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This paper describes full-scale engine studies conducted to determine the feasibility and compatability of ammonia combustion in various systems. Briefly outlined is the spark-ignition investigation undertaken by the Army Laboratory to learn the potential and effect of ammonia as a fuel and to study the influence of engine variables on combustion. A study of compression-ignition performance was made to ascertain the ability of ammonia to be pumped in existing injection systems and various means of achieving ammonia combustion were explored. Conclusions drawn from these studies on the use of ammonia as a fuel are given.

Cylinder pressure variation is a fundamental and widespread combustion problem in spark-ignited engines. The basic factors causing this problem are variations both in the start and in the rate of combustion. These variations occur not only from cycle to cycle within each cylinder but may also show up as consistent differences between cylinders. Our test results indicate that the major cause of cyclic combustion rate variation is the mixture velocity differences that exist within the cylinder near the spark plug at the time of ignition. As yet we do not know how to reduce the cyclic mixture velocity variations and thus reduce the problem at its origin. However, it is possible to circumvent some effects of cyclic pressure variation by increasing the average combustion rate.

Anhydrous ammonia has been demonstrated to operate successfully as a fuel for spark ignition engines. Principal requirements are that it be introduced in the vapor phase and partly decomposed to hydrogen and nitrogen. Spark timing for maximum performance must be advanced slightly for ammonia but sensitivity to spark timing is little greater than with hydrocarbons. Increasing the cylinder wall temperature aids in effecting successful and reliable operation. The maximum theoretically possible indicated output using ammonia vapor is about 77% of that with hydrocarbon. Specific fuel consumption increase twofold at maximum power and 2-1/2 fold at maximum economy when using ammonia as a replacement for hydrocarbon.

The influence of nonequilibrium in the expansion gases of spark ignition engines has been studied theoretically to determine how power output and exhaust gas composition might be affected. Comparing a gas which is frozen in composition during expansion with a composition which continuously is in equilibrium shows the difference in expansion work can be as large as 10%. Maximum influence is in the fuel-air ratio range of chemically correct mixture. It was found that carbon monoxide and nitric oxide concentrations in the exhaust more nearly reflect the frozen composition than the equilibrium expansion. This is particularly true for the range of mixture ratios -- from lean to chemically correct.

As a means toward further improving the Curtiss-Wright rotary combustion (RC) engine series, test work during the past year has concentrated on the two-rotor 200 hp class liquid cooled engine, application testing of this engine in vehicles, boats, and engine generator sets, and evaluation of basic component and engine design studies covering aircooled, fuel injected, and spark ignited engines with heavy fuels for aircraft and other applications. Field tests have established acceptable automotive, marine, and power generation performance levels. In addition, operation on heavy fuels and aircooling at high-performance levels has been demonstrated, with attendant basic engine improvements. This paper reviews the recent development and test program at Curtiss-Wright aimed at bringing the RC engines closer toward production engine status.

This paper describes the reduction in observed unburned exhaust products when a spark ignition engine is operated with the I.F.P. process of variable mixture strength. The principle of the process is first explained; then the influence of the mixture strength on carbon monoxide and hydrocarbons in exhaust gases is shown. A comparison of normal carburetion processes and I.F.P. process, based on a stratification of the intake gases, shows how the extension towards the lean mixtures of the limit of the mixture strength results in the reduction of unburned products in the exhaust gases.

A nondimensional representation for a four stroke spark ignition engine was obtained that included the transient charging and exhaust effects. Two basic advantages accrued from this approach; the design and operating parameters that evolved from the nondimensional approach are truly basic in nature, which makes the computer solution more universally applicable to all engines. The inclusion of the transient effects made the representation more realistic and of particular value in the study of engine breathing problems. The effect of valve timing, cam design, valve dimensions, and inlet temperature on engine performance were studied with the computer model.

This paper sets up a mathematical model for measuring end-gas temperatures in spark ignition engines and the compression temperatures in compression ignition engines. The model is based on a modified thermodynamic equation, for which the nonlinear least square method is used to fit the parameters.

This paper deals with the commercial version of the spark-ignition engine. Methods are discussed whereby future engines may be increased in horsepower output and reduced in weight and size. Variable compression methods, charge stratification, fuel injection, and turbocharging are discussed as means of increasing engine output. Unconventional engines are discussed, but it is felt they do not have any appreciable application to commercial spark-ignition of the future. It is concluded that commercial spark-ignition of tomorrow will remain essentially as we know it today except that it will be more compact and will weigh less per horse-power or per cubic foot.

Studies were conducted using spark-ignited reciprocating engines to evaluate ammonia as an alternate fuel for certain military applications. Conventional engines were found to perform poorly on ammonia. Several practical methods for improving engine performance while burning ammonia are described which include increased spark energy, increased compression ratio, engine supercharging, and hydrogen addition to the fuel. Dissociation of ammonia was investigated as a practical means for supplying hydrogen to an engine. The study indicates that satisfactory engine performance can be obtained while burning ammonia. Auxiliary equipment and controls necessary for vehicular use will require development.

Good fuel economy has long been emphasized as the goal of vehicle power trains. Gas turbines, in an effort to equal the fuel economy of diesel and spark ignition engines, have compromised vehicle response. The hydrostatic transmission mated to a gas turbine gives a fresh approach to improving vehicle response while allowing the turbine to retain its good efficiency. The hydrostatic transmission benefits both free and fixed turbine power trains.

Three factors are of consequence when considering the comparative performance of alcohols and hydrocarbons as spark ignition engine fuels. These are: relative amounts of products of combustion produced per unit of inducted charge, energy inducted per unit of charge, and latent heat differences among the fuels. Simple analysis showed significant increases in output can be expected from the use of methyl alcohol as compared to hydrocarbon and somewhat lesser improvement can be expected from ethyl alcohol. Attendant increases in fuel consumption, disproportionate to the power increase, can also be predicted. More sophisticated analysis, based upon thermodynamic charts of combustion products, do not necessarily improve correspondence between prediction and engine results.

This paper discusses the combustion problems in various types of commercial vehicle engines. Rate of pressure rise and peak pressure control the design of the engine structure and the amount of air which can be burned. These factors limit the design and use of hybrid engines. Knock is discussed in relation to spark-ignition and compression-ignition engines on which new data are presented. New data indicate that changes in fuel-air ratio and spark advance which lower spark plug and deposit temperatures increase exhaust valve temperatures. Ash deposits, spark plugs, and exhaust valves are most likely to trigger preignition.

The “Dyna-Star” engine concept makes possible very compact, lightweight designs for both diesel and spark ignition engines within the area of current industrial practice, and with low manufacturing cost potential. This article describes in detail the various configurations examined to date and provides pertinent development data concerning size, weight, and performance characteristics of the Dyna-Star engines currently being developed in the Thiokol laboratories.

The combustion process in a spark ignition engine has been investigated in terms of flame development and subsequent propagation throughout the combustion chamber. Multiple ionization gaps coupled with advanced electronic instrumentation were used to detect progression of the flame in three dimensions. New information concerning knocking combustion has shown that there is no need to postulate any discontinuity in the rate of the combustion process to explain the occurrence of knock.

The ignition of very lean fuel-air mixtures by means of a turbulent flame, and the operation of a stratified-charge engine employing a single, auxiliary combustion chamber to serve that requirement are considered. A suitable modification of the CFR engine demonstrates the principle. Results indicate a greater development potential to efficiently convert hydrocarbon fuels to mechanical energy at part loads than that which exists for the modern, conventional, spark-ignition engine. The system described is shown to be inherently rough from the combustion standpoint, but is less fuel sensitive, and does not recognize antiknock quality as a factor of major importance. The effect of combustion chamber and fuel system design parameters on part-load economy, full-load combustion roughness, and air utilization are discussed in terms of experimental data. The relationship of the turbulent-flame engine to other experimental stratified-charge designs is briefly discussed.

A comprehensive cycle analysis has been developed for four-stroke spark-ignited engines from which the indicated performance of a single cylinder engine was computed with a reasonable degree of accuracy. The step-wise cycle calculations were made using a digital computer. This analysis took into account mixture composition, dissociation, combustion chamber shape (including spark plug location), flame propagation, heat transfer, piston motion, engine speed, spark advance, manifold pressure and temperature, and exhaust pressure. A correlation between the calculated and experimental performance is reported for one engine at a particular operating point. The calculated pressure-time diagram was in good agreement with the experimental one in many respects. The calculated peak pressure was 10 per cent lower and the thermal efficiency 0.8 per cent higher than the measured values. Thus this calculational procedure represents a significant improvement over constant volume cycle approximations.