An experiment to purify diesel exhaust gas using an electric trap and three types of catalysers

Abstract

Diesel engine exhaust gas is known to be one cause of photochemical smog, which is so damaging to city environments. However, because of its high thermal efficiency and economic advantages, the diesel engine is not easily dispensable. The authors have previously conducted a series of experiments to assess the purifying effects of a diesel gas purification device employing an electric trap. It has been confirmed that an extraction rate of 60 ∼ 75 % for black smoke can be achieved using this apparatus, but the extraction effect for nitrogen oxides (NOx) is insufficient if the electro-trap device is used on its own. To improve its performance, experiments have now been undertaken using the same device in combination with various types of attached catalysers to oxidise and remove the nitrogen in the exhaust gas. Utilising a commercial 3-way catalyser, it proved difficult to maintain the gas at a suitable temperature, so that no outstanding result could be obtained. Nor was any significant result observed from the use of an ozoniser. However, with a zeolyte catalyser, it was possible to achieve a NOx reduction of 20 ∼ 30 %. This latter experiment is reported in the present paper.