Study on the coupling effect of fuel physicochemical characteristic and intake pressure on HC emission

The coupling impacts between intake pressure and fuel physicochemical properties on hydrocarbon (HC) emission were studied through testing a modified single-cylinder compression ignition engine at the intake pressures of 120 kPa, 150 kPa and 180 kPa, fueled with pure diesel (B00), n-butanol-diesel blends with the blend ratio of 20% n-butanol-80% diesel by mass (B20) and B20 + EHN (adding 0.7% mass fraction 2-ethylhexyl nitrate (EHN) into B20) respectively. The results showed that: when ignition delay period is basically the same, the difference in HC emission between B00 and B20 + EHN fuel is relatively small. In the meantime, critical points of intake oxygen concentration appeared under all intake pressures. When the intake oxygen concentration was lower than the critical point, the difference in in-cylinder combustion temperature caused by the difference in cetane number would amplify HC emission difference. At the intake pressures of 120 kPa, 150 kPa and 180 kPa, the critical point value of intake oxygen concentrations were 16%, 15% and 13% respectively.