Effects of EGR and Pilot Injection on Characteristics of Combustion and Emissions of Diesel Engines with Low Ignitability Fuel 2012-01-0853

Characteristics of diesel combustion with low cetane number fuels with similar distillation temperatures to ordinary diesel fuel, including fuels with cetane number 32 and 39 (LC32, LC39), and a blend of n-cetane (n-hexadecane) and iso-cetane (2, 2, 4, 4, 6, 8, 8-heptamethylnonane) with cetane number 32 (CN32), were investigated. The effects of cooled exhaust gas recirculation (EGR) and pilot injection on characteristics of combustion and exhaust gas emissions with these fuels were examined in a naturally aspirated, single cylinder, diesel engine equipped with a common-rail fuel injection system. Even with the low cetane number fuels, quiet combustion with low levels of exhaust gas emissions comparable to ordinary diesel fuel was established by suitable control of intake oxygen levels and pilot injections. At light (0.3 MPa IMEP (indicated mean effective pressure)) and medium (0.5 MPa IMEP) loads, low smoke, low nitrogen oxides (NOx), and quiet combustion is possible by decreasing intake oxygen concentration with EGR. At high (0.7 MPa IMEP) loads, pilot injection can suppress NOx emissions and the maximum rate of pressure rise to levels similar to ordinary diesel fuel. Smoke emissions at low intake oxygen and NOx emissions at high intake oxygen with the low H/C ratio fuel, LC32, are higher than with CN32, the high H/C ratio fuel at the same cetane number.