Abstract
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.
Highlights
In traditional diffusion combustion, the non-uniform distribution of the temperature and the mixing-controlled propagation of the diffusion flame [1,2] leads to the formation of large amounts of soot and NOx [3]
In order to make the diesel engine adapt the stringent limits on exhaust emissions, both domestic and foreign researchers are committed to exploring a cleaner and higher-efficiency combustion regime, such as the low temperature combustion (LTC) [4]
The ignition delay period of diesel is increased [5] by applying the technologies like exhaust gas recirculation (EGR), high injection pressure, or intake valve variable timing [6,7,8]
Summary
The non-uniform distribution of the temperature and the mixing-controlled propagation of the diffusion flame [1,2] leads to the formation of large amounts of soot and NOx [3]. In order to break through the obstacle of the advanced combustion mode, dual-fuel injection mode by using high-ignitable fuel to ignite low-ignitable fuel is considered as a potential method to achieve LTC [12,13] This mode is able to control the heat releasing in-cylinder according to different loads by adjusting the composition of the mixture [14,15]. The self-ignition first occurs in a high-ignitable area and spreads to the premixed mixture area in is injected into the cylinder directly which forms reactivity stratification with the homogeneous the combustion chamber [17,18,19]. Combining with EGR, the dual-fuel injection mode can control the main combustion phase and combustionSage duration high-load conditions. Heat and the accumulated heat release amount in a specific interval
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