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).
Journal page detailing tests on engine ring-sticking, analysis of used oil, and methods for reducing carburetor icing.
| Identifier | ExFiles\Box 154a\2\ scan0014 | |
| Date | 10th March 1938 | |
| 14 S.A.E. JOURNAL (Transactions) Vol. 44, No. 1 peratures at which sticking takes place in 5 hr. of running. After 5 hr. of running the cylinder is lifted and the rings are inspected. If sticking has occurred, the engine is dismantled and the extent of the sticking determined, that is, whether the top ring (or bottom ring) is stuck “all ’round,” “one-fourth,” “one-half stuck,” or merely “stuck at one horn.” If no sticking has taken place, then this test is repeated at a temperature 5 deg. cent. higher, after cleaning the engine. Evidence of ring-sticking is sometimes obtained while the engine is on load by piston blowby and drop in power output. In such cases the test is stopped and, if necessary, it is repeated at a lower temperature. Occasionally blowby takes place, but the rings are found to be free when the engine is dismantled. In such cases the blowing is caused by the ring gaps coming into line vertically with one another. Generally speaking, the J.A.P. engines show no fall in mean effective pressure and no appreciable blowby until the top ring has stuck for more than one-third of its length. The use of a nitrogen-hardened (“nitrided”) steel cylinder and of a cast-iron cylinder with chromium-plated bore has been found to have no appreciable effect either on the relative or absolute ring-sticking temperatures of such lubricating oils as have been examined. Appendix 2 Single-Cylinder Norton Air-Cooled Engine This engine (Model 30) is produced for racing and highspeed motorcycle work. Its dimensions are as follows: Bore and stroke, 79 x 100 mm. Swept volume, 490 cc. (30 cu. in.). Compression ratio, 7.25:1. Aluminum-alloy piston with two cast-iron pressure and one scraper ring (above gudgeon pin). Cylinder, cast iron. Cylinder-head, bronze with aluminum-alloy fins. Overhead valves and camshaft. The general arrangement of the Norton engine on the bench as regards braking, temperature control, and so on, is similar to that of the J.A.P. engines. The lubrication is by the dry-sump system, with a scavenge pump returning the oil from the crankcase to an external oil reservoir. From the latter the oil is supplied to the engine by means of a delivery pump. Test Conditions Engine speed, 3000 or 3250 r.p.m. Load, approximately full throttle with mixture strength about 10 per cent below that for maximum power (B.m.e.p., approximately 125 lb. per sq. in.). Rate of delivery of oil by feed pump, approximately 100 pt. per hr. Cylinder-barrel temperature (inlet side), 175 deg. cent. The diametral clearance of the piston is adjusted to the following: Bottom of skirt, 0.005 in. Top of skirt, 0.009 in. Third land, 0.016 in. Second land, 0.022 in. Top land, 0.026 in. The side clearances of the pressure piston-rings vary from 0.003 to 0.007 in. according to the length of test, the lower clearance giving rise to ring-sticking in 5 hr. on most oils, whilst the higher clearances allow of 50 hr. or more of running before sticking occurs. To avoid detonation a gasoline of 80-85 octane number (Motor Method) is used and, to eliminate the possible effect of ethyl fluid on ring-sticking, non-leaded fuel is employed. Appendix 3 Bristol Single-Cylinder Engine Tests on used oil Oil | Duration of test, hr. | Oil consumption, pt. per hr. | General condition of engine after test | Sediment, percent by weight, Insoluble in petroleum ether | Sediment, percent by weight, Insoluble in benzol | Ash, percent by weight | Sludge in used oil, gm. per pt. oil A | 65½ | 1.4 | Very clean | 0.74 | 0.63 | 0.09 | 0.14 B | 65½ | 1.2 | Very clean | 1.0 | 0.16 | 0.09 | 0.5 D | 65½ | 0.95 | Dirty | 0.84 | 0.64 | 0.07 | 4.7 E | 65½ | 1.2 | Very dirty | 1.0 | 0.75 | 0.08 | 4.1 F | 75 | 0.85 | Clean | 0.73 | 0.55 | 0.07 | 1.2 G | 75 | 0.84 | Clean | 0.76 | 0.64 | 0.08 | 2.4 The sludge results in the last column were obtained by filtration of the used oils through paper and by removing the oil-soluble material by extraction with petroleum ether. The ash contents also were determined and subtracted from each deposit. It is evident that the sediment contents of the used oils bear little or no relation to the general condition of the engine, or to the quantity of sludge removable from the oils by filtration. On the other hand, the sludge results give a very fair indication of the state of the engine. Reduction of Carburetor Icing HEATING of the intake air, the most generally used method of eliminating carburetor ice, has the serious drawback of reducing the effective octane number of the fuel used. By this statement I mean that heating of the intake air will cause the engine to operate at higher cylinder temperatures and to detonate at lower power outputs. It will then be seen that the application of carburetor heat while operating at manifold pressures near the limit for the fuel in use may cause overheating and detonation, so that the engine power will be impaired seriously. This effect of carburetor heat on engine detonation, and the loss in maximum power from reduced volumetric efficiency, make it desirable to avoid the use of unnecessary heat when operating at or near maximum power outputs, and was the chief reason for our search for a substitute for continuous application of heat to the carburetor. Having found that we could tell when we were in or near icing conditions, we studied all the factors which would affect the rate of icing, and came to the conclusion that adherence to the following rules would reduce the tendency to ice in any given weather conditions: When the atmospheric dew point is above freezing: 1. Operate at as lean a mixture as is consistent with other instructions. (The less fuel evaporated, the less the cooling, and, therefore, the less heat needed, when heat is required.) 2. Maintain full cruising power. (In our tests more icing was reported at lower powers with a given dew point.) 3. Maintain as high a cruising altitude as possible. (Because there is less moisture at higher altitudes, and also because glides to lower altitudes tend to produce ice.) If the above precautions are not sufficient to prevent ice, it is necessary to heat the intake air. Excerpts from the paper: “Carburetor Icing,” by Robert Sanders, Engineering and Research Corp., presented at the National Aeronautic Meeting of the Society, Washington, D.{John DeLooze - Company Secretary} C., March 10, 1938. | ||