Reducing Hydrocarbon Emissions in Gasoline Engine Warm-up
Yokohama2006/F2006P276

Abstract

In order to comply with ever stricter emission standards for gasoline engines, reducing the hydrocarbon emissions during the cold start and warm up phases is taking on particular importance. This paper reports on the results of tests on influencing air-fuel-mixing conducted at the Institute for Measurement Technology and Reciprocating Machines at Otto-von- Guericke-University Magdeburg. This work was carried out as part of an FVV project. Using reduced intake valve lifts combined with an adjustment of valve timing made it possible to demonstrate hydrocarbon emissions and specific fuel consumption could be reduced considerable for an engine at operating temperature, (1). This outcome was the point of departure for investigating the potential of a small valve gap in cold start and warm-up operating states. Its delayed heating has not yet allowed the catalytic converter to achieve its full effectiveness in these engine operating states so that measures which reduce the raw emissions and shorten the response time of the catalytic converter are effective means to comply with emission standards, (2). In particular, the following internal engine influences were investigated: intake valve lift, intake valve opening time, valve timing and intake cam profile. In addition, for what proved to be the optimal variant, the influence of: exhaust spread, injection time, injection pressure increase, engine start temperature drop and masking around the valve seat were tested for HC raw emissions. In closing, the potential of flow control valves (FCV) in the manifold was analysed in comparison with a small valve gap. Both techniques of simulation (PROMO and FIRE) were used and engine tests were conducted in work on the research project. Tests to supplement and verify the 3D simulations were performed on a flow test bench under steady state conditions. The tests on the small valve gap revealed that reducing intake valve lift from 9 mm to 2 mm and intake valve opening time from 146 °cam angle to 90 °cam angle and having an asymmetrical cam profile (steep rise - flat drop off) noticeably improved the cold start / warm-up behavior of a gasoline engine. If instead a flow control valve is optimally positioned in the intake manifold, striking improvements can also be achieved. Similar improvements in the engine tests could not be achieved with the tested masks around the valve seat. However, flow tests indicate a modified, optimized mask could improve cold start / warm-up behavior.

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