Effects of Oxygenates and Aromatics in Gasoline on Vehicle Particulate Emissions 2021-01-0542
There have been tremendous improvements in China fuel quality in recent years in conjunction with newly implemented vehicle emissions standards to combat air pollution. The focus of concern is particulate emissions from gasoline engines especially from high volume gasoline direct inject (GDI) engines, therefore the China 6 (GB 18351.6-2016) emission standard introduces strict PM/PN requirements.
Because the fuel and vehicle are an integrated system, the composition of gasoline is one of the factors affecting PM/PN emissions. Ethanol and aromatics are widely used as octane boosters, changing the composition of China’s gasoline pool. In this study, two gasoline oxygenates, ethanol and methyl tert-butyl ether (MTBE), and heavy aromatic hydrocarbons were studied in vehicles with a GDI engines. Vehicle tests were performed on the Worldwide Harmonized Light Vehicles Test Cycle (WLTC).
In order to investigate the effect of oxygenates on PM/PN emissions, one group of the test fuels were designed with a base fuel blending either ethanol or MTBE or mix of the two at different levels. Another group of the test fuels were designed with different levels of aromatics by carbon numbers. Particulate Matter Index (PMI) and Particulate Evaluation Index (PEI) of the fuels in both groups are determined. For the fuels in the oxygenates group, emission tests results illustrate that the PN emissions has poor correlation with either fuel indices or oxygen content meaning that the fuel indices need to be corrected based on the oxygenates. The fuel blends with 10% of ethanol show a relatively higher PN emissions than other oxygenated test fuels. The aromatic fuel results show a good correlation between particulate emissions, fuel indices and heavy aromatic hydrocarbons. PN emissions increase with the increase of heavy aromatics content while the total aromatics remains the same. An increase of total aromatics does not necessarily lead to increase in the PN emissions as long as there is control and reduction of heavy aromatic hydrocarbons.