| 英文摘要 |
In recent years, the vehicle particle emissions standards had been included by regulations. The new measurement technology and control regulations for particle emissions can be expected. Hence, the development of particle concentration measurement system is essential. The purpose of this is to develop a measurement system for screening motorcycle exhaust particle emissions.
The measuring system consisted of a buffer chamber, dehumifier, cyclone, and measurement instruments. The test particles were generated by a four-stroke engine of 125 cc motorcycle installed on the dynamometer. The particle size distribution, hygroscopic characteristic, and water content of emissions were evaluated for choosing the particle selector and dehumifier. Afterward, the different instruments were employed for measuring particle number and mass concentration on engine idle condition. The test dehumifiers including dilutor, Nafion drayer and ice bath. The particle selector was the cyclone. The particle number and mass concentration were measured by filter weighting, SMPS, FMPS, CPC, AE51, Dusttrak, and opacity meter.
The results indicated that the engine emission at idle mode (1750 rpm) had a particle CMD of 0.05μm, GSD of 1.8 and number concentration of 104~105 #/cm3. The particles generated from engine emissions did not growth even if the RH achieved 100 %. Hence, the purpose of dilution was to decrease the sample temperature and avoid the water condensed on the sampling tube. The sample water content was 7 % and 10 % at idle mode and the full speed mode, respectively. The water content increased with increasing engine speed. The dilution ratio of 10 was enough for avoiding water
condensed, but the drawback is the low particle concentration because of the dilution. The Nafion dryer had no particle loss for particles (30 ~ 750 nm) and had excellent dehumifiy efficiency. The expensive price was the drawback of Nafion. The ice bath is most cheap and simple method to decrease temperature and humidity.
The cyclone had the same particle penetration curve with US EPA PM2.5 size-selection curve at the flow rate of 16.7 and 3 L/min. The particle characteristic measure by 27 motorcycles indicated that the particle mode is 50 nm. The mass concentration and number concentration of 19 carburetor engines were 730.4±187.6 μg/m3 and 2×106±721725 #/cm3, respectively. For 8 electronic injection engines, the mass concentration and number concentration were 139.6±78.8 μg/m3 and 1.2×105±8562 #/cm3. The multi-reflection opacity meter (light path= 13 m) had a detection limit of 1 mg/m3 when the number concentration was 104~105 #/m3 and particle size was 70nm. Hence the opacity meter had no response for the motorcycle particle emissions. The regression value of mass concentration on FMPS, SMPS, AE51 and CPC measurements were 0.785, 0.764, 0.698 and 0.961. The highest correlation existed between the filter weighting and AE51. Hence, the combination of AE51 and ice bath dehumifier were recommend method for the motorcycle particle emission screening.
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