In-cylinder oxygen concentration estimation for diesel engines via transport delay modeling

In addition to the main injection, current diesel engines often use one or more pilot injections and one or more post injections to better control the combustion process. The mass of fuel delivered and the timing of these injections has a strong affect on the combustion temperature, the heat release rate, the torque production and the formation of harmful emissions. As the cylinder conditions change and in particular as the in-cylinder oxygen concentration changes, the fuel injection masses and timings must be adjusted to achieve a desired trade-off between emissions production and fuel consumption. Alternative combustion modes are particularly sensitive to the cylinder conditions. Incorrectly estimating the cylinder contents can cause inefficient combustion and can increase the emissions produced during transient operations. Current in-cylinder oxygen concentration estimators do not account for the transport delay of the recirculated exhaust gas and are therefore less accurate during transients. By incorporating the effects of the time-varying transport delay, the plug flow based oxygen concentration model presented in this paper is able to dynamically predict the in-cylinder oxygen concentration of every induction event. The robust performance of the proposed model is demonstrated through comparisons to a high-fidelity GT-Power engine model.