Investigations of Ammonia Emissions from Euro 5 Passenger Cars Over a Legislative Driving Cycle

Abstract

AbstractVehicular 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. Ammonia is not produced within the cylinder of an internal combustion engine in significant quantities. 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 its formation and emission depends on a wide range of factors. This study presents a brief literature review, and later reports on experimental data presenting ammonia emissions data from four Euro 5 passenger cars, using three different petrol fuels. All vehicles were tested on BOSMAL’s chassis dynamometer over the New European Driving Cycle. For three of the vehicles, undiluted ammonia was quantified directly at tailpipe. The fourth vehicle was subjected to further investigations with the aid of Fourier Transform Infra-Red (FTIR) analysis of a range of compounds, including ammonia. Emission factors observed for the three vehicles are generally low in comparison to other studies, which may be a result of the favourable laboratory conditions, the relatively small, low-emission engines and the driving cycle employed. Second-by-second data obtained from a single vehicle operating on two fuels revealed small but significant differences in ammonia emissions, including the time of the initial ammonia surge. A range of metrics were examined to determine possible correlations between ammonia and other pollutants. No significant correlations were found; there was however some evidence of a trade-off between ammonia and NOx. A brief analysis of NH3 emissions in the context of RNC emissions revealed ammonia to make up roughly 40 % of the reactive nitrogen compounds (RNCs) released over the duration of the test cycle. Thus, the ammonia emissions observed are low but non-trivial and the issue of ammonia emissions and direct and indirect impacts on air quality is an important research direction. This paper reports on a continuation of an ongoing test programme conducted at BOSMAL focussing on unregulated emissions (including ammonia) from light-duty vehicles and the effects of increased proportions of ethanol in petrol on regulated and unregulated emissions.KeywordsAmmonia (NH3)Three-way catalyst (TWC)Reactive nitrogen compounds (RNCs)Light-duty vehiclesUnregulated emissions