Role of fuel and free diffusion of furan/diesel and methyl heptanoate/diesel blends spray on combustion characteristics

Furan and methyl heptanoate are potential substitute fuels for high energy density and renewability. Free spray diffusion after injection greatly influences the combustion process. In this study, the effects of free diffusion of pure diesel (D100) and four blends (F10, F20 (10 %, 20 % furan and 90 %, 80 % diesel), MH10, MH20 (10 %, 20 % methyl heptanoate and 90 %, 80 % diesel)) spray on combustion characteristics were investigated in a constant volume bomb. The results show that the effects of fuel properties on gas-liquid area and gas-to-liquid ratio of area (GTL_ar) at free diffusion stage are more significant. The GTL_ar of F20 and MH20 reaches about 1.86, while D100 is 0.82. At 140 MPa, the peak flame area of F20 and MH20 exceeded 750 mm², while D100 was near 600 mm². When the gas-liquid area and GTL_ar increase, the flame temperature increases. At 140 MPa, the flame KL of F20 and MH20 is net-zero, while the flame KL of D100 is above 3. It reveals that blending furan and methyl heptanoate is beneficial to reduce soot formation due to higher temperature and oxygen content, respectively. These findings provide a basis for the engine application and bioenergy efficient utilization of furan and methyl heptanoate as renewable energies.