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).
The methods of instrumentation and development for a two-cycle engine, focusing on pressure wave analysis.
| Identifier | ExFiles\Box 148\2\ scan0100 | |
| Date | 28th November 1938 | |
| -7- METHODS OF INSTRUMENTATION AND DEVELOPMENT. With a commercial two-cycle engine it is of the utmost importance to obtain good scavenging consistent with high fuel economy and to that end a careful study must be made of the exhaust, intake and cylinder head pressure waves if the engine is to be developed in the most efficient form. The most practical way of carrying out this investigation lies in the use of indication. Low pressure indicators were therefore developed for the exhaust and intake manifolds, the high pressure type being used in the cylinder head. This latter was incorporated in the sparking plug itself, so as not to influence combustion characteristics or wave formations. The indicators were the variable resistance type formed from a pile of carbon discs. They functioned perfectly throughout the time they were used, had virtually no hysteresis or time lag and were constant from day to day which avoided the need of recalibration every time they were used. Their natural frequencies were above any frequency likely to occur in an engine. The indicators formed one arm of a wheatstone bridge and the change of voltage was measured either by a galvanometer or cathode ray type of oscillograph. The indicator cards so obtained were automatically photographed and all three records, intake, exhaust and cylinder head appeared on one record with a common crank angle base line. See sketch. It was thus possible to see exactly what size and frequency waves were being formed in various parts of the engine. In one case for instance it was practically impossible to run the engine at 1100 r.p.m. light, and fuel consumption was more than double what it should have been. On taking an indicator card under these conditions, it was obvious that the reasons for the phenomenon was that waves of such magnitude were being built up in the exhaust manifold that some of the gas was actually returning to the cylinders, and in fact these pressure waves | ||