Energy Conversion and Combustion Characteristics of Diesel and N-Alcohol Blends (N-Propanol to N-Hexanol) Under Low Ambient Temperature and Different Injection Pressures

To reveal the effects of different alcohols addition to diesel on the energy conversion characteristics and combustion characteristics under low ambient temperature, diesel and four sets of blends (the volume ratio of n-propanol/diesel, n-butanol/diesel, n-pentanol/diesel, and n-hexanol/diesel being 20%/80%) were formulated. To explore the possibility of compensating for the decrease in heat value of alcohol blended fuel by increasing injection pressure, the experiments were also carried out under injection pressure of 80–160 MPa. It was discovered that the blending of alcohols into diesel significantly improved the energy conversion efficiency, and n-propanol was the most significant. In addition, the energy conversion efficiency was increased the most when the injection pressure was 120 MPa, and the energy conversion efficiency of n-propanol/diesel blend fuel was increased by 6% compared to pure diesel. However, as the carbon chain length of the alcohols increased, energy conversion efficiency gradually decreased. In addition, the impact of alcohol additives on the ignition process depends on the balance between two opposing effects, the dilution promotion effect, and the cooling inhibition effect. Both n-propanol and n-butanol blended with diesel fuel led to increased ignition delay time and combustion durations, which negatively impacted the cold start success rate and energy conversion efficiency of compression ignition engines. However, n-hexanol was found to reduce ignition delay time and combustion duration while simultaneously reducing soot radiance, making it a favorable choice as an alcohol additive for diesel fuel.