Study Of Fuel Injection Parameters On Combustion And Emission Characteristics In Premixed Compression Ignition Engines

Nowadays the premixed compression ignition engine has played a majorrole around the world with its high efficiency, good power and low CO2emissions. Its combustion process and emissions are directly affectedby the combustion chamber fuel and air distribution both on space and time,and fuel-air mixed conditions are closely related with fuel injectionparameters. Injection parameters are part of combustion boundaryconditions， and then fuel injection parameters adjustment is anindispensable effective method for optimizing combustion process,reducing NOx and Soot emissions.Based on CAN communication protocol，we developed an engine fuelinjection parameter real-time control system and studied the effects ofinjection parameters on premixed compression ignition engine combustionas well as emission characteristics. This experiment is conducted mainlyon a premixed compression ignition engine matching electronicallycontrolled high pressure common rail, turbocharged and intercooled. Themajority content of this research is about adjustment on fuel injectionpressure, main injection timing, and pilot injection timing, pilotinjection quantity and so on. We also analyzed the multi-parametersadjustment on the optimization of compression ignition engine cylindercombustion process and emissions. For this reason, this study examinedeffects of premixed compression ignition combustion processes throughfuel properties of gasoline/diesel blends coupled with fuel injectionparameters for premixed compression ignition engines, explored thepotential ability of fuel injection parameters and fuel property controlling premixed compression ignition engine collaboratively forachieving high efficiency clean premixed compression combustion. Theresults as follows:(1) Increasing injection pressure can improve mixing process of oiland gas inside cylinder, shorten the combustion duration, and enhancecombustion constant volume. At the same time, it also can increase theamount of premixed combustion quantity and reduce exhaust smoke. However,high injection pressure can increase the incomplete combustion and leadto more emissions, such as CO and HC, and decline engine economy.(2) The effects of main injection timing on premixed combustionprocess are obvious. With the advance of main injection timing, premixedcombustion quantity increases remarkably. Meanwhile, the main injectiontiming has a good linear correlation with CA50, and we can use CA50todescribe the effect of main injection timing on combustion and emissionfurther. The indicated thermal efficiency first increases and thendecreases along with the advance of main injection timing, and reach itspeak at3°CA ATDC.(3) The effects of pilot injection timing on combustion are mainlyaffected by pilot injection ignition. Combined with the main injectiontiming advance, pilot injection timing adjustment can ensure the welldevelopment of premixed oil-gas before main injection ignition, increasethe premixed combustion ratio. However, it will reduce the thermalefficiency and have little influence on increasing premixed combustionratio in case of too early pilot injection timing.(4) In the case of too early pilot injection timing, increasing pilotinjection quantity can enhance the premixed combustion ratio becausepilot injection cannot ignite before main injection ignites, but it willlead to the increase of CO and HC as the results of incomplete combustion and the thermal efficiency lowers slightly. Therefore, increasing pilotinjection quantity based on pilot injection optimization is a verypowerful way to improve premixed combustion ratio.(5) The blend of gasoline/diesel fuels can improve fuel ignitabilityand volatility under heavy load conditions, and benefit premixedcombustion from a perspective of fuels. It also can cause the increaseof NOx emissions, but have little impact on thermal efficiency.In summary, this study achieved the goal that the optimizationparameters can improve premixed combustion ratio by adjusting fuelinjection parameters on premixed compression ignition engine，includinginjection pressure, main injection timing, pilot injection timing, pilotinjection quantity and so on. In addition, it proposed new ways and meansof further improvement of premixed combustion process through thecooperative control of fuel injection parameter and fuel characteristics,and also provided the theoretical and practical instruction for achievinghigh efficiency cleaning combustion mode in future.