Abstract
A new four-stroke carburetor motorcycle engine without any engine adjustments was used to study the impact of fuel aromatic content on exhaust emissions of criteria air pollutants (CO, THC, and NOx). Three aromatic fuels were tested, containing 15, 25, and 50% (vol) aromatics mixed with gasoline. A commercial unleaded gasoline was also tested as a reference case (RF). The experimental data indicated that a lower aromatic content (25 and 15 vol%) in gasoline reduced the amounts of THC and NOx by more than 10% compared to the reference fuel (aromatic content 30 vol%). CO emissions, on the other hand, did not appear to be related to the aromatic content of gasoline. The excess air ratio (λ) values for the aromatic test fuels were lower than 1.0, i.e., under fuel-rich conditions, and CO emissions increased due to lack of oxygen. In contrast, high NOx emissions appeared in a near stoichiometric air-fuel ratio, and decreased as the fuel mixture approached lean or rich conditions. The results also showed that decreasing the aromatic content from 50 to 25 and 15 vol% in gasoline may result in a reduction of benzene emissions from the motorcycles without a catalyst converter. This study shows that decreasing the aromatic content in gasoline may reduce the emissions of THC, NOx, and benzene, but not CO, from four-stroke carburetor motorcycles.
Highlights
Worldwide urban air pollution is estimated to be responsible for 865,000 premature deaths every year and about 60% of these deaths occur in Asia (World Health Organization, 2007; Colbeck et al, 2011)
The experimental data indicated that a lower aromatic content (25 and 15 vol%) in gasoline reduced the amounts of THC and NOx by more than 10% compared to the reference fuel
The low level of variance in the heating value of each test fuel may have contributed to the lack significant differences in fuel consumption for gasolines with different aromatic content
Summary
Worldwide urban air pollution is estimated to be responsible for 865,000 premature deaths every year and about 60% of these deaths occur in Asia (World Health Organization, 2007; Colbeck et al, 2011). Gasoline vehicles (including passenger cars and motorcycles) are important contributor of the air pollution in urban areas (Srivastava et al, 2008; Tsang et al, 2008; Zhang et al, 2008; Chien et al, 2009). Many Asian countries, such as China, India, Indonesia, Taiwan, and Thailand, have a large and growing number of low engine capacity motorcycles (motorcycles with two- or four-stroke engines). Motorcycles with displacements of 50–125 cm are far more popular than heavy-duty motorcycles (displacement > 250 cm3) in Taiwan and other Asian countries. Small motorcycles have carburetor engines with a single cylinder and do not have electronic fuel injection systems. Carburetor engines often change the air-fuel ratio for different working conditions, and this
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