A Numerical Analysis of the Emissions Characteristics of Biodiesel Blended Fuels

Abstract

Computer simulations were conducted to study the combined effects of methyl soyate (biodiesel) blends with no. 2 diesel fuel on diesel engine (D.I.) performance. Diesel engine emissions and heat release rates were some of the parameters studied. The results from the computer simulations were compared against previously published results (Choi et al., 1997) from engine tests conducted on a single cylinder version of the Caterpillar 3400 series heavy duty diesel engine. The experiments and simulations were performed over a range of injection timings allowing particulate versus NOx trade-off curves to be a generated. Phillips 66 certified no. 2 diesel fuel was used as the baseline; mixtures of 20 percent and 40 percent by volume of methyl soyate with the baseline no. 2 diesel fuel were used as the biodiesel blends. The multidimensional KIVA-II code (ERC version 2.4) was used to better understand the factors controlling the formation of NOx and soot. KIVA-II modeled the high load, single injection combustion of the baseline #2 diesel fuel and the biodiesel blends. The code was changed to account for different fuel effects and the computational results were then compared against the experimental data. It is concluded that the increased NOx observed with the use of biodiesel fuels (in spite of their lower heats of combustion) is due to increased local temperatures as a result of enhanced fuel/air mixing and increased spray penetration. The increased spray penetration results from the higher fuel viscosity of the biodiesel blended fuels which leads to reduced injection durations.