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).
Effects of jacket temperature, air-fuel ratio, and engine design on fuel octane requirements and performance.
| Identifier | ExFiles\Box 150\1\ scan0014 | |
| Date | 15th April 1935 guessed | |
| 8 DIVISION OF REFINING Jacket Temperature and Mixture Ratio Felt Fig. 11 indicates the effect of jacket temperature on octane requirement and torque. Higher temperatures demand better fuels, and cause a very large sacrifice of torque as well. Graph 1 (Fig. 11) Y-axis: Fuel Octane No. for Incipient Knock Right Y-axis: Percent of Torque at 212° F.{Mr Friese} X-axis: Jacket Temperature - Deg. F.{Mr Friese} Curves: Torque, Octane No. Bore, 3¼ in. Stroke, 3⅞ in. Speed, 800 r.p.m. Intake air temperature, 85 deg. F.{Mr Friese} Throttle opening, full. Cylinder-head material, cast iron. Compression ratio, 5.4. Jacket temperature, deg. F.{Mr Friese}, varied. Air-fuel ratio, 13.5. Spark advance, maximum power. The Effect of Variation in Jacket Temperature on the Torque and Fuel Anti-knock-Value Requirements of a Single-Cylinder Engine. FIG. 11 Fig. 12 shows that mixture ratio affects knocking. A change of air-fuel ratio from 9.4 to 13.0 to 1 changes the octane requirement by 12 units, and a change from 13.0 to 16.0 to 1 permits an octane-number change of 18 units. Obviously, mixture ratio is one of the most important factors in the problem; but, unfortunately, the air-fuel ratio for maximum knock is not far different from that for maximum power; hence little can be done to improve the situation. A multi-cylinder engine with perfect fuel distribution, designed to run at the maximum-economy air-fuel ratio, would run on a lower-grade fuel than one designed for best power; but maximum economy at full throttle is seldom desired, and perfect distribution would necessitate the use of highly volatile fuels or liberal intake-manifold heating, or both—and the latter would tend to increase knocking. Graph 2 (Fig. 12) Y-axis: Fuel Octane No. for Incipient Knock Right Y-axis: Percent of Maximum Torque X-axis: Air-Fuel Ratio Curves: Torque, Octane No. Bore, 3¼ in. Stroke, 3⅞ in. Speed, 800 r.p.m. Intake air temperature, 85 deg. F.{Mr Friese} Throttle opening, full. Cylinder-head material, cast iron. Compression ratio, 5.75. Jacket temperature, 190 deg. F.{Mr Friese} Air-fuel ratio, varied. Spark advance, maximum power. The Effect of Variation in Air-Fuel Ratio on the Torque and Fuel Anti-knock-Value Requirements of a Single-Cylinder Engine. FIG. 12 Mixture Temperature To Be Observed Fig. 13 shows the effect of intake air temperature. The influence of variable heating of the charge in the intake manifold would be similar. As would be expected, the higher temperatures raise the octane requirement, and considerably decrease power output. It is, therefore, highly desirable that there be as little pre-heating of carburetor air or mixture as possible, and the increasing ability of refiners to supply more volatile fuels permits a reduction in intake-manifold heating. Knock Increases with Volumetric Efficiency Knocking tendency increases along with volumetric efficiency, whether the latter is due to decreased throttling at some point in the induction system or to greater manifold pressure resulting from supercharging or decreased altitude. Fig. 14 indicates the effect of throttling a single-cylinder engine. Both octane requirement THE RELATION OF FUEL OCTANE NUMBER TO ENGINE COMPRESSION RATIO 5 Image (Fig. 4) Caption: Cylinders and Heads Used in Study of Relation of Cylinder Displacement to Fuel Octane-Number Requirement. FIG. 4 The Relation of Cylinder Displacement and Fuel Anti-knock Value to Compression Ratio for Incipient Knock. FIG. 5 Graph (Fig. 5) Y-axis: Compression Ratio for Incipient Knock X-axis: Cylinder Bore—Inches Curves: 3 7/8" Stroke, 5" Stroke L-Head, Single-Cylinder Engine. Bore, varied. Stroke, 3⅞ in. and 5 in. Speed, 600 r.p.m. Throttle opening, full. Cylinder-head material, cast iron. Fuel octane No., 80. Compression ratio, varied. Jacket temperature, 212 deg. F.{Mr Friese} Air-fuel ratio, maximum knock. Spark advance, maximum power. | ||