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).
Study of power loss with detonation, analyzing the effects of spark advance, spark plugs, fuel additives, and compression ratios on preignition.
| Identifier | ExFiles\Box 148\2\ scan0222 | |
| Date | 1st April 1939 | |
| April, 1939 POWER LOSS WITH DETONATION 159 Fig. 11 - The curves show that preignition was practically un-influenced by spark advance plug it preignited and stopped with almost no detonation; yet, with the C-25 plug, it was possible to develop a terrific detonation without preignition. This range of spark plugs did not have as much influence on the results in the standard CFR cylinder as in the special Army cylinder, as can be seen from the dotted lines of Fig. 12. Since the principal difference between these cylinders lay in the effectiveness of their cooling, it seems that a test might be developed to measure the effectiveness of cylinder cooling at least roughly, by the sensitivity of the preignition compression ratio to spark plugs having various temperatures. The next step was a study of the effect of the antiknock value of gasoline on preignition. Blends of tetraethyl lead were made with Pennsylvania grade gasoline, and the curves in Fig. 13 show that increased lead additions allowed steadily increased compression ratios, with their resulting increases in power output. The two curves in this figure represent the results of the hottest and coldest plugs in the series. Fig. 14 shows similar curves for benzol blends with the same gasoline. It is of more than passing interest that the colder plug developed consistently more power than the hotter plug in both of these tests. It would thus appear that, although the compression ratio for preignition is almost independent of spark advance, it is closely proportional to antiknock value, but the actual relationship is influenced strongly by the effectiveness of cylinder and spark-plug cooling. Power Increase By Speed Vs.{J. Vickers} Compression While investigating the effect of compression ratio on temperatures of combustion-chamber parts, it was desired to note the effect of engine speed also on these temperatures, since both affect power output. Increasing engine power by raising either the compression ratio or speed caused a rise in the temperature of spark plug, piston, and intake valve. Since such temperatures are usually the limitation to the power which can be taken from a well-designed engine, it was desired to find which method of raising power gave the greater power increase for a given temperature rise. Graph Text: Fig. 11: - Y-Axis: SCALE PULL LB. - X-Axis: COMPRESSION RATIO - Labels: AUDIBLE KNOCK, MAXIMUM POWER, PREIGNITION, SPARK ADVANCE Fig. 12: - Y-Axis: COMPRESSION RATIO FOR PREIGNITION - X-Axis: AC SPARK PLUG NUMBER - Legend: VALUES RUN ON CFR CYLINDER, VALUES RUN ON ARMY CYLINDER - Lines: SPECIAL H, BENZOL PLUS 50% A-2, AVIATION, RT-10, C-6, A-2 - Caption: Fig. 12 - Effect of spark plugs on preignition compression with various gasolines Fig. 13: - Y-Axis: SCALE PULL - LB. - X-Axis: PREIGNITION COMPRESSION RATIO - Labels: SPARK PLUG, C-25, 140, 186.0, OCTANE NO., ETHYL FLUID (CC. PER GAL.), ADDITIONS OF TETRAETHYL LEAD - Caption: Fig. 13 - Effect of spark plug on preignition compression with blends of tetraethyl lead and Pennsylvania gasoline of varying octane number Fig. 14: - Y-Axis: SCALE PULL - LB. - X-Axis: PREIGNITION COMPRESSION RATIO - Labels: SPARK PLUG, C-25, 140, 186.0, OCT. NO, % BENZOL, ADDITIONS OF BENZOL - Caption: Fig. 14 - Effect of spark plug on preignition compression with blends of benzol and Pennsylvania gasoline of varying octane number | ||