National Center for Metropolitan Transportation Research Final Report METRANS Research Project 08-01: Combustion and Emission Characteristics of Biofuels Used for Transportation

The world faces both an energy crisis and the problem of global warming due to increasing emissions of green-house gases, particularly CO2. Because of dwindling petroleum reserves in the USA, there is an urgent need to develop alternative fuels. Bioderived fuels are one of the most viable and affordable alternatives. We focus on several biofuels, specifically dimethyl-ether (DME), a clean fuel derived through processing of biomass-derived syngas, and several low molecular weight methyl-esters as surrogates of fatty acid methyl-ester (FAME) type biofuels. We study the fundamental combustion characteristics of these fuels and their pollutant emissions, particularly nitrogen oxides (NOx). We provide insight into the combustion characteristics of DME and its high temperature kinetics. We measure laminar flame speeds and extinction limits of DME/air mixtures using the counterflow configuration and compare them to published experimental data and to numerical simulations using an updated kinetic model. Sensitivity and reaction pathway analyses provide insight into the controlling physico-chemical processes. The laminar flame speeds and extinction limits of two C4 (methyl butanoate (MB) and methyl crotonate (MC)), and one C10 (methyl decanoate (MD)) FAME were measured and analyzed. The NOx emissions of MB, MC, and MD were measured, simulated, and compared with those of npentane, n-decane and n-dodecane. These studies gave a better understanding of the processes that lead to NOx formation and means to minimize such emissions during the use of biofuels. Project data and simulations are a key step towards meeting the long-term goal of the development and testing of surrogates and the attendant detailed kinetic mechanism of methyl-stearate, a FAME with a straight chain saturated hydrocarbon section with 18 carbon atoms, typically found in common biodiesel fuels.