Effect of Multiple Injection Strategies on the Spray Atomization and Reduction of Exhaust Emissions in a Compression Ignition Engine Fueled with Dimethyl Ether (DME)

Abstract

This experimental research paper presents the effect of multiple injection strategies on the neat dimethyl ether (DME) fuel atomization and reduction of exhaust emission characteristics within a compression ignition (CI) engine. Pilot and split injections under various injection mass (minj) and timing (tinj) conditions as a multiple injection strategies were applied to reveal its effect on the improvement of spray atomization and the reduction of exhaust emissions in terms of spray tip penetration, Sauter mean diameter (SMD), rate of heat release (ROHR), indicated mean effective pressure (IMEP), and generation of exhaust emissions (such as CO, HC, NOX, and soot). These experimental results were then compared with those from diesel fuel cases. It was revealed that multiple injection strategies for DME fuels lead to poor atomization characteristics, because the second injection of fuel influences both the density and velocity of spray droplets at the points of measurement. This issue can be resolved by controlling the injection mass and the second injection timing, or by increasing the injection pressure. However, multiple injection strategies can achieve a simultaneous reduction of NOX and soot emissions in comparison to single injection results, and NOX emissions gradually decreased with the advance of the first injection timing without increasing soot emissions due to a lower C−H ratio. It was also observed that the concentrations of HC and CO emissions for DME are influenced by the first injection timing. For a retarded first injection timing (BTDC 20°), HC and CO emissions for DME indicated relatively low levels, in comparison to the single injection case.