Development of a reduced diesel/PODEn mechanism for diesel engine application

Polyoxymethylene Dimethyl Ethers (PODEn) is a promising diesel alternative fuel, with a high cetane number and oxygen content, which can reduce the emissions of soot. In this study, a new simplified n-heptane–n-butylbenzene –PODEn–polycyclic aromatic hydrocarbon (PAH) mechanism for diesel engine application was developed. In this model, a mixture of n-heptane and n-butylbenzene is regarded as representative substance of diesel. First, the detailed mechanism of PODEn is simplified by using the methods of rate of production (ROP), direct relation graph with error propagation (DRGEP), and sensitivity analysis. The simplified PODEn sub-mechanism was coupled to the simplified multi-component diesel mechanism of n-heptane–n-butylbenzene–PAH to construct a simplified model of n-heptane–n-butylbenzene–PODEn–PAH containing 179 species and 769 reactions. Then the key dynamic parameters of the PODEn sub-model were optimized using the sensitivity analysis method. To confirm the rationality and reliability of the optimized diesel/PODEn reduced mechanism, the experimental values such as laminar flame velocity, component concentration and ignition delay were verified. The verification results show that there was little difference between the simulated values and the test values. Finally, the proposed mechanism was coupled to the computational fluid dynamic (CFD) software CONVERGE to predict the emission characteristics and combustion of an actual diesel engine under different mixing ratios of PODEn. The results for in-cylinder pressure and heat release rate (HRR), carbon monoxide (CO), nitrogen oxide (NOX) and soot emissions modeled by proposed mechanism are well in line with the test data, indicating that the newly developed diesel/PODEn reduced mechanism can simulate the combustion and emission of diesel engines.