Characteristics of Engine Emissions Using Biodiesel Blends in Low-Temperature Combustion Regimes

Abstract

Combustion and emissions of different biodiesel−diesel blends in a multicylinder diesel engine were investigated in this study. The engine used a modern common-rail fuel injection system that can achieve high injection pressures and multiple injections. The future diesel engines are likely to be operated in low-temperature combustion regimes to reduce exhaust emissions. Therefore, the performance of biodiesel in such operating conditions needs to be determined. The present results showed that biodiesel blends generally produced lower soot emissions and higher NOx emissions compared to regular diesel fuel. Results showed that the injection timing shift is not the reason for the NOx emissions increase using biodiesel. The increase in injection pressure will reduce soot emissions, while the use of exhaust gas recirculation will reduce the NOx emissions for all fuels. Reductions in NOx and soot emissions were achieved by using double injections with appropriate injection timings and fuel distributions. It was found that the use of pilot injection allowed late main injections for simultaneous soot and NOx reductions. In the low-temperature combustion regimes (i.e., late injection and/or high exhaust gas recirculation), the 20% biodiesel blend produced almost identical emissions as the regular diesel fuel, while 100% biodiesel still produced relatively higher NOx and lower soot emissions. Nonetheless, NOx emissions will not be a concern at low-temperature combustion conditions when 20% biodiesel blends are used.