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Previous work done at the University of Michigan shows the capability of the vacuum-insulated catalytic converter (VICC) to retain heat during soak and the resulting benefits in reducing cold start emissions. This paper provides an improved version of the design which overcomes some of the shortcomings of the previous model and further improves the applicability and benefits of VICC. Also, newer materials have been evaluated and their effects on heat retention and emissions have studied using the 1-D after treatment model. Cold start emissions constitute around 60% to 80% of all the hydrocarbon and CO emissions in present day vehicles. The time taken to achieve the catalyst light-off temperature in a three-way catalytic converter significantly affects the emissions and fuel efficiency. The current work aims at developing a method to retain heat in catalytic converter, thus avoiding the need for light-off and reducing cold start emissions effectively.

Selective Catalytic Reduction (SCR) catalysts used in Lean NOx Trap (LNT) - SCR exhaust aftertreatment systems typically encounter alternating oxidizing and reducing environments. Reducing conditions occur when diesel fuel is injected upstream of a reformer catalyst, generating high concentrations of hydrogen (H₂), carbon monoxide (CO), and hydrocarbons to deNOx the LNT. In this study, the functionality of an iron (Fe) zeolite SCR catalyst is explored with a bench top reactor during steady-state and cyclic transient SCR operation. Experiments to characterize the effect of an LNT deNOx event on SCR operation show that adding H₂ or CO only slightly changes SCR behavior with the primary contribution being an enhancement of nitrogen dioxide (NO₂) decomposition into nitric oxide (NO). Exposure of the catalyst to C₃H₆ (a surrogate for an actual exhaust HC mixture) leads to a significant decrease in NOx reduction capabilities of the catalyst.

The buildup of deposits in EGR coolers causes significant degradation in heat transfer performance, often on the order of 20-30%. Deposits also increase pressure drop across coolers and thus may degrade engine efficiency under some operating conditions. It is unlikely that EGR cooler deposits can be prevented from forming when soot and HC are present. The presence of cooled surfaces will cause thermophoretic soot deposition and condensation of HC and acids. While this can be affected by engine calibration, it probably cannot be eliminated as long as cooled EGR is required for emission control. It is generally felt that “dry fluffy” soot is less likely to cause major fouling than “heavy wet” soot. An oxidation catalyst in the EGR line can remove HC and has been shown to reduce fouling in some applications. The combination of an oxidation catalyst and a wall-flow filter largely eliminates fouling. Various EGR cooler designs affect details of deposit formation.

A diesel fuel and air diffusion flame burner system has been designed for laboratory simulation of diesel exhaust gas. The system consists of mass flow controllers and a fuel pump, and employs several unique design and construction features. It produces particulate emissions with size, number distribution, and morphology similar to diesel exhaust. At the same time, it generates NOx emissions and HC similar to diesel. The system has been applied to test plasma discharges. Different design discharge devices have been tested, with results indicating the importance of testing devices with soot and moisture. Both packed bed reactor and flat plate dielectric barrier discharge systems remove some soot from the gas, but the designs tested are susceptible to soot fouling and related electrical failures. The burner is simple and stable, and is suitable for development and aging of plasma and catalysts systems in the laboratory environment.

Nonthermal plasma discharges in combination with catalysts are being developed for diesel aftertreatment. NOx conversion has been shown over several different catalyst materials. Particulate removal has also been demonstrated. The gas phase chemistry of the plasma discharge is described. The plasma is oxidative. NO is converted to NO2, CH3ONO2 and HNO3. Hydrocarbons are partially oxidized resulting in aldehydes and CO along with various organic species. Soot will oxidize if it is held in the plasma. When HC is present, SO2 is not converted to sulfates. Suitable plasma-catalysts can achieve NOx conversion over 70%, with a wider effective temperature range than non-plasma catalysts. NOx conversion requires HC and O2. Electrical power consumption and required exhaust HC levels increase fuel consumption by several percent. A plasma catalyst system has demonstrated over 90% particulate removal in vehicle exhaust.

Previously reported experiments revealed the presence of a small number of clusters or very small particles in the effluent of a nonthermal plasma reactor when treating a simulated engine exhaust mixture. These clusters are smaller than 7 nm. The quantity of clusters is orders of magnitude smaller than the particulate diesel or gasoline engine exhaust typically contains. In this report, we describe further experiments designed to determine the chemical composition of the clusters. Clusters were collected on the surface of a silicon substrate by exposing it to the effluent flow for extended time periods. The resulting deposits were analyzed by high mass resolution SIMS and by XPS. The SIMS analysis reveals NH4+, CH6N+, SO-, SO2-, SO3- and HSO4- ions. XPS reveals the presence of N and S at binding energies consistent with that of ammonium sulfate.

Projected NOx and fuel costs are compared for a plasma-catalyst system and an active lean NOx catalyst system. Comparisons are based on modeling of FTP cycle performance. The model uses steady state laboratory device characteristics, combined with measured vehicle exhaust data to predict NOx conversion efficiency and fuel economy penalties. The plasma system uses a proprietary catalyst downstream of a plasma discharge. The active lean NOx catalyst uses a catalyst along with addition of hydrocarbons to the exhaust. For the plasma catalyst system, NOx conversion is available over a wide temperature range. Increased electrical power improves conversion but degrades vehicle fuel economy; 10 J/L energy deposition costs roughly 3% fuel economy. Improved efficiency is also available with larger catalyst size or increased exhaust hydrocarbon content. For the active lean NOx system, NOx conversion is available only in a narrow temperature range.

There is a need for an efficient, durable technology to reduce NOx emissions from oxidative exhaust streams such as those produced by compression-ignition, direct-injection (CIDI) diesel or lean-burn gasoline engines. A partnership formed between the DOE Office of Advanced Automotive Technology, Pacific Northwest National Laboratory, Oak Ridge National Laboratory and the USCAR Low Emission Technologies Research and Development Partnership is evaluating the effectiveness of a non-thermal plasma in conjunction with catalytic materials to mediate NOx and particulate emissions from diesel fueled light duty (CIDI) engines. Preliminary studies showed that plasma-catalyst systems could reduce up to 70% of NOx emissions at an equivalent cost of 3.5% of the input fuel in simulated diesel exhaust. These studies also showed that the type and concentration of hydrocarbon play a key role in both the plasma gas phase chemistry and the catalyst surface chemistry.

NOx reduction efficiency under simulated lean burn conditions is examined for a non-thermal plasma in combination with borosilicate glass, alumina, titania, Cu-ZSM-5 and Na-ZSM-5. The non-thermal plasma alone or with a packed bed of borosilicate glass beads converts NO to NO2 and partially oxidizes hydrocarbons. Alumina and Na-ZSM-5 reduce a maximum of 40% and 50% of NOx respectively; however, the energy cost is high for Na- ZSM-5. Cu-ZSM-5 converts less than 20% with a very high energy consumption. The anatase form of titania reduces up to 35% of NOx at a relatively high energy consumption (150J/L) when the catalyst is contained in the plasma region, but does not show any appreciable conversion when placed downstream from the reactor. This phenomenon is explained by photo-activation of anatase in the plasma.

Recent work has shown that energy efficiencies as well as yields and selectivities of the NOx reduction reaction can be enhanced by combining a plasma discharge with select catalysts. While analysis of gas phase species with a chemiluminescent NOx meter and mass spectrometer show that significant removal of NOx is achieved, high background concentrations of nitrogen preclude the measurement of nitrogen produced from NOx reduction. Results presented in this paper show that N2 from NOx reduction can be measured if background N2 is replaced with helium. Nitrogen production results are presented for a catalyst system where the catalyst is in the plasma region and where the catalyst is downstream from the plasma. The amount of N2 produced is compared with the amount of NOx removed as measured by the chemiluminescent NOx meter. The measured nitrogen from NOx reduction accounts for at least 40% of the total NOx removed for both reactor configurations.

A dielectric barrier discharge device has been built to test nonthermal plasma discharges for simulated diesel exhaust NOx removal. The device has also been tested with selected catalysts located after the plasma. Emissions are measured by conventional automotive emission analyzers, plus FTIR. Dielectric barrier discharges without catalyst convert input NO to a mix of NO2, HONO, HNO3, and organic nitrates. At 30 J/l energy deposition, approximately 26% of the input NO is “lost”. Some of the hydrocarbon input is converted to a variety of species, including CO, CO2, aldehydes, and alcohols. A Cu-ZSM catalyst after the plasma device eliminates the apparent NOx conversion seen with the bare plasma. This indicates that the apparent NOx conversion of the bare plasma is actually conversion to some (unmeasured) species which can be reconverted to NOx by the Cu-ZSM catalyst. Placing a proprietary catalyst within the plasma results in significant NOx conversion.