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).
Procedure for examining noises in a 12-cylinder engine and determining permissible detonation using a Strobophonometer.
| Identifier | ExFiles\Box 165\4\ img168 | |
| Date | 1st September 1932 | |
| -2- Application to a multicylinder Engine. To examine and compare the noises emitted by the cylinders of a 12 cylinder engine the microphone would have to be mounted in a rubber pad as previously described and held on to the cylinder jacket opposite the cylinder being investigated. It might be possible to hold the pad and microphone in position merely by suction. For a 4-stroke engine the listening period for each cylinder could not exceed 720/12 = 60° of crankangle if overlapping of firing periods is to be avoided. The adjustment of the instruments would not be touched during the test and then the scale readings for each cylinder will represent the relative noise emitted by the cylinders. It is estimated that it will take 7 mins. to fix the microphone and obtain the reading for each cylinder and hence the test for a twelve cylinder engine would occupy 84 mins. This time would probably be reduced with practice. Possible sources of error in making the above measurements. The scale reading for a given intensity of sound depends on the efficiency of the valves and hence for routine testing it is necessary to standardise the instrument before use. This may be done by placing the microphone near a buzzer and adjusting the controls until a "standard" deflection is obtained. This corrects for any changes in the valves. Since the reading of the instrument is proportional to the vibrations of the cylinder jackets, the reading will not be proportional to the rate of pressure rise or other combustion conditions producing detonation unless the cylinder construction is identical. Hence the readings obtained on the end cylinders may not be strictly comparable with those of the centre cylinders. Use of Strobophonometer to determine degree of permissible detonation. It would be necessary to conduct all these tests on the same type of engine (i.e. engines with identical cylinder construction). Having standardised the strobophonometer by means of the buzzer the scale deflection would be found when the engine was running without detonation. | ||