轻型机动车尾气排放劣化率模型构建及应用研究

Vehicle emissions have become important contributors to air pollution in the city due to the dramatic growth of vehicle population in recent year. Although a series of strict vehicle emissions standards have been developed and enforced within a relatively short period of time, the contributions of vehicle emissions to air pollution are still large, which has begged several questions: whether or not the reduction of vehicle emissions due to the enforcement of higher emission standards is overshadowed by the increase of emissions due to the population growth? Or the increase of emissions due to engine deterioration is much higher than the emissions reduction due to higher emission standards? Answers to these questions will play a key role in policy making regrading emissions reduction and air quality improvement. Light duty vehicles accounts for the majority of the vehicle population in the city, and thus are focused in this study. The objective here is to develop a vehicle emission deterioration rate model for light duty vehicles and assess its impact on emissions inventory development. A longitudinal study was designed and conducted. A certain number of light duty vehicles with different ages and cumulative mileages were selected for measurements of emissions, driving cycles, and activities periodically over a four-year time frame. Vehicle emissions were measured both in the lab and real-world while driving cycles and activities were both measured in the real-world. Measurements were then used to develop a vehicle emission deterioration rate model. Deterioration rates derived from this study were also used to assess its impact on emission inventory development. Results of this research can be used to adjust the vehicle emissions related regulations for reduction of vehicle emissions and air quality improvement, for example, changing or adding a testing cycle in the Inspection/Maintenance (I/M) to assure that the emissions level of a testing vehicle can be truly quantified.

在尾气排放标准日益严格的形势下，城市机动车尾气排放对空气污染的贡献依然巨大。到底是机动车数量对尾气排放的贡献大，还是由于发动机劣化而造成的尾气排放增加对空气质量的影响大？问题的了解对于制定有效的机动车管理制度，减少排放，改善空气质量有显著的意义。本研究以轻型机动车为例，构建尾气排放劣化模型并评价其对排放清单估算的影响。研究采用时间纵向研究（Longitudinal Study）的方法,选择不同车龄（或里程）的轻型机动车，对其尾气排放、行驶工况、以及车辆活动信息进行较长时间跨度内(四年)间歇性、分阶段连续测量，并利用测量数据建立尾气排放劣化率模型。尾气排放测量分别在实验室预设工况和实际道路工况下进行。行驶工况和车辆使用情况的测量则均在实际道路工况下进行。根据模型获得的尾气排放劣化率也用于评价其对机动车尾气排放清单估算的影响。本项目所得的研究成果可用于城市机动车管理政策调整与改善。

本项目通过对预先选定的车辆进行实际道路条件下的纵向跟踪测量，量化分析轻型汽油机动车的尾气排放劣化率及其对尾气排放清单估算的影响。同时，利用车辆年检数据分析评价影响尾气排放劣化率的关键因素，并构建相应的尾气排放劣化率模型。研究表明，轻型汽油机动车尾气排放劣化率随着污染物的不同而不同，在不同的累积行使里程阶段其展现出的劣化速率也不近相同。平均而言，CO2, CO, HC, NO的排放劣化率分别为 0.000491 g/km2, 0.020481 mg/km2, 0.006968 mg/km2, 及0.000653 mg/km2。相比与相应的排放因子，结合轻型汽油机动车的年均行使里程 （约1万公里/年），若考虑尾气排放劣化率的影响，目前的尾气排放清单依污染物不同而应相应提高3-12%。此外，研究同时表明，机动车的尾气排放控制技术，机动车的使用特征，以及发动机本身的技术参数等都是影响尾气排放劣化率的重要因素。因此，为了更好的量化尾气排放劣化率，未来尚需持续开展不同车型、不同技术及使用特征的机动车现实条件下尾气排放的纵向测量。