Normal Heptane-Diesel Combustion and Odorous Emissions in Direct Injection Diesel Engines

This study investigated normal heptane (N-heptane)-diesel combustion and odorous emissions in a direct injection diesel engine during and after engine warmup at idling. The odor is a little worse with N-heptane and blends than that of diesel fuel due to overleaning of the mixture. In addition, formaldehyde (HCHO) and total hydrocarbon (THC) in the exhaust increase with increasing N-heptane content. However, 50% and 100% N-heptane showed lower eye irritation than neat diesel fuel. Due to low boiling point of N-heptane, adhering fuel on the combustion chamber wall is small and as a single-component C7 fuel, relatively high volatile components present in the exhaust are low. This may cause lower eye irritation. On the contrary, bulk in-cylinder gas temperature is lower and ignition delay significantly increases for 50% and 100% N-heptane due to the low boiling point, high latent heat of evaporation, and low bulk modulus of compressibility of N-heptane than standard diesel fuel. This longer ignition delay and lower bulk in-cylinder gas temperature of N-heptane blends deteriorate exhaust odor and emissions of HCHO and THC.