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IN THIS PAPER the author discusses the significance of the various tests for motor fuels, particularly in the light of extensive research work along these lines in the past few years by various industrial laboratories and the United States Bureau of Standards. A bibliography of the literature on the subject supplements the paper. Although a large part of the public still seems to assume that the principal difference to the car user between different grades of gasoline is in mileage per gallon, actually, if today's best and poorest commercial gasolines are compared, the difference in mileage is very small compared with the differences in engine-starting ability, antiknock quality, vapor-locking tendency and liability to injure the engine or the fuel-induction system.

WEATHERING of gasoline occurs in fuel tanks, carbureter float-bowls and vacuum tanks of automotive equipment, the extent being dependent upon conditions of temperature and pressure. If there is sufficient fuel loss due to weathering, the vapor-locking tendency of the gasoline is reduced. Experiments were made in laboratory equipment to determine the amount of loss and the decrease in vapor-locking tendency of a number of gasolines under various conditions. The factors varied were temperature, pressure, time and the size of opening to the gasoline container. In general it was found that there is very little loss until the vapor pressure of the gas-free gasoline exceeds the external pressure. When the vapor pressure of the gasoline exceeds the external pressure, loss occurs until the vapor pressure becomes equal to the external pressure if sufficient time is allowed for the vapors to escape through the opening.

PREVIOUS reports on the investigation of vapor lock in airplane fuel-systems have indicated that the tendency of aviation gasolines to cause trouble from vapor lock could be predicted from the standard A.S.T.M. distillation-data on the gasolines. The present paper deals with experiments made for the purpose of comparing the predicted conditions for vapor lock with those actually found in typical fuel-feed systems to cause trouble from this source. In gravity-feed systems, the predicted and experimentally observed conditions for vapor lock are in good agreement. On the suction side of a fuel pump, vapor lock occurs in a number of cases at lower temperatures than those predicted, particularly under conditions representing high-altitude flying in a system employing a long suction-lift.

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.

MAJOR problems that have been encountered in the operation under contract of that portion of the Transcontinental Air Mail line between Chicago and San Francisco are outlined and discussed briefly. The more serious difficulties cited are: first, the operation of a single type of airplane from points at altitudes as great as 6400 ft. as well as at sea level, together with the fact that, in the case of this particular line, the heaviest loads are carried between the points of greatest altitude; second, the proper design of cowling and manifolding for the operation of the air-cooled radial engine at the extremes of temperature that are encountered throughout the year; and, third, the need for an engine that is geared down to the propeller or an engine delivering its normal power at a lower engine-speed.

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.

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The undisputed economy of the Diesel-type engine using heavy fuel oil is recognized, as no other power-generating unit of today shows better thermal efficiency. It is the result of the direct application of fuel in working cylinders. Transmission processes, such as the burning of fuel under a boiler to produce a working agent which must be carried to the prime mover, are less economical. The various factors which enter into a comparison between steam and heavy-oil installations are illustrated. The subject is treated in a more or less elementary manner. The diagrams and sketches are intended to explain the working principles of such examples of two and four-cycle engines as are now in actual operation in cargo ships, these being of the single-acting type. Double-acting and opposed-piston-type engines have been built and are being tried out. The working processes of two-cycle and four-cycle engines are illustrated and described in some detail, inclusive of critical comment.

The author states that the objects of the paper are to define and trace the development of the various processes of carburetion, and to offer such suggestions along these lines as may assist the investigator in developing motorboats, automobiles and self-contained unit motor cars for railway purposes. The surface carburetor is mentioned chiefly as of historic interest. In considering the jet carbureter the author discusses the proportion of gas desired, the effect of the varying inertia of the air and the liquid gasoline and the breaking up of the combustible needed. Following sections review the devices for using kerosene, such as gasoline jet carbureters to which heat is applied, devices of the fixed gas type, the introduction of combustible directly into the cylinder, forcing combustible directly upon a hot surface in the cylinder and devices which raise the combustible to the boiling point.

In order to achieve lean burn engine control system, it is necessary to develop high accuracy air fuel ratio control technology including transient driving condition and lean burn limit expansion technology. This paper describes the following. 1 The characteristics of the transient response of the fuel supply are clarified when various kinds of air flow measuring methods and fuel injection methods are used. 2 To achieve stable combustion in lean mixture, fine fuel droplet mixture, whose diameter is less than 40 μm, needs to be supplied.

The sequential fuel injection, in which fuel is injected into swirl being generated for mixture stratification, was used to pursue the potential of a lean burn engine for its performance improvement. As a result, it has been found that the most effective method to increase thermal efficiency while reducing NOx emission level is to combine a high-compression compact combustion chamber located on exhaust valve side in cylinder head with DICS (Dual induction Control System). This method was used to build a high-compression lean burn concept vehicle, which was evaluated for compliance to various emission standards. Testing showed that the concept vehicle can improve fuel economy by 10.5% on the Japanese 10-mode cycle, by 8.3% on the ECE mode cycle, and by 6.3% on the U.S. EPA test mode cycle while meeting respective emission standards.