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Exhaust Valve Seat Leakage
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English
Abstract
A 1.9L four cylinder engine was evaluated for leakage of cylinder charge through the exhaust valve seats. Fast FID HC analyzer traces reveal leakage. Static leakdown tests do not correlate with the Fast FID measurement, unlike previously published reports for a different engine. The causes of exhaust valve seat leakage are likely to be
- Flakes of cylinder deposits lodging in the valve seat
- Valve seat distortion due to the thermal and pressure loading of the cylinder head structure
Because deposit related effects are very history dependent, it is very difficult to obtain quantitative results.
Some experimental observations:
- Static pressure leakage measurements show variation of leakage area with cylinder pressure, caused by flexing of the valve head.
- Dynamic leakage results are history dependent. Leakage is reduced after running at high speed/load, and gradually build up during extended light load low speed operation.
- Valve closing forces can apparently affect leakage
- Particles of cylinder deposits are present in the exhaust port. These particles have composition similar to cylinder deposits but lower in carbon content and higher in oil ash. Particles were observed having 20-200 micron size. These deposits can lodge in the valve seat and contribute to leakage.
A brief survey of several other engines indicated the presence of leaks. It is likely that most engines exhibit exhaust valve seat leakage at least at some times.
It is difficult to assess the effect of these leaks on exhaust hydrocarbon emissions because of the complexity of the engine history dependence. Limited data suggest a 5% contribution is possible.
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Authors
Topic
Citation
Hoard, J. and Moilanen, P., "Exhaust Valve Seat Leakage," SAE Technical Paper 971638, 1997, https://doi.org/10.4271/971638.Also In
References
- Meernik, Paul R. Alkidas, Alex C. “Impact of Exhaust Valve Leakage on Engine-Out Hydrocarbons SAE Paper 932752
- Boam, D.J. Finlay, I.C. Biddulph, T.W. Lee, R. Bloomfield, J. Green, J.A. Woods, W.A. “The sources of unburnt hydrocarbon emissions from spark ignition engines during cold starts and warm-up” IMechE paper C448/064
- “Detailed Thermal and Structural Evaluation of the Ford CT20 Cylinder Head” confidential report number 12-36-002 Hsu et.al. Adapco February 13 1990