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Diesel Particulate Filters (DPF) are widely used to meet 2007 and beyond EPA Particulate Matter (PM) emissions requirements. During the soot loading process, soot is collected inside a porous wall and eventually forms a soot cake layer on the surface of the DPF inlet channel walls. A densely packaged soot layer and reduced pore size due to Particulate Matter (PM) deposition will reduce overall DPF wall permeability which results in increasing pressure drop across the DPF substrate. A regeneration process needs to be enacted to burn out all the soot collected inside the DPF. Soot mass is not always evenly distributed as the distribution is affected by the flow and temperature distribution at the DPF inlet. As a result, the heat release which is determined by the burn rate is locally dependent. High temperature gradients are often found inside DPF substrate as a result of these locally dependent burn rates.

The main objective of this paper is to investigate the performance of partial filtration DPF substrates using 3-D Computational Fluid Dynamics (CFD) methods. Detailed 3-D CFD simulations were performed for real world sizes of DPF inlet and outlet channel geometries. Two concepts of partial filters were studied. The baseline geometry was a standard DPF with the front plugs removed. The second concept was to eliminate half of outlet plugs in addition to the inlet plugs to improve the pressure drop performance. The total filter efficiency was defined in current study to quantify the overall filter filtration efficiency which combines the effects from wall flow efficiency and flow through efficiency. For baseline case, 45% of total exhaust gas was found to go through the inlet channels, and the total trap efficiency was as high as 60%. However, only a 10% pressure loss reduction was found due to the removal of the outlet channel plugs from the DPF inlet side.

New emissions certification requirements for medium duty vehicles (MDV) meeting chassis dynamometer regulations in the 8,500 lb to 14,000 lb weight classes as well as heavy duty (HD) engine dynamometer certified applications in both the under 14,000 lb and over 14,000 lb weight classes employing large diameter exhaust pipes (up to 4″) have created new exhaust stream sampling concerns. Current On-Board-Diagnostic (OBD) dyno certified particulate matter (PM) requirements were/are 7x the standard for 2010-2012 applications with a planned phase in down to 3x the standard by 2017. Chassis certified applications undergo a similar reduction down to 1.75x the standard for 2017 model year (MY) applications. Failure detection of a Diesel Particulate Filter (DPF) at these low detection limits facilitates the need for a particulate matter sensor.

The Urea Selective Catalytic Reduction (SCR) technology is one of the major mature exhaust aftertreatment technologies which are demonstrated to be able to lower tail pipe NOx emission by 90%. The system consists of a urea injection at upstream pipe and a downstream SCR converter. A well mixed flow (exhaust gas and NH3) in front of SCR substrate, which is usually constrained by tight design packaging, is very critical to ensure the desired performance. Current paper addresses the geometrical effects on flow mixing by using three dimensional Computational Fluid Dynamics (CFD) tool. The mixing enhancement is achieved by adding flow mixer. The shapes and locations of flow mixers, as well as the number of blades inside mixer are investigated to show the effect on fluid mixing in downstream along the flow direction. Results show great improvement of flow mixing by adding a delta wing mixer.

F-oval substrates have been widely used in automotive applications for Close Coupled Converters (CCC) of SI engines and pre-Diesel Oxidation Catalysts (DOC) of CI engines under tight packaging constraints where there is no space for other substrates with the same volume such as H-oval, a Y-oval or round substrates. Although flow uniformity in the front of a substrate is extremely important, it is very challenging to obtain excellent flow uniformity with an F-oval substrate. Current study is focused on how to optimize inlet cone design to achieve optimal flow uniformity by using 3-D Computational Fluid Dynamics (CFD) tools. First, exhaust mass flow rate and inlet cone length are investigated to understand their effects on flow uniformity and pressure loss. Then, based on a relatively short straight cone, angle cones are built.

The urea Selective Catalytic Reduction (SCR) exhaust system has been proved to be the reliable aftertreatment device with the capability of reducing tail pipe NOx emission by 75% to 90%, HC by 50% and Particulate Matter (PM) by 30%. Constrained by increasingly stringent packaging envelope, flow mixing in front of substrate is becoming one of the major concerns to achieve ideal performance of higher NOx conversion and lower ammonia (NH3) slip. Three dimensional CFD simulations are performed in current study to investigate flow mixing phenomenon in a SCR system. First, for a traditional tube injector with single or multiple nozzles, the effects of mass flow rates of injected NH3 and exhaust gas on flow mixing and pressure loss are investigated. Then, a concept of ring shape injector with multiple nozzles are initiated and built for 3-D CFD simulations. The comparisons of flow mixing index and injection pressure are made between two type injectors.

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.

The main objective of the current paper was to investigate the fluid flow and pressure loss characteristics of DPF substrates with asymmetric channels utilizing 3-D Computational Fluid Dynamics (CFD) methods. The ratio of inlet to outlet channel width is 1.2. First, CFD results of velocity and static pressure distributions inside the inlet and outlet channels are discussed for the baseline case with both forward and reversed exhaust flow. Results were also compared with the regular DPF of same cell structure and wall material properties. It was found that asymmetrical channel design has higher pressure loss. The lowest pressure loss was found for the asymmetrical channel design with smaller inlet channels. Then, the effects of DPF length and filter wall permeability on pressure loss, flow and pressure distributions were investigated.

Emissions sample probes are widely used in engine and vehicle emissions development testing. Tailpipe bag summary data is used for certification, but the time-resolved (or modal) emissions data at various points along the exhaust system is extremely important in the emission control technology development process. Exhaust gas samples need to be collected at various locations along the exhaust aftertreatment system. Typically, a tube with a small diameter is inserted inside the exhaust pipe to avoid any significant effect on flow distribution. The emissions test equipment draws a gas sample from the exhaust stream at a constant volumetric flow rate (typically around 10 SLPM). The sample probe tube delivers exhaust gas from the exhaust pipe to emissions test equipment through multiple holes on the surface of tube. There can be multiple rows of holes at different axial planes along the length of the sample probe as well as multiple holes on a given axial plane of the sample probe.

A uniform flow inside a Diesel Particular Filter (DPF) is very critical to ensure the desired performance and durability of the filter system. In current paper, a systematically study was performed to investigate the geometrical effects on flow uniformity in the front of diesel particular filter by using Computational Fluid Dynamics (CFD) tool. The studies were focused on the effects of spiral rib inside inlet tube; inlet and outlet cones, length and angle of inlet cone. In all the numerical simulations, mesh sizes were carefully controlled to yield accurate and consistent results. No improvement on flow uniformity index was observed by adding a signal spiral rib in the inlet tube in front of diffuser (inlet cone), and even worse in the case with a single deeper rib. On the contrary, pressure loss increases rapidly.

The ability to accurately predict skin temperatures of catalytic converter and manifold is very important for a robust/durable design of the vehicle exhaust system, especially in the development of close coupled converter system. In this paper, Computational Fluid Dynamics (CFD) is used to calculate the skin temperature of complicated components in vehicle exhaust system such as catalytic converter. Generally, a catalytic converter consists of substrate, mat, outer shell, inner cone, cone insulation, and outer cone. 3-D compressible turbulent fluid flow with heat transfer involved in force and natural convections, heat conduction and radiation is numerically simulated. First, both numerical calculation and experimental tests are conducted for a catalytic converter under the same operation conditions to evaluate the accuracy of current numerical method. Good agreement is found between CFD prediction and experimental tests.

Stricter emission standards are forcing automakers to attach catalytic converters directly to the exhaust manifold. Mounting catalytic converter at or near the exhaust manifold helps to reduce the increase in emissions that occurs during the first few minutes after a cold engine is started. The spike occurs because cold engines require a richer air-fuel mixture to run smoothly. The emission standards can be met only by new designs of exhaust system with the catalyst being as close as possible to the engine, and with the thin walled exhaust manifolds. With concept-to-customer timing continuously shrinking in the automotive industry, the need to quickly validate the engineering designs is becoming ever more critical. It is no longer acceptable to design a component, produce soft tooling, build and test a prototype, analyze what failed, and then redesign.