Experimental study on the combustion process and performance of diesel engines fueled by emulsion diesel with novel organic additives

Transportation is one of the major contributors to the world's energy consumption and greenhouse gases emissions. The need for increased efficiency has placed diesel engine in the spotlight due to its superior thermal efficiency and fuel economy over gasoline engine. However, diesel engines also face the major disadvantage of increased NO_x emissions. To address this issue, three types of emulsion fuels with different water concentrations (5%, 10% and 15% mass water) are produced and tested. Novel organic materials (glycerin and ployethoxy-ester) are added in the fuel to provide extra oxygen for improving combustion. NP-15 is added as surfactant which can help to reduce the oil and water surface tension, activates their surface, and maximizes their superficial contact areas, thereby forming a continuous and finely dispersed droplets phase. The stability of the emulsion fuels is tested under various environmental temperature for one year, and no significant separation is observed. It is better than normal emulsion fuel which can only maintain the state for up to three months. The combustion process and performance of the emulsion fuels are tested in a four-stroke, four cylinder diesel engine. The results indicate that the water droplets enclosed in the emulsion fuel explode at high temperature environment and help to break up the big oil droplets into smaller ones, thereby significantly increase the surface area of the oil droplets and enhance the heat transfer from hot gas to the fuel. As a result, the fuel evaporation is improved and the combustion process is accelerated, leading to an improved brake thermal efficiency (up to 14.2%). Meanwhile, the presence of the water causes the peak temperature of the flame to drop, thereby significantly bringing down the NO_x emissions by more than 30%.