A combined experimental and computational approach to improve catalyst flow uniformity and light-off behaviour

This study is concerned with the systematic approach to improve catalyst flow uniformity and light-off behaviour through the basic understanding of exhaust flow characteristics. An experimental and computational approach to the unsteady compressible flow for exhaust manifold and close-coupled catalyst (CCC) system attached to a four-cylinder double overhead camshaft gasoline engine was performed to investigate the flow distribution of exhaust gases and finally to increase the conversion efficiency of catalyst. An experimental study was conducted to measure the velocity distributions inside the exhaust manifold and CCC under practical engine conditions by using laser Doppler velocimetry. In this study, through experiment and calculation, the effects of the geometric configuration of exhaust manifold on flow structure and its maldistribution in the monolith were mainly investigated to understand the exhaust flow patterns in terms of flow uniformity and to obtain the better light-off for further emission reduction. On the basis of the design guidance resulting from this fundamental study, an improved exhaust manifold (type II) was designed and manufactured. The effects of improved exhaust flow characteristics on vehicle emission were demonstrated through the vehicle emission tests.