Investigations into Multiple Premixed Compression Ignition Mode Fuelled with Different Mixtures of Gasoline and Diesel

A study of Multiple Premixed Compression Ignition (MPCI) with mixtures of gasoline and diesel is performed on a light-duty single cylinder diesel engine. The engine is operated at a speed of 1600rpm with the same fuel mass per cycle. By keeping the same intake pressure and EGR ratio, the influence of different blending ratios in gasoline and diesel mixtures (90vol%, 80vol% and 70vol% gasoline) is investigated. Combustion and emission characteristics are compared by sweeping the first (−95 ∼ −35deg ATDC) and the second injection timing (−1 ∼ 9deg ATDC) with an injection split ratio of 80/20 and an injection pressure of 80MPa.

The results show that compared with diesel combustion, the gasoline and diesel mixtures can reduce NO_x and soot emissions simultaneously while maintaining or achieving even higher indicated thermal efficiency, but the HC and CO emissions are high for the mixtures. The NO_x emission of the gasoline and diesel mixture is kept less than 0.4 g/kWh with about 25% EGR and at some points the soot emission is less than 0.06 1/m, which is equivalent to 0.5FSN. With the same first injection timing, increasing the portion of diesel in the fuel brings high pressure rise rate and soot emission due to the early combustion phase and short mixing time, but it can reduce CO and HC emissions. Retarding the second injection timing can significantly increase the soot emission, especially for the mixture containing less gasoline component. The ignition delay of the second stage combustion is almost the same for three fuels and the second injection finishes before the ignition.