Effect of an oxidation catalyst and a three-way catalyst on odorous emissions in internal combustion engines

Abstract

This study investigated the effect of an oxidation catalyst on odorous emissions in a direct-injection diesel engine at idling. In cold or low-temperature idling, where engines are started from cold condition at ambient temperatures, the effectiveness of the oxidation catalyst to reduce total hydrocarbons (THCs) and aldehydes is low owing to the low catalyst temperatures, and the odour reduction is insignificant. In hot or high-temperature idling, where exhaust temperatures exceed 200°C, THCs and aldehydes are reduced by more than 90 per cent and the odour reduction is more than one point, a significant odour reduction. Below a catalyst temperature of 200°C, objectionable exhaust odour appears. The gasoline engine also emits a strong exhaust odour when the catalyst condition is poor or there is a mismatch of air—fuel ratio. The effect of a three-way catalyst on the exhaust odour was investigated in a gasoline engine. In rich engine operation condition, there are more THCs, carbon monoxide (CO), and nitrogen oxides (NO x) before the catalyst. After the catalyst in this condition, the THCs, CO, and NO x are significantly reduced, but there is a very sharp and unpleasant odour of ammonia, which is produced inside the catalyst owing to the reduction of NO x.