The impact of premixed n-butanol mixture on the heat release rate was investigated based on a modified light-duty diesel engine. The results show that reactivity stratification is formed in the cylinder through n-butanol port fuel injection (PFI) and diesel direct injection (DI). The initial heat release rate of the diesel/butanol dual-fuel combustion is restrained due to the low ignitability of butanol and the high volatility. Because of the auto-ignition of diesel, premixed n-butanol undergoes a high-temperature reaction, which has an active influence on the heat releasing of diesel/butanol dual-fuel combustion. With the increase of the amount of premixed n-butanol injected, the heat release rate in the initial combustion period has a critical value. When the n-butanol injection quantity is less than 13 mg/cycle, the initial heat release rate of dual-fuel combustion is lower than the pure diesel combustion because the lean premixed n-butanol/air mixture limits the flame propagation. When the fuel injection rate of n-butanol is higher than 13 mg/cycle, the heat release rate is accelerated, leading to obvious flame propagation.

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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.