Peter Treiber

New Approaches to Catalyst Substrate Application for Diesel Engines

Nearly all real Diesel engine operation is leading to low exhaust temperatures. Standard catalyst technique remains therefore for significant time below light off. To improve the conversion behavior two approaches were made: placement of tailor fitted catalysts as close as possible to the engine exhaust port before turbocharger and usage of close coupled catalysts with the so-called hybrid design. Both measures are providing visible progress in reducing Diesel engine emissions. Tests were made with modern Diesel engines both for passenger cars and heavy duty vehicles. INTRODUCTION Since its invention the Diesel engine became the most efficient type of power unit and it seems to be that this is true for the future too. Although Diesel engines in the past were used more as the work horses between all the engine applications this situation changed especially in Europe within the last five years. Today even racing cars [1] and luxury vehicles [2, 3, 4] are powered by Diesel engines. Reasons are as well the outstanding good fuel consumption and in some countries the attractive price of Diesel fuel as the impressive torque of modern direct injection Diesel engines with one or two turbo chargers and intercoolers. In addition to all these positive items the exhaust emission behavior is good with respect to hydrocarbon, carbon monoxide and carbon dioxide emissions. Nitrogen oxides and especially particulate emissions are the unfavorable aspects of the Diesel engine. The success in emission control on all other engines types and the rising numbers of Diesel engine driven vehicles made it absolutely necessary to improve the exhaust emissions of Diesel engines too. Challenging standards of the future [5, 6, 7, 8] gave the starting signal for intensive research and development work on Diesel engines worldwide. With the experience of tailor fitted solutions for metallic substrates for gasoline engines automotive catalysts efforts were made to develop components which are providing substantial progress in the emission control of Diesel engines. As a result of the very efficient combustion process Diesel engines are showing relatively low exhaust gas temperatures especially under real driving conditions at partial load and speed. While at gasoline engines the main emission control problem is how to get after engine start as quick as possible light off temperature of the catalytic converter Diesel engines have an additional problem. They tend to fall below light off temperature again during deceleration and low idling modes e. g. in the European driving cycle (figure 1). Figure 1: Temperature comparison of catalysts in underfloor position (1,9 l TDI 4-cylinder with a V6 – cylinder gasoline engine in EU III cycle) The measures described below are taking this particularly into account. Figure 2 depicts a scheme of an engine which shows the possible locations to install catalysts. The closest position to the engine is the catalyst in the exhaust ports of the cylinder head. The next position is the exhaust manifold leading to the turbocharger or the position right in 0 200 400 600 80