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From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Analysis of engine detonation tests with various cylinder head, gasket, and valve modifications.

Identifier  ExFiles\Box 134\2\  scan0018
Date  27th May 1935
  
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on Sheet 7 of the curves. It will be seen from this curve that the high power head gives a maximum detonation of only 4 feet (at 1250 R.P.M.). By fitting a thinner cylinder head gasket (.022 thick) the figure can be reduced to 2 ft., but this thickness of gasket would be too thin for normal use. When using the 6.8 compression ratio with normal gasket thickness the maximum detonation is 10 ft. at 1500 R.P.M.

The effect on detonation of the sodium cooled exhaust valve is shown on sheet 7 (twin inlet head) and on sheet 9 (single inlet head). In the case of the former it will be noticed that the sodium cooled exhaust valve entirely cuts out the high speed detonation. This tendency is not so marked with the single inlet valve head.

Sheet 8 shows the effect of various modifications to the characteristics of the combustion chamber when using a single flat-headed inlet valve. Curve 1 represents normal conditions with a .057" thick gasket between cylinder and head; thus at T.D.C. the small lamina of gas above the piston is .057" thick. Curve 2 refers to a pack- ing .025" thick having been placed under the cylinder, thus increasing the thickness of the "gas lamina" to .082" and incidentally decreasing the compression ratio from 6.17 to 6.03. Curve 3 is for a "gas lamina" .022" thick and a compression ratio of 6.55. Curve 4 is for conditions similar to curve 1, except that the inlet valve is now absolutely flush with surface of cylinder head (previously it lay .014" below the surface) and the compression ratio 6.23. Curve 5 is as curve 4 but with a "gas lamina" .022" thick and a compression ratio of 6.61.

Sheet 10 of the curves shows a comparison of types of inlet valves with a normal un-cooled exhaust valve and is self explanatory. It should be noted that on sheets 7 and 9 the scale used for the detonation figures is 10 feet per inch, but on sheets 8 and 10, 20 feet per inch is used. The B.M.E.P. figures given on the curves are uncorrected for temperature or pressure. All the detonation tests depicted on the curves were carried out under almost identical conditions of barometric pressure.
  
  


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