Optimization of the Performance and Emissions of Soy Biodiesel Blends in a Modern Diesel Engine

As the world is faced with continued petroleum demand, the need for alternative fuels which are renewable and domestically available is becoming apparent. Biodiesel is one such attractive alternative fuel which has physical and chemical properties similar to, and miscible with conventional diesel. While biodiesel does have many advantages, due to fuel property differences including oxygenation and a lower calorific value than diesel fuel, biodiesel combustion often results in higher fuel consumption and higher nitrogen oxide (NO_x) emissions than diesel combustion. Stock diesel engine design and decision making target optimal performance with conventional diesel fuel, leading to suboptimal results for biodiesel. This study aimed to determine the appropriate engine decision making for the air/fuel ratio (AFR), exhaust gas recirculation (EGR) fraction, injection (rail) pressure, and start of main fuel injection (SOI) in a modern common rail diesel engine using variable geometry turbo-charging and operating with varying blend ratios of diesel and soy-based biodiesel fuel mixtures to minimize brake-specific fuel consumption (BSFC) and adhere to strict combustion noise, NO_x and particulate matter (PM) emission constraints. When operating with the stock engine decision making, biodiesel blend combustion resulted in increases in NO_x of up to 39% and fuel consumption increases up to 20% higher than the nominal diesel levels but also had substantial reductions in PM. Through modulation of the AFR, EGR fracton, rail pressure, and SOI at several operating points, it was demonstrated that the optimal engine decision-making for biodiesel shifted to lower AFRs and higher EGR fractions in order to reduce NO_x, and shifted to more advanced timings in order to mitigate the observed increases in fuel consumption at the nominal settings. The optimal parameter combinations for B5 (5% biodiesel and 95% diesel), B20 (20% biodiesel and 80% diesel) and B100 (100% biodiesel) still maintained substantial PM reductions but resulted in NO_x and noise levels below nominal diesel levels. However, these parameter combinations had little impact on reducing the biodiesel fuel consumption penalty but did improve the thermal efficiency of biodiesel blend combustion.