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.