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).
Analysis of piston friction, heat loss, and mechanical efficiency at various engine speeds, comparing standard and Aerolite pistons.
| Identifier | ExFiles\Box 144\3\ scan0028 | |
| Date | 13th February 1934 | |
| -3- Of these (1) amounts to 123.4 B.T.U's/minute or .674%, while (2) accounts for 23.7 B.T.U's/minute or .129%. The heat given to cooling water by Piston Friction amounts to 1080 B.T.U's/minute or 5.9%. The total heat given to the cooling water amounts to 3465 B.T.U's/minute or 18.94% of the total heat supplied. The Piston Friction with standard H.D.1209 Pistons is rather high when compared with Aerolite Pistons, which show a reduction of 430 B.T.U's/minute. Piston Friction, as will be seen on the chart, accounts for approximately 70% of the total Friction and Pumping losses. During our tests we also determined the mechanical efficiency at 4250 and 3500 r.p.m. as well as 400 r.p.m., and we find that there is a rapid fall in efficiency as the speed increases above 3500 r.p.m. as shown below. R.P.M. Mech. Efficiency. 3500 79.5% 4000 73.2% 4250 61.9% So that before we may expect any increase in Power at high speeds or a step up in the Power Peak r.p.m., we must definitely reduce our mechanical losses. Since Piston Friction accounts for 70% of these losses it would appear that we should start by reducing the Piston Friction to a minimum consistent with our standards as regards knocks etc. We can definitely go quite a long way towards achieving this as shown by the results of Aerolite Pistons which were really quite good as regards knocks. With regard to the heat given to the oil, a certain amount of heat is radiated by the crankcase, and this we may assume to be proportioned to the temperature difference between the crankcase and the surrounding air. The oil inlet temperature to the bearings we kept constant at 90°C, so that our results would be as near to road conditions as possible. We could have used a higher inlet temperature but this would have increased the temperature of the crankcase, and so increasing also the amount of heat radiated, which would have its effect on the temperature rise of the oil across the engine, since the greater the amount of heat radiated | ||