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Effects of measurement method, coolant temperature and fuel composition on soot emissions were examined by engine experiments. By reducing the pressure fluctuation in the sampling line, the measured soot emissions with better stability and reproducibility could be obtained. With lower coolant temperatures, larger soot emissions were yielded at much advanced fuel injection timings. Compared to gasoline, soot emissions with a blend fuel of normal heptane, isooctane and toluene were significantly decreased, suggesting the amounts of aromatic components (toluene or others) should be increased to obtain a representative fuel for the predictive model of particulate matter in SIDI engines.

A phenomenological model for high-pressure direct injection natural gas-diesel dual-fuel marine engine was developed, which includes natural gas mixing process using Musculus discrete control volume transient diesel jet model, combustion process using quasi-steady model and Woschini heat transfer model, NO generation using Zeldovich mechanism. Effects of natural gas injection pressure and the start of injection timing on the mixing and combustion process were investigated. The results indicated that increasing the injection pressure with fixed injection mass, the NO emission decreased. While the start of injection timing was before TDC, retarding the injection start timing will increase NO generation.