Chapter 5 Gasoline fuel supply system Section 1 Fuel mixture formation and combustion Gasoline is the mixture of a variety of hydrocarbons distilled from petroleum. National standard prescribes that the octane number of gasoline indicates the gasoline number,and the size of the gasoline number reflects the gasoline's ability to avoid detonating combustion. Gasoline is the liquid that is very easy to evaporate,which begins to evaporate from around 320K to 470K or so when the evaporation is completed,and the selfignition temperature is higher,but under the condition of exogenous fire it easily catches fire. According to different ways of gasoline supply,gasoline engine can be divided into two categories of carburetor and injection type. 1.Combustible Mixture Formation In the internal combustion engine,in order to make the fuel burning away in a very short period of time,the fuel must be made to very small particles uniformly mixed with air as much as possible.The current approach is to make the fuel fully evaporate,which causes the evaporation of particles and air mixture combustion According to the characteristics of gasoline,when the gasoline engine works, 机被电子工程学家 Automobile and Tractor Northwest A&F University
Automobile and Tractor Northwest A&F University Chapter 5 Gasoline fuel supply system Gasoline is the mixture of a variety of hydrocarbons distilled from petroleum. National standard prescribes that the octane number of gasoline indicates the gasoline number, and the size of the gasoline number reflects the gasoline's ability to avoid detonating combustion. Gasoline is the liquid that is very easy to evaporate，which begins to evaporate from around 320K to 470K or so when the evaporation is completed, and the selfignition temperature is higher, but under the condition of exogenous fire ，it easily catchesfire. According to different ways of gasoline supply, gasoline engine can be divided into two categories of carburetor and injection type. 1. Combustible Mixture Formation In the internal combustion engine, in order to make the fuel burning away in a very short period of time, the fuel must be made to very small particles uniformly mixed with air as much as possible. The current approach is to make the fuel fully evaporate, which causes the evaporation of particles and air mixture combustion. According to the characteristics of gasoline, when the gasoline engine works， Section 1 Fuel mixture formation and combustion
Chapter 5 Gasoline fuel supply system Section 1 Fuel mixture formation and combustion generally the gasoline and air mixture in the intake passage is sent into the cylinder, and compressed by the end of electric spark that ignites the mixture for completing work. For the full evaporation of gasoline,one way is to create an environment that is conducive to evaporate,such as increasing temperature,lower pressure,increasing surface area of evaporation,accelerating air flow speed and so on,which can be achieved through the carburetor.Another method is to use pressure fuel injection system to pulverize the gasoline to form the mixture. In order to achieve that mixture in the cylinder can burn quickly and completely, in addition to better fuel pulverization,evaporation and uniformly mixed with air,it also requires the appropriate ratio of fuel and air.The gasoline and air mixture ignition range is excess air coefficient a =0.4-1.4,and when a is different,the internal combustion engine power and fuel consumption rate are very different. Experiments show that when a is 0.85-0.95,internal combustion engine produces maximum power,and when a is 1.05-1.15,internal combustion engine has the minimum fuel consumption rate. 机械电子工程学度 Automobile and Tractor Northwest A&F University
Automobile and Tractor Northwest A&F University Chapter 5 Gasoline fuel supply system generally the gasoline and air mixture in the intake passage is sent into the cylinder, and compressed by the end of electric spark that ignites the mixture for completing work. For the full evaporation of gasoline, one way is to create an environment that is conducive to evaporate, such as increasing temperature, lower pressure, increasing surface area of evaporation， accelerating air flow speed and so on，which can be achieved through the carburetor. Another method is to use pressure fuel injection system to pulverize the gasoline to form the mixture. In order to achieve that mixture in the cylinder can burn quickly and completely, in addition to better fuel pulverization, evaporation and uniformly mixed with air, it also requires the appropriate ratio of fuel and air. The gasoline and air mixture ignition range is excess air coefficient α = 0.4-1.4, and when α is different, the internal combustion engine power and fuel consumption rate are very different. Experiments show that when α is 0.85-0.95，internal combustion engine produces maximum power, and when α is 1.05-1.15，internal combustion engine has the minimum fuel consumption rate. Section 1 Fuel mixture formation and combustion
Chapter 5 Gasoline fuel supply system Section 1 Fuel mixture formation and combustion According to different loads of automotive gasoline engine mixture components required can be divided into three cases: 1.small load uis0.7-0.9 2.middle load .0 uis0.9-1.1 3.heavy load full load 0.8 uis0.8-0.9 0.6 30 40 60 P.(% B Figure 5.1 Gas mixture used by gasoline engine under different loads A.small load B.middle load C.heavy load 1.power mixture 2.economy mixture 3.theory mixture 机被有电子工程原 Automobile and Tractor Northwest A&F University
Automobile and Tractor Northwest A&F University Chapter 5 Gasoline fuel supply system According to different loads of automotive gasoline engine ， mixture componentsrequired can be divided into three cases: 1. small load α is 0.7－0.9 2. middle load α is 0.9－1.1 3. heavy load & full load α is 0.8－0.9 Figure 5.1 Gas mixture used by gasoline engine under different loads A. small load B. middle load C. heavy load 1. power mixture 2. economy mixture 3. theory mixture Section 1 Fuel mixture formation and combustion
Chapter 5 Gasoline fuel supply system Section 1 Fuel mixture formation and combustion 2.The Combustion of Mixture 2.1 Normal combustion Flame propagation caused by the spark plug discharge,the mixture gradually burning to release heat until complete combustion finished,this combustion is called the normal combustion of gasoline engine. According to the characteristics of the pressure change,combustion process is divided into three stages (1)ignition delay period,also known as induction period,it is from ignition by the spark plug to the cylinder pressure increasing sharply that significantly separates from compression line. The duration of ignition delay period is relevant to the ingredients of mixture, temperature of cylinder gas pressure,gas flow,spark energy,residual gas and so on.Ignition delay period should be as short as possible and maintain its stability. 械电子工程学 Automobile and Tractor Northwest A&F University
Automobile and Tractor Northwest A&F University Chapter 5 Gasoline fuel supply system 2. The Combustion of Mixture 2.1 Normal combustion Flame propagation caused by the spark plug discharge, the mixture gradually burning to release heat until complete combustion finished, this combustion is called the normal combustion of gasoline engine. According to the characteristics of the pressure change， combustion process is divided into three stages： (1) ignition delay period, also known as induction period, it is from ignition by the spark plug to the cylinder pressure increasing sharply that significantly separates from compression line. The duration of ignition delay period is relevant to the ingredients of mixture, temperature of cylinder gas pressure, gas flow, spark energy, residual gas and so on.Ignition delay period should be as short as possible and maintain its stability. Section 1 Fuel mixture formation and combustion
Chapter 5 Gasoline fuel supply system Section 1 Fuel mixture formation and combustion (2)clear burning period,also known as rapid combustion period or flame propagation period,it is from froming the center of flame to the flame propagation throughout the whole chamber,that is the pressure reaches its highest point. At this stage most of the fuel combustion is the main period of combustion,the piston is close to UDP,and the cylinder pressure is rising rapidly. The shorter clear burning period and the closer to UDP,the better gasoline engine economy and power are,but it may cause pressure growing too fast together with large noise and vibration,rough work and emissions pollution. (3)later burning period,also known as supplementary combustion period,it is the period after pressure of highest point. The burning has been away from UDP,the speed of bumning is slow,conversion efficiency of heat and power is significantly reduced,and most of the heat releases in the form of increasing the heat load of the engine. Later burning period should be as short as possible. 业机被有电子工程原 Automobile and Tractor Northwest A&F University
Automobile and Tractor Northwest A&F University Chapter 5 Gasoline fuel supply system (2) clear burning period, also known as rapid combustion period or flame propagation period,it is from froming the center of flame to the flame propagation throughout the whole chamber, that is the pressure reachesits highest point. At this stage most of the fuel combustion is the main period of combustion, the piston is close to UDP, and the cylinder pressure is rising rapidly. The shorter clear burning period and the closer to UDP, the better gasoline engine economy and power are, but it may cause pressure growing too fast together with large noise and vibration, rough work and emissions pollution. (3) later burning period，also known as supplementary combustion period，it is the period after pressure of highest point. The burning has been away from UDP, the speed of burning is slow, conversion efficiency of heat and power is significantly reduced, and most of the heat releases in the form of increasing the heat load of the engine. Later burning period should be as short as possible. Section 1 Fuel mixture formation and combustion
Chapter 5 Gasoline fuel supply system Section 1 Fuel mixture formation and combustion 2.2 Abnormal combustion All kinds of combustion that in nature are different from normal combustion are called abnormal combustion. Abnormal combustion of gasoline engine can be divided into two types of knocking combustion and surface ignition. (1)knocking combustion In the normal process of flame propagation,unburnt fuel mixture in the position of later burning period,has been spontaneous combustion before the flames reach, then this part of the pre-prepared mixture is burning fast so that the local pressure and stability get abnormal increase that is accompanied by shock waves. The external characteristics of knocking combustion are:the cylinder with a sharp sound of metal percussion,also known as engine knock.It can cause slight deflagration,the engine power increase,and fuel consumption rate decrease,but when knocking combustion is serious,causing overheating,mechanical damage, power decrease,and fuel consumption rate increase. 状械电子工程学膜 Automobile and Tractor Northwest A&F University
Automobile and Tractor Northwest A&F University Chapter 5 Gasoline fuel supply system 2.2 Abnormal combustion All kinds of combustion that in nature are different from normal combustion are called abnormal combustion. Abnormal combustion of gasoline engine can be divided into two types of knocking combustion and surface ignition. (1) knocking combustion In the normal process of flame propagation, unburnt fuel mixture in the position of later burning period, has been spontaneous combustion before the flames reach, then this part of the pre-prepared mixture is burning fast so that the local pressure and stability get abnormal increase that is accompanied by shock waves. The external characteristics of knocking combustion are: the cylinder with a sharp sound of metal percussion, also known as engine knock. It can cause slight deflagration, the engine power increase，and fuel consumption rate decrease, but when knocking combustion is serious, causing overheating, mechanical damage, power decrease, and fuel consumption rate increase. Section 1 Fuel mixture formation and combustion
Chapter 5 Gasoline fuel supply system Section 1 Fuel mixture formation and combustion (2)surface ignition Those who do not rely on electric spark ignition but mixture ignition by hot surface of the combustion chamber,its ignition timing cannot be controlled. Premature ignition is known as preignition.Preignition can accelerate combustion speed,increase cylinder pressure and temperature,and make the engine work roughly.Preignition can induce the deflagration,which increases surface ignition and promotes each other and more harm. 3.The Effect of Use Factors on Combustion 3.1 Mixture density a=0.8-0.9,combustion temperature is high;flame propagation has the maximum speed;pressure growth rate and power are large;and the possibility of knocking combustion increases. a=1-1.1,Complete combustion,low fuel consumption,good economy,and large NOx emissions. 机械电子工程学 Automobile and Tractor Northwest A&F University
Automobile and Tractor Northwest A&F University Chapter 5 Gasoline fuel supply system (2) surface ignition Those who do not rely on electric spark ignition but mixture ignition by hot surface of the combustion chamber, its ignition timing cannot be controlled. Premature ignition is known as preignition. Preignition can accelerate combustion speed, increase cylinder pressure and temperature, and make the engine work roughly. Preignition can induce the deflagration, which increases surface ignition and promotes each other and more harm. 3. The Effect of Use Factors on Combustion 3.1 Mixture density α＝0.8-0.9，combustion temperature is high; flame propagation has the maximum speed; pressure growth rate and power are large; and the possibility of knocking combustion increases. α＝1-1.1，Complete combustion, low fuel consumption, good economy, and large NOx emissions. Section 1 Fuel mixture formation and combustion
Chapter 5 Gasoline fuel supply system Section 1 Fuel mixture formation and combustion a1.2,slow flame speed,incomplete combustion,poor economy, HC emissions increase and unstable work. 42 41 09 8 16 15 B 14 10.m0a19 410 340 270 1.00.90.8 Figure 5.2 The effects of mixture density on power and economy of gasoline engine (air throttle and speed are constant 械电子工程学酸 Automobile and Tractor Northwest A&F University
Automobile and Tractor Northwest A&F University Chapter 5 Gasoline fuel supply system Figure 5.2 The effects of mixture density on power and economy of gasoline engine （air throttle and speed are constant ） α＜0.8 or α ＞1.2， slow flame speed, incomplete combustion, poor economy, HC emissions increase and unstable work. Section 1 Fuel mixture formation and combustion
Chapter 5 Gasoline fuel supply system Section 1 Fuel mixture formation and combustion 3.2 Ignition advance angle When the ignition advance angle is too large,most of the gas mixture will burn in the compression process,the compression power consumed by piston increases, cylinder pressure rises,and knocking combustion increases. intake pipe When ignition advance angle is speec vacuum degree 0 too small,the combustion extends to 33kP阳 the expansion process,the maximum cylinder pressure and temperature drop,heat transmission loss increases,the exhaust temperature 2 rises,power and thermal efficiency 1200/mn 54 decrease,NOx emissions are large. 20 10 40 50 9(4 99 () Figure 5.3 Gasoline engine ignition time adjusting feature (a)air throttle full opening (b)speed n=6000 r/min 八被与电子工程原 Automobile and Tractor Northwest A&F University
Automobile and Tractor Northwest A&F University Chapter 5 Gasoline fuel supply system 3.2 Ignition advance angle When the ignition advance angle is too large, most of the gas mixture will burn in the compression process, the compression power consumed by piston increases, cylinder pressure rises, and knocking combustion increases. When ignition advance angle is too small, the combustion extends to the expansion process, the maximum cylinder pressure and temperature drop, heat transmission loss increases, the exhaust temperature rises , power and thermal efficiency decrease, NOx emissions are large. Figure 5.3 Gasoline engine ignition time adjusting feature (a) air throttle full opening (b) speed n=6000 r/min Section 1 Fuel mixture formation and combustion
Chapter 5 Gasoline fuel supply system Section 1 Fuel mixture formation and combustion 6.0 4.0 2.0 10080 604020020406080100120140 upper dead point Figure 5.4 The effects of ignition advance angle on cylinder pressure change (Ignition advance angle increases gradually from 1 to 6 points in the curves 业机电子工程学 Automobile and Tractor Northwest A&F University
Automobile and Tractor Northwest A&F University Chapter 5 Gasoline fuel supply system Figure 5.4 The effects of ignition advance angle on cylinder pressure change (Ignition advance angle increases gradually from 1 to 6 points in the curves ) Section 1 Fuel mixture formation and combustion