The diesel engine plays a dominant role in the field of (maritime) transportation and is expected to do so in the coming years. Depletion of fossil fuels and environmental impact are relevant concerns, widely acknowledged by the international community. NOx contributes to acid deposition and eutrophication. Regulations on NOx emissions become more stringent, such as the North Sea becoming a NECA area in 2021. In diesel engine emissions NOx mainly consists of NO.
Given the relevance of NO-emissions a prediction tool is useful. Hohlbaum has suggested a 2-zone in- cylinder model approach to predict NO-emissions. The cylinder volume is divided in two zones, one containing fresh air, the other hosting secondary combustion. In the flame front, which separates both zones, primary combustion takes place at an air excess ratio smaller than unity. Air also passes the flame front, effecting the composition in secondary combustion zone, where NO-formation is calculated using the extended Zel’dovich formulation.
The inclusion of gas properties by means of an equations of state is investigated as an opportunity to reduce the uncertainty in the assumptions in the original model formulation. Measurements on a 4 cylinder MAN engine are used to evaluate simulation results.
Matching the simulated cylinder volume to the actual cylinder volume using the fuel flow, requires an additional tuning parameter - the partition of the cylinder volume in two zones at start of combustion - since the original assumption no longer holds.
The original tuning parameter - the air excess ratio in the flame front - in combination with the newly introduced tuning parameter proved insufficient to match the simulated to the measured fuel flow. Therefore, the constant air flow passing the flame front is adjusted. Changing the flow profile made it possible to match the simulated to the measured fuel consumption. The simulated NO emission where 2.7 times higher than the measured values in the operating point investigated.
A more complete analysis of flow profiles at different operating points is still required.