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This paper presents a study of fuel performance in spark ignition engines in relation to abnormal combustion phenomena such as surface ignition and rumble. This was accomplished by observation of the distribution of flame arrivals at ion gaps located within the engine cylinders, or peak pressure position, in terms of crank angle degrees. By this means, the surface ignition behavior and mass burning rates of LIB (leaded isooctane-benzene) and commercial fuel components were studied in multi-cylinder engines at 10:1 and 12:1 C.R. Additional information was obtained in two instrumented CFR engines operated at 10:1 and 6.75:1 C.R. It is concluded that the abnormally high peak cylinder pressures giving rise to rumble result from cycles in which combustion occurs early. Early combustion was caused by deposit-ignition of the charge but was also strongly affected by mass burning rate of the charge.

Due to the many losses in the conversion of heat to mechanical energy a gallon of fuel provides less than 1/4 of its mechanical equivalent of useable energy at the flywheel. These losses are described and an attempt is made at cataloguing them and appraising their magnitude at one speed and road load corresponding to the speed and road load of a compact car operating at 40 miles per hour on a level road. Some areas where improvements in efficiency may be obtainable through future research and development are discussed. A speculative estimate is made as to possible future efficiency increases based on this study.

RELIABLE predictions of the improvements in efficiency that can be obtained by raising the compression ratio of spark-ignition engines are of obvious value in the long-range planning of both the automotive and petroleum industries. New equipment and techniques were developed to measure indicated power by obtaining accurate pressure-volume measurements in each cylinder, thus permitting true friction to be determined as the difference between the indicated power of all cylinders and the simultaneously measured brake power. Tests were conducted on a 4-cylinder engine at compression ratios of 7/1 and 12/1.

With the advent of automotive engines having very high horsepower capacities, the problem of part-load economy has become serious. One method of improving the efficiency of the spark-ignition engine at light load is the use of mixture-ratio control to effect load variations. Charge stratification makes this method of load-control possible. In this paper the principles involved in stratification are discussed, and a new method for producing stratification is described. The results of engine tests using this method are presented to show the method is workable, and that the predicted advantages actually are obtained. “…there is little doubt that, sooner or later, the system of working with a stratified charge will become commercial, … it is possible and the high efficiency theoretically obtainable from it can be approached.” (1)* Harry R. Ricardo, 1922

THIS paper presents flame temperature and pressure data taken on a spark-ignited CFR engine. Data are presented for the four variables of cyclic reproducibility, knock, air/fuel ratio, and ignition timing. The data indicate that cycle-to-cycle irreproducibility may be caused by variations in the initial rate of flame propagation from the spark.

THIS paper discusses a method of measuring compression temperature by means of the absorption of light. An optical-electronic system measures the change in color of a trace of iodine gas that has been added to the intake mixture. From these measurements the temperature of the iodine and by inference, the temperature of the gases, is determined. The apparatus used is described briefly and the test results obtained in measuring compression and end-gas temperatures in a spark-ignition engine are also presented.

High speed photographs of the combustion process in an engine equipped with a quartz window, in the cylinder head are described. The optical path was so arranged that direct and shadowgraph images of flames could be separately photographed on the same film at the same time in conjunction with flywheel timing marks. Simultaneous pressure-time records were also obtained. The photographs confirm the well-known fact that knock occurs immediately after the portion of fuel still unreached by the flame spreading from the spark plug spontaneously ignites and begins to burn very rapidly. Cylinder pressure then rises so fast that acoustic resonance develops in the combustion gases and is heard as knock. Four types of combustion phenomena in the engine were investigated: normal flames, “cool” flames, “hot” flames, and knock. With no spark ignition, cool flames start at the valve end of the L-head combustion chamber and end at the far side over the piston.

PREIGNITION, Mr. Heron points out, is an old, if not well-known, disease of Otto-cycle engines. Despite its long history, however, there is much confusion in the terms used to describe it and the other forms of uncontrolled combustion in spark-ignition engines. The author has tried to bring some order out of the confusion by defining the three terms: knock, preignition, and autoignition. He also relates his experiences with destructive, runaway preignition in aircraft engines during World War I. THIS paper and the four that follow, by Melby-Diggs-Sturgis, Hirschler-McCullough-Hall, Williams-Landis, and Winch, constitute the complete Symposium on Preignition that was presented at the 1953 SAE Summer Meeting. Discussion of all papers is published at the end of the last paper in the group, by Winch.

The air standard cycle, the ideal fuel-air cycle and the fundamental concepts of combustion in a spark ignition engine are briefly described. The effect of combustion processes at various air fuel ratios on power, efficiency and composition of exhaust products are reviewed. It is recognized some degree of incomplete combustion is always present, and the effects of “poor” combustion on engine operations are discussed.

An investigation of spark-ignition reciprocating engines indicates that considerable improvement in engine power and fuel consumption and in airplane range and payload can be achieved by compounding them with exhaust-gas turbines. The improvement in performance increases with the degree of compounding and the attendant increase in complexity of the system. The compression-ignition compound engines also appear to offer a possibility of appreciable gains over the spark-ignition systems; however, it is anticipated that a greater amount of development time will be required for the practical realization of the predicted performance of the compression-ignition system than of the spark-ignition engine.

IT has been found by the authors that fuels fed to a crbureted spark-ignition engine may undergo severe “prereactions” during the compression stroke prior to spark ignition as differentiated from “preflame” reactions which take place ahead of the advancing flame front in the remaining unburned part of the air/fuel mixture in the cylinder after ignition. It appears that the extent of prereactions is a function of fuel type and engine operating variables. The alteration or prereaction of fuels increases with severity of engine operation. Intake temperature and compression ratio are major variables affecting engine severity. These tests show that the prereactions play an important part in the knocking phenomenon.

THIS paper describes available injection systems for spark-ignition engines. In the near future, the authors predict, simplified injection pump designs, probably of the single-plunger type, will be universally available for both compression-ignition and spark-ignition engines. The authors also say that recent developments in injection system components substantiate the claims of the injection equipment suppliers that they will meet the demands for low-cost equipment.

COMPRESSION ratios will increase gradually to about 8:1 for small spark-ignition engines and 7:1 for large engines as fuel improvements permit, engineers estimate. This increase will probably be accomplished with some sort of valve-in-head design. The higher ratios will call for better cooling to prevent detonation and more rigid construction for shock control. The tendency toward increased deposits will be curbed by better piston rings, closer-fitting pistons, cooled valves, and cooled spark plugs. In fuel systems, the ultimate aim is a simple, easily serviced, moderately priced fuel-injection system. Meanwhile, pressure carburetion is likely to be the next advance. Fuel pumps in or near the tank would give the higher pump pressure needed for pressure carburetion and improve atomization and distribution. Supercharging to increase power by raising compression pressure instead of compression ratio will be thoroughly investigated.

A NUMBER of the more important contributions made recently to our knowledge of the process of combustion in the engine cylinder are reviewed briefly in this paper. Of the possible lines of attack which promise to lead to further improvements in the control of gaseous combustion as a source of power, the following are stressed: Of the possible lines of attack which promise to lead to further improvements in the control of gaseous combustion as a source of power, the following are stressed: 1. Finding new mixtures which are inherently more powerful or more economical; 2. Finding new methods of altering the mass rate of burning, the completeness of combustion and, hence also, the rate of increase in pressure; 3. Preventing preignition in spark-ignition engines and facilitating ignition in compression-ignition engines; 4. Suppressing detonation.