Abstract: In this study, the effect of coupling three intake pressures (120, 150, and 180 kPa) and the Cetane number, ignition delay period of fuel on hydrocarbon (HC) emissions was investigated by using a modified single-cylinder light-duty diesel engine. Pure combustion diesel (B00), B20 fuel (mixed with a mass fraction of 20% n-butanol and 80% pure diesel), and B20 + 2-ethylhexyl nitrate (EHN) (0.7% mass fraction of EHN added to B20) were used as fuels for experimental research. Experiment results show that, comparing the hydrocarbon emissions of B00 and B20+EHN, HC emissions almost does not change with the intake oxygen concentration when the intake oxygen concentration is higher than 13%, and the HC emissions under different pressures is basically maintained in the range of 0~1 g/(kw·h). The comparison of hydrocarbon emissions of B20 and B20+EHN shows that the critical oxygen concentration is 16%, 15% and 13% respectively under intake pressures of 120, 150 and 180 kPa. The in-cylinder combustion temperature and combustion duration are the main factors affecting the difference of HC emissions between the two fuels. When the intake oxygen concentration is lower than the critical point of each intake pressure, the difference of combustion temperature in cylinder caused by different cetane number increases the difference of HC emission. With the decrease of oxygen concentration, the influence degree of combustion temperature in cylinder increases.