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).
Article from 'Automotive Industries' discussing methods for improving vehicle fuel economy and performance through testing and analysis.
| Identifier | ExFiles\Box 50\3\ Scan039 | |
| Date | 27th January 1921 | |
| 162 AUTOMOTIVE INDUSTRIES THE AUTOMOBILE January 27, 1921 Broader Viewpoint Needed in Effort to Solve Fuel Problem Author demonstrates the importance of breaking away from outworn notions, and shows how by thorough tests and careful analysis of results it has proved possible to nearly double the mileage of a given car per gallon of fuel, while at the same time power is increased, and general performance bettered. New constant clearance piston also described. By A. {Mr Adams} L. Nelson* THE object of this paper is to appeal for a broader viewpoint and give a few illustrations and tests which show that the solution of a problem may lie in an entirely different method than that which often becomes stereotyped by sheer usage, rather than by its specific merit. We know off-hand the general engine characteristics of our engines at full, three-quarter, one-half, and one-quarter load. We know the power, friction losses, economy and the like. This is all very proper and applies very well to what the engine can do, but how about the more important questions of engine characteristics while working at loads that it is called upon to carry in the car? How much specific information can we give off-hand on these more important engine characteristics so vital to the solution of the fuel problem? PARTICULARS CONCERNING CAR TESTED, TEST CONDITIONS, COURSE, ETC. Outdoor temperature (average), deg. fahr. . . . 76 Barometer (average) in. of mercury . . . 30.15 Weight of car with fuel and two spare tires, lb. . . . 4,340 Weight of driver, lb. . . . 180 Total weight of car and driver, lb. . . . 4,520 Tires . . . Firestone Cord Size of tires, in. . . . 33 x 5 Air pressure, rear tires, lb. per sq. in. . . . 50 Air pressure, front tires, lb. per sq. in. . . . 45 Course . . . IndiaIndianapolis Speedway Pavement . . . Brick Length of course, miles . . . ½ Direction of driving . . . North and south Revolutions of rear wheel per mile . . . 600 Exhaust cutout . . . Open Oil . . . Mobiloil B Power Required to Drive the Car at Constant Speed Fig. 1 shows the engine brake horsepower required to drive the car tested, the brake horsepower available and the percentage of available power used at each speed. The method of obtaining these data was to drive the car on a given course at constant speeds corresponding to a fixed carbureter throttle setting, then to remove the engine from the car to the dynamometer stand and determine the power developed at those settings and the engine speed corresponding to the car speeds. It was necessary to duplicate very accurately the fixed throttle settings when the engine was put on the dynamometer; hence, a micrometer adjusting screw was attached to the carbureter throttle-shaft. The speed of the car was obtained by timing with a stop-watch on a ½-mile measured course, driving in both directions for each setting, to eliminate the effect of wind resistance, and taking the average speed. The engine speed was calculated from the number of revolutions per mile made by the rear wheels. Several important details, such as cooling water temperatures, oil temperatures, air pressure under the engine hood, and the like, need not be given here. For accurate work it is suggested that, in addition to the use of fixed throttle settings, manometer readings be taken of the intake-manifold depression together with the air temperature. Referring again to Fig. 1, note that at average driving speed the engine is working at only 16 to 19 per cent of full load. Poor economy is caused by misapplication of the engine rather than poor engine economy. The analysis should give us relative values on which to consider the feasibility of using two-speed rear axles, or more speeds in the transmission. Or *Condensed from a paper presented at the annual meeting of the Society of Automotive Engineers. Mr. Nelson is chief engineer of the Premier Motor Corporation. Fig. 1—Comparison of engine power with power required to propel car; showing low load factor Fig. 2—Effect of valve timing and compression on mean effective pressure Graph 1 Text: - Y-Axis: HORSEPOWER AND PERCENT B.H.P. AVAILABLE - X-Axis: CAR SPEED IN MILES PER HOUR - Curves: ENGINE B.H.P. AVAILABLE 4.5 TO 1 AXLE GEARS, B.H.P. USED PERCENT, ENGINE B.H.P. REQUIRED, AVAILABLE B.H.P. REQUIRED Graph 2 Text: - Y-Axis: BRAKE M.E.P. LB. PER SQ. INCH - X-Axis: REVS. PER MINUTE—HUNDREDS - Curves: DELAYED INLET VALVE CLOSING C, HIGH COMPRESSION-CONVENTIONAL TIMING B, LOW COMPRESSION-CONVENTIONAL TIMING A | ||