In-Cylinder Mass Estimation Using Cylinder Pressure

To meet future pollutant emissions standards, it is crucial to be able to estimate the cycle by cycle in-cylinder mass and the composition of the combustion chamber charge. This charge consists of residual gases from the previous cycle, fresh air and fuel. Consequently, the estimation of the fresh air mass based on total in-cylinder mass is a function of residual gas fraction. This estimation is essential to compute the fuel mass to be injected. This paper proposes an algorithm, based on physical equations, which estimates the in-cylinder total mass based on cylinder pressure. A residual gas model, which computes the burned gas fraction, is then used to determine the fresh air mass. The paper shows that the algorithm, tested on a Spark Ignited engine, is very robust to noise. To test the estimator several parameters are varied: valve timing, cylinder pressure sampling period, residual gas fraction, cylinder pressure offset and exhaust gas temperature.