In the past, the Navy has investigated new renewable diesel engine fuels in comparison to conventional petroleum-based fuels using some previously published combustion metrics based on ignition delay, maximum rate of heat release and combustion phasing. These metrics quantify new fuel combustion changes using a conventional heat release analysis as compared to the base fuel. When combustion changes exceed established levels, fuel may be deemed marginal or unacceptable. In this study, these metrics are applied to Primary Reference diesel Fuel (PRF) mixtures in the range from 35 to 65. As expected, significant combustion variations are observed with lengthening ignition delay and increasing maximum heat release rate resulting from lower Cetane Number (CN) fuel. In this work, these steady-state metrics were then applied to predict the worsening of cold start engine performance. It is seen that the acceptable (‘green’) range of combustion change variations provides for acceptable cold engine starting performance. As the steady-state combustion changes become moderately more significant (‘yellow’), the cold start performance degrades. With very substantial steady-state combustion metric changes (‘red’), the cold start nature becomes unacceptable. This study shows that excellent correlation between steady-state engine performance and cold start behavior is possible.

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