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 with graphs showing the effects of compression and axle gear ratios on engine performance and fuel economy.
| Identifier | ExFiles\Box 50\3\ Scan046 | |
| Date | 27th January 1921 | |
| January 27, 1921 AUTOMOTIVE INDUSTRIES THE AUTOMOBILE 169 Fig. 20 (at left)—Characteristic curves of engine performance with 5 to 1 compression ratio when throttled to give power output sufficient to propel car when using 2.5 to 1 axle gear Fig. 21 (at right)—Same as Fig. 20 but using 3.5 to 1 axle gears Fig. 22 (at left)—Curves showing relation between car speed and fuel consumption when using 5 to 1 compression ratio Fig. 25 (at right)—Curves showing the effect of change in axle gear ratio from 2.5 to 1 to 4.5 to 1 upon fuel consumption, thermal and mechanical efficiency at various car speeds. Compression ratio 5 to 1 10.5 at 400 r.p.m. to 37 per cent at 2800 r.p.m. The most important increase is that of the brake thermal efficiency. This ranges from 8 to 26 per cent. Fig. 24 shows the result of increased compression ratio when keeping the rear-axle gears the same; namely, 3.5 to 1. The mechanical efficiency remains practically the same, due to identical engine speeds in each case. The increase in brake thermal efficiency ranges from 19 per cent at 10 m.p.h. to 41 per cent at 60 m.p.h. The saving in gasoline is from 16 to 28 per cent, and, at average driving speed, about 18 per cent. Fig. 25 gives the comparative results of using the rear-axle gear ratios of 2.5 to 1, and 4.5 to 1, respectively with 5 to 1 compression ratio. The percentage increase in mechanical efficiency is very marked; the maximum gain is 42 per cent at 36 m.p.h. At 10 m.p.h. it is 27 per cent and at 60 m.p.h. it is 26 per cent. The maximum increase in the brake thermal efficiency is 53 per cent, at 29 m.p.h. It is 48 per cent at 10 m.p.h. and 29 per cent at 60 m.p.h. The gasoline saved is 30 per cent at 10 m.p.h.; 34 per cent at 29 m.p.h.; and 23 per cent at 60 m.p.h. Fig. 26 gives the percentage increase in miles per gallon in the case of using 2.5 to 1 axle gears with 5 to 1 compression pistons, as against the use of 4.5 to 1 axle gears and 4.25 to 1 compression pistons. The increase in miles per gallon is 70 per cent at 10 m.p.h.; 95 per cent at 20 m.p.h.; 81 per cent at 30 m.p.h.; 68 per cent at 40 m.p.h.; 76 per cent at 50 m.p.h.; and 104 per cent at 60 m.p.h. These are worth while increases in economy that cannot be passed by lightly, yet they are by no means as great as the economy that is possible. Let us next consider the economy that is possible even with our present engines. For the sake of a name let us call it the 'ideal' economy. Fig. 23 (at left)—Curves showing comparative effect on engine characteristics at full load of change of compression ratio from 4.25 to 1 to 5 to 1 Fig. 24 (center, above)—Curves showing effect of change in compression ratio (4.25 to 1 to 5 to 1) on fuel consumption, thermal and mechanical efficiency at various car speeds, with 3.5 to 1 axle ratio Fig. 26 (center, below)—Per cent increase in miles per gallon of fuel when using an axle gear ratio of 2.5 to 1 and compression ratio of 5 to 1, as compared to using an axle gear ratio of 4.5 to 1 and compression ratio of 4.25 to 1 Fig. 27 (at right)—Curves comparing economy possible under 'ideal' conditions of gear ratio, engine size and load, with economy determined in test when using 5 to 1 compression ratio and two different axle gear ratios Text from graphs: Fig 20: (Y-axis: MILES PER IMP. GAL., BRAKE HORSEPOWER, MECHANICAL EFFICIENCY % AND INCHES OF MERCURY), (X-axis: ENGINE SPEED—HUNDREDS OF R.P.M.), (Curves: MECHANICAL EFFICIENCY, INDICATED THERMAL EFFICIENCY, BRAKE THERMAL EFFICIENCY, MILES PER IMP. GAL., LBS. GASOLINE PER B.H.P. HR., BRAKE HORSEPOWER, INTAKE MANIFOLD DEPRESSION INCHES MERCURY) Fig 21: (Y-axis: INDICATED & BRAKE THERMAL EFFICIENCY, MECHANICAL EFFICIENCY % AND INCHES OF MERCURY), (X-axis: ENGINE SPEED—HUNDREDS OF R.P.M.), (Curves: MECHANICAL EFFICIENCY, INDICATED THERMAL EFFICIENCY, LBS. GASOLINE PER B.H.P. HR., BRAKE THERMAL EFFICIENCY, CAR SPEED M.P.H., MANIFOLD DEPRESSION INCHES MERCURY, BRAKE HORSEPOWER) Fig 22: (Y-axis: MILES PER GALLON), (X-axis: CAR SPEED—MILES PER HOUR), (Curves: TEST NO 8A (REAR AXLE GEARS 2.5 TO 1), TEST NO 6A (4.5 TO 1)) Fig 25: (Y-axis: RATIO OF RESULTS), (X-axis: CAR SPEED—MILES PER HOUR), (Curves: BRAKE THERMAL EFFICIENCY RATIO, MECHANICAL EFFICIENCY RATIO, INDICATED THERMAL EFFICIENCY RATIO, RATIO OF GASOLINE CONSUMPTION PER B.H.P. HR.) Fig 23: (Y-axis: HORSEPOWER, MECHANICAL EFFICIENCY, BRAKE THERMAL EFFICIENCY %), (X-axis: ENGINE SPEED—HUNDREDS OF R.P.M.), (Curves: RATIO OF 4.25 TO 1 COMP. PISTONS TO 5 TO 1 COMPRESSION PISTONS, BRAKE THERMAL EFFICIENCY RATIO, BRAKE HORSEPOWER RATIO, MECHANICAL EFFICIENCY RATIO, INDICATED THERMAL EFFICIENCY RATIO) Fig 24: (Y-axis: RATIO OF RESULTS), (X-axis: CAR SPEED—MILES PER HOUR), (Curves: BRAKE THERMAL EFFICIENCY RATIO, MECHANICAL EFFICIENCY RATIO, RATIO OF GASOLINE CONSUMPTION PER B.H.P. HR.) Fig 26: (Y-axis: PERCENT INCREASE), (X-axis: CAR SPEED—MILES PER HOUR) Fig 27: (Y-axis left: PERCENT INCREASE), (Y-axis right: MILES PER GALLON), (X-axis: CAR SPEED—MILES PER HOUR), (Curves: PERCENT INCREASE 'IDEAL' MILES PER GAL. OVER RESULTS OF TEST WITH 4.5 TO 1 AXLE GEARS, PERCENT INCREASE 'IDEAL' MILES PER GAL. OVER RESULTS OF TEST WITH 2.5 TO 1 AXLE GEARS, 'IDEAL' MILES PER GAL. BASED ON S.F.V. L.B. PER B.H.P. HR. AND B.H.P. REQUIRED TO DRIVE CAR, MILES PER GAL. 2.5 TO 1 AXLE GEARS TEST NO. 7A, MILES PER GAL. 4.5 TO 1 AXLE GEARS TEST NO. 6A) | ||