A Study on Biodiesel NO_x Emission Control With the Reduced Chemical Kinetics Model

In this paper, the effects of the start of injection (SOI) timing and EGR rate on the nitrogen oxide (NO_x) emissions of biodiesel-powered diesel engine are studied with computational fluid dynamics (CFD) coupling with a chemical kinetics model. A surrogate biodiesel mechanism consisting of two fuel components is employed as the combustion model of soybean biodiesel. The in-cylinder combustion processes of the cases with four injection timings and three exhaust gas recirculation (EGR) rates are simulated. The simulation results show that the NO_x emissions of biodiesel combustion can be effectively improved by SOI retardation or increasing EGR rate. The calculated NO_x emissions of the cases with default EGR rate are reduced by 20.3% and 32.9% when the injection timings are delayed by 2-degree and 4-degree crank angle, respectively. The calculated NO_x emissions of the cases with 24.0% and 28.0% EGR are reduced by 38.4% and 62.8%, respectively, compared to that of the case with default SOI and 19.2% EGR. But higher EGR rate deteriorates the soot emission. When EGR rate is 28.0% and SOI is advanced by 2-degree, the NO_x emission is reduced by 55.1% and soot emission is controlled as that of the case with 24% EGR and default SOI.