Closed-Loop Control Framework for Fuel-Flexible Combustion of Biodiesel Blends

This paper presents a closed-loop control framework for fuel-flexible combustion control of biodiesel blends. This framework consists of two parts: blend detection and blend accommodation. Blend detection can be accomplished by an experimentally-validated dynamic estimator using exhaust oxygen and air-fuel ratio information. Blend accommodation can be accomplished by changing the control variables that the engine control module uses, namely, replacing exhaust gas recirculation fraction with combustible oxygen mass fraction, replacing total injected fuel mass with total injected fuel energy, and replacing start of main injection timing with end of main injection timing. With the conventional control structure it is experimentally shown that pure biodiesel (B100) produced 38% more brake specific nitrogen oxides (BSNOx) than pure conventional diesel (B0). With the new proposed structure, B100 produced not only lower BSNOx than B0, but also higher torque, higher brake thermal efficiency, lower particulate matter, and lower combustion noise than B0. Comparable experimental results are also presented for B5 and B20 blends.