Abstract: A closed-loop control algorithm that reduces the increases in nitrogen oxides (NOx) commonly observed with biodiesel combustion while retaining particulate matter (PM) reductions with variable biodiesel blend fractions. One embodiment includes a control algorithm that is closed-loop with regards to combustible oxygen mass fraction (COMF) instead of exhaust gas recirculation (EGR) fraction. Yet another algorithm includes biodiesel blend estimation and “fuel-flexible” accommodation. A physics-based model has also been developed which predicts experimentally observed engine performance and emissions for biodiesel.

Abstract: While the materials compatibility challenges have largely been met in “flex-fuel” vehicles, the engine and aftertreatment operation has not been optimized as function of fuel type (i.e. ethanol, biodiesel, etc.). The full-scale introduction of alternative fuels is most likely going to occur as blends with conventional fuels. This is seen to some extend with the limited introduction of E85 (85% ethanol, 15% gasoline) and B20 (20% biodiesel, 80% conventional diesel.). This further exacerbates the challenge of accommodating variable fuel properties, as there will be differences in combustion properties due to both the type of alternative fuel (i.e. pure biodiesel vs. pure diesel) and blend ratio (i.e. B20 vs. B80). Real-time estimation of the fuel blend is key to the optimized use of two-component fuels (e.g. diesel-biodiesel, gasoline-ethanol, etc.). The approach outlined here uses knowledge of the exhaust composition, fuel and air delivery rates to the engine to estimate the fuel blend.