Investigation of the combustion characteristics of gasoline compression ignition engine fueled with gasoline-biodiesel blends

Abstract

This research investigates the combustion characteristics of gasoline compression ignition engines fueled with gasoline-biodiesel blends. A single-cylinder diesel engine, modified from a commercial four-cylinder engine, was investigated in Gasoline compression ignition (GCI) mode. Also studied were the effects of the different gasoline blends on the variation of the fuel flow rate (on a mass basis). Gasoline blended with a range of 5-20 % biodiesel and pure diesel was injected into the measuring vessel with various injection pressures and durations by a seven-hole Bosch injector and a common-rail system. The injection pressures were varied from 200 to 1350 bar, and the injection duration was from 800 to 1050 ms while repeating the injection 1000 times for each run. To characterize the combustion, the test engine was mounted with an AC dynamometer and the pressure traces were measured using a piezo-electric pressure transducer. Only pure gasoline mixed with five percent biodiesel as a lubricity enhancer was injected into the cylinder while varying the injection pressure. The injection pressures were set at 600 and 1000 bar while the injection duration was altered to control the same equivalent ratio (λ = 1). Operated in the low-speed condition, the engine speed was fixed at 1200 rpm. Other engine parameters including engine oil, coolant water, and intake air temperature were controlled at the same operating condition for each experiment. To understand the combustion characteristics such as Heat release rate (HRR) and burning duration, the data was analyzed with the one-zone thermodynamic model. Exhaust emissions (CO, NOX and THC) were measured using an exhaust gas analyzer for each case, as well. The results showed that fuel properties had an effect on the injection flow rate. Higher viscosity fuel resulted in a lower injection rate. The injection pressure showed the greatest effect on the fuel flow rate. The higher the injection pressure, the higher the injection flow rate. At the same injection pressure and duration, the injection flow rate was reduced with an increase in the amount of biodiesel in the blend. In terms of combustion phenomena, a 5 % gasoline-biodiesel blend (GB05) showed the most significant differences in combustion when injected at high versus low injection pressures. At the higher injection pressure, the benefits of using diesel fuel were clear, but GB05 combustion at high pressures resulted in increased concentrations of undesirable emissions. On the other hand, GB05 fuel presented clear advantages when injected at a lower pressure. Depending on the injection pressure, the merits of gasoline on the exhaust emission were evaluated, especially with respect to CO, NOX and THC emissions reductions.