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PRESENT-DAY cars are not capitalizing on the continued efforts of the petroleum industry to provide better fuels, the authors believe. The wide differences found in the octane-number requirements of individual cylinders, plus the failure to obtain uniform mixture distribution from cylinder to cylinder without resorting to fuels of aviation-grade volatility have led them to reach this conclusion, they explain. The probability that significant reduction in the average antiknock requirements of cars might be effected without making any major changes in the engine is indicated by a survey of the technical literature, they point out. The extensive studies of ignition-system characteristics and gasoline-mixture distribution as affecting detonation reported in their paper bring out the following pertinent points: 1. Variations actually occurring in the spark advance from cylinder to cylinder may vary the octane-number requirement of individual cylinders by about 10 points. 2.

HIGH output per cubic inch of piston displacement is desirable not alone for the purpose of being able to transport more payload faster, but more particularly for the invariably associated byproduct of lower specific fuel consumption, and especially at road-load requirements. The only way of accomplishing this purpose is through the use of higher compression ratios, and the limiting factors for this objective are fuel distribution and the operating temperatures of the component parts. A manifold is proposed which not only definitely improves distribution at both full and road loads, but has the inherent additional advantage of reducing the formation of condensate, thus still further facilitating a reduction in road-load specific fuel consumption. Hydraulic valve lifters, obviation of mechanical and thermal distortion, and controlled water flow are the essentials in improved cooling.

THE importance of the material of the piston ring has too long been relegated to the background as compared with such design factors as ring proportions, ring loadings, circularity, point pressure, and so on; therefore, this paper concentrates on the material factors - such as composition, structure, and surface finish - which should go into the modern piston ring. The causes of piston-ring wear are analyzed and classified under three headings - abrasion, corrosion, and erosion. Various types of coating materials, both metallic and non-metallic, employed to reduce the severity of scuffing or scoring, are considered. Test results are revealed that indicate that superficial coatings reduce piston-ring wear from scuffing and erosion, and that a very thin coating of tin was more effective than other types of metallic and non-metallic coatings.

SYMPATHIZING with the engineer who finds that the high efficiency designed into his engine fails to produce the anticipated increase in average miles per gallon obtained under normal driving conditions, the authors touch upon some of the factors, many of them out of the engine designer's control, which may completely mask the expected improvement. In so doing, they start with an engine of known specific consumption and show the effect of air resistance, chassis friction, gear ratio, and car weight on constant-speed road economy, comparing calculated values with actual test values available. Also discussed are such factors as climatic variations, traffic operation, cross-country driving and the individual driver, which have a definite effect upon economy, but over which the designer has little or no control. The effect of these factors is illustrated by the spread in tank mileage shown by a number of cars of similar model in fleet operation.

THE most striking improvements in lubricating oils for automotive-type Diesel engines have been obtained through the use of soap-type additives, the authors contend, and several brands of this compounded oil are now available to Diesel engine operators. The paper deals particularly with this type of addition agent and reviews the improvements obtained through its use. Using such an oil, compounded with the calcium soap of dichlorostearate acid, the authors claim that five of the six properties considered necessary for a Diesel-engine crankcase oil are exhibited, namely-detergency which aids in preventing ring-sticking; high film strength which reduces the danger of scuffing, scratching, or galling under severe conditions; a high degree of oiliness which reduces wear under normal operating conditions; low carbon-forming tendency; and adequate crankcase stability which promotes cleanliness of the engine and maintains lubrication efficiency.

MR. TAUB predicts that the time for intensive work on the fuel-economy problem, such as has been done recently in England, is near at hand because of the imminence of increased fuel taxation. Tank mileage, he explains, depends on the ability of an engine to utilize lean mixtures- not just lean mixture from the carburetor, but modification of an engine to burn these lean mixtures without interference with flexibility or performance in any way. A study of what happens in the combustion chamber is cited as the major opportunity for engineering improvement in the ability to burn lean mixtures. In his discussion of his work at Vauxhall Motors, Mr. Taub considers wide gaps and their effect on ignition lag, long-reach spark plugs, tappet adjustment, effect of higher compression ratios, variation per cycle, detonation, and means of forecasting combustion roughness.

RESULTS of tests on several motor cars reported in his paper, Mr. MacCoull comments, “make one wonder if it is economically necessary for a car to be completely free from knock at all times.” Use of a spark retarded slightly from that required for optimum power, he found, resulted in a trivial power loss, but appreciably lowered the octane requirement. In additional tests on a single-cylinder CFR engine, where power output and various temperatures were studied, as the compression was raised above the critical compression ratio, the author found that: 1. Power output increased steadily with compression ratio if the spark advance was adjusted for maximum power at each ratio. The limit apparently was set by preignition. 2. If the spark was retarded to the threshold of knock at each compression ratio, the power increased and then dropped off rapidly at higher compressions. 3.

FUTURE engine developments for powers between 2000 and 4000 bhp and the author's views on the form which such engines will take, together with optimum cylinder sizes and number of cylinders, are covered in the latter part of Mr. Banks' paper. Because it concerns the possible future development of military aviation in America as well as his own Country, the author considers this part the important one. In the first part, he gives a short résumé of the aviation fuel position in Great Britain, and then goes on to describe some work which he has done in conjunction with the British Air Ministry and one of the aero engine manufacturers on very high-duty aviation engines. He also discusses what, in his opinion, is a characteristic of the American two-valve hemispherical cylinder head relative to British four-valve engines in regard to fuel behavior. He continues, mentioning certain new developments, such as the treatment of poppet type exhaust valves with Brightray.

NEITHER severe military maneuvers, such as power dives and inverted flight, nor icing conditions will affect appreciably the operation of the aircraft carburetor described in his paper, Mr. Kittler asserts. To back his claim, he points to over 1½ years experience with several hundred of these carburetors since the start of their development in 1935. After a discussion of the problems of icing, maneuverability, and metering, the author details the construction and operation of the type of carburetor finally developed. This carburetor is unlike commonly known types, he explains, in that the fuel level is controlled by a double-diaphragm mechanism instead of by the conventional float mechanism. In place of the fixed venturi and butterfly throttle construction is a variable-venturi mechanism which forms both the throttles and the venturi. Metering is governed, Mr.

ACTUAL computation of the vibratory crankshaft stresses, although a laborious process beset with many difficulties, should offer the best chance for an intelligent evaluation of the crankshaft torsional-vibration characteristics in aircraft engines and of whether the amplitudes are dangerous or within safe limits, Mr. Masi concludes. In a discussion of the various methods used, their relative merits, and allied problems, he shows that the simple expediency of using fixed allowable amplitude limits, for certain classes of engines, determined from experience, is likely to lead to erroneous conclusions. A novel method, which has been used on numerous engines by the Naval Bureau of Aeronautics, is suggested by Mr. Masi. It consists of determining the twist of the crankshaft with the application of rated engine torque and basing the allowable vibration amplitude on the amount of the twist.

RECENT developments in fuel-refining processes have developed new safety fuels, and have revived general interest in the subject, Mr. Mock reports. “Safety” or fireproof aircraft fuels, he explains, must be less volatile than gasoline and should have a flash point of about 105 F, a distillation range between 375 and 475 F, and about 87 octane rating. In his paper he summarizes the program probably necessary before such fuels can be employed successfully in every-day service operations. Three methods of fuel feed are discussed: injection into the cylinder, into the intake pipes, and into the supercharger. Injection into the cylinder, he reports, has been tested on a full-scale engine on the dynamometer with some success, but it was not flown. Injection into the supercharger, he feels, is attractive because of its simplicity. Five detail problems are listed: injection equipment; changes in engine and cylinder; fuel-air metering and power control; starting; and installation.

THE trend in poppet valves during the past year, like many other advances in science, Mr. Colwell points out, has been an improvement upon existing performance, rather than an entirely new development. To effect a steady improvement in existing designs, the study of fundamentals, such as grain flow, structure, forging temperatures, coolants, and interior construction, has been resorted to, and thorough research on valve steels has been carried out, he reports. In the study of valve steel, 300 analyses were examined; intensive work was done on 20; and 4 showed definite merit, he says. Grain flows in aircraft valves made by the extrusion and gather-upset processes are compared. Results of an investigation of sodium cooling and head designs of aircraft valves by means of glass valves are reported and illustrated. Four outstanding automotive valve steels are analyzed chemically and physically - Silcrome No. 1, Silcrome XB, Silcrome X-10, and Silcrome XCR. Mr.

PISTON-RING irons are not the “best-wearing” irons, contends Mr. Lane in his discussion of bore wear from the standpoint of the materials commonly used for high-speed automotive diesel and aircraft-engine cylinders, liners, and rings. Measured on a weight-loss basis under direct comparison with other conventional iron structures, piston-ring irons normally give relatively high weight-loss figures. But piston-ring irons do have the significant and desirable faculty of wearing away with very little tendency to accumulate wear products on their rubbing surface. In fact, this ability is probably of equal or greater importance than actual low weight loss. In his paper Mr. Lane reports the results of several years of laboratory wear-testing research, correlated in many instances with actual service experience, from the viewpoints of hardness, structure, and chemical composition.

DEVELOPMENT and service properties of a new compounded diesel-engine lubricating oil are described in this paper. Properties of the oil brought out by the author include anti-ring-sticking value; prevention of lacquer formation; reduction of carbonaceous deposits; that it is non-corrosive to all types of bearing metals; and that it reduces piston-ring and cylinder wear at both high and low temperatures. Although recommended specifically for diesel engines, the oil also is suggested for gasoline engines particularly where engine deposits are troublesome.

SIX major causes of bearing failures are catalogued, which include matters of engineering and design, procurement practices, misuse and abuse in operation, faulty installations, unsuitable lubricants, and mechanical faults in the bearings themselves. Although there are four general types of bearing materials in common use today for main and rod bearings - tin-base babbitts, high-lead babbitts, cadmium alloys, and copper-lead mixtures, the author shows that not one of them is a universal bearing material - each has its own particular field of usefulness, and these fields are defined in terms of maximum unit pressure, Zn/P, PV, oil-reservoir temperature, and crankshaft hardness. Design factors that react against indicated satisfactory performance are considered, including strength and stiffness of the bearing structure, oil flow to the rod bearing, restrictions in feed grooves, oil clearance, and so on. Standards of design pertaining to these points are set up.