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THE effect of gas pressure on piston friction was investigated, in the laboratory of the Massachusetts Institute of Technology, by driving with an electrical dynamometer a six-cylinder engine with the valves removed and the valve-stem bushings plugged. Air under pressure was admitted to the closed space made up of the cylinders, valve passages, and manifolds, and a constant air pressure was maintained on the pistons. Under these conditions, it was found that the friction increased approximately as a linear function of the pressure and the running speed. The effect of jacket-water temperature on piston friction was marked, but it could not be directly connected with the absolute viscosity of the oil at the temperature of the jacket water. Tests run with gas pressure relieved from behind the piston rings indicated that about a fourth of the rate of increase in friction with pressure is due to gas pressure behind the rings.

A DISTINCTION is to be made between non-continuous-wear and continuous-wear measurements. To the former class belong measurements where the piston-rings are weighed or the cylinders and piston diameters are measured. Such a method takes a great deal of time, not only because of the long duration of the test itself but also because of the time necessary for the removal of the pistons, weighing, measuring, and re-assembling the engine. In the latter method, cylinder wear is measured by determining the ash content of oil dripping from the piston while the engine is running. A standard fuel and lubricating oil is used, and wear is expressed as a “wear factor”-the ratio between the weight of ash collected on the sample used and the weight of ash collected from the standard sample. This factor correlates well with actual wear measurements. Wear decreases with decreasing load, but increases again with very light loads within specified limits.

THIS paper gives a brief resumé of the development of the Rolls-Royce Kestrel engine and then analyzes the requirements of the high-performance engine of the future, developing at least 1500 b.hp. and operating on fuels of high knock ratings. The problems investigated include those of engine form, fuels, detonation, waste-heat disposal, cooling drag, cooling medium, and the mechanical and operational features. Conclusions deduced from the arguments are: (a) Compression ratios, charge density, and rotational speeds will need to increase and, therefore, cylinder bores and strokes will decrease; it may be necessary to adopt the sleeve-valve type. (b) The arrangement of the engine will tend to multithrow crankshafts with more than two pistons per crankpin.

DURING the past decade the general trend of aircraft-engine design has continued toward increased piston displacement, higher crankshaft speed, higher brake mean effective pressure, and improved materials. These changes have had a marked influence on increasing the overall performance of the airplane by improving take-off, bettering climb, permitting higher cruising speeds at greater altitude, increasing periods between overhaul, and improving the reliability of the powerplant. Although of secondary importance until quite recently, today fuel economy has become a major objective in both military and commercial operation. Fuel consumption is a function, generally speaking, of engine design, of the properties of the fuel itself, and of the procedure for introducing and regulating the fuel-air mixture in the operation of the powerplant.

THE engine considered in this paper is an eight-in-line of 3 1/16-in. bore and 4¼-in. stroke having a piston displacement of 250 cu. in. After comparing the performances of the “FD” and the 8-250 engines, Mr. Sparrow relates in detail the changes made in the engine under consideration and states the results obtained by tests, also commenting thereon. The subjects considered include valve timing and lift, intake pulsations, distribution, compression ratio, ignition, blowby, oil consumption, cylinder-block cracking, valves and valve seats, valve springs, pistons, crankshaft failure, connecting rods, and bearings. Numerous data are presented in chart form, together with other pertinent illustrations of the subjects discussed.

THIS paper points out how the problems of decreasing oil-consumption and blow-by and preventing piston-slap are affected by different piston and piston-ring characteristics, and some of the things that can be done toward solving them. Improvements made in pistons-as to design, materials and construction-are cited. Problems concerning oil-control are stated, and means for solving them are set forth. Interesting figures on piston-ring-wear tests are presented and the conclusion regarding them is that the wear of pistons, piston-rings and cylinders, is due almost entirely to factors which, though usually present, are outside influences. These include abrasive material entering with the intake air, crankcase sludge, excessive choking, cold starting, and blow-by. Wear inside the cylinders cannot be eliminated without the use of improved air-filters and oil-filters, and by improved cold-starting conditions.

THE need for improvement of fuel consumption in modern aircraft is stressed. The basic economy of oil engines for airline service is briefly summarized, together with the effect of lower fuel consumption on the range and payload of airplanes. The theoretical efficiencies of the Otto and Diesel cycles are compared with the efficiency actually obtained on present aircraft engines. The data are presented in condensed graphic form for easy comparison. A prediction is made of the fuel economy that may be expected from the gasoline aircraft-engine in the near future, together with a summary of the means required to obtain it. The prospective place of the compression-ignition engine in commercial and military service is briefly outlined. An analysis of the weight possibilities of compression-ignition engines as compared to present gasoline engines is made.

The general design problem is considered by reference to the principle of similarity. The principle is briefly reviewed and applied to lubrication, propeller drives, cooling and detonation. It is shown that while small engines should be capable of a larger output per square inch of piston area, in practice the reverse is the case. It is also shown that small engines should, in general, operate at a higher efficiency than large ones. A promising line of attack for improving the lubrication of small engines is indicated.

THERE has, for many years, been a demand for an automotive engine more economical in operation than the gasoline engine. As the Diesel engine had early established a good reputation for economy, the development work on a more economical automotive engine quite naturally centered around this type of engine. Additional advantages can, however, be gained by combining fuel injection with spark ignition, and an engine of this type has been developed by K. J. E. Hesselman of Stockholm, Sweden. This engine is generally called the Hesselman engine. In the spark-ignition fuel-injection engine the charge is formed at a certain time before the spark occurs, and this makes it possible to mix fuel and air thoroughly whereby high output is secured. Engines operating on fuel oil with a compression ratio of 7.5 : 1 have given a brake mean effective pressure of over 125 lb. per. sq. in.

THE purpose of this paper is, first, to set down the methods which have been considered in the effort to develop a gasoline-type engine which will operate satisfactorily on non-volatile fuels, such as furnace or heating oil: Second, to describe briefly commercial examples of the use of these various methods: Third, to analyze the possibilities of these several processes with regard to power and efficiency, comparing them-as well as the results to be expected from the use of motor gasoline-with those of an engine operating on aviation gasoline as a basic standard. Mr. Dutcher concludes that there are cases where horsepower hours per dollar's worth of fuel can be just as-or more-important than horsepower per pound of engine.

DR. SCHNAUFFER presents in this paper the results of research on and measurements of combustion processes in internal-combustion engines by means of a slow-motion camera and a micro-chronometer. This method for flame-propagation indication depends on the physical property of flame to ionize air gaps and hence make them conductors of electric current. The recording equipment used is very simple, he says, and can be simplified still further if only visual inspection of the combustion processes is desired. He gives also a brief review of the history of combustion-process research, and a bibliography. Using this method, all the conditions affecting the speed of flame-propagation in a high-speed spark-ignition engine were examined, and Dr. Schnauffer emphasizes that the results were accurate. Neon lamps can be substituted for an oscillograph, if desired, and are less expensive; further, this makes possible the registration of an unlimited number of test points.

SINCE the power output of an engine is practically proportional to the weight of the charge, the object has been to increase the weight of the charge burned. The weight of charge inducted by an aircraft engine and the supercharger power required to supply this charge depend among other factors upon how completely the engine is scavenged. In the conventional four-stroke-cycle engine only the exhaust gases in the displacement volume are forced out of the cylinder by the piston on the exhaust stroke; consequently, the engine cannot induct a charge of greater volume than that of the displacement volume, whereas if the clearance volume could be scavenged also, the engine could induct a charge equal to the displacement plus the clearance volume.

MANY improvements in shock-absorbing apparatus have been made during the last two years, the most notable being in dash control and devices for temperature compensation. Two types of hydraulic absorbers, the piston and the vane types, have been in use during this period. Both constructions function around the hydraulic principle of forcing a fluid through an orifice of some type. So-called automatic shock-absorbers were much heard of during 1932. The various kinds of control used are examined herewith to determine whether or not some particular type of velocity-load diagram is most desirable. After describing the inertia-controlled shock-absorber, Mr. Kindl enlarges upon its various features. The equipment used for testing purposes is illustrated. In conclusion, he states that future experimental work undoubtedly will increase the perfection of this type of shock absorber.

COMPARATIVE tests were made, both on the block and in the same motorcoach chassis, of a 525-cu.-in. gasoline and a 495-cu.-in. Diesel engine. The block tests are reported fully in charts, including curves for torque and power against piston displacement and engine weight. Corrected curves are given on the basis of equal piston displacement and for the Diesel engine throttled enough so that it would not smoke. Road tests included fuel consumption, acceleration, hill climbing and top speed, which are also recorded in charts. Other sections of the paper deal with costs of manufacture and maintenance and present and prospective conditions as to supply and cost of Diesel fuel. Stress is laid on the facts that automotive Diesel engines require a much higher grade of fuel than do the larger and slower Diesel units and that more gasoline than fuel oil can be obtained from a given amount of crude.