A Study of the Thermochemical Conditions in the Exhaust Manifold Using Secondary Air in a 2.0 L Engine

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. This gives information on the conditions at which auto ignition takes place and recommendations for exhaust system design and engine calibration are derived. It may be further used to improve system reliability and ensure reduction in cold start emissions at different start conditions. The thermodynamical conditions in the engine and exhaust system are calculated by means of a 1-D CFD³ program. The simulation of the auto ignition conditions in the exhaust manifold is computed with the CHEMKIN program package.