Diesel Fuel Cetane Number Effects on Engine Efficiency and Emissions

Abstract

Diesel engine combustion is heavily impacted by the chemical and physical properties of the fuel being used. Fuel composition plays a role in the in-cylinder behavior of the fuel and the emissions produced during combustion. Particularly, the Cetane Number (CN) of the fuel, which quantifies the ignition characteristics of the fuel, significantly impacts the quality and mode of the combustion. In this study, a low CN (30) Fuels for Advanced Combustion Engines (FACE) fuel is blended with two higher CN fuels; a Palm Methyl Ester (PME) biofuel and a Fischer-Tropsch Gas to Liquids (GTL) diesel. The blends are formulated to match the CN of 55 of a high CN FACE fuel.

The fuel blends are used to operate a light-duty diesel engine to identify the combustion characteristics of the fuel under a moderate load, approximately 4.5 bar Brake Mean Effective Pressure (BMEP), with high and low levels of Exhaust Gas Recirculation (EGR). To decouple combustion phasing effects within the cycles, the 50% mass fraction burned point is matched for all fuels by adjusting the start of fuel injection timing. The performance of the blended fuels is then compared to the high and low CN FACE fuels. The CN of each fuel is found to be the primary driving factor in the emissions and efficiency achieved. The low CN FACE fuel produced higher NOx emissions and lower combustion efficiency under high and low EGR operation than each of the high CN fuels. The PME and GTL fuel blends produced lower smoke emissions than the high CN FACE fuel under high EGR operation, but slightly higher NOx, CO, and THC emissions under both high and low EGR operation.