Autoignition study of LPG blends with diesel and HVO in a constant-volume combustion chamber

There is an increasing interest in reducing CO2 as far as it is the main responsible of greenhouse gas (GHG) emissions. Since the contribution of heavy-duty (HD) vehicles to GHG emissions of the road transport sector reaches 24% in the European Union, Liquefied Petroleum Gas (LPG) is suggested as a promising alternative fuel to be introduced in HD vehicles. The main drawback when using LPG in diesel engines is its poor autoignition behavior. To overcome this difficulty is possible to mix LPG with Hydrotreated Vegetable Oil (HVO) or diesel fuel, which acts as an ignition improver. This work has focused on LPG-HVO blends up to 75 %m/m LPG content, with lower LPG content admixtures included. Another measure to promote autoignition is using advanced injection strategies, particularly at low thermal conditions in the combustion chamber. This study concluded that 25LPG-75HVO blend (without any injection strategy modification) and 50LPG-50HVO blend (with advanced injection strategy) show better autoignition behavior than diesel fuel at low thermal conditions. At usual combustion conditions, LPG-HVO blends up to 75 %m/m LPG content can be supplied using an advanced injection strategy, and achieving similar autoignition behavior than diesel. LPG and HVO contents in the blend can be balanced depending on the thermal conditions. Therefore, a novel injection system with an in-line mixing valve capable of managing the instantaneous LPG/HVO ratio for compression ignition engines, is suggested. Testing these blends with advanced injection strategies using the in-line mixing system in a real HD engine would confirm these results.