The effect of the fuel aromatic content on soot and heavy hydrocarbon emissions from a single-cylinder direct-injection diesel engine has been investigated burning a pure parafinic fuel (n-tetradecane), a tetradecane-toluene mixture (70-30 vol%) and two diesel oils with different aromatic content. All experiments were at various air-fuel ratios with constant engine speed and injection timing advance. The detailed chemical analysis of exhaust heavy hydrocarbons in terms of mass percentage of paraffins, monoaromatics, polyaromatics and polar compounds, and the gas chromatography-mass spectrometry of each hydrocarbon class have been compared with the original fuel analyses in order to discriminate the unburned fuel compounds from the combustion-formed products. The soot emission rate has been found to be independent of the fuel aromatic content, but the fuel affects the quality and quantity of heavy hydrocarbon emission. Low amounts of heavy hydrocarbons, mainly partially oxidized compounds, are emitted from tetradecane combustion, whereas diesel fuel oils produced high emissions of heavy hydrocarbons, mainly unburned fuel compounds. This is particularly evident at high air-fuel ratios and can be attributed to the longer ignition delay and lower volatility of the diesel fuel oils with respect to tetradecane. However, higher emissions of heavy hydrocarbons have been found for tetradecane-toluene diesel combustion compared with tetradecane combustion, even though the addition of toluene to tetradecane has not modified the ignition delay of the fuel. Furthermore the addition of toluene reduced only the oxidation of the fuel paraffin, which survived the combustion process, as is evidenced by the quantitative determination of unburned tetradecane emitted in the two cases. These findings seem to indicate that toluene and, in general, the presence of aromatic compounds in the fuel, inhibit the paraffin oxidation, leading to a high emission of heavy hydrocarbons mainly composed of unburned fuel paraffinic compounds. The emission of polynuclear aromatic hydrocarbons (PAH) from tetradecane and tetradecane-toluene diesel combustion indicates that these compounds are combustion-formed products, but unburned fuel PAH are the main components of PAH emitted by the diesel fuel oils.
Effect of fuel aromaticity on diesel emissions
Barbella Rosalba;Ciajolo Anna;
1989
Abstract
The effect of the fuel aromatic content on soot and heavy hydrocarbon emissions from a single-cylinder direct-injection diesel engine has been investigated burning a pure parafinic fuel (n-tetradecane), a tetradecane-toluene mixture (70-30 vol%) and two diesel oils with different aromatic content. All experiments were at various air-fuel ratios with constant engine speed and injection timing advance. The detailed chemical analysis of exhaust heavy hydrocarbons in terms of mass percentage of paraffins, monoaromatics, polyaromatics and polar compounds, and the gas chromatography-mass spectrometry of each hydrocarbon class have been compared with the original fuel analyses in order to discriminate the unburned fuel compounds from the combustion-formed products. The soot emission rate has been found to be independent of the fuel aromatic content, but the fuel affects the quality and quantity of heavy hydrocarbon emission. Low amounts of heavy hydrocarbons, mainly partially oxidized compounds, are emitted from tetradecane combustion, whereas diesel fuel oils produced high emissions of heavy hydrocarbons, mainly unburned fuel compounds. This is particularly evident at high air-fuel ratios and can be attributed to the longer ignition delay and lower volatility of the diesel fuel oils with respect to tetradecane. However, higher emissions of heavy hydrocarbons have been found for tetradecane-toluene diesel combustion compared with tetradecane combustion, even though the addition of toluene to tetradecane has not modified the ignition delay of the fuel. Furthermore the addition of toluene reduced only the oxidation of the fuel paraffin, which survived the combustion process, as is evidenced by the quantitative determination of unburned tetradecane emitted in the two cases. These findings seem to indicate that toluene and, in general, the presence of aromatic compounds in the fuel, inhibit the paraffin oxidation, leading to a high emission of heavy hydrocarbons mainly composed of unburned fuel paraffinic compounds. The emission of polynuclear aromatic hydrocarbons (PAH) from tetradecane and tetradecane-toluene diesel combustion indicates that these compounds are combustion-formed products, but unburned fuel PAH are the main components of PAH emitted by the diesel fuel oils.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.