Experimental study of influence of Liquefied Petroleum Gas addition in Hydrotreated Vegetable Oil fuel on ignition delay, flame lift off length and soot emission under diesel-like conditions

The fundamental behaviour on ignition and combustion characteristics of blends of Hydrotreated Vegetable Oil and Liquid Petroleum Gas was investigated in a constant high pressure, high temperature combustion chamber, using a prototype lab-scale injection system adapted from a conventional common-rail system to conduct the injection events, ensuring that fuel was liquid at any point of the injection system and avoiding the formation of fuel vapour bubbles that could alter the injected fuel behaviour. The ignition delay, flame lift-off length and the soot formation were studied by means of high-speed imaging techniques, for different operating conditions. The aim of the work is to characterize the effect of Hydrotreated Vegetable Oil-Liquid Petroleum Gas blend ratios on the previously mentioned parameters. Experimental results show that the behaviour of the fuel blends follow the expected trends of conventional diesel type fuels when varying ambient temperature, density and injection pressure. Hydrotreated Vegetable Oil, being the highest reactivity fraction, controls auto ignition of the blend. However, Liquid Petroleum Gas acts as combustion inhibitor increasing both ignition delay and lift-off length as its ratio in the blend increases. As a consequence, the differences observed in terms of flame radiation suggest that increasing Liquid Petroleum Gas fraction reduces soot formation as it promotes a higher air/mixture.