A review of combustion control strategies in diesel HCCI engines

Abstract

ABSTRACTHomogenous charge compression ignition (HCCI) has attracted much attention recently owing to its potential for significantly reducing NOx and particulate emissions whilst achieving high thermal efficiency. Commencement of the combustion in a HCCI engine is not the result of the ignition of fuel by spark or fuel injection; it is the result of auto-ignition of the entire fuel–air mixture. This becomes the sensitive parameter (auto-ignition temperature) to control combustion. Research and development of HCCI diesel engines has been pursued along three main technical routes, depending on the mixture preparation process involved. First, injecting the fuel into the intake air – similar to a conventional port fuel injection SI engine – or early and late direct injection into the cylinder. The second approach is low temperature combustion by using a high exhaust gas recirculation rate coupled with a different injection strategy, thus improving premixing. The third technique is modifying the fuel characteristics. Thus, alcohol, hydrogen natural gas, ethers and n-heptane/iso-octane have been studied. It has been established using the above techniques will result in stable combustion even at higher engine loads. Using alternate fuels like alcohol, hydrogen natural gas and ethers showed significant improvements in fuel economy and reductions in NOx and particulate matter.