Optical study on spray and combustion characteristics of diesel/methyl heptanoate blend fuels

Methyl heptanoate, as a renewable oxygenated fuel produced from algal biomass, holds tremendous potential in achieving low-carbon goals. Optical studies were conducted on the spray and combustion characteristics of diesel and diesel/methyl heptanoate blends with blending ratios of 10 % and 20 % (noted as MH10 and MH20 respectively) in constant volume combustion chamber. The results reveal that as the blending ratio of methyl heptanoate increases, the liquid phase spray penetration distance (LSPD) elongates, the liquid phase spray average cone angle (LSACA) decreases, and the liquid phase spray projected area (LSPA) shows no significant difference. The gas-liquid phase spray penetration distance (G-LSPD), gas-liquid phase spray average cone angle (G-LSACA), and gas-liquid phase spray projected area (G-LSPA) of MH20 are smaller than those of MH10 but larger than those of D100. Furthermore, a higher blending ratio of methyl heptanoate leads to a shorter combustion duration and a higher combustion temperature. Soot emissions of MH20 significantly decrease. Additionally, with the increase of injection pressure, the LSPD, G-LSPD, LSACA, LSPA and G-LSPA of all three fuels increase significantly, and soot emissions of all fuels decrease significantly. Soot emissions of MH20 were reduced to only 4 % of that of D100 under low-pressure injection.