Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hong Kong.
Sci Total Environ. 2011 Nov 15;409(24):5292-300. doi: 10.1016/j.scitotenv.2011.08.054. Epub 2011 Sep 21.
Instantaneous CO, NO, and HC emissions and exhaust flow rates from four LPG taxis, which adhered to Euro 2-4 emission standards, were measured using a sophisticated portable emission measurement system (PEMS). Instantaneous air/fuel ratios, emission rates, and emission factors at different operating modes were derived to explore the emission characteristics of these four taxis. Results show that gaseous emissions from these four taxis exceed emission standards, due to extended vehicle use and poor maintenance. NO emissions from newer taxis are lower whilst CO and HC emissions of the Euro 4 taxi are similar to those of Euro 2 taxis during idling and low speed travel. The taxis emit lower amounts of gaseous pollutants whilst idling and emit the highest amounts of CO and NO whilst accelerating. Large fluctuations in air/fuel ratios can be observed from the Euro 4 taxi during idling, indicating a malfunction of fuel supply control to the engine. Such fluctuations are not observed from the other taxis. This shows that a Euro 4 taxi is not necessarily cleaner than a Euro 3 taxi. Emission factors derived from on-board measurements are applied to estimate gaseous emissions from the taxi fleet; these results show that emissions are higher during peak hour traffic conditions. An estimate of the taxi fleet's emissions whilst the older taxis are replaced is also calculated. It can be seen that faster replacement of older taxis can lead to reductions in gaseous emissions from the taxi fleet. This study shows that the PEMS is an adequate tool for measuring emissions from LPG vehicles and that there is an urgent need to enforce emission standards on taxis. This study also shows that on-board measurements should be incorporated in the estimation of emissions from other vehicle types. This would result in better emission estimations under local traffic conditions.
使用先进的便携式排放测量系统（PEMS）测量了四辆符合欧 2-4 排放标准的液化石油气出租车的瞬时 CO、NO 和 HC 排放以及废气流量。根据不同的运行模式得出了瞬时空燃比、排放率和排放因子，以探讨这四辆出租车的排放特性。结果表明，由于车辆使用时间延长和维护不善，这些出租车的气态排放超过了排放标准。较新的出租车的 NO 排放较低，而欧 4 出租车在怠速和低速行驶时的 CO 和 HC 排放与欧 2 出租车相似。出租车在怠速和加速时排放的 CO 和 NO 量最高，同时排放的气态污染物量较低。在怠速时，可以从欧 4 出租车观察到空燃比的大幅波动，表明发动机燃料供应控制出现故障。其他出租车则没有观察到这种波动。这表明，欧 4 出租车并不一定比欧 3 出租车更清洁。从车载测量得出的排放因子被应用于估算出租车车队的气态排放；这些结果表明，在高峰时段交通条件下排放量更高。还计算了在更换较旧出租车时出租车车队排放量的估算值。可以看出，更快地更换较旧的出租车可以减少出租车车队的气态排放。本研究表明，PEMS 是测量液化石油气车辆排放的有效工具，迫切需要对出租车执行排放标准。本研究还表明，应将车载测量纳入其他车辆类型排放的估算中。这将导致在当地交通条件下更好的排放估算。
