An Experimental and Simulation Study of Increases in Fuel Consumption and NOX Emissions in a Biofueled Diesel Engine

Abstract

Alternative fuel vehicles are gaining importance as a means of reducing petroleum dependence. One attractive option is biodiesel, a renewable diesel fuel produced from plant or animal fats, since it significantly reduces carbon monoxide, unburned hydrocarbon, and particulate matter emissions as well as carbon dioxide when considered on a full life cycle basis. However, biodiesel combustion also typically results in increased fuel consumption and nitrogen oxide (NOx) emissions relative to petroleum diesel. In order to determine the cause of and develop mitigation strategies for increased biodiesel fuel consumption and NOx emissions, an accurate simulation model was developed and validated. Key fuel properties as well as ignition delay characteristics were implemented in a previously validated whole engine model to reflect soy-biodiesel fuel. The model predictions were within 5% of experimental results for most values at the three operating points. Using this biodiesel model, the “biodiesel NOx effect” was linked to the near stoichiometric equivalence ratios for biodiesel.

Stock and Optimized Performance and Emissions with 5 and 20% Soy Biodiesel Blends in a Modern Common Rail Turbo-Diesel Engine

“…This may lead to an equivalence ratio closer to 1 for biodiesel blends in the rich premixed region of the mixing-controlled combustion process, resulting in higher temperatures and increased NO x formation. Shifting to a lower AFR may raise the local premixed zone equivalence ratio, thereby reducing NO x . , …”

“…Shifting to a lower AFR may raise the local premixed zone equivalence ratio, thereby reducing NO x . 31,32 The B20 and B5 optimal settings also shift to higher EGR fractions at all but one operating location to reduce NO x . This is consistent with the fact that increasing the EGR fraction is an effective tool for mitigating NO x by lowering flame temperatures and in-cylinder oxygen concentrations.…”

“…Figure 23 shows the relationship between the energy content and the BSFC penalties experienced by each fuel blend at the nominal ECM settings. Assuming that the B0 used for these experiments has a lower heating value (LHV) of 43 MJ/kg and B100 has a LHV of 37.5 MJ/kg, 31 there appears to be a slightly nonlinear relationship between the LHV and BSFC penalty experienced by each of the fuel blends with the B0 nominal settings. This indicates that, while the LHV appears to be the main driver for BSFC increases, there may be other property differences that influence combustion efficiency, as shown in Figure 22.…”