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).
Engine design, focusing on swirl, volumetric efficiency, and supercharging in diesel engines.
| Identifier | ExFiles\Box 133\3\ scan0056 | |
| Date | 3rd March 1939 | |
| -3- Rm{William Robotham - Chief Engineer}/Edl/R.3.3.39. A.E.C. also stated that the lubricating oil consumption was worse, and this point was admitted by Ricardo's. With reference to the Comet chamber, A.E.C. stated that the swirl cavity in the piston top had to be re-designed with any change in engine conditions or size. It appears to be a case of trial and error, the only evidence of correct air swirl being the carbon formation on the piston and the marks made by the spray holes. Volumetric Efficiency and Swirl. Swirl, it was stated was essential to the satisfactory operation of a Diesel engine, indiscriminate turbulence being of no value whatever. A suitable swirl speed is about ten times engine speed, anything much less than this being insufficient to clear the fuel away. This swirl may be induced on the induction stroke, or forced on the compression stroke, the former method, however, involves masked valves or seats, having a serious effect on volumetric efficiency, or, alternatively, specially shaped ports which rather tie up the head design for a main engine. Compression induced swirl is definitely preferable and the most obvious method of obtaining this is by using an ante-chamber of some description. Valve timing does not have the same effect on power output as is experienced on a petrol engine, a result borne out by tests on the 4-stroke unit run by R.R. in 1930-1933. Ricardo's stated, however, and were very emphatic on this, that the only logical way to obtain a good performance from a Diesel engine was to supercharge it, and they showed us an engine which had run @ 300 B.M.E.P. on a compression ratio of 10:1 with 3 atm. boost (presumably absolute). Compared with our petrol engines, this appears rather a poor boost response as 300 B.M.E.P. can be obtained on a Merlin s/c unit with just over 2 atm. abso. supercharge. The condition of the Ricardo unit so far as we could see, however, was good. With regard to valving, the inlet valve was 1.1 times the size of the exhaust valve, the valve lift being one third of the diameter. | ||