Fuel blend fraction estimation for fuel-flexible combustion control: Uncertainty analysis

“Fuel-flexible combustion control” strategies require accurate fuel composition information. A physics-based fuel blend fraction estimator for lean-burn combustion is used to assess the impact of uncertain variables on the estimator accuracy. For biodiesel blends in a diesel engine, the strategy is shown to be minimally affected by biodiesel feedstock variations, and expected fuel flow and oxygen sensor errors. However, observed airflow estimate errors are expected to lead to large estimator errors. When applied to ethanol blends, the estimator error is lower due to a higher stoichiometric mixture fraction for ethanol, and inherent differences in typical lean-burn gasoline engine operating conditions.