Experimental Investigation to Specify the Effect of Oxygenated Additive Content and Type on DI Diesel Engine Performance and Emissions 2004-01-0097

The reduction of brake specific consumption and pollutant emissions are issued as future challenges to diesel engine designers due to the depletion of fossil fuel reserves and to the continuous suppression of emission regulations. These mandates have prompted the automotive industry to couple the development of combustion systems in modern diesel engines with an adequate reformulation of diesel fuels and have stirred interest in the development of “clean” diesel fuels. The use of oxygenated fuels seems to be a promising solution towards reducing particulate emissions in existing and future diesel motor vehicles. The prospective of minimizing particulate emissions with small fuel consumption penalties seems to be quite attractive in the case of biodiesel fuels, which are considered as an alternative power source. Studies conducted in diffusion flames and compression ignition engines have shown a reduction of soot with increasing oxygen percentage. However, the effects of the type of oxygenated additive and oxygen content on gaseous and particulate emissions obtained from modern DI diesel engines have not been fully investigated. An experimental investigation is conducted to determine the effect of oxygen content and oxygenate type on DI diesel engine performance and emissions. One conventional and three oxygenated fuels are examined having an oxygen content ranging from 0% to 9%. The fuels are prepared by blending a biodiesel compound (RME), Diglyme and Butyl-Diglyme with a low sulfur diesel fuel in various proportions. An experimental installation is prepared and engine tests are conducted on a naturally aspirated single-cylinder Ricardo Hydra research engine. The measurements are carried out at various operating conditions. The experimental findings reveal an increase of in-cylinder pressure due to the increase of cetane number. In addition, a slight increase of bsfc is observed due to the small decrease of fuel heating value with the increase of the oxygen content. A decrease of ignition delay is observed with increasing oxygen content following thus, the increase of cetane number. A considerable reduction of soot, carbon monoxide and unburned hydrocarbon emissions is witnessed while; nitric monoxide emissions are increased when the oxygen content is increased from 3% to 9%. Similar effects are observed when replacing the rapeseed methyl ester with a mixture of diglyme and butyl-diglyme and the oxygen percentage remains unaltered. As revealed, a reduction of tailpipe soot without overall considerable penalties in bsfc and NO_x emissions can be achieved in modern DI diesel engines using oxygenated additives at elevated percentages (30% by mass).