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Passenger and light duty diesel vehicles will require up to 90% NOx conversion over the Federal Test Procedure (FTP) to meet future Tier 2 Bin 5 standards. This accomplishment is especially challenging for low exhaust temperature applications that mostly operate in the 200 - 350°C temperature regime. Selective catalytic reduction (SCR) catalysts formulated with Cu/zeolites have shown the potential to deliver this level of performance fresh, but their performance can easily deteriorate over time as a result of high temperature thermal deactivation. These high temperature SCR deactivation modes are unavoidable due to the requirements necessary to actively regenerate diesel particulate filters and purge SCRs from sulfur and hydrocarbon contamination. Careful vehicle temperature control of these events is necessary to prevent unintentional thermal damage but not always possible. As a result, there is a need to develop thermally robust SCR catalysts.

This paper presents the development of an analytical model that complements laboratory based experiments to provide a tool for Selective Catalyst Reduction (SCR) applications. The model calibration is based on measured data from NOx reduction performance tests as well as ammonia (NH3) adsorption/desorption tests over select SCR catalyst formulations in a laboratory flow reactor. Only base metal/zeolite SCR samples were evaluated. Limited validations are presented that show the model agrees well with vehicle data from Environmental Protection Agency Federal Test Procedure (EPA FTP) emission assessments. The model includes energy and mass balances, several different NH3 reactions with NOx, NH3 adsorption and desorption algorithms, and NH3 oxidation.

This paper presents a study of urea SCR catalyst aging characteristics and implementation into an analytical model that complements laboratory based experiments for a dynamometer-aged SCR brick. The model calibration is based on measured data taken from a 120k-mile simulated dynamometer-aged base metal/zeolite SCR. Dynamometer aging led to non-uniform axial deterioration with more severe deactivation toward the front of the SCR brick compared to the rear. Data from a 120k-mile simulated hydrothermally oven-aged SCR (uniform axial aging) is used to establish baseline aged NOx performance and NH3 adsorption/desorption behavior. An axial deterioration factor is applied to the baseline model to account for differences between oven and dynamometer aging. The model is exercised using engine out vehicle data to examine how different aging processes (oven vs. dynamometer) affect overall NOx performance during the EPA FTP (Environmental Protection Agency Federal Test Procedure).

High gas prices combined with demand for improved fuel economy have prompted increased interest in diesel engine applications for both light-duty and heavy-duty vehicles. The development of aftertreatment systems for these vehicles requires significant investments of capital and time. A reliable and robust qualification testing procedure will allow for more rapid development with lower associated costs. Qualification testing for DPFs has its basis in methods similar to DOCs but also incorporates a PM loading method and regeneration testing of loaded samples. This paper examines the effects of accelerated loading using a PM generator and compares PM generator loaded DPFs to engine dynamometer loaded samples. DPFs were evaluated based on pressure drop and regeneration performance for samples loaded slowly and for samples loaded under accelerated conditions. A regeneration reactor was designed and built to help evaluate the DPFs loaded using the PM generator and an engine dynamometer.

Urea selective catalytic reduction (SCR) catalysts have the capability to deliver the high NOx conversion efficiencies required for future emission standards. However, the potential for the occasional over-temperature can lead to the irreversible deactivation of the SCR catalyst. On-board diagnostics (OBD) compliance requires monitoring of the SCR function to make sure it is operating properly. Initially, SCR catalyst performance metrics such as NOx conversion, NH3 oxidation, NH3 storage capacity, and BET surface area are within normal limits. However, these features degrade with high temperature aging. In this work, a laboratory flow reactor was utilized to determine the impact on these performance metrics as a function of aging condition. Upon the completion of a full time-at-temperature durability study, four performance criteria were established to help determine a likely SCR failure.

A laboratory flow reactor study was utilized to determine the durability impact of alkali metal (Na and K) exposure on three Pt/Pd-based diesel oxidation catalysts (DOC), two vanadium-based selective catalytic reduction (SCR) catalysts, and two Cu/zeolite-based SCR catalysts. All catalyst samples were contaminated by direct deposition of Na or K by an incipient wetness technique. The activity impact on the contaminated DOCs was accomplished by evaluating for changes in CO and HC light-off. The activity impact on the contaminated SCR catalysts was accomplished by evaluating for changes in the Standard SCR Reaction, the Fast SCR Reaction, the Ammonia Oxidation Reaction, and the Ammonia Storage Capacity. Contamination levels of 3.0 wt% Na was found to have a higher negative impact on Pt-based and zeolite containing DOCs for T-50 CO and HC light-off.

This paper describes the pressure loss characteristics of a variety of substrates (with and without washcoat) that have different cell densities, lengths, and diameters. Both experimental and analytical approaches were used to determine pressure loss characteristics. Engine dynamometer testing was conducted as an experimental approach to measure pressure losses at several different speed and load points. A simple, but comprehensive, analytical model was also developed to estimate pressure loss and equivalent power loss in an exhaust system. The model provides for losses due to the substrate resistance and the inlet/outlet headers. The experimental approach demonstrated that the model was an effective tool to provide assistance during the screening of exhaust system design alternatives.

An analytical model was developed to simulate both sulfur adsorption and desorption characteristics based on the laboratory determined parameters. Diesel Lean NOx Trap (LNT) was tested under laboratory conditions to examine desulfation (deSOx) characteristics. Effects of different Lean/Rich (L/R) cycling of Air-Fuel ratio during the deSOx mode were investigated. The gradient of adsorbed sulfur along the axial direction of the sample LNT was also examined. The gradient of sulfur deposit, together with different L/R cycling combinations for the deSOx mode was critical to develop the efficient sulfur removal strategies. The model considered energy and mass balances during sulfur adsorption and desorption modes to predict the catalyst temperature and the amount of sulfur adsorbed and removed. HC and CO oxidation reactions as well as the oxygen storage were considered to estimate heat generated by the exothermic reactions.