The negative impact of deteriorating air quality on public health etc. is receiving growing attention. As a result the contributing emission sources are increasingly regulated. Thus, the emissions of road transport - being one of the largest contributors - are under constant pressure. As such, the evolving legislation on emissions of new cars is forcing to ultra low emitting vehicles. To assist in the development of those vehicles an on-board measuring system capable of determining ppm level emissions of carbon monoxide (CO), total hydrocarbons (THC) and nitrogen oxides (NOx) is realised. This system combines the latest in laboratory grade analysers with a high speed condensing type sampling system in a state-of-the-art shock proof design. The regulated emission components can be detected to at least one ppm. The data-acquisition allows for the simultaneous retrieval of engine and vehicle parameters in order to calculate on-line mass based time resolved emissions that can be quickly linked to relevant parameters of the emission control system. The data treatment is automated under LabView. The on-board system is validated by over 130 comparative simultaneous measurements on a Constant Volume Sampling chassis dynamometer. The tests are executed on three modern light duty vehicles of which one ultra low emitting Euro 4 certified petrol one. The comparison revealed that differences in emissions are below 10% except for very low levels i.e. underneath 0.02 g/km where the reference system is thought to be more inaccurate than the on-board one. On-board emission measurements performed on a Euro 4 petrol vehicle showed differences of more than a decade when compared to the type approval cycle on chassis dynamometer. An in-depth analysis revealed that outside this cycle the engine can be differently calibrated resulting in deviations from the stoichiometric air to fuel ratio and subsequent raise in emissions. Also, very short emission events could be studied such as NOx raised during accelerations immediately following a motoring period. This could be attributed to a slightly lean air fuel mixture just at the start of fuel injection. (Author/publisher)
Abstract