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An overview is given on the state of the art of a new catalytic exhaust gas aftertreatment device for diesel engines. The function of a precious metal based, flow-through type diesel oxidation catalyst is explained. Much attention is paid to the durability of the diesel oxidation catalyst and especially to the influence of poisoning elements on the catalytic activity. Detailed data on the interaction of poisoning elements such as sulfur, zinc and phosphorus with the catalytic active sites are given. Finally it is demonstrated that it is possible to meet the stringent emission standards for diesel passenger cars in Europe with a new catalyst generation over 80.000 km AMA aging.

The California LEV1 II program will be introduced in the year 2003 and requires a further reduction of the exhaust emissions of passenger cars. The cold start emissions represent the main part of the total emissions of the FTP2-Cycle. Cold start emissions can be efficiently reduced by injecting secondary air (SA) in the exhaust port making compliance with the most stringent standards possible. The thermochemical conditions (mixing rate and temperature of secondary air and exhaust gas, exhaust gas composition, etc) prevailing in the exhaust system are described in this paper. This provides knowledge of the conditions for auto ignition of the mixture within the exhaust manifold. The thus established exothermal reaction (exhaust gas post-combustion) results in a shorter time to light-off temperature of the catalyst. The mechanisms of this combustion are studied at different engine idle conditions.

To date, several non-SCR catalysts and catalytic systems have been suggested for NOX reduction under oxygen rich (lean) conditions, such as those which exist in diesel engine exhaust gas. However, the performance of such catalysts and catalyst systems is not clear when used on actual diesel engines. This paper reports on experimental results obtained when lean NOx catalysts are applied to diesel engine exhaust. Particularly, the catalysts' NOx performance is examined when secondary hydrocarbons are added as reducing agents directly in the exhaust gas stream. In addition, the effect of different catalyst formulations and secondary hydrocarbon addition on particulate emissions is monitored. Finally, partial system optimization is performed and the applicability of such catalysts and systems to engines operating under the US Heavy Duty Transient Cycle is examined.

Further advancements in engine development lead to increased fuel efficiency and reduced CO₂ emission. Such low emission engine concepts require most advanced exhaust gas aftertreatment systems for lowest possible tailpipe emissions. On the other hand, the exhaust gas purification by catalytic measures experiences more and more challenges due to constantly reduced exhaust gas temperatures by more efficient engines. These challenges can be overcome by traditional catalyst heating strategies, which are known to increase fuel consumption and emissions. Alternatively, electrically heated catalysts ("EHC") can be utilized to provide a very efficient method to increase gas temperatures directly in the exhaust catalyst. This way the energy input can be tailored according to the component need and the energy loss in the system can be minimized.

Future stringent emission limits both in the European Community and USA require continuously increased conversion efficiency of exhaust after-treatment systems. Besides the obvious targets of fastest light-off performance, overall conversion efficiency and durability, catalytic converters for maximum output engines require highly optimized flow properties as well, in order to create minimum exhaust backpressure for low fuel consumption. This work deals with the design, development and serial introduction of a close coupled main catalyst system using the innovative technology of Perforated Foils (PE). By means of PE-technology, channel-to-channel gas mixing within the metal substrate could be achieved leading to dramatically reduced backpressure values compared with the conventional design.

Several different possibilities will be described and discussed on the processes of reducing NOx in lean-burn gasoline and diesel engines. In-company studies were conducted on zeolitic catalysts. With lean-burn spark-ignition engines, hydrocarbons in the exhaust gas act as a reducing agent. In stationary conditions at λ = 1.2, NOx conversion rates of approx. 45 % were achieved. With diesel engines, the only promising variant is SCR technology using urea as a reducing agent. The remaining problems are still the low space velocity and the narrow temperature window of the catalyst. The production of reaction products and secondary reactions of urea with other components in the diesel exhaust gas are still unclarified.

The awareness concerning environmental issues and the economical need for fuel savings leads to the introduction of new, highly efficient Diesel engines for passenger cars. An engine with common rail injection system could meet this target and, with the help of an advanced diesel exhaust aftertreatment system also fulfilled the new legislative emission regulations. Besides the efficient oxidation of carbon monoxide (CO), hydrocarbons (HC) and diesel particulates, such a system also requires a moderate reduction efficiency for nitrogen oxides (NOx) under excess oxygen conditions. The present paper illustrates the further progress in catalytic NOx-reduction under excess of oxygen by hydrocarbon enrichment using the common rail injection system.

This paper reports first results of research and development work to achieve Nox reduction under lean diesel exhaust gas conditions by using a special coated, zeolite based monolith catalyst. Much attention is paid to the optimization of the activated zeolite system and the influence of group Ib and VIII elements of the periodic system. A major part of the paper deals with the influence of hydrocarbons, carbon monoxide, sulfur dioxide and water on the activity of the catalyst. Another aspect discussed is the influence of the residence time of the exhaust gas components. The thermal stability and the influence of poisoning elements on the catalyst performance is demonstrated by model gas reactor tests on oven and engine aged samples. Finally, first results on the performance of the catalyst system in a vehicle dynometer test are given.

A new method for the analysis of the gas flow in an internal combustion engine has been developed. It is based on the interactive coupling between commercially available three (STAR-CD) and one dimensional (PROMO) fluid dynamics codes. With this method the detailed transient flow distribution for any engine component of interest can be calculated taking into account the overall gas dynamic interaction with other engine components. The underlying physics and numerics are outlined. A description of the coupling procedure ensuring proper communication between the two computer codes is given. Also addressed is the averaging procedure adopted at the 3D boundaries, including the influence of the 1D/3D interface placement. A first application of this new method is presented, in which the gas flow in a turbo-charged DI-diesel-engine is simulated.

This paper compares 4 different EGR systems by means of simulation in GT-Power. The demands of optimum massive EGR and fresh air rates were based on experimental results. The experimental data were used to calibrate the model and ROHR, in particular. The main aim was to investigate the influence of pumping work on engine and vehicle fuel consumption (thus CO2 production) in different EGR layouts using optimum VG turbine control. These EGR systems differ in the source of pressure drop between the exhaust and intake pipes. Firstly, the engine settings were optimized under steady operation - BSFC was minimized while taking into account both the required EGR rate and fresh air mass flow. Secondly, transient simulations (NEDC cycle) were carried out - a full engine model was used to obtain detailed information on important parameters. The study shows the necessity to use natural pressure differences or renewable pressure losses if reasonable fuel consumption is to be achieved.

To support the application and design of exhaust gas aftertreatment systems for gasoline fueled passenger cars based on hydrocarbon adsorber catalysts, a computer model was developed. This model is based on simplified, lumped kinetics for the adsorption and desorption of hydrocarbons and for the oxidation of CO and hydrocarbons. Also included in the model are convective transport of heat and mass in the gas phase, mass and heat transfer to the washcoat layer, and diffusion with reaction in the washcoat layer. The continuity equations for this model with the appropriate boundary conditions were solved for a single channel assuming adiabatic behavior. After validation of the prediction on experimental results, this model was used to perform a simple parametric study on the influence of inlet temperature,CO concentration, washcoat loading, adsorber content, and cell density on the HC emission.

The regulations for mobile applications will become stricter in Euro 6 and further emission levels and require the use of active aftertreatment methods for NOX and particulate matter. SCR and LNT have been both used commercially for mobile NOX removal. An alternative system is based on the combination of these two technologies. Developments of catalysts and whole systems as well as final vehicle demonstrations are discussed in this study. The small and full-size catalyst development experiments resulted in PtRh/LNT with optimized noble metal loadings and Cu-SCR catalyst having a high durability and ammonia adsorption capacity. For this study, an aftertreatment system consisting of LNT plus exhaust bypass, passive SCR and engine independent reductant supply by on-board exhaust fuel reforming was developed and investigated. The concept definition considers NOX conversion, CO2 drawback and system complexity.

The present paper describes the results of a joint development program focussing on a system approach to meet the proposed EURO III and IV emission standards for a passenger car equipped with a 3.2 liter, 18 valve gasoline engine. Starting with the in-production configuration of a EURO II certified vehicle (model year 1997) the following improvement points were investigated in detail. By the introduction of a close-coupled catalyst in combination with engine measures to improve the catalyst light-off the proposed EURO III limits were met. The proposed EURO IV hurdle could be overcome by further using secondary air injection during cold-start in combination with an increased precious metal loading for the close-coupled catalyst.

To meet LEV/ULEV - requirements, a considerable amount of development work was necessary to ensure suitable efficiency and durability of catalyst systems [1, 2, 3]. In addition to active emission reduction systems like the Electrically Heated Catalyst (EHC), Exhaust Gas Ignition (EGI) and the burner, passive systems like the HC-trap and Closed-Coupled Catalysts (CCC) are practical solutions to fulfill tighter emission requirements [4, 5, 6, 7]. Depending on the application, thermo-mechanical stresses, vibrations and efficiency degradation through aging increases with the reduction of the distance between the engine and the catalytic converter. Therefore, the test procedures which were suitable for converters which were to be placed in underfloor positions, needed to be modified according to the load spectra acting on close-coupled catalysts. This paper describes a new test strategy used during the development and design verification phase of catalytic converter systems.

SOF and de-NOx catalysts are applied to heavy-duty diesel trucks which are regulated by European 13 mode or Japanese 13 mode cycles. Precious metal free catalysts can reduce SOF at low temperatures without increasing sulfates up to 670C. This catalyst shows little deterioration after 400 hours of high temperature engine aging. 32% PM and 47% SOF reduction is observed under 13 mode tests when the exhaust gas temperature exceeds 700C (ECE-13 mode). This precious metal free catalyst is suitable for diesel trucks, especially trucks with natural aspirating engine whose exhaust gas temperature is very high. De-NOx catalysts with a 300-500C NOx reduction temperature window are applied to the Japanese heavy-duty test cycle (Japan 13 mode). When secondary diesel fuel is added under modes 8 to 12, (secondary fuel addition only when catalyst inlet temperature is more than 300C), 19-25% NOx can be reduced with 2-4% fuel penalty.

Fundamental research work was undertaken to elucidate the mechanism of hydrogen sulfide formation on three-way automotive exhaust catalysts during the lean to rich engine operation sequence and to identify the role of the different catalyst components in this phenomenon. Based upon this knowledge, new catalysts were developed with reduced ability to form hydrogen sulfide by minimizing the storage of sulfur oxides. Engine dynamometer tests confirmed that the suppression of the hydrogen sulfide formation was obtained without loss of catalyst activity or aging stability. The role of the catalyst's age in the hydrogen sulfide formation is discussed. The development presented shows that it is possible to avoid “scavengers” to minimize the emission of hydrogen sulfide from three-way emission control catalysts.

This paper gives an overview of the development work for an aftertreatment system, used in hand held powertools to fulfil the corporate average US Limits. The paper will start with a description of the annual reductions in US Limits with differences in CARB and EPA legislation and the consequences of the legislation in Europe from 2007 onwards. There then follows a chapter describing space restrictions in the given muffler leading to a maximum size for the substrate. Tests results are shown, giving an idea of additional measures taken to avoid dangerous temperatures on the muffler surface and of the emitted exhaust gas. The exothermic temperature increase created under service conditions imposes an additional thermal load from the catalyst back towards the engine itself. Therefore, some modifications regarding gas flow and positioning of the catalyst had to be made to find an adequate solution for series production.

Diesel particulate mass emissions and their corresponding size distributions have been investigated on a diesel passenger car at steady state conditions using standard filters and a cascade impactor. These tests have been carried out at two different engine operating conditions (2100 rpm, 2.7 and 13.3 kW, respectively) corresponding to low and high exhaust gas temperatures. Two diesel fuels differing in their sulfur content (150 ppm and 2500 ppm S) have been used for these investigations. The particulate size distribution after diesel oxidation catalyst was found to be affected by the sulfur content of the diesel fuel and by the exhaust gas temperature. Interpretations of these results on a mechanistic basis are given. The diesel particulate emission studies have been extended to dynamic vehicle tests.

The introduction of gasoline direct injection technology into the European market will depend mainly on the availability of an effective and durable aftertreatment system, in order to reach future stringent European emission standards. NOx storage technology provides a reasonable chance of fulfilling future emission goals, but durability problems such as thermal degradation and sulfur poisoning have yet to be overcome. The present paper is dedicated to these problems, and demonstrates the progress achieved so far. The influence of different aging modes and aging severity on the NOx conversion efficiency of an advanced generation of NOx storage catalysts, is described in detail. It was found that the severity of aging at comparable catalyst bed temperatures, increases in the following order: hydrothermal aging in N2/H2O < engine aging w/o fuel cut at λ-1 < furnace aging in air < engine aging with fuel cut at λ-1.