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).
Page from an automotive journal detailing engine performance characteristics with diagrams and graphs.
| Identifier | ExFiles\Box 50\3\ Scan045 | |
| Date | 27th January 1921 | |
| 168 AUTOMOTIVE INDUSTRIES THE AUTOMOBILE January 27, 1921 [Diagram of an engine cooling system with Section A.A. indicated] Fig. 13—Diagram of cooling water circulating system, showing method of cooling radiator used during block tests Fig. 17 gives the engine characteristic under constant-speed driving conditions with 4.25 to 1 compression ratio and 3.5 to 1 axle gears. It will be seen that the full-load brake characteristics have been changed greatly, while the indicated characteristics have changed but little. The friction losses, which include the pumping losses, very materially lower the mechanical efficiency. Note that the engine is pumping against an intake-manifold depression of 15 in. of mercury at the lower speeds and the mechanical efficiency at 800 r.p.m. is only 58 per cent, compared with 91.7 per cent at full load. Fig. 18 gives the engine characteristic when using the 5 to 1 compression pistons, everything else on the engine being identically the same. The readings given are not "snap" readings. The engine in all tests was kept running continuously and the results shown are those at which the engine runs with stability; that is, the result to which the engine settles at any given speed. It will be noticed that the maximum brake mean effective pressure is still at 1000 r.p.m., but it has increased from 86.2 (see Fig. 15) to 96.9 lb. per sq. in. It will also be noticed that the increase is greater as the speed increases. The peak of the power greatly increased, being 0.527 lb. per b.hp. per hr. at 1000 r.p.m. as compared to 0.613 lb. per b.hp. per hr. in the case of 4.25 to 1 compression. The mechanical efficiency is not as good below 800 r.p.m., but it is much better at the high speeds, being 81.4 per cent as compared with 76.1 per cent at 2400 r.p.m. The maximum brake thermal efficiency is increased from 21.1 to 24.8 per cent. Fig. 19 gives the engine characteristics at constant car speed, with 5 to 1 compression ratio and 4.5 to 1 axle gears. Fig. 20 is for 2.5 to 1 and Fig. 21 is for 3.5 to 1 axle gears. Fig. 21 can be compared directly to Fig. 17, the only difference being the compression ratios. It will be noticed that the mechanical efficiency has not been materially changed; however, the fuel economy has been very materially increased. It is very gratifying to note that the relative increases are even greater than those at full-load. At 1000 r.p.m., the brake thermal efficiency has been increased from 11.5 to 14.1 per cent, and at 2100 r.p.m. it has been increased from 16.4 to 23.2 per cent. Fig. 22 shows the miles per gallon at various car speeds for 5 to 1 compression ratio. This can be directly compared to Fig. 16. The results are materially higher all along the line. The overall increase at 15 m.p.h. is from 16.4 to 31 miles per gal., when changing both the compression and the axle gears. On long road tests the results agree very closely with the curves considering the amount of time the engine is idled and the nature of the driving. On the speedway the results can be duplicated at constant driving speeds. They can be further increased by using light engine oil and higher tire pressure than those used in the tests to set the standard of brake horsepower required. Comparison of Results Fig. 23 gives a comparison of the engine full-load characteristics. The comparison as a whole is entirely in favor of the higher compression ratio, but shows a very slight loss in mechanical efficiency below 800 r.p.m. The increase in brake horsepower is marked, especially at the higher speeds. The percentage increase in power ranges from Fig. 17 (at left)—Characteristic curves of engine performance with 4.25 to 1 compression ratio when throttled to give power output sufficient to propel car on level road when using 3.5 to 1 rear axle gear ratio. Fig. 18 (center)—Characteristic engine performance curves at full load. Compression ratio 5 to 1. Fig. 19 (at right)—Same as Fig. 17 but using 4.5 to 1 axle gears and 5 to 1 compression ratio Graph Labels: Fig. 17 (left graph): Axes: Y-axis (left): MECHANICAL EFFICIENCY %, AND INCHES OF MERCURY; Y-axis (right): MILES PER HR. HORSEPOWER, EFFICIENCY %; X-axis: ENGINE SPEED - HUNDREDS OF R.P.M. Curves: MECHANICAL EFFICIENCY %, INDICATED THERMAL EFF. %, BRAKE THERMAL EFFICIENCY %, MILES PER GAL., CAR SPEED, BRAKE HORSEPOWER, FRICTION HORSEPOWER, INTAKE MANIFOLD DEPRESSION IN. MERCURY, LB. GASOLINE PER B.H.P. HR. Fig. 18 (center graph): Axes: Y-axis (left): MECH. EFFICIENCY %, LB. PULL; Y-axis (right): THERMAL EFFICIENCY %, GASOLINE CONSUMPTION LB. PER B.H.P. HR.; X-axis: ENGINE SPEED - HUNDREDS OF R.P.M. Curves: MECHANICAL EFFICIENCY %, LB. PULL, INDICATED THERMAL EFFICIENCY, BRAKE THERMAL EFFICIENCY, BRAKE M.E.P., BRAKE HORSEPOWER, GASOLINE CONSUMPTION LB. PER B.H.P. HR., FRICTION HORSEPOWER. Fig. 19 (right graph): Axes: Y-axis (left): MILES PER HR., HORSEPOWER, THERMAL EFFICIENCY %; Y-axis (right): MECHANICAL EFFICIENCY %, AND INCHES OF MERCURY; X-axis: ENGINE SPEED - HUNDREDS OF R.P.M. Curves: INDICATED THERMAL EFFICIENCY, BRAKE THERMAL EFFICIENCY, MILES PER GAL., CAR SPEED, BRAKE M.E.P., BRAKE HORSEPOWER, INTAKE MANIFOLD DEPRESSION IN MERCURY, LB. GASOLINE PER B.H.P. HR., LB. GASOLINE PER I.H.P. HR. | ||