Experimental Investigation of Combustion Timing of HVO, RME and Diesel Fuel in a Euro6 Car Engine during Transient Driving Cycles 2019-24-0138

The current targets to decrease greenhouse gases production, to reduce fossil fuel dependency and to gain energy security and sustainability are driving demand on combustion engine fuels from renewable sources. This effort resulted in utilization of first generation biofuels. Unfortunately, these fuels brought new dilemmas and challenges in general, such as food production competition and land use and, in case of fatty acid methyl esters for compression ignition engines, also technical challenges such as storage stability and deposit formation. Utilization of particle filters and sensitive fuel systems are driving effort to develop compatible renewable biofuels which can be utilized at higher than current shares. Hydrotreated vegetable oils (HVO), as industrially produced biofuels, exhibit some beneficial properties compared to traditional fatty-acid methyl esters especially in terms of oxidation stability, injector fouling, energy content and cetane number. The aim of this study was to investigate heat release rates when three neat fuels (diesel, RME and HVO) are utilized in a current passenger car with a EURO 6 diesel engine at a wide range of operating regimes extracted from various currently used driving cycles. The results show significant effect on combustion of fuel injected during the pilot injection for HVO, with strongly reduced ignition delay and with higher heat release rate compared to diesel fuel, while the effect of RME is small and ambiguous. Other combustion phases were basically similar with reduced delay between the injection event and the onset of the heat-release. In some cases, carefully orchestrated combustion of fuel injected during first and second injections creating continuous heat release designed for diesel operation was maintained for RME, but broken-up into nearly two separate heat release peaks for HVO. At higher loads, diesel and RME behaved mostly similarly, but HVO exhibited a dramatic reduction of the premixed combustion phase. In some operating points, the ECU seems to be adjusting the injection timing to keep combustion timing unchanged during some combustion events.