Diesel Engine Control Strategy for Biodiesel Blend Accommodation Independent of Fuel Fatty Acid Structure

Abstract

Growing dependence on foreign oil for transportation as well as greenhouse gas emissions have created a need for advancement in clean and renewable fuel technologies. Biodiesel, a renewable fuel produced from plant oils or animal fats, generally produces lower carbon dioxide, carbon monoxide and particulate matter emissions. However, the use of biodiesel in a diesel engine has certain challenges including lower power output and up to 40% higher nitrogen oxide (NOx) emissions compared to diesel. Biodiesel usage in colder climates is also challenging due to its relatively high cloud point. Based on studies done to understand the effect of biodiesel combustion on engine power and NOx emissions, control strategies are developed to mitigate these challenges. This includes control of the total energy of injected fuel in order to get same the power output for diesel and biodiesel. In order to maintain consistent NOx emissions between diesel and biodiesel, the fraction of oxygen available for combustion contributed by the fuel, air and recirculated exhaust gases is maintained constant. This fuel flexible control strategy greatly reduced or completely eliminated increases in emissions of NOx of up to 30% while largely maintaining the power capacity of the engine when operating with biodiesel. It is also shown with experimental validation that these control techniques are robust to changes in the fatty acid composition of biodiesel, which could vary significantly depending on the feedstock used to produce biodiesel or additional processing done on the fuel in order to make it suitable for cold weather operation.