The real-world emission factors (EFs) and emission performance of bi-fuel (CNG/GAS) vehicles have been seriously investigated by the emission scientists and urban planners. In the present study, we propose an almost new practical methodology and perform on-road experiments on 60 bi-fuel vehicles to discuss the impacts of vehicle speed, fuel type, usage, and accumulated mileage on the CO, HC, and NO_x EFs. 80% and 20% of the tested vehicles were private cars (PCs) and taxis (TXs), respectively. TXs and PCs are compared together based on their emission performances, emission characteristics, vehicular specific power (VSP) distributions, and type of fuel. The results show that in the entire cases except for GAS-PCs, CO EFs increased with vehicle speed. Although CNG vehicles show less HC EFs, they produce higher NO_x mileage-based EFs compared to gasoline ones. NO_x mileage-based EFs decrease with vehicle accumulated mileage, whereas the opposite trend was observed for the CO and HC EFs. Burning CNG rather than gasoline decreases 70% and 42% of CO, and 70% and 85% of HC mileage-based EFs in PCs and TXs, respectively. The influence of burning CNG on NO_x emission of TXs seems to be insignificant, but NO_x was more emitted by a factor of 1.7 in CNG PCs. Accumulated mileage has a destructive effect on combustion quality, especially in CNG vehicles. The factors of usage and accumulated mileage could considerably develop the VSP distribution and fuel consumption rate of GAS vehicles, while they have no detectable impact on that of CNG vehicles.

排放科学家和城市规划人员已经认真研究了双燃料（CNG / GAS）车辆的实际排放因子（EFs）和排放性能。在本研究中，我们提出了一种几乎全新的实用方法，并在60种双燃料汽车上进行了道路实验，以讨论车速，燃料类型，使用情况和累积里程对CO，HC和NO _x EF的影响。 。被测车辆的80％和20％分别是私家车（PC）和出租车（TX）。根据排放性能，排放特性，车辆比功率（VSP）分布和燃料类型，将TX和PC进行比较。结果表明，在除GAS-PC之外的所有情况下，CO EF均随车速增加。尽管CNG车辆显示出较少的HC EF，但它们产生的NO较高_x基于里程的EF与汽油相比。基于NO _x里程的EFs随着车辆的累积里程而减少，而对于CO和HC EFs则观察到相反的趋势。在PC和TX中，燃烧CNG而非汽油可分别减少70％和42％的CO以及70％和85％的基于HC里程的EF。在没有燃烧CNG的影响_X的TX发射似乎是微不足道，但NO _X更由1.7 CNG电脑的一个因素发射。累积的行驶里程对燃烧质量具有破坏性影响，尤其是在CNG车辆中。使用和累积里程的因素可以极大地发展GAS车辆的VSP分布和燃油消耗率，而对CNG车辆却没有可察觉的影响。