Impact of alternative fuels and hydrogen-enriched gaseous fuel on combustion and emissions in diesel engines

The utilisation of alternative fuels, specifically gaseous fuel, in diesel engines has some disadvantages such as reduced engine thermal efficiency and increased exhaust gas emissions, although showing good results in reducing soot and NOX, simultaneously. Therefore, the effect of the hydrogen – enriched gaseous fuel in the dual fuelled combustion process was studied as a mean of improving further the combustion process and control emissions. The hydrogen addition was very effective in overcoming the penalty of the biogas or LPG-diesel dual fuelled engine operation. With the presence of hydrogen the oxidation rate of combustion product was improved thus reducing emissions (HC, CO and PM except NOX) whilst the engine thermal efficiency was also improved. The implementation of exhaust gas recirculation (EGR) and advanced injection timing showed great potential for dual fuelled engine. The utilisation of EGR at high LPG concentration further improved soot – NOX trade-off through low in-cylinder temperatures and reduced amount of liquid fuel used for combustion. Moreover, the properties of the injected diesel fuels as a pilot fuel have been shown to significantly affect the combustion process, rate of heat release, and emissions formation and oxidation. Oxygenated fuel like RME contributed to the reduction of emissions, except NOX, while a high cetane number fuel like GTL showed better tolerance to EGR addition and soot – NOX trade-off