Diesel engine modeling by means of CFD (computational fluid dynamics) has become a more and more important tool in the development process for new engine design. An adequate and reliable Diesel engine model relies on many features. Beside the combustion and spray modeling, the question what model fuel should be used is discussed and in the past, a mixture of n-decane and α-methylnaphthalene, denoted as IDEA fuel, was found to be a good surrogate fuel for Diesel for the conventional Diesel combustion mode. New combustion designs such as PCCI (premixed charged compression ignition) are a possible solution for the strict upcoming emission limits. Due to a shift to lower temperatures and better homogenization, less NOx and soot is formed.
To model these combustion designs, a re-evaluation of the model fuel that is to be used is required when the benefit of a detailed chemical reaction mechanism is favored in the combustion modeling. Therefore, engine experiments with Diesel, IDEA, pure n-decane and n-heptane are carried out for various loads, rail pressures, EGR (exhaust gas recirculation) rates and speeds. The measured indicated pressure, apparent heat release and emissions from exhaust gas analysis are used to evaluate which fuel should be chosen as model fuel.
Among the three proposed fuels, the IDEA-fuel shows a good agreement when compared with Diesel fuel. N-decane has less soot formation due to the missing aromatic compounds whereas n-heptane has similar to n-decane less soot formation. Moreover, n-heptane has a larger NOx formation because of a greater heat release and a smaller mean gas temperature. However n-decane ignites much earlier than n-heptane and IDEA fuel. Therefore it is considered that only IDEA fuel is a suitable surrogate fuel for Diesel in the new combustion regime.