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. Over last more than two decades, the 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.
The technical aspects are more pronounced as advanced technologies employed to mitigate pollutants related adverse effects are applied, mandating stringent fuel properties, while demand for fuels from renewable sources is rising. 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, exhibits some beneficial properties compared to traditional fatty acid methyl esters especially in terms of oxidation stability, injector fouling, energy content and cetane number.
Different combustion properties of HVO are supposed to lead to different heat release rates and potentially to adverse effects such as higher engine-out PM and/or NOx. Current engines are, due to advanced technologies used in-situ and for exhaust gas aftertreatment, complex systems, the performance of which can be affected by the fuel. Adjustment of engine ECU for each renewable fuel and its share in a blend with fossil fuel can not be expected so each developed fuel is to be tested and its potential evaluated.
The aim of this study is 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 only, changes of the ratio of premixed to non-premixed combustion can be addressed. Diesel and RME behaved mostly similarly, but HVO exhibited a dramatic reduction of the premixed combustion phase.
The post injection heat releases were mostly difficult to address, because they are overlapped by the main combustion phase and no significant effects of HVO or RME have been usually recorded.
In some operating points, the ECU seems to be adjusting the injection timing to keep combustion timing unchanged during some combustion events.
This paper demonstrates the potential of combustion analysis at multiple engine operating points using data obtained from chassis dynamometer driving cycles, suggesting similar analysis can be done with data obtained during on-road operation of an ordinary production vehicle. It also demonstrates that the combustion of HVO, presented so far, albeit mixed with diesel and not neat as used here, as a drop-in fuel, tends to be advanced relative to diesel fuel. While the operation appeared to be normal on all fuels, it is possible that additional benefits associated with HVO usage may be sought by adjusting the injection timing and phasing to fuel properties.
Martin Pechout, David Macoun
Czech University of Live Sciences
14th International Conference on Engines & Vehicles