More Compact, more Efficient, more Cost-Effective: Close Coupled Catalyst for Heavy Commercial Vehicles

The engine of heavy commercial vehicles is designed for lowest fuel efficiency at high loads. However, in other operating situations, engines hardly release any heat. Although this benefits the fuel efficiency level it presents a challenge to exhaust gas aftertreatment systems. If the exhaust gas is already at a low temperature at the engine, a long pipe section between the engine and the exhaust gas aftertreatment system, fitted to the chassis between the wheels, is even more disadvantageous as the exhaust gas continues to cool. Particularly in inner-city traffic, it can be difficult to ensure an adequate conversion temperature. Installing the DOC close to the engine changes this. With this set-up, heat loss through the flow path can be disregarded. As the efficiency of the DOC increases with the operating temperature, the volume of the DOC can be reduced. As such, when Continental carried out a test with the DOC near the engine, it was able to reduce the volume of the DOC by 30% from 11.3 to 7.8 liters.

Continental uses the new CS catalyst substrate in its solution, where the DOC is installed near the engine. With this corrugated foil material, the waved structure exhibits a slight slant angle (hence the name Crossversal Structure, “CS”). By combining alternating left and right diagonal waves, the DOC structure manages without an intermediate foil for the first time. As a result, the amount of materials used and the weight decrease by 20%. At the same time, the efficiency of the NO_x converter increases as the diagonal course of the waves generates turbulence, which brings nitrogen oxide in exhaust gas in better contact with the catalytic-coated surface of the substrate.

Successfully installing the DOC close to the engine results in additional benefits according to Rolf Brück, Head of Catalysts Product Line, Fuel & Exhaust Management: “For example, the higher temperature level enables earlier release for the injection of the urea solution downstream of the DOC. As a result, NO_x conversion starts earlier.” The higher temperature in conjunction with the structured metallic foil materials, on which the urea solution is sprayed, results in the complete evaporation of the urea solution. This prevents the build-up of deposits downstream. These deposits would restrict cross sections, impair the control quality of the exhaust gas aftertreatment system and destroy gas-conveying components such as flexible elements.

With the long-term and likely complete re-location of the exhaust gas aftertreatment system towards the engine, the volume requirement for parts fitted to the chassis decreases, freeing up space for an increased fuel tank volume. “Installing the exhaust gas aftertreatment system near the engine is a prerequisite. If you don’t start at the front then you won’t have the benefits at the back,” Brück adds.