Experimental evaluation of sensitivity of low-temperature combustion to intake charge temperature and fuel properties

Main challenge for mineral diesel in achieving low-temperature combustion is its poor volatility characteristics, which results in relatively inferior fuel–air mixtures. In this experimental study, feasibility of mineral diesel–fueled premixed homogeneous charge compression ignition (PHCCI) combustion was explored by employing an external charge preparation technique. An external mixing device called “fuel vaporizer” was developed for improving the fuel–air mixing. To investigate the effect of fuel properties on PHCCI combustion, this study was carried out using a variety of additives blended with mineral diesel, which included low-quality high-volatile fuel (kerosene), low-cetane high-volatile fuels (ethanol and gasoline) and high-cetane low-volatile fuel (biodiesel). To investigate the effects of intake charge temperature (T_i), experiments were performed at three T_is (160, 180 and 200 °C) and six different relative air–fuel ratios (λ = 1.5–5.25). In all experiments, exhaust gas recirculation (EGR) rate was maintained constant at 10%. Experimental results showed that combustion phasing was significantly affected by the fuel properties and T_i. At lower engine loads, volatile additives improved start of combustion, combustion phasing and heat release rate; however, excessive knocking was seen at higher engine loads. Diesoline (15% v/v gasoline with mineral diesel) and diesosene (15% v/v kerosene with mineral diesel) showed significant improvement in engine performance characteristics, while B20 (20% v/v soybean biodiesel with mineral diesel) delivered relatively higher indicated specific fuel consumption (ISFC). Increasing T_i affected fuel–air mixing, which resulted in slightly lower carbon monoxide (CO) and hydrocarbon (HC) emissions, but higher T_i led to excessive knocking and resulted in slightly higher oxides of nitrogen (NO_x) emissions. Addition of volatiles reduced particulate emissions; however, increasing T_i led to slightly higher particulate emissions. Presence of significant number of nanoparticles during combustion of B20 was another important finding of this study. Overall, it was concluded that addition of volatile additives such as gasoline, alcohols and kerosene, in addition to optimized T_i can improve mineral diesel–fueled PHCCI combustion and can lead to potentially expanded operating window.