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 effects of exhaust back pressure on engine power and heat flow.
| Identifier | ExFiles\Box 24\5\ Scan032 | |
| Date | 29th April 1925 | |
| R.R. 493a (50m) (D.B. 175 25-9-24) J.H.D. EXPERIMENTAL REPORT. -3- Expl. No. REF: HS{Lord Ernest Hives - Chair}/ACL/LG29.4.25. to open up the throttle and the heat flow increases although the power at the flywheel is the same. What it amounts to is that although our B.HP. is the same for the larger throttle opening, the back pressure has increased our pumping losses but we have increased our I.HP. If, for instance, we remove the back pressure, keep the throttle opening the same and the speed the same, by increasing the load, the result will be an increase of B.HP. but our heat flow will be the same. We can therefore say, from consideration of the results of these tests :- (1) That the heat flow to the cooling water for a particular throttle opening and speed is not increased by exhaust back pressure but the reduced power caused by the back pressure gives a greater value to the ratio heat flow per B.HP. Under road conditions apparently two conditions could exist :- (a) For a fixed throttle position the speed of the car would be reduced by back pressure, also the water circulation and fan speed, and although the heat flow would be approximately the same, the radiator would be less able to deal with this quantity of heat. (b) The road speed could be kept constant and with increased back pressure the throttle would have to be opened wider which would give an increased heat flow. Note :- By introducing exhaust back pressure by means of the cutout we did not interfere with the exhaust circulation through the 'hot-spot'. We have not yet determined what influence the hot spot temperature has on heat flow but are arranging to do this on the 40/50 HP. HS{Lord Ernest Hives - Chair}/ACL. | ||