An Empirical Study to Extend Engine Load in Diesel Low Temperature Combustion

In this work, engine tests were performed to realize EGR-enabled LTC on a single-cylinder common-rail diesel engine with three different compression ratios (17.5, 15 and 13:1). The engine performance was first investigated at 17.5:1 compression ratio to provide baseline results, against which all further testing was referenced. The intake boost and injection pressure were progressively increased to ascertain the limiting load conditions for the compression ratio. To extend the engine load range, the compression ratio was then lowered and EGR sweep tests were again carried out. The strength and homogeneity of the cylinder charge were enhanced by using intake boost up to 3 bar absolute and injection pressure up to 180 MPa. The combustion phasing was locked in a narrow crank angle window (5~10° ATDC), during all the tests. The results indicate that a lower compression ratio helps to extend the engine load, while a combination of both intake boost and injection pressure is necessary to maintain low-NOx and low-soot emissions, and to mitigate the fuel efficiency penalty. This research intends to identify the major parameters that affect diesel LTC performance and to provide guidelines for improving the performance of such combustion modes.