Comparative study on combustion and emission characteristics of gas-to-liquid with diesel on a burner and a naturally aspirated compression ignition engine

Abstract

ABSTRACT Due to the consumption of fossil fuels and the generation of harmful emissions by diesel engines, researchers are seeking alternative fuels for diesel, for example, gas-to-liquid (GTL). However, most studies on combustion and emission of GTL focused on the fuel burned on turbocharged heavy-duty diesel engines. The purpose of this study is to reveal the combustion, fuel economy, and emission characteristics of GTL by a burner and a naturally aspirated (NA), fuel direct injection compression ignition light-duty engine. Comparative experiments of the GTL to fossil diesel were carried out, respectively. The burner has good consistency with the diesel engine in revealing emission trends. The results of the burner test showed that GTL produced less flame smoke and its flame height was 5.3% lower than diesel. The results of the engine bench test revealed that the combustion and emissions of the GTL with diesel were significantly different. Compared to diesel, the ignition of GTL began earlier from 1.5°CA to2.5°CA though the combustion was slower in contrast to diesel. The diffusion combustion maximum pressure was considerably 4.8% higher and occurred earlier with 2.2°CA-3°CA, and the premixed combustion peak pressure of GTL was slightly beyond the diesel. The peak of premixed combustion heat release rate (HRR) for GTL was less than that of diesel by 18.9%. While the peak HRR of diffusion combustion was greater by 38.4%. The maximum PRR value of GTL was lower than that of diesel leading to soft combustion. In all test conditions, the brake specific fuel consumption of GTL averagely reduced by 4.7% against diesel, and the brake thermal efficiency was on average 4.3% higher. GTL engine can reduce regular emissions of carbon monoxide, hydrocarbons, nitrogen oxide (NOx), smoke, and particle number (PN) simultaneously. It is worth noting that GTL improved the trade-off issue of NOx and smoke, simultaneously reducing 18.8% NOx and 24.1% smoke on average. The experimental results reveal the GTL is an appropriate alternative fuel for light-duty diesel engine without modification of mechanical fuel system.