c) dimensionless pressure pCJ=p0; and (d) molecular mass of detonation products mCJ on the initial temperature and pressure for stoichiometric iso-octane–air mixture [95]; 1—p0 ¼ 0:5 atm, 2—1.0, 3—2.0, 4—5.0, and 5—10.0 atm. G.D. Roy et al. / Progress in Energy and Combustion Science 30 (2004) 545–672 553
G.D. Roy et al. Progress in Energy and Combustion Science 30(2004)545-672 mpensates for the initial energy increase, so that the detonation velocity is virtually independent of the initial temperature. In line with this logic, the temperature of detonation products increases only slightly with the initial temperature(Fig 2b). An important parameter such as the detonation pressure(Fig. 2c)decreases with temperature because the pressure ratio is proportional to the initial fluid density. Due to dissociation, the molecular mass of detona- tion products decreases, however, insignificantly. At the low end, the initial pressure should not affect the detonation velocity, but at higher pressures the equilibrium in the reaction products is shifted towards polyatomic molecules, which lie at lower energy levels. Hence, reduced dissociation of the products increases slightly the detonation Fig 3. Detonation properties of homogeneous JP-10-air mixture velocity(Fig. 2a), temperature(Fig. 2b), and molecular btained by using thermodynamic code tEP [96,97: 1-dcj mass(Fig. 2d). Dimensionless detonation pressure is almost insensitive to the initial pressure(Fig. 2c). It should be noted that at very low initial pressures the detonation parameters pressure Pay/po(c), and molecular mass ua(d)on the initial e affected by losses to the walls of even quite wide tubes temperature To and pressure Po of a stoichiometric homo- (this effect is not taken into account in thermodynamic geneous iso-octane-air mixture [95]. The effect of the initial calculations of Fig. 2). All the features of Fig. 2 are temperature on the detonation velocity is insignificant confirmed by the measurements and are typical for (Fig. 2a). According to elementary considerations, the initial detonations of high hydrocarbons internal energy is just added to the reaction heat and an As JP-10 is considered as one of prospective fuels for ease in the initial temperature should slightly increase the PDE applications, Fig. 3 shows the calculated detonation detonation velocity. However, the actual influence of the properties of homogeneous JP-10-air mixture [96] that initial temperature on the detonation velocity is more are very similar to those presented in Fig. 1. The complex since due to dissociation the reaction heat drops as properties presented in Fig. 3 were obtained by usin the final temperature in the products rises. This partl thermochemical equilibrium code TEP [971 which does c2750 A Fig. 4. Predicted dependencies of (a)detonation velocity Dc.(b)temperature Tc, (c)dimensionless pressure Pcr/po, and(d)molecular mass uc of detonation products on the molar fraction of HP vapor a admixed to the stoichiometric homogeneous iso-octane-air(solid curves)and
pressure pCJ=p0 ðcÞ; and molecular mass mCJ ðdÞ on the initial temperature T0 and pressure p0 of a stoichiometric homogeneous iso-octane–air mixture [95]. The effect of the initial temperature on the detonation velocity is insignificant (Fig. 2a). According to elementary considerations, the initial internal energy is just added to the reaction heat and an increase in the initial temperature should slightly increase the detonation velocity. However, the actual influence of the initial temperature on the detonation velocity is more complex since due to dissociation the reaction heat drops as the final temperature in the products rises. This partly compensates for the initial energy increase, so that the detonation velocity is virtually independent of the initial temperature. In line with this logic, the temperature of detonation products increases only slightly with the initial temperature (Fig. 2b). An important parameter such as the detonation pressure (Fig. 2c) decreases with temperature because the pressure ratio is proportional to the initial fluid density. Due to dissociation, the molecular mass of detonation products decreases, however, insignificantly. At the low end, the initial pressure should not affect the detonation velocity, but at higher pressures the equilibrium in the reaction products is shifted towards polyatomic molecules, which lie at lower energy levels. Hence, reduced dissociation of the products increases slightly the detonation velocity (Fig. 2a), temperature (Fig. 2b), and molecular mass (Fig. 2d). Dimensionless detonation pressure is almost insensitive to the initial pressure (Fig. 2c). It should be noted that at very low initial pressures the detonation parameters are affected by losses to the walls of even quite wide tubes (this effect is not taken into account in thermodynamic calculations of Fig. 2). All the features of Fig. 2 are confirmed by the measurements and are typical for detonations of high hydrocarbons. As JP-10 is considered as one of prospective fuels for PDE applications, Fig. 3 shows the calculated detonation properties of homogeneous JP-10–air mixture [96] that are very similar to those presented in Fig. 1. The properties presented in Fig. 3 were obtained by using thermochemical equilibrium code TEP [97] which does Fig. 4. Predicted dependencies of (a) detonation velocity DCJ; (b) temperature TCJ; (c) dimensionless pressure pCJ=p0; and (d) molecular mass mCJ of detonation products on the molar fraction of HP vapor cA admixed to the stoichiometric homogeneous iso-octane–air (solid curves) and n-heptane–air (dashed curves) mixtures [95]. Fig. 3. Detonation properties of homogeneous JP-10-air mixture obtained by using thermodynamic code TEP [96,97]; 1—DCJ; 2—pCJ=p0; 3—TCJ=T0: 554 G.D. Roy et al. / Progress in Energy and Combustion Science 30 (2004) 545–672