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Energy-based and oxygen-based biodiesel blend level estimation methods for diesel engines

Biodiesel is an alternative fuel derived from vegetable oils, animal fats, or other sources, and it can be made into biodiesel blends by mixing with conventional diesel. To achieve optimal engine combustion as well as minimal emissions with biodiesel blends, on-board blend level estimation system is one of the prerequisites. The paper explores two possible approaches of estimation: 1) oxygen-based method, which differentiates diesel and biodiesel by evaluating oxygen fraction in exhaust; 2) energy-based method, which estimates the blend level by taking advantages of the fact that biodiesel has lower calorific content than diesel. By measuring injected fuel mass and calculating net heat release based on measurement of in-cylinder pressure, energy content of the fuel was estimated, thus was the biodiesel blend level. In oxygen-based method, wideband oxygen sensor can be utilized to measure exhaust oxygen concentration. The influence of exhaust gas recirculation (EGR) on this method and its estimation accuracy were also analyzed and demonstrated. A high-fidelity, direct injection, diesel engine model was developed in GT-Power for validation purpose. Through simulations, the effectiveness of these two estimators was evaluated and their accuracies were compared.