RDE Testing of Passenger Cars: The Effect of the Cold Start on the Emissions Results 2019-01-0747

This paper discusses the importance of the inclusion of emissions from the cold start event during legislative on-road tests on passenger cars (RDE - real driving emissions tests conducted under real-world driving conditions, as defined by EU legislation). Results from a recently-registered gasoline-powered vehicle are presented, with the main focus on the comparison of exhaust emission results: excluding/including the cold start during the initial phase of the RDE test. Cold start is the most challenging aspect of emissions control for vehicles with spark ignition engines and the inclusion of the cold start event in RDE test procedure has wide-ranging implications both for the testing process and compliance with RDE legislation via optimisation of aftertreatment systems and the engine calibration. In addition to some theoretical arguments, the results of an RDE-compliant test performed using the aforementioned procedures are presented. The tests were carried out on a passenger car with a spark-ignition engine with direct fuel injection; the vehicle met the Euro 6c emission standard. For the test performed, the impact of the emissions associated with cold start have a smaller impact than was assumed, because the distance covered by an RDE-compliant test is high (>48 km) and the ambient temperature was not low. However, the not-to-exceed limits must also be respected for the urban phase of the test, where the number of kilometres available to ‘dilute’ the cold start is more limited. Implications for the testing process, emissions control and the future emissions profile for vehicles with such engines are discussed.