The Study Of Spray And Combustion Characteristics Of Pilot-main Injection Under Two-injection Strategy In A Constant Volume Combustion Chamber

Energy shortage and environmental pollution promoted the development of biodiesel.However,more NO_x emissions will be produced when biodiesel was applied to the engine.Nowadays,multiple injection strategy is commonly used in compression ignition engine,which can improve the ignition and soot oxidation process of the main injection by using the pilot injection,so that the NO_x and soot emission can be reduced simultaneously.Applying multiple injection strategy and biodiesel to the engine can improve engine efficiency on the basis of reducing NO_x emissions.And the detailed pilot-main injection interaction in multiple injection need to be better understood to refine and further advance fuel injection strategies that lead to higher engine efficiency and lower emissions.This paper uses two different testing methods to study the pilot-main injection interaction of fatty acid methyl ester/diesel blended fuel,the first is the Mie scattering imaging technology to study the effects of the pulse width ratio of the pilot and main injection and the dwell time between the pilot and main injection on the spray cone angle and penetration length of the main injection under different injection pressure and environment temperature.The second is the luminosity imaging and OH chemiluminescence technique to study the effects of the two-injection strategy and the dwell time between the pilot and main injection on the ignition delay time and flame lift-off length of the main injection.The spray characteristics of the main injection when using two-injection strategy was studied by using Mie scattering imaging method,the results show that under the condition of 600 ?,the spray cone angle change curve of the main injection shows stable after decreasing and then decreasing again,the penetration length of the main injection increases firstly and then shows stable fluctuations.Using two-injection strategy,main injection spray cone angle and penetration length were greater than the single injection whose injection pulse width was same to the main injection.However,when using two-injection strategy,the development speed of the penetration of the main injection was slower than the single injection at the early stage.When the total pulse width of the pilot and main injection was equal,the different pulse width ratio between the pilot and main injection had little influence upon the spray cone angle and penetration length,and when the main pulse width was equal,the spray cone angle of the main injection was biggest and the development speed of the penetration of the main injection was slowest when the pulse width ratio was 25%/75%,and the penetration length was smallest when the pulse width ratio was 20%/80%.Under the condition of 400 ?,different dwell time had no effect on the spray cone angle of the main injection.Under the condition of 500 ?,when the dwell time is 0.9 ms,the spray cone angle and penetration length of the main injection were biggest.Under the condition of 600 ?,the dwell time was greater,the spray cone angle of the main injection was smaller,the development speed of penetration at the early stage was faster,and the dwell time had no effect on the penetration length.By using the luminosity imaging and OH chemiluminescence technique at the same time,the effect of the two-injection strategy and dwell time on the combustion characteristics of the main injection were studied,the results showed that when using two-injection strategy,the flame lift-off length was greater than the single injection,and with the increase of the dwell time between the pilot and main injection,the flame lift-off length decreased and the OH distribution gradually moved to both sides of the flame.Besides,the ignition delay time of the main injection was smaller than the single injection and increased with the increase of the dwell time.Using biodiesel/diesel blended fuel,the spray and combustion interaction mechanism of the pilot and main injection in two-injection strategy was studied,and some achievements have been obtained.It has a certain reference value for the further study.