DI diesel engine performance and emissions from the oxygen enrichment of fuels with various aromatic content

An experimental investigation was conducted on a direct injection diesel engine using conventional and oxygenated diesel fuels. The main scope is to examine the effect of fuel oxygen enhancement for fuels with various aromatic content on engine performance characteristics and, mainly, on pollutant emissions. A mixture of diethylene glycol dimethyl ether (diglyme) and diethylene glycol dibutyl ether (butyl-diglyme) of approximately 20% by mass were added to a high-paraffinics and two commercial diesel fuels of varying aromatic fractions. An experimental apparatus was installed and engine tests were carried out on a naturally aspirated DI diesel engine at various operating conditions. The measurements were comprised of cylinder pressure diagrams, fuel consumption, exhaust smokiness, and exhaust gas emissions (nitrogen oxides, unburned hydrocarbons, and carbon monoxides). According to the experimental findings, the addition of oxygenated agents results in earlier initiation of combustion and in an increase of maximum combustion pressure, mainly due to the increase of cetane number. Fuel oxygen enrichment results in an increase of brake specific consumption and a reduction of combustion duration. The addition of glycol ethers in the diesel fuels is accompanied by a significant decrease of soot opacity and a reduction of carbon monoxides and unburned hydrocarbons with a small penalty on nitrogen oxides. The relative change of diesel exhaust emissions and bsfc caused by the fuel oxygen enhancement depends almost entirely on the engine operating conditions without association with total aromatic percentage. Finally, the fuel oxygen addition appears to be more effective in the reduction of soot, CO, and HC emissions than is the decrease of fuel aromatic content.