Search Results

It has been reported that particulate emissions from diesel vehicles could be associated with damaging human health, global warming and a reduction in air quality. These particles cover a very large size range, typically 3 to 10 000 nm. Filters in the vehicle exhaust systems can substantially reduce particulate emissions but until very recently it was not possible to directly characterise actual on-road emissions from a vehicle. This paper presents the first study of the effect of filter systems on the particulate emissions of a heavy-duty diesel vehicle during real-world driving. The presence of sulfur in the fuel and in the engine lubricant can lead to significant emissions of sulfate particles < 30 nm in size (nanoparticles).

It is well known that the catalytic efficiency and durability of an automotive catalytic converter can be significantly affected by its design. This paper demonstrates the potential for further improvement in both the durability and efficiency by using a novel catalytic converter concept based on a large frontal area, high cell density substrate. This concept requires that attention be paid to optimization of the flow as well as of the mounting system. The converter design is determined with a computational fluid dynamic (CFD) simulation and the effect of this design on the temperature distribution in the substrate is calculated and measured. Due to this novel converter concept the maximum substrate temperature is reduced, which results in a better aging behavior. This improvement allows a reduction in precious metal content without a loss in efficiency.

Catalytic converter substrates for automobile emission control have to operate under the hostile conditions of the automotive exhaust. This paper will first discuss the mechanical and physical properties to ensure durable mechanical function of the catalytic substrate and converter system. High temperature mechanical and thermal shock substrate requirements and properties will be discussed. The functionality of a catalytic converter is significantly influenced by the catalytic coating. At the same time, substrate characteristics as will be shown, also effect converter functional parameters like back pressure, light-off and conversion efficiency. The importance of the substrate parameters cell shape, cell density and substrate mass and their effect on thermohydraulic parameters like heat- and mass transfer factors for various cell structures and substrates will be presented.

Governing bodies world-wide are setting increasingly tighter emission standards to help improve air quality. US and Californian LEV/ULEV standards are pace setting, European Stage II legislation has just become effective. In Brazil, the upcoming 1997 standards are also demanding for tighter emission control. The monolithic ceramic honeycomb catalytic converter -for more than the past 20 years- has been a reliable key element in the automotive emission control systems. In order to help meet tightened emission regulation as well to satisfy even more stringent durability requirement, an advanced thinwall ceramic Celcor XT has been developed for increased geometric surface area and reduced backpressure. The product properties as well as FTP and ECE emission and durability test results are being described in this paper. Converter system durability is also determined by robust canning and mounting systems. A durable mounting concept, especially for preconverters, is being described.

Three European gasoline vehicles, homologated to European Stage II limits, and two US gasoline vehicles, certified to Californian TLEV limits, were evaluated over the new European test cycle for year 2000 standards and the US Federal Test Procedure. Three advanced catalyst technologies were tested on these vehicles, in the original equipment converter position in all but one case, without any additions or changes to the existing emission control system. Prior to testing they were aged on a cycle representing 80,000 km road durability. Up to 30% reductions in emissions were achieved from those for which the vehicles were homologated, at an incremental cost in precious metal of 12 - 23 US$ per liter of catalyst compared to the original converter precious metal value (precious metal prices of 16 July 1996).

The long-term durability of a ceramic racetrack converter is examined using the systems approach. Each of the converter components is characterized with respect to its behavior under simulated mechanical and thermal loads. In particular, the impact of three different washcoats on key physical properties, and the load vs. deformation characteristics of three different insulation mats are examined from mechanical and thermal durability point of view. Similarly, the can deformation at elevated temperature is taken into account to ensure adequate mounting pressure on ceramic monolith under all operating conditions. The temperature distribution at the midbed of the catalyst during engine dynamometer testing, together with the component properties data, are then used in a finite element model to compute thermal stresses in the monolith as function of engine load and speed.