Experimental investigation on particulate emissions of a direct injection diesel engine fueled with diesel–diethyl adipate blends

Euro V diesel fuel blended with 8.1%, 16.4%, 25% and 33.8% by volume of diethyl adipate (DEA), corresponding to 3%, 6%, 9% and 12% by mass of oxygen in the blended fuels, were tested on a 4-cylinder direct-injection diesel engine. Experiments were conducted under five engine loads at a steady speed of 1800 rev/min to investigate the effects of the blended fuels on combustion and particulate emission characteristics. The results indicate an increase in ignition delay and the amount of heat release in the premixed burning phase, while a decrease in both diffusive and total combustion duration with an increase in DEA in the fuel. Compared to the diesel fuel, the particulate mass concentration and the total number of particles are reduced significantly, whereas the proportion of soluble organic fraction (SOF) in the particles increases with increasing DEA in the fuel. The increase in SOF might increase the toxicity of the particles. Moreover, the geometric mean diameter (GMD) of the particles shifts towards smaller size. A diesel oxidation catalyst was used and found to further reduce both particulate mass and total number concentration. The results also show that the DOC could reduce the finer particles more effectively.

Research highlights
► DEA leads to longer ignition delay and increases the amount of heat release in the premixed burning phase, whereas it reduces the diffusive combustion phase and the total combustion duration.
► The particulate mass concentration and the particle number concentration increase with engine load but decrease with increasing DEA in the blended fuel.
► With an increase in DEA in the blended fuel, there is an increase in the proportion of soluble organic fraction (SOF) in the particulate, which might increase the toxicity of the particulate.
► DOC can further reduce the particulate mass and total number concentration, but increase the GMD of the particles.