The drive for reduced emissions from diesel exhausts has led to a reduction in the amount of oil present in the air stream in automotive diesel engines. This, in turn, has led to an increase in the wear of inlet valves and seat inserts in diesel engines. Three types of valve/seat insert failures occur in internal combustion engines, namely; valve recession, guttering and torching. The most prevalent failure mechanism in diesel engines is valve recession. This is caused by material removal from the valve and/or the seat insert.
Several test-rigs have been developed that are capable of providing a valid simulation of the wear of both inlet valves and seat inserts used in automotive diesel engines:
An impact wear rig used to assess the fundamental wear characteristics of materials being investigated.
A valve testing rig that is used to investigate the effect of component geometry on valve wear.
A motorised cylinder-head used to investigate the effect of valvetrian dynamics on valve wear.
Investigations have shown that the valve and seat insert wear problem involves two distinct mechanisms; impact of the valve on the seat insert on valve closure and sliding of the valve on the seat insert under the action of the combustion pressure. Both have a large influence on valve recession. It is in combination, however, that they have the largest effect. In tests run on the bench test-rig using impact and sliding in combination it took a few thousand cycles to achieve wear attained in several hundred thousand cycles in the frictional sliding tests.
Wear has been shown to increase with valve closing velocity, combustion load and misalignment of the valve relative to the seat insert. Lubrication of the valve/seat interface reduced valve recession, on the material combination tested, by a factor of ten.
A semi-empirical wear model for predicting valve recession has been developed based on the fundamental mechanisms of wear determined during test work. Model predictions were compared with engine tests as shown in the graph to the right. The model can be used to give a quantitative prediction of the valve recession to be expected with a particular material pair or a qualitative assessment of how parameters need to be altered in order to reduce recession.
Software called RECESS has been developed to run the semi-empirical valve recession model.
- Slatter, T., Taylor, H., Lewis, R., King, P., (2009), Influence of Laser Hardening on Wear in the Valve & Valve Seat Contact”, Wear, Vol. xxx, ppxx-xx (presented at WOM 2009) (ISSN xxxx-xxxx
- Slatter, T., Lewis, R., Broda, M., (2008), “The Influence of Induction Hardening on the Impact Wear Resistance of Compacted Graphite Cast Iron” (presented at the DGM International Symposium on Friction, Wear and Wear Protection, Aachen, Germany, 9th-11th April), in Fischer, A., Bobzin, K., Editors, Friction, Wear and Wear Protection, Wiley. (ISBN 978-3527323661).
- Slatter, T., Lewis, R., Dwyer-Joyce, R.S., (2006), “Valve Recession Modelling”, SAE Paper 2006-01-0365 (presented at the Society of Automotive Engineers International Congress, Detroit, 4-6 April 2006)
- Slatter, T., Lewis, R., (2006), “Valve Recession – Investigating the Importance of Impact Wear”, Proceedings of Tribology 2006, IMechE, London,12-13 July.
- Lewis, R., Dwyer-Joyce, R.S., Slatter T.J., Brooks, A.C., (2004), “Valve Recession: From Experiment to Predictive Model”, Proceedings of the VDI Conference on Ventriltrieb und Zylinderkopf, pp79-93 (invited) (ISBN 3 18 091813 6).
- Lewis, R., Dwyer-Joyce, R.S., (2003), “Combating Automotive Engine Valve Recession: A Case Study”, Tribology and Lubrication Technology, Vol. 59, No. 10, pp48-51 (ISSN 0024 7154).
- Lewis, R., Dwyer-Joyce, R.S., (2002), “Design Tools for Predicting Inlet Valve Recession and Solving Valve Failure Problems”, Journal of Engines, Transactions of the SAE 2001, pp105-114 (ISBN 0 7680 1099 3) (presented at the SAE International Spring Fuel and Lubricants meeting, Orlando, USA, 7-9 May, 2001, in SP-1624, pp105-114 (ISBN 0 7680 0788 7)).
- Lewis, R., Dwyer-Joyce, R.S., (2002), “Wear of Diesel Engine Inlet Valves and Seat Inserts”, Journal of Automobile Engineering, Proceedings of the IMechE Part D, Vol. 216, pp205-216 (ISSN 0954 4070).
- Lewis, R., Dwyer-Joyce, R.S., Josey, G., (2000), “Investigation of Wear Mechanisms Occurring in Passenger Car Diesel Engine Inlet Valves and Seat Inserts”, Journal of Fuels and Lubricants, Transactions of the SAE 1999, pp610-618 (ISBN 0 7680 0695 3) (presented at the Society of Automotive Engineers International Congress held in Detroit in March 1999 (ISSN 0148 7191)) (also in Holt, D.J., editor, The Diesel Engine, PT 109, SAE (ISBN 07680 1302 X)).
- Lewis, R., Dwyer-Joyce, R.S., Josey, G., (2000), “Design and Development of a Bench Test-Rig for Investigating Diesel Engine Inlet Valve and Seat Wear”, Transactions of Mechanical Engineering, Institution of Engineers Australia, Vol. ME24, No. 1, pp39-46 (ISSN 0727 7369).