Investigation of Performance and Emissions of Premixed Combustion of Hydroprocessed Esters and Fatty Acids (HEFA) in a CRDI Research Engine With Methanol PFI

Abstract An investigation of the performance and emissions of premixed combustion of a synthetic paraffinic kerosene sustainable aviation fuel (SAF) consisting of hydroprocessed esters and fatty acids (HEFA) was conducted using a CRDI research engine with ultra-low sulfur diesel (ULSD) as a reference. In a constant volume combustion chamber (CVCC), HEFA exhibited a shorter ignition delay, confirmed by its higher derived cetane number (DCN) at 58.6 compared to ULSD at 48. Further investigation was carried out at 5 bar indicated mean effective pressure (IMEP) with the addition of EGR to control combustion and mitigate NOx. Methanol, a low reactivity fuel, was port fuel injected (PFI) at 50% with HEFA (by mass) and ULSD to investigate its cooling effect on in-cylinder temperatures as a means of mitigating NOx. Combustion pressure for HEFA was found to be greater than ULSD in most cases and occurred sooner. The apparent heat release rate (AHRR) was notably lower for HEFA than for ULSD in most cases, while the addition of methanol resulted in an increased duration of the low temperature heat release region for both HEFA and ULSD. With addition of EGR and PFI, several negative temperature coefficient regions were observed correlating with the pilot, primary, and tertiary direct injections. HEFA saw more than a 10% reduction in NOx than ULSD in CDC. The addition of EGR resulted in further reduction of NOx compared to ULSD at equal operating points. Implementing EGR and 50% methanol PFI with HEFA reduced NOx emissions by over 70% compared to ULSD in CDC. In all studied cases, CO2 emissions for HEFA were slightly reduced compared to ULSD at matched operating parameters, while CO increased compared to ULSD. Lastly, both ULSD and HEFA achieved a combustion efficiency of 97% in CDC at 5bar IMEP. The combustion behavior of the studied HEFA in combination with the emissions reduction suggests potential suitability as a substitute for ULSD in some applications.