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Urea-selective catalytic reduction (SCR) catalysts are the leading aftertreatment technology for diesel engines, but there are major challenges associated with meeting future NOx emission standards, especially under transient drive cycle conditions that include large swings in exhaust temperatures. Here we present a simplified, transient, one-dimensional integral model of NOx reduction by NH₃ on a commercial small-pore Cu-zeolite urea-SCR catalyst for which detailed kinetic parameters have not been published. The model was developed and validated using data acquired from bench reactor experiments on a monolith core, following a transient SCR reactor protocol. The protocol incorporates NH₃ storage, NH₃ oxidation, NO oxidation and three global SCR reactions under isothermal conditions, at three space velocities and at three NH₃/NOx ratios.

Aftertreatment modeling capabilities are an important part of the diesel engine manufacturer's efforts to meet the quickly approaching EPA 2007 heavy-duty emissions regulations. A critical, yet poorly understood, component of particulate filter modeling is the representation of the soot oxidation rate. This term directly influences most of the macroscopic phenomenon of interest, including filtration efficiency, heat transfer, back pressure, and filter regeneration. Intrinsic soot cake properties such as packing density, permeability and heat transfer coefficients remain inadequately characterized (1). The work reported in this paper involves subgrid modeling techniques which may prove useful in resolving these inadequacies. The technique involves the use of a lattice Boltzmann modeling approach. This approach resolves length scales which are orders of magnitude below those typical of a standard computational fluid dynamics (CFD) representation of an aftertreatment device.

A minimally invasive spatially resolved capillary inlet mass spectrometer has been used to quantify EGR/air mixing in a Cummins V-8 medium-duty diesel engine. Two EGR-system hardware designs were evaluated in terms of EGR-air mixing at the intake manifold inlet and port-to-port EGR charge uniformity. Performance was assessed at four modalized-FTP engine conditions. One design is found to be considerably better, particularly at three of the four engine conditions. Specific questions such as the effect of maximizing mass air flow on EGR mixing, and if particular cylinders are EGR starved are investigated. The detailed performance characteristics suggest areas to focus improvement efforts, and serve as a foundation for identifying the non-uniformity EGR barriers and origins.

NOx sorbate, or “trap”, catalysts have achieved >90% reduction of NOx from lean exhaust streams over a broad range of temperatures. Since diesel can be used as the reductant for NOx sorbate catalysts, the sorbate catalyst technology offers great potential for NOx control in a broad range of mobile diesel applications. Traditionally, the longevity of NOx sorbate catalysts in diesel exhaust applications has been limited by sulfur masking of NOx sorption sites. Two methods to control sulfur compounds and their associated effects will be presented here. Upstream sulfur sorbate, or “trap”, catalysts are used to control the rate of sulfur masking by diverting sulfur away from the NOx sorbate catalyst. Desulfation of NOx sorbate catalysts can lead to the removal of sulfur compounds from the catalyst and reactivation of NOx sorption sites. Data demonstrating sulfur control with both of these methods will be presented here.

A correlation between reflectance type smoke measurements and dry particulate concentrations in diesel exhaust is derived from first principles. The model has one free parameter; the mass-average diameter of the exhaust particulates. Data from the literature indicates that particulate diameters can vary depending upon the injection hardware, fuel properties, and combustion chamber design. Older engines typically have larger average particulate radii and run at higher smoke numbers. Using a simple linear relationship between smoke number and mass-averaged particulate diameter, a good match is obtained between the derived model and experimental data. As a further validation of the model, a technique is derived by which any correlation between smoke and particulate concentration can be validated with only a smoke meter, provided it has multiple draw capabilities. Using this novel technique, the correlation derived here is shown to be functionally correct.