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The increasing severity in emission standards around the world has been accompanied by the development of more active, durable catalysts. With a view to investigating the effects of high thermal aging on the catalyst performance and structure, the relationships of washcoat composition, washcoat structure, and PGM location with respect to catalyst activity were clarified using a model gas test, as well as physical and chemical characterization methods. The influence of newly developed washcoat components and PGM location on catalyst performance are also demonstrated by engine bench tests. The results obtained in this study indicate the newly developed Pt/Rh catalyst techologies are appropriate for future applications in which the catalyst will be exposed to extremely high temperature and flowrates.

New advanced Pd only, Pd:Rh and Pt:Pd:Rh catalysts are compared with a current platinum rhodium catalyst after poisoning and thermal ageing. The results indicate that at equivalent precious metal cost (at 1994 prices) the advanced palladium based catalysts achieve significantly improved performance compared with current Pt, Rh and Pd technology. The new Pd:Rh formulation is recommended for close coupled locations and the Pt:Pd:Rh formulation recommended for underfloor locations where residual fuel lead may be present. The formation of H2S is shown to be low with the palladium based catalysts. Finally, it is shown that the new catalysts with balanced oxidation and reduction capability perform better in multi-brick systems than addition of a highly loaded palladium only front brick.

With the advent of stricter vehicle emission standards, the improvement of three way catalyst performance and durability remains a pressing issue. A critical consideration in catalyst design is the potential for variations in fuel sulfur levels to have a significant impact on the ability to reach TLEV, LEV, and ULEV emission levels. As a result, a better understanding of the role of PGM composition in the interplay between thermal durability and sulfur tolerance is required. Three way catalysts representative of standard Pd-only, Pd/Rh and Pt/Rh formulations were studied over a variety of aging and evaluation conditions. The parameters investigated included aging temperature, air fuel ratio and sulfur level. Evaluations were performed on a 1994 TLEV vehicle using different sulfur level fuels. The effect of PGM loading was also included within the study.

Determining what exhaust gas recirculation (EGR) control parameters have the largest impact on engine performance and emissions is of critical importance when developing an EGR-equipped engine. These tests studied the effects of varying the net charge mass, the fresh air charge mass, the indicated power, and the oxygen equivalence ratio at various EGR fractions. The research was carried out on a direct-injection, natural gas fuelled, pilot-ignited four-stroke heavy-duty engine using Westport Innovations Inc.'s pilot-ignited, direct injection of natural gas technology. The testing was carried out using a prototype injector and the standard diesel-fuelled engine's combustion chamber. The results indicate that fuel efficiency, as well as emissions of Nitrogen Oxides (NOx) and Carbon Monoxide (CO) depend primarily on the EGR level, and not on the values of the EGR control parameters.

The performance characteristics of a commercial lean-NOX trap catalyst were evaluated between 200 and 500°C, using H2, CO, and a mixture of both H2 and CO as reductants before and after different high-temperature aging steps, from 600 to 750°C. Tests included NOX reduction efficiency during cycling, NOX storage capacity (NSC), oxygen storage capacity (OSC), and water-gas-shift (WGS) and NO oxidation reaction extents. The WGS reaction extent at 200 and 300°C was negatively affected by thermal degradation, but at 400 and 500°C no significant change was observed. Changes in the extent of NO oxidation did not show a consistent trend as a function of thermal degradation. The total NSC was tested at 200, 350 and 500°C. Little change was observed at 500°C with thermal degradation but a steady decrease was observed at 350°C as the thermal degradation temperature was increased.

The use of exhaust gas recirculation (EGR) to control NOx emissions from direct-injection engines results in the reintroduction of exhaust particulate matter (PM) into the intake manifold. The influence of this recirculated PM on emissions from a pilot-ignited direct injection of natural gas engine was studied by installing a filter in the EGR system. Comparison tests at fixed engine conditions were conducted to identify differences between filtered and unfiltered EGR. No significant variations in gaseous or PM mass emissions were detected. This indicates that the recirculated PM is not contributing substantially to the increases in PM mass emissions commonly observed with EGR. Reductions in black carbon and ultra-fine particle exhaust concentrations in the exhaust were observed at the highest EGR fractions with the filter installed.

In a collaborative programme, the effects of gasoline sulphur content on regulated emissions from three-way catalyst equipped vehicles have been studied. The programme evaluated the sulphur tolerance of three different catalyst formulations on the same range of vehicles. The catalyst chemistries were chosen to be representative of typical current formulations in different markets, as follows: 1. Platinum/Rhodium (Pt/Rh) 2. Platinum/Rhodium/Nickel (Pt/Rh/Ni) 3. Palladium/Rhodium (Pd/Rh) Each vehicle/catalyst combination was tested with fuels containing sulphur at nominal levels of 50, 250 and 450 ppm weight. All fuels were produced using the low sulphur fuel as a base and doping to 250 and 450 ppm S with a mixture of nine sulphur compounds, typical of those actually occurring in European gasolines. The results show clear differences between the magnitudes of the sulphur effect with different catalyst formulations.

Progress made in reducing engine-out particulate emissions has prompted a revival in the design of flow-through oxidation catalysts for diesel engine applications. Effort in this area has focused primarily in the area of SOF control for the further reduction of particulate emissions. The work reported here covers some of the catalyst design parameters important for SOF and gas phase pollutant control. This is illustrated with both laboratory reactor and engine evaluation data for several formulary and operating parameters. Platinum-based catalysts are shown to be generally the most active, but they require treatments or additives to reduce the inherently high activity of platinum for the oxidation of SO2 present in the exhaust. The effect of additives and their loading on the oxidation activity of Pt/alumina for HC, CO, SOF and SO2 oxidation is discussed in detail and additives are identified which reduce SO2 oxidation with minimal effect on HC, CO or SOF oxidation activity.

Compression ignition engines, including those that use natural gas as the major fuel, produce emissions of NOx and particulate matter (PM). Westport Inc. has developed the pilot-ignited high-pressure direct-injection (HPDI) natural gas engine system. Although HPDI engines produce less soot than comparable conventional diesel engines, further reductions in engine-out soot emissions is desired. In diesel engines, multiple injections can help reduce both NOx and PM. The effect of post injections on HPDI engines was not studied previously. The present research shows that late injection of a second gas pulse can significantly reduce PM and CO from HPDI engines without significantly increasing NOx or fuel consumption. In-cylinder pressure measurements were used to characterize the heat release resulting from the multiple injections. Experiments showed that most close-coupled split injection strategies provided no significant emissions benefit and less stable operation.

In a consortium of European industrial partners and research institutes, a combination of industrial development and scientific research was organised. The objective was to improve the catalytic NOx conversion for lean burn cars and heavy-duty trucks, taking into account boundary conditions for the fuel consumption. The project lasted for three years. During this period parallel research was conducted in research areas ranging from basic research based on a theoretical approach to full scale emission system development. NOx storage catalysts became a central part of the project. Catalysts were evaluated with respect to resistance towards sulphur poisoning. It was concluded that very low sulphur fuel is a necessity for efficient use of NOx trap technology. Additionally, attempts were made to develop methods for reactivating poisoned catalysts. Methods for short distance mixing were developed for the addition of reducing agent.

Selective NOx recirculation (SNR), involving adsorption, selective external recirculation and decomposition of the NOx by the combustion process, is itself a promising technique to abate NOx emissions. Three types of materials containing Ba: barium aluminate, barium tin perovskite and barium Y-zeolites have been developed to adsorb NOx under lean-burn or Diesel conditions, with or without the presence of S02. All these materials adsorb NO2 selectively (lean-burn conditions), and store it as nitrate/nitrite species. The desorption takes place by decomposition of these species at higher temperatures. Nitrate formation implies also sulfate formation in the presence of SO2 and SO3, while the NO2/SO2 competition governs the poisoning of such catalysts.

The SNR-technique is a new NOx aftertreatment system for lean burn gasoline and diesel applications. The objective of SNR is NOx removal from lean exhaust gas by NOx adsorption and subsequent selective external recirculation and decomposition of NOx in the combustion process. The SNR-project is composed of two major parts. Firstly the development of NOx adsorbents which are able to store large quantities of NOx in lean exhaust gas, and secondly the NOx decomposition by the combustion process. Emphasis of this paper is the investigation of NOx reduction in the combustion process, including experimental investigation and numerical simulation. The NOx decomposition process has been proven in diesel and lean-burn gasoline engines. Depending on the type of engine NOx-conversion rates up to 90 % have been observed. Regarding the complete SNR-system, including the efficiency of the adsorbing material and the NOx decomposition by the combustion, a NOx removal of more than 50% is achievable.

The objective of this effort was to develop an understanding of how different converter substrate cell structures impact tailpipe emissions and pressure drop from a total systems perspective. The cell structures studied were the following: The catalyst technologies utilized were a new technology palladium only catalyst in combination with a palladium/rhodium catalyst. A 4.0-liter, 1997 Jeep Cherokee with a modified calibration was chosen as the test platform for performing the FTP test. The experimental design focused on quantifying emissions performance as a function of converter volume for the different cell structures. The results from this study demonstrate that the 93 square cell/cm2 structure has superior performance versus the 62 square cell/cm2 structure and the 46 triangle cell/cm2 structure when the converter volumes were relatively small. However, as converter volume increases the emissions differences diminish.

The use of pilot-ignited, direct-injected natural gas in a heavy-duty compression-ignition engine has been shown to reduce emissions while maintaining performance and efficiency. Adding recirculated exhaust gas (EGR) has been shown to further reduce emissions of nitric oxides (NOx), albeit at the cost of increased hydrocarbons (tHC), carbon monoxide (CO), and particulate matter (PM) emissions at high EGR fractions. Previous tests have suggested that reducing the delay between the diesel and natural gas injections, increasing the injection pressure, or adjusting the combustion timing have individually achieved substantial emissions benefits. To investigate the effectiveness of combining these techniques, and of using them over a wide range of operating conditions, a series of tests were carried out. The first set of tests investigated the interactions between these effects and the EGR fraction.

The effect of changing catalyst precious metal ratios and loadings on close coupled catalytic converter efficiencies has been studied. The three precious metals were platinum, palladium and rhodium. The specific matrix used for the development of response surface models is a central composite design and provides the capability of visually optimising the precious metal loadings. Catalysts were evaluated using perturbed scans. lightoff curves from the dynamometer aged, and vehicle emission tests. These scans show percent conversion efficiencies of the three legislated gases; HC, CO and NOx, over a range of Air Fuel Ratios (λ). Whilst lean and rich lightoff curves provide indications of conversion efficiencies at varying temperatures. Prior to testing the catalysts were aged, using an accelerated dynamometer ageing process, to 80K simulated kilometres. The catalysts were then fitted to a vehicle and chassis roll emission tests conducted.

Dual-fuel combustion strategies combining a premixed charge of natural gas and a pilot injection of diesel fuel offer the potential to reduce CO2 emissions as a result of the high Hydrogen/Carbon (H/C) ratio of methane gas. Moreover, the high octane number of methane means that dual-fuel combustion strategies can be employed on compression ignition engines without the need to vary the engine compression ratio, thereby significantly reducing the cost of engine hardware modifications. The aim of this investigation is to explore the fundamental combustion phenomena occurring when methane is ignited with a pilot injection of diesel fuel. Experiments were performed on a single-cylinder optical research engine which is typical of modern, light-duty diesel engines. A high-speed digital camera recorded time-resolved combustion luminosity and an intensified CCD camera was used for single-cycle OH*chemiluminescence imaging.

In the USA, hydrogen sulfide emissions from three-way catalytic converter-equipped automobiles are effectively suppressed by the addition of nickel to catalyst formulations. This approach is generally not utilized in catalyst formulations for Europe because of European concern about the health, safety and environmental issues surrounding the use of nickel. A modified form of iron oxide has been identified which suppresses hydrogen sulfide emissions from three-way catalysts. This suppression has been achieved without affecting the fresh or aged performance of the catalyst, a problem often encountered with other materials. The performance and durability of catalyst formulations incorporating the new material are demonstrated with a variety of aging and evaluation protocols.

When performing catalyst modeling and parameter tuning it is desirable that the experimental data contain both transient and stationary points and can be generated over a short period of time. Here a method of creating such concentration transients for a full scale engine rig system is presented. The paper describes a valuable approach for changing the composition of engine exhaust gas going to a DOC (or potentially any other device) by conditioning the exhaust gas with an additional upstream DOC and/or SCR. By controlling the urea injection and the DOC bypass a wide range of exhaust compositions, not possible by only controlling the engine, could be achieved. This will improve the possibilities for parameter estimation for the modeling of the DOC.

Future US emissions limits are likely to mean a sophisticated nitrogen oxide (NOx) reduction technique is required for all vehicles with a diesel engine, which is likely to be either NOx trap or selective catalytic reduction (SCR) technology. To investigate the potential of SCR for NOx reduction on a light duty vehicle, a current model vehicle (EUII M1 calibration), of inertia weight 1810 kg, was equipped with an urea-based SCR injection system and non-vanadium, non-zeolitic SCR catalysts. To deal with carbon monoxide (CO), hydrocarbon (HC) and volatile organic fraction (VOF), a diesel oxidation catalyst was also incorporated into the system for most tests. Investigations into the effect of placing the oxidation catalyst at different positions in the system, changing the volume of the SCR catalysts, increasing system temperature through road load changes, varying the SCR catalyst composition, and changing the urea injection calibration are discussed.

Pilot-ignited direct injection of natural gas fuelling of a heavy-duty compression ignition engine while using recirculated exhaust gas (EGR) has been shown to significantly reduce NOx emissions. To further investigate emissions reductions, the combustion timing, injection pressure, and relative delay between the pilot and main fuel injections were varied over a range of EGR fractions while engine speed, net charge mass, and oxygen equivalence ratio were held constant. PM emissions were reduced by higher injection pressures without significantly affecting NOx at all EGR conditions. By delaying the combustion, NOx was reduced at the expense of increased PM for a given EGR fraction. By reducing the delay between the pilot and main fuel injections at high EGR, PM emissions were substantially reduced at the expense of increased total hydrocarbon (tHC) emissions. In this research, no attempt was made to optimize the injector or combustion chamber for natural gas fuelling with EGR.