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Vehicular ammonia emissions are currently unregulated, even though ammonia is harmful for a variety of reasons, and the gas is classed as toxic. Ammonia emissions represent a serious threat to air quality, particularly in urban settings; an ammonia emissions limit may be introduced in future legislation. Production of ammonia within the cylinder has long been known to be very limited. However, having reached its light-off temperature, a three-way catalyst can produce substantial quantities of ammonia through various reaction pathways. Production of ammonia is symptomatic of overly reducing conditions within the three-way catalyst (TWC), and depends somewhat upon the particular precious metals used. Emission is markedly higher during periods where demand for engine power is higher, when the engine will be operating under open-loop conditions.

For over a decade, the EU has required in-service conformity testing of heavy-duty road vehicles. This paper briefly discusses the practical aspects of the test requirements, how they have evolved and how they compare to other precedents, such as the heavy-duty engine dynamometer-based type approval testing procedure, as well as broadly equivalent EU requirements for light duty vehicles. Emissions requirements for heavy-duty vehicles are work-specific, but based on standard test results a range of other parameters can be calculated to yield distance-specific, tonnage-distance specific, CO2-specific and (gravimetric) fuel-specific results. At present, CO2 and fuel consumption are not subject to any limits per se during on-road testing (and this is the case for both heavy and light duty vehicles); nevertheless, the aforementioned parameters must be measured and such results can be of interest for a variety of reasons.

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.