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POINTING out the difference between scientific and industrial progress as manifested by heat theory and engine design and the Carnot and Otto cycles, the author discusses the working principles of combustion. A simple synopsis of internal combustion is presented, followed by a discussion of influence of spark-plug location on detonation and pressure rise and some observations on overcooling and flame quenching. The reasons underlying the decision to use a particular type of engine in an automobile are commented on, and this is followed by a discussion of the limitations imposed upon induction and combustion by such a choice. The advance in combustion-chamber design is traced from the early T-head through the L-head, in various forms, the overhead-valve, the hemispherical and four-valve types. Drawings of the different heads supplement the text and some comparative power curves are included.

THIS paper is an analysis of the economic value of the use of high compression, from the viewpoints of fuel cost, carbon-removal cost and engine performance. Charts and tables, based on ranges of fuel cost, compression ratio and cost of carbon removal, and on assumed increases in economy from the higher compression, are used to evaluate the economies that can be effected under these assumptions. The same methods can be applied with actual data to determine the economic value of a doped or improved fuel that makes high compression without detonation possible. Methods are given also that will show the car designer what gains in power can be made by an increase in the compression. Attention is called to the fact that improvement in fuel economy under these conditions may not be so great as expected unless it is accompanied by a change in gear ratio.

ADVENT of engines operating at higher compression and higher speed than engines used a few years ago in automotive vehicles has necessitated refinement of all engine accessories, including the ignition equipment. It is necessary that the ignition units give unfailing performance at top speed of the engine without sacrifice of long life of the units. Storage-battery ignition, with a generator as a source of energy, is used almost universally in this Country today, and is asserted to be the cheapest, simplest, easiest to service and most reliable system known for vehicles in which a storage battery is required for starting, lighting and other purposes. The electrical circuit used in the ignition system of automobiles today is almost identical with that designed for the 1912-model Cadillac, which was equipped with the Delco electrical engine-starter, except for refinements and greater reliability.

DUAL carbureters, as equipment for eight-cylinder passenger-car engines, have recently come into special prominence and, compared with a single carbureter, give a gain in power in the middle-speed range, between 1400 and 2800 r.p.m. This is an adaptation from airplane-engine practice, in which greater power-output and better distribution have been realized by multiplying carbureter units as the number of cylinders is increased. An absence of overlapping and interfering suction-strokes and the use of larger manifold-passages are apparently responsible for this gain. Tests made on a number of eight-cylinder engines of both the in-line and the V-types confirmed this gain, which was, however, unaccompanied by any particular gain in fuel economy.

WE are entering a period in which the refiner is making a conscientious effort to give his fuel high antiknock value and such effective volatility that it will give superior performance in any automobile engine in which it is used. The present tendency is away from the misleading values such as color and gravity. Ease of starting and good acceleration, particularly of a cold engine, demand high partial volatility even more than antiknock value, while the development of maximum power and a high fuel efficiency in modern engines supplying a large amount of heat to the mixture demand a relatively high end-point in the distillation test. The author discusses the difficulties of using fuels possessing these characteristics in such engines, and indicates the desirability of the automotive and the oil industries cooperating in finding a solution of their joint problem of suiting the engines and the fuels to each other.

DETAILS are given of the method of control of the engine so that quantitative and reproducible measurements of detonation and comparisons with spectra can be made. Typical data are tabulated and photographs are shown of the free-burning flames of hydrogen, carbon monoxide, methane, gasoline in a blow-torch, and the like. The spectra of explosion and of detonation in the engine confirm earlier conclusions. By means of a synchronous shutter, the spectra of radiation during the four quarters of a stroke are obtained for straight-run gasoline under detonating and non-detonating conditions for the same fuel containing tetraethyl lead, aniline and iodine as knock suppressers and for cracked-gasoline blends. The outstanding result is that, during detonation, the first-quarter spectrum extends far into the ultra-violet, that of the second quarter, a somewhat less distance; the third and fourth quarters are characterized by very little radiation energy.

NAVAL aviation confined its activities to training and to coastal patrol during the World War. This limited operation was necessitated by the small amount of materiel suitable for operation over water, the strategical and geographical situation which determined the nature of the naval operations, the very limited performance of seaplanes of that period, and the fact that warships were not equipped for handling aircraft or prepared for aircraft cooperation. At the end of the War, naval aviation was made part and parcel of the fleet. Fighting airplanes are required to gain and maintain control of the air. Observation airplanes are used for short-range scouting and also for controlling long-range fire of capital ships by reporting the fall of shot to the ship by radio. For torpedo and bombing work, the first requirement is large weight-carrying capacity.

Progress has been made steadily in the application of superchargers to racing automobiles, and the author of the following paper has no doubt that the supercharger will be adopted as standard equipment on passenger automobiles of the better class within the next few years. Builders of the Mercedes car have placed on the market two models regularly equipped with a supercharger of the Roots blower type, and the increased power, flexibility and speed of these cars have shown the public the great possibilities obtainable by the supercharger. In addition to the foregoing advantages, the supercharger gives greater mechanical efficiency and fuel economy.

The marked advance that has been made in the last 10 years in constructional details and in performance of airplane engines and in airplane performance is reviewed, beginning with the year 1916 when the Curtiss OX-5 eight-cylinder water-cooled engine was brought to its final stage of development. The author describes briefly each type of engine produced successively by the company he represents and tells of the changes that were made to improve the performance. From the 8-cylinder V-type the constructors changed to the 6 and 12-cylinder water-cooled type and are now developing a 9-cylinder air-cooled radial engine that was built in 1925. An important field of usefulness is foreseen for the air-cooled engine.

The purpose of the paper is to point out the basic policies which have resulted in the fostering of air-cooled-engine development by the Navy, and to indicate where the development has led. Two roles played by naval aviation are designated “air service” and “air force.” The former term refers to the functions of naval aircraft which are contributory to the ships of the fleets, such as scouting and the control of gun-fire. The latter term refers to the functions which involve the use of aircraft as an integral and component part of the Navy's striking force, such as combat, bombing and torpedo launching. Seven different types of aircraft are required by the Navy for its different purposes, these being airplanes for training, fighting, observation, scouting, torpedoing, bombing, and patrol use.

In undertaking any experimental work the first step is to plan carefully each successive step. Literature bearing on the subject should be examined to learn what work others have done on the problem and avoid needless duplication of effort. If the testing of only a simple accessory is involved, the results the device is intended to accomplish should be studied and an effort made to discover the designer's reason for believing that it will accomplish them. All conditions under which such a device must operate should be listed and the information needed from which to draw conclusions as to whether the device will meet them successfully should be determined. Before starting the actual work of testing, it is good policy to plan the necessary charts for presentation of the report. This preliminary work means that the investigator will start well prepared but not with his mind made up as to what the results will be.

What the Diesel engine has done, its possibilities of development and future application to automotive service are major topics of the paper. When modified for automotive use, the author asserts that the Diesel engine would not only allow the burning of cheaper fuel and provide greater fuel economy, but give immediate opportunity to use the two-stroke cycle; that is, it would generate about twice the power for an equal weight of mechanism, compared with present power attainment. In addition, the two-stroke cycle makes possible partial or entire elimination of exhaust-valves, exhaust through ports being better in every respect, and the Diesel-engine principle affords the possibility of a two-stroke-cycle double-acting engine in which, theoretically, four times the power of the present gasoline engine would be available.

Piston friction is much the largest item of mechanical loss in an engine, amounting to fully one-half the indicated horsepower at light loads. Although opinions differ as to the most desirable temperature of the jacket-water for full-load operation, no question has arisen as to that for part load. It should be as high as possible, in order that piston friction can be reduced by keeping down the viscosity of the oil on the bearing surfaces, and that complete vaporization of the fuel may be secured. By reducing the friction of the piston and improving the vaporization, steam-cooling increases economy, which, on a number of cars of different makes, has been found to average 20 per cent more miles per gallon. Water is practically a non-conductor of heat. Boiling water, or a mixture of water and steam, is far more effective for cooling than is water that is not boiling.

The two-fold purpose of the tests described was to acquire as many data as possible regarding the peculiar requirements of motorbuses, as viewed from the standpoint of power requirements and fuel economy, and to analyze the discrepancy found so often between the performance of an engine on the test block and the fuel economy obtained from the same engine under actual service conditions. Following a general statement of conditions to be met, and an examination of the problems of the manufacturer as to why his choice of the various units and accessories is such a vital factor in fuel economy, the improvements accomplished are enumerated, together with the reasons and inclusive of the desirable and undesirable features of carbureter specification and miscellaneous factors. The test equipment and methods are specified and discussed, the results obtained when using a steam cooling-system are presented and the general results are stated and commented upon.

Since the road-service tests of the four special fuels supplied by the Research Department, made under 1922 summer-weather conditions, gave results that were deemed inconclusive, arrangements were made for a repetition of both series of tests under the winter-weather conditions of 1923 to determine whether the relative fuel mileages for different fuels are dependent on the temperature at which car operation is conducted. The paper is a report upon the results obtained. Four fuels that bore a relation to those used in the 1922 summer tests were specified and means adopted whereby knowledge of their quality was concealed from the drivers, special emphasis being placed on crankcase-oil dilution and on the performance as reflected by the drivers' comments.

Economy tests carried out in France indicate that it is possible to obtain a larger number of miles per gallon from cars made there than from cars made in this Country. The author states that it would be well to make a careful study of the factors influencing car economy and to assure that our future car models take full advantage of all possible means of increasing their economy. Figures are presented showing the extent to which economy can be increased by changing such factors as the carbureter adjustment, time of the spark, rear-axle ratio and speed of driving. A car that normally will go 21 miles per gal. under favorable test conditions at 20 m.p.h. was increased to 43 miles per gal. at 20 m.p.h. The study is not complete but has gone far enough to demonstrate its value. This progress report is presented to stimulate thought.

That all of the variable factors of automobile friction-losses such as the quantity and viscosity of lubricants, the efficiency of worm-gearing and part-load Modifications are not appreciated, is indicated by an examination of the literature on this subject which reveals a lack of necessary data. Experiments to determine the mechanical losses, including all friction losses between the working gases in the engine and the driving-wheels of the vehicle, are described and supplementary data are included from Professor Lockwood's experiments at Yale. Three distinct possibilities for increasing the fuel economy of a motor vehicle are specified and enlarged upon, gearset experiments to secure and develop data for a four-speed gearset being then described and commented upon at length; photographs and charts illustrative of the equipment used and the resultant data are included.

The author states that considerable thought has been devoted recently to the relation of fuel end-point to fuel economy. It has been shown that, provided an intimate mixture of fuel-vapor and air is secured, such a mixture will not condense at the ordinary temperatures of the intake. However, on the contrary, crankcase dilution, an excess of deposited carbon, low mileage per gallon of fuel and ignition trouble are being experienced. There appears to be a discrepancy between the efficiency that should be attained and what is actually attained. To investigate this the Bureau of Standards undertook a brief series of experiments to rough out a line of procedure. Regarding compression of a dry mixture, curves are shown to illustrate that gasoline vapor compresses when “dry.” Detonation was evident when using one spark-plug and there was no detonation when using two spark-plugs.

Two serious problems confront the automotive industry in connection with the present fuel shortage, the securing of a much higher degree of fuel economy with existing equipment and the matter of future designs. These problems are of nearly equal importance. Because its fuel bill constitutes the second greatest item of expense for the Fifth Avenue Coach Co., operating in New York City, it is constantly experimenting with devices of various kinds to improve fuel economy. Of the different devices that it has tested, the thermostatic temperature-control for the carbureter appears to afford greatest possibilities of saving, and the author presents the results of tests of this device in actual service on motor vehicles.

Design factors are considered from the thermodynamic standpoint only, which excludes several factors affecting power and economy. The problem of air heating includes a consideration of its influence on pressure, the consequent lowering of pressure being counteracted to some extent by the resulting improvements in carburetion and distribution and by more rapid and complete combustion; the effects of delayed combustion, with a study of the thermodynamic conditions and possible improvements; and the results that are actually obtainable from lean and rich fuel mixtures. Fuel economy is difficult because its factors conflict with those of power. The benefit of the expansion of any elastic working medium to economy is emphasized. Charts from previous papers, showing the ratio of air to fuel by weight, are referred to and discussed, best economy being obtained with mixtures leaner than those giving maximum power.