This paper describes the results of an experimental campaign carried out on three urban buses fuelled by natural gas, aimed at measuring pollutant emissions and fuel consumption in real driving conditions. The buses, used for public transport in three Italian cities, were equipped with a Portable Emission Measurement System. Emission tests were performed over the routes on which the buses operate in their service, and cold start emissions were also investigated. The results showed that the differences in CO and NOx emissions can be attributed to the calibration of the fuel supply system. PM emissions were low and similar to those reported in the literature for other CNG buses, while CO₂ and fuel consumption were affected by the driving cycle. Cold start strongly impacted CO and NOx emissions because of the effect of temperature on catalytic converter efficiency, with cold over-emissions strongly dependent on ambient and coolant temperatures at engine start.

本文描述了在三辆以天然气为燃料的城市公交车上进行的实验活动的结果，旨在测量实际驾驶条件下的污染物排放和燃料消耗。这些用于意大利三个城市公共交通的公共汽车配备了便携式排放测量系统。排放测试在公交车运营的路线上进行，还调查了冷启动排放。结果表明，CO 和 NOx 排放量的差异可归因于燃料供应系统的校准。PM 排放量很低，与文献中报道的其他 CNG 公共汽车的排放量相似，而 CO ₂和油耗受驾驶循环的影响。由于温度对催化转换器效率的影响，冷启动强烈影响 CO 和 NOx 排放，冷态过度排放在很大程度上取决于发动机启动时的环境和冷却剂温度。