Study On Combustion Characteristics And Reliability Of Gas-to-Liquid Engine

Using alternative clean fuels is an effective way to solve problems of petroleum crisis and environment pollution. As a new alternative, Gas-to-Liquid fuel (GTL) has special properties with high cetane number, nearly zero sulfur and low aromatics contents, which indicates lower emissions for internal combustion engines than conventional diesel fuel. However, when GTL is used in current diesel engines directly, It is very necessary to do many researches on combustion and emission performance of GTL engine, as well as elastomer compatibility with GTL and GTL lubricating ability.First, GTL-diesel blend fuels with different GTL volume fractions were prepared. Fuel properties of these blends were studied. Then, the relationship between the fuel properties and GTL fraction was formulated. Most of the properties of blends have good linear relationship with GTL fraction in the blends.Spray characteristics of GTL was examined via high speed digital camera. GTL exhibits little difference with that of the diesel fuel, but shorter spray penetration and later injection, compared to diesel. The injection process of gas-to-liquid (GTL) fuel was investigated on a fuel pump test rig. Fuel injection rate and fuel line pressure of GTL and conventional diesel fuels were measured on a fuel pump test bench and sound speed was calculated at various operating conditions. The results of GTL injection process show that the pump speed and load have significant effects on fuel injection rate and line pressure of pump and nozzle ends. When compared to diesel, at the same test point, GTL shows fuel injection rate and the peak values of line pressure at pump and nozzle ends are lower, and quantity of fuel injection per cycle with GTL is less. It is worth noting that the fuel injection timing of GTL retards slightly, moreover, fuel injection duration is shorter. The calculated sound speed of GTL is smaller than that of diesel fuel.Study of combustion flame characteristics of GTL was conducted in a burner using high pixel digital camera and three-base-color method. Compared to diesel, smoke of GTL combustion flame is lower, the length of GTL flame is shorter by 5.3% and the average temperature is equivalent to diesel. Power and economy performance, combustion and emission characteristics of natural aspirated engine CA498 and turbocharged engine fueled with GTL and blends were studied under different engine operating conditions according to ECE R49 13-mode and US 13-mode cycles. The results show that fuel consumption, thermal efficiency and engine-out emissions including CO, HC, NOx, Soot and CO2 of GTL are all better than those of diesel.Combining advantages of oxygenated fuels including methanol, ethanol and isopropanol, and low-emission GTL fuel, combustion and emission characteristics of port fuel injection of oxygenated fuels combined with directly injection of GTL were conducted. Compared to single GTL direct injection, although GTL compound combustion produces high CO and HC emissions, port fuel injection of methanol, ethanol and isopropanol can reduce NOx and soot emission simultaneously. Especially, larger premixed ratio of oxygenated fuels can reduce NOx and soot significantly.The compatibility of four kinds of elastomers popular used in automobiles with GTL was investigated. The parameters of mass, volume, hardness, tensile strength, ultimate elongation and tear strength of Nitrile-Butadiene Rubber (NBR), Ethylene-Propylene-non conjugated Diene Rubber (EPDM), Fluoroelastomer (FKM) and Chlorinated Polyethylene (CPE) were measured before and after 504-hour immersion in GTL and variation rate of the parameters were calculated. The results show that all the parameters of the EPDM vary significantly and those of the NBR, FKM and CPE change slightly. Especially, FKM reveals the best compatibility with GTL.The lubricating ability of GTL was studied by four-ball apparatus and fuel pump test bench which is specially built up for long-term running. Some parameters concerned about wear of metal balls and plunger couples were measured. The results show that the wear is smaller than limitation and satisfies the lubricating requirements for GTL added with lubrication.