1994-03-01

Novel Emission Technologies with Emphasis on Catalyst Cold Start Improvements Status Report on VW-Pierburg Burner/Catalyst Systems 940474

Intensive research and development activities which have been carried out by automotive manufacturers and suppliers of the automotive industry are currently focused on new solutions to meet the strict exhaust gas emission standards defined by LEV, ULEV and EG III. While both CO and HC emissions have been curtailed further and require novel emission technologies, the latter takes on a higher priority due to drastic reduction imposed by ULEV regulations. In current emission control systems with three-way catalysts, the major part of these emissions is created during cold start and warm-up phases when the catalyst temperature is below its light-off temperature.
The present paper reports on burner/catalyst systems for improving the catalyst's cold start performance, which is a novel technology compared to other known technologies such as electrically heated catalysts (EHC) and adsorbers. The burner system heats up the catalyst rapidly to its light-off temperature and reduces the cold start emissions without a noticeable fuel penalty. The present paper describes the current state of development of this burner/catalyst system. It provides conversion data obtained from vehicles of Volkswagen Group and suggests additional improvements to reduce cold start emissions further.
THE THREE-WAY catalyst, which is used in large-volume production, permits a reduction of exhaust emissions by approximately 90%. The ULEV standard for NMOG of 0.04 g/mi requires another reduction of about the same percentage. This cannot be achieved with the current technology. More than 80% of the HC and CO emissions are generated during the first few minutes after cold start since the catalyst has not reached its light-off temperature. During this phase it is especially the HC emissions that have to be reduced drastically. The adsorber technology [1]* and the EHC system [2, 3, 4, 5 and 6] are two of the viable solutions to combating cold start emissions. The burner/catalyst system, developed by Pierburg and Volkswagen, is a third viable approach to achieve this goal. Initial results for the burner/catalyst system have been published recently [7]. In the meantime many automotive manufacturers are engaged in similar development projects [8]. The present paper describes the current state of development of this burner/catalyst system including all components as well as control functions and safety measures.

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