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 a<0.8 or a >1.2,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