Computational Fluid Dynamics (CFD) Applications in Vehicle Exhaust System 2008-01-0612

Computational Fluid Dynamics (CFD) is becoming a very popular tool for numerical predictions of flow distribution, pressure loss, heat transfer, internal and external combustion and has been widely used in automotive, aerospace, marine and even medical industries. In automotive industry, CFD tool is used and customized in five major areas: vehicle aerodynamic effect; thermal management (cooling and climate control); cylinder combustion; engine lubrication and exhaust system performance. Current paper will focus on CFD applications in one of vehicle subsystems - exhaust system. Increasingly stringent emission requirements are enforced by Environment Protect Agency (EPA) to reduce harmful chemical components such as CO, NO, NO2. Exhaust systems are becoming more complicated and usually consist of one or multiple catalytic converters with one or multiple substrates inside.

Exhaust flow distribution inside substrate directly affects not only the conversion efficiency of emission targets and durability of substrates, but also system back pressure (contributed by pressure loss through substrate) which needs to be minimized for desired engine output power. Also, thermal management of exhaust system is another crucial task to prevent any damage due to elevated temperature.

Current paper is targeted to discuss and summarize the applications of 3-D CFD numerical simulations in following areas:

1. 1
   Flow distribution in front of substrate
2. 2
   Pressure loss through exhaust system
3. 3
   Skin temperature prediction
4. 4
   Heat loss analyses
5. 5
   Oxygen sensor related issues
6. 6
   Middle belt converter design
7. 7
   Urea injection for SCR system
8. 8
   Detail DPF studies
9. 9
   Providing input for FEA analysis

For each of those areas, a few examples of CFD results are discussed. The purpose of this paper is not to give the detailed instructions of how to conduct 3-D CFD simulation for exhaust system and its component, but to provide a guideline of where CFD tool can be used to initiate new concepts or optimize exist designs in above areas.