The effects of synthetically designed diesel fuel properties – cetane number, aromatic content, distillation temperature, on low-temperature diesel combustion

Abstract

This study investigated the effects of synthetically designed diesel fuel properties i.e. cetane number (CN), aromatic content, and 90% distillation temperature (T90) on the combustion characteristics and exhaust emissions in low-temperature diesel combustion (LTC). LTC was achieved by a similar approach to previous work via alteration of injection strategy, a cooled heavy EGR rate at low speed and low load, and at 1500rpm and 2.6bar BMEP in a 1.9L common rail direct injection diesel engine. The test fuels were synthetically designed, whose properties constitute CNs of 30 and 55, aromatic contents of 20% and 45%, and T90 temperatures of 270 and 340°C. In LTC operating conditions, the CN is found to be the most dominant factor in the ignition delay time, followed by the T90 temperature for the lower CN fuels, and the aromatic content for the higher CN fuels. Given a CN, the location of mass fraction burned (MFB) 5% and MFB50% showed a linear relationship, and thus the aromatic content and T90 temperature effects can be diminished by adjusting the start of injection timing. PM was strongly dependent on the ignition delay time regardless of fuel types: no PM was observed as long as the ignition delay time was longer than 18°CA. For CN55 fuels, the NOx emission showed strong dependence on the location of MFB50% regardless of fuel types, i.e. NOx decreases as the MFB50% location retards. For CN30 fuels, the aromatic content acts as a crucial factor in the increase of NOx as similar to the studies of conventional diesel combustion.