Sensitivity of combustion noise and NOx and soot emissions to pilot injection in PCCI Diesel engines

New combustion concepts have been recently developed with the purpose to tackle the problem of the high emission levels of traditional direct injection Diesel engines. A good example is the premixed charge compression ignition (PCCI) combustion, a strategy in which early injections are used, causing a burning process in which more fuel is burned in premixed conditions, which affects combustion noise. The use of a pilot injection has become an effective tool for reducing combustion noise. The main objective of this paper is to analyze experimentally the pollutant emissions, combustion noise, and performance of a Diesel engine operating under PCCI combustion with the use of a pilot injection. In addition, a novel methodology, based on the decomposition of the in-cylinder pressure signal, was used for combustion noise analysis. The results show that while the PCCI combustion has potential to reduce significantly the NOx and soot emission levels, compared to conventional Diesel combustion strategy, combustion noise continues to be a critical issue for the implementation of this new combustion concept in passenger cars.