Particulate number and NOx trade-off comparisons between HVO and mineral diesel in HD applications

The increase in worldwide greenhouse gas emissions and costs for fossil fuels are forcing fuel suppliers and engine manufacturers to consider more sustainable alternatives for powering internal combustion engines. One very promising equivalent to mineral diesel fuel is hydrotreated vegetable oil (HVO) as it is highly paraffinic and offers similar combustion characteristics. This fuel offer the potential of not requiring further engine hardware modification together with correspondingly lower exhaust gas emissions and better fuel consumption than mineral diesel. In this paper the spray and combustion characteristics of HVO and its blends are investigated and compared with mineral diesel (European standard). Evidence of the reported reductions in NOx emissions has proven contradictory with some researchers reporting large reductions, whilst others measured no differences. This paper reports the results from comparison of three different experimental tests methods using diesel/HVO binary fuel blends. The macroscopic spray characteristics have been investigated and quantified using a constant volume spray vessel. Engine performance and exhaust emissions have also been characterised using a HD diesel engine in its original configuration (mineral diesel fuel-ready) and then in a recalibrated configuration optimised for HVO fuel. The results show that the engine injection control and also the fuel quality can influence the formation of NOx and particulate matter significantly. In-particular a potential pilot injection proved highly influential upon whether NOx emissions were reduced or not. When optimising the fuel injection, a reduction in NOx emissions of up to 18% or reductions of PN of up to 42–66% were achieved with simultaneous savings in fuel consumption of 4.3%