A Computational Fluid Dynamics Study on Improving Raw Fuel Injection Distributions in Front of Diesel Oxidation Catalysts

Abstract

To increase the conversion efficiency of the exhaust gas in the advanced catalytic converters of modern diesel engines, the raw fuel injection technique (injecting diesel fuel in front of the catalytic converter) is introduced for raising exhaust temperatures to achieve emission reductions. When implementing this technique, special care is required as the flow distribution of the injected fuel droplets must be uniformly distributed to ensure the uniformity of internal temperatures across the cross sectional area of the catalytic converter. If a hot spot occurs inside due to uneven flow and the internal temperature exceeds the melting point of the substrate, this may cause substrate cracking which leads to failure of the device. The current study aimed to apply a computational fluid dynamics program to explore the possibility of improving flow distributions of fuel droplets injected in front of the catalytic converter installed on the tested engine’s exhaust system. Based on the literature, two methods—namely, a baffle and an extended pipe—were introduced and compared to the original exhaust system configuration.. The study also took into account the back pressure, the temperature distribution and the conversion efficiency of the exhaust gas within the catalytic converter. The results of the simulation showed that the flow/ temperature distributions and the emission reductions were significantly improved by using these two methods. The baffle gave the best result. However, the drop in back pressure was also increased due to the complexity of its structure but was still under the design criteria.