2. C5 Adiabatic Flame Temperature For a combustion process that takes place adiabatically with no shaft work, the temperature of the products is referred to as the adiabatic flame temperature This is the maximum temperature that can be achieved for given reactants. Heat transfer, incomplete combustion, and dissociation, all result in lower temperature. The maximum adiabatic flame temperature for a given fuel and oxidizer combination occurs with a stoichiometric mixture(correct proportions such that all fuel and all oxidizer are consumed ). The amount of excess air can be tailored as part of the design to control the adiabatic flame temperature. The considerable distance between present temperatures in a gas turbine engine and the maximum adiabatic flame temperature at stoichiometric conditions is shown in Figure A-1l of Part 1, based on a compressor exit temperature of 1200"F(922 K) An initial view of the concept of adiabatic flame temperature is provided by examining two reacting gases, at a given pressure, and asking what the end temperature is. The process is shown schematically at the right, f= Final state where temperature is plotted versus the Actual path percentage completion of the reaction. I 4h The initial state is i and the final state is f, with the final state at a higher Constant P temperature than the initial state. The State i solid line in the figure shows a Constant p representation of the“ actual” process. To see how we would arrive at the final Percentage 00% state the dashed lines break the state completion of reaction cha into two parts. Process()is reactie process, we would need to extract hear? at constant Tand P. To carry out such Suppose the total amount of heat extracted per unit mass is q,. The relation between Schematic of adiabatic flame temperature the enthalpy changes in Process(1)is h,-h where qn is the"heat of reaction For Process(2), we put this amount back into the products to raise their temperature to the final level. For this process, hf-h2=q1, or, if we can approximate the specific heat as constant (using some appropriate average value)Cpa (T-12)=q1. For the overall process there is no work done and no heat exchanged so that the difference in enthalpy between initial and final states is zero: Ah, t The temperature change during this second process is therefore given by(approximately) 2C-72.C.5 Adiabatic Flame Temperature For a combustion process that takes place adiabatically with no shaft work, the temperature of the products is referred to as the adiabatic flame temperature. This is the maximum temperature that can be achieved for given reactants. Heat transfer, incomplete combustion, and dissociation, all result in lower temperature. The maximum adiabatic flame temperature for a given fuel and oxidizer combination occurs with a stoichiometric mixture (correct proportions such that all fuel and all oxidizer are consumed). The amount of excess air can be tailored as part of the design to control the adiabatic flame temperature. The considerable distance between present temperatures in a gas turbine engine and the maximum adiabatic flame temperature at stoichiometric conditions is shown in Figure A-11 of Part 1, based on a compressor exit temperature of 1200o F (922 K). An initial view of the concept of adiabatic flame temperature is provided by examining two reacting gases, at a given pressure, and asking what the end temperature is. The process is shown schematically at the right, 1 2 ∆h1 Constant P a Actual path ∆h f = Final state where temperature is plotted versus the percentage completion of the reaction. T ∆h2 The initial state is i and the final state is f, with the final state at a higher Constant P temperature than the initial state. The State i 2 solid line in the figure shows a representation of the “actual” process. 0 Percentage 100% To see how we would arrive at the final completion state the dashed lines break the state of reaction change into two parts. Process (1) is reaction at constant T and P. To carry out such a process, we would need to extract heat. Suppose the total amount of heat extracted per unit mass is q1. The relation between Schematic of adiabatic flame temperature the enthalpy changes in Process (1) is h2 − =− h q1 = ( )unit i ho f mass where q1 is the “heat of reaction”. For Process (2), we put this amount back into the products to raise their temperature to the final level. For this process, h − h2 = q1, or, if we can approximate the specific heat as constant (using f some appropriate average value) cpav. (T − T2 ) = q1 . For the overall process there is no work done f and no heat exchanged so that the difference in enthalpy between initial and final states is zero: ∆h1 + ∆h = 0. 2 = ∆hadiabatic The temperature change during this second process is therefore given by (approximately) 2C-7