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).
Test report on engine compression pressures and performance with large versus small inlet valves, and a new cylinder block.
| Identifier | ExFiles\Box 179b\3\ img203 | |
| Date | 4th February 1933 | |
| -13- The results are plotted for an engine speed range of 1500 to 2200 R.P.M. on FIG.3. With the larger valves, the volumetric efficiency is approximately 2% greater above 1900 R.P.M. Below this speed it decreases and the curves cross at about 1600 R.P.M. Compression Pressures with large and small inlet valves. In these tests the engine was run up to speed on its own power and when the temperature conditions had settled down the engine was motored over and the compression pressures measured on a Farnborough indicator. The measurements were thus taken as nearly as possible under normal running condition The results of the tests are shown in Fig.4. for a speed range of 1500 R.P.M. to 2200 R.P.M. The first peculiarity is the shape of the curves which is definitely stepped as though some ramming effect were taking place. If this were measured without attaching a pipe to the inlet ports, then one would have expected the volumetric efficiency curve also to be stepped. Actually it is a smooth curve showing a falling off in volumetric efficiency with increase in speed and hence under the conditions of measurement there was no ramming effect. The second peculiarity is that the compression pressure is about 20 lbs/sq.in. greater with the smaller inlet valves although the volumetric efficiency is 2% less. Assuming for the moment that the volumetric efficiency figures are correct and hold for the breeches pipe on the inlet ports and that leakage of gas is the same in both cases, then the air must be cooler at the end of compression with the large valves than with the smaller. If the compression index is the same in both cases this implies a lower suction temperature which is possible since the velocity of gas past the inlet valve is reduced in the case of the large inlet valve and the turbulence in the cylinder may therefore also be less and less heat is imparted to the air during the suction stroke. It is concluded, therefore, that the lower compression pressure and higher volumetric efficiency with the larger valve are not impossible. SERIES 2. New cylinder block machined to fit the Bosch injector without sleeves or bushes and hence the cooling of the injector should have been improved. A power check (Test 2c gave 91.2 lbs/sq.in. B.M.E.P. and a specific consumption of .523 lbs/BHP/Hr. but after 10 mins. the power decreased by 6 lbs/sq.in. This was attributed to the overheating of the injector and the cooling arrangements would therefore appear to be still inadequate. This opinion was strengthened by the | ||