Combustion and Emission Characteristics of Soybean Oil Biodiesel (SOB) and Gasoline Blends in a Partially Premixed Compression Ignition Engine

Abstract

In the previous studies, partially premixed compression ignition (PPCI) combustion can obtain good combustion controllability, performance and emissions in diesel engines with gasoline. This article focuses on achieving soybean oil biodiesel (SOB)/gasoline PPCI combustion in a single cylinder diesel engine through moderate and low operating loads. Combustion and emission characteristics of SOB and gasoline blends in a PPCI engine have been studied. The results show that low temperature ignition property of gasoline can be improved by doping SOB. The best SOB addition is 30% in volume fraction which has the highest indicated thermal efficiency: 52%, and better emission characteristic compares to pure gasoline. Further experiments on PPCI combustion of 30% SOB/gasoline blend with different fuel injection timings and exhaust gas recirculation (EGR) ratios have been carried out to find out impacts of fuel injection timing and EGR on PPCI combustion. The results show that both the fuel injection timing and EGR can affect performance and emissions of the PPCI engine. For the consideration of engine emissions and efficiency, 12 ºCA BTDC fuel injection timing is the best choice. 26% hot EGR (EGR without cooling) and 40% Quasi-EGR (CO₂ as an EGR simulation gas) are the best for low load (0.158 MPa BMEP) and moderate load (0.395 MPa BMEP), separately. When EGR ratio increases to 50%, both hot EGR and Quasi-EGR could reduce NO_x emission more than 70% while the fuel consumption increases slightly.