Oxygen fraction estimation for diesel engines utilizing variable intake valve actuation

Advanced diesel engine architectures employing flexible valve trains enable emissions reductions and fuel economy improvements through advanced combustion strategies. These combustion strategies, such as pre-mixed charge compression ignition (PCCI), homogenous charge compression ignition (HCCI) and low temperature combustion (LTC), are controlled and enabled through the use of flexible valve trains. The in-cylinder oxygen concentration serves as a critical input in controlling these strategies. Unfortunately, the in-cylinder oxygen concentration is extremely difficult to measure on production engines. However, the oxygen concentrations in the intake and exhaust manifold can be utilized to calculate the in-cylinder oxygen concentration when the charge and residual in-cylinder mass are available. A model-based observer is developed to estimate the oxygen concentration in the intake and exhaust manifolds. The oxygen concentration estimates will be sensitive to errors in the mass flows of the manifold filling dynamics. To improve the EGR flow measurement, a high-gain observer is implemented to provide a more accurate EGR flow estimate. The observer estimates the oxygen concentrations to within 0.5% O₂ and converges in less than 0.5 seconds.