By Roger Lewis, Rob Dwyer-Joyce
An “Engineering study sequence” name. Valve put on and its impact upon engine functionality nonetheless offers a majorchallenge to the tribologist. even if new valve fabrics and construction thoughts are continually being constructed, those advances were outpaced by way of calls for for elevated engine functionality. The force for decreased oil intake and exhaust emissions, use oflead-replacement and low-sulphur fuels, and the creation of different fuels resembling gasoline all have implications for valve and seat insert wear.Automotive Engine Valve Recession goals to supply the reader with an entire knowing of valve recession. the elemental nature of touch and put on among valves and valve seats is taken into account, via an summary of the fundamental good points of valve operation and the doubtless critical difficulties linked to put on and valve recession in car engines. an outline isthen given of an experimental learn of valve put on and the advance of precise gear for the simulation of engine working stipulations conducted within the college ofMechanical Engineering, collage of Sheffield, UK.CONTENTS INCLUDE:IntroductionValve operation and designValve failureAnalysis of failed componentsValve and seat put on trying out apparatusExperimental reports on valve wearDesign instruments for prediction of valve recession and fixing valve failure difficulties.
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This indicates that the lacquer formation on the valves in the full load test could have been caused by the high temperatures experienced at the valve seating face, leading to oxidation of lubricating oil present as a result of valve stem leakage. A reduction in heat transfer from the valve head would have occurred as a result of the lacquer formation, further increasing the valve head temperature and increasing the probability of the lacquer build-up progressing. 46 Analysis of Failed Components The fact that no lacquer was found on the valves from the part load tests can be explained by the lower temperatures experienced.
Concluded that change in seat angle and suitable material pairing alone would not solve problem . Reduced wear . ‘Recession was reduced by approximately 75 per cent when seat angle was reduced from 45 to 30 degrees’ . Lubrication of contact between valve and seat Reduced wear . ‘Very effective method for reducing wear’ . ‘Considerable’ reduction in seat wear obtained by injecting lubricating oil into the inlet manifold . Reducing speed of valve impact Reduced wear . ‘The most powerful means of reducing wear is to keep impact velocities as low as possible’ .
Increased rigidity of valve disc; 5. greater rigidity of valve mechanism; 28 Valve Failure 6. welding material onto valve seats; 7. smaller valve diameter; 8. reducing speed of valve impact; 9. increasing seating face width. Introduction of the 30 degrees seating face angle, more effective cooling of the cylinder head bottom, and greater rigidity of the valve and valve mechanism reduced wear rates by about 50 per cent. It should be noted, however, as mentioned in the previous section, that changes such as reducing the valve seating face angle may not always be possible as they will change flow characteristics and may adversely affect engine performance.
Automotive Engine Valve Recession (Engineering Research Series (REP)) by Roger Lewis, Rob Dwyer-Joyce