An optical study on the spray and combustion characteristics of coal-derived naphtha/diesel blends in a constant volume combustion chamber

Coal-derived naphtha (CDN) is well suited as an additive for diesel to achieve soot reduction in diesel engines; however, there is no study so far to qualitatively reveal the mechanisms through the spray and combustion processes. In this paper, the spray and combustion characteristics of CDN/diesel blends with 10%, 20%, 30% and 40% CDN in volume were studied under various injection pressures in a constant volume combustion chamber. In addition, gasoline/diesel blend with 20% gasoline in volume was also studied for comparison. Results show that, compared with pure diesel, CDN/diesel blends have the improved fuel spray evaporation, the notably reduced peak integrated natural flame luminosity and soot formation. The blend with 40% CDN shows the greatest soot formation reduction of 39.7% under 100 MPa injection pressure. When the volume fraction of gasoline and CDN are both 20% in blends, there is little difference in spray characteristics, but CDN/diesel blend exhibits a greater advantage in soot formation reduction. Under the test conditions, increasing the injection pressure may improve fuel-air mixing to some extent, but its effect on reducing soot formation is not significant, especially at higher CDN proportions.