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Development of High-Efficiency Rotary Engines

Combustion engines are typically only 20-30% efficient at part-load operating conditions, resulting in poor fuel economy on average. To address this, LiquidPiston has developed an improved thermodynamics cycle, called the High-Efficiency Hybrid Cycle (HEHC), which optimizes each process (stroke) of the engine operation, with the aim of maximizing fuel efficiency. The cycle consists of: 1) a high compression ratio; 2) constant-volume combustion, and 3) over-expansion. At a modest compression ratio of 18:1, this cycle offers an ideal thermodynamic efficiency of 74%. To embody the HEHC cycle, LiquidPiston has developed two very different rotary engine architectures ? called the ?M? and ?X? engines. These rotary engine architectures offer flexibility in executing the thermodynamics cycle, and also result in a very compact package. In this talk, I will present recent results in the development of the LiquidPiston engines. The company is currently testing 20 and 40 HP versions of the ?M?
Technical Paper

Pistons and Oil-Trapping Rings for Maintaining an Oil Seal

PROVISION is made, in the piston and rings described by the author, for an adequate flow of heat from all parts of the piston-head to the cylinder-wall by means of adequate cross-section of aluminum alloy in the head and a tongue-and-groove type of piston-ring structure which provides a greater amount of surface than is usual for heat transfer. A labyrinth oil-seal is provided which aids heat transference and prevents leakage past the piston-rings, and the heat transfer is said to be such that the heat does not destroy the oil seal between the piston and the ring. Charts are included that show the effects in reduced temperatures, oil consumption and gas leakage with the construction described. Attention is given also to a skirt construction most suitable to use with the piston-head and rings described.
Technical Paper

Engine Cooling

FROM 25 to 35 per cent of the heat energy of the fuel inducted into the cylinders of an internal-combustion engine must be eliminated by the cooling system. As this waste requires the expenditure of energy, the devising of an efficient cooling system is imperative. The author, who is a leading American authority on engine problems, discusses the theory of liquid-cooling, gives heat-transfer and temperature-balance equations that must be satisfied and points out the three interrelated variable factors that must be incorporated in their most economical relation. The cooling system must be studied as a whole, rather than from the standpoint of any particular unit. Some commonly held beliefs regarding fans, fuel-pumps and oil-temperature control are controverted. Five elements necessary for an efficient cooling system are enumerated.
Technical Paper

Fundamentals of Automotive Lubrication

SATISFACTORY performance of a lubricant depends upon characteristics of the lubricant, operating conditions and design of the device in which the lubricant is used. Applied lubrication requires a study of the relation among these factors in their effect upon performance. The authors treat journal bearings, ball and roller bearings and gears. Equations are given for journal bearings operating under various conditions of design, lubrication, friction and heat dissipation. The authors conclude that neither ZN/P nor PV alone is adequate as a measure of the power dissipated by a bearing, a composite relation involving both terms being required over a large part of the operating range. They show that each bearing has a minimum value of ZN/P below which it may get into the unstable region of thin-film lubrication and fail.
Technical Paper


The development of intake-manifolds in the past has been confined mainly to modifications of constructional details. Believing that the increased use of automotive equipment will lead to a demand for fuel that will result in the higher cost and lower quality of the fuel, and being convinced that the sole requirement of satisfactory operation with kerosene and mixtures of the heavier oils with alcohol and benzol is the proper preparation of the fuel in the manifold, the authors have investigated the various methods of heat application in the endeavor to produce the minimum temperature necessary for a dry mixture. Finding that this minimum temperature varied with the method of application of the heat, an analysis was made of the available methods on a functional rather than a structural basis.
Technical Paper


In the first part of the paper, a general quantitative comparison of air, water and oil-cooled cylinders is given as it relates to the subject of heat-transfer and temperature drop. Unfortunately, the discussion does not include experimental data, but the assumptions are stated clearly and a large range of values is covered in Table 2 so that any desired values can be chosen. A thorough and comprehensive discussion of the steam or the radio-condenser type of cooling is given under the headings of Steam Cooling Systems, Characteristics of Steam Cooling Systems, Cooling Capacity of Radiators Used To Condense Steam and Present State of Development. In the second part, an attempt is made to give a thorough but brief discussion of the performance or of the operating characteristics of radiators from the point of view of the car, truck or tractor designer. The cooling of aircraft engines is not considered.
Technical Paper


Annual Meeting Paper - The heat-dissipating properties of three types of radiator core have been investigated at the Mason Laboratory, Yale University. These include the fin-and-tube, the ribbon and the air-tube groups, so classified according to the flow of the water and the air. The ratio of the cooling surface to the volume is shown to be nearly the same in the fin-and-tube and the air-tube cores, while that of the ribbon core is somewhat greater. A formula is derived for computing the heat-transfer coefficient, which is defined as the number of heat units per hour that will pass from one square foot of surface per degree of temperature-difference between the air and the water and is the key to radiator performance, as by it almost any desired information can be obtained. When the heat-transfer coefficients have been found for a sufficiently wide range of water and air-flows the cooling capacity of a radiator can be computed for any desired condition.
Technical Paper

Combustion Control by Cylinder-Head Design

DETONATION and shock, the two principal barriers to increased compression, are subject to a degree of control which can readily make possible the use of compression ratios in the neighborhood of 6-1 on commercial fuel without objectionable effects and without sacrifice of output. Since detonation depends primarily upon the temperature attained by the residual unburned gas, it can be controlled by combustion-chamber design which intensifies the heat transfer from the unburned gas to the walls. The shock tendency, which originates in the pressure-time characteristic of combustion, can be controlled only by deliberate incorporation of the desirable anti-shock characteristic in the chamber design by a method of calculation which is explained in detail.
Technical Paper

Development and Application of HEATED WINGS

THIS report, a discussion of the design problems in heated surface anti-icing equipment, consolidates and compiles all of the heat transfer data known to be available from past experimentation and considered to be required for current and future designs. Consequently, the author believes that the discussion contained herein will be of assistance in some degree to designers and engineers confronted with problems relating to heated surface anti-icing. The report deals with a rapid means of calculating heated wing requirements, charts of heat transfer coefficients, a discussion of instrumentation techniques, and a method of calculating surface temperatures in dry air.
Technical Paper


ADEQUATE fuel feeding at altitude, these authors point out, is a matter of vapor elimination, either by preventing its formation or by removing it from the system in the event that its formation cannot be prevented. The effect of vapor is invariably to cause failure of the fuel flow if it forms in sufficient quantity in any part of the fuel system that lies between the fuel tank and the carburetor. This paper gives the results of a study of the conditions that bring about this type of fuel failure, and describes means of exploring the phenomena experimentally so that it can be ascertained in advance of manufacture if remedial steps are necessary. The greatly accelerated rate at which designs of military aircraft with increased performance have been developed, they explain, has added materially to the difficulty of feeding vapor-free fuel to the carburetors at the higher altitudes.
Technical Paper

The Influence of Engine Oils on Aircraft-Engine Performance

OIL cooling of aircraft powerplants is increasingly difficult. The weight and drag of the oil coolers necessary with the present maximum “Oil-in” temperature of 185 deg. fahr. (85 deg. cent.) are both decidedly objectionable. It appears possible to increase the “oil-in” temperature to about 220 deg. fahr. (104 deg. cent.) with oils which can be produced by the newer refining methods. The use of an “oil-in” temperature of 220 deg. fahr. would render possible a material reduction in weight, size and drag of oil coolers in comparison with present practice. Oils suitable for use at 220 deg. fahr. “oil-in” temperature would not be likely to cause a material increase of engine-starting difficulty, as they would only be used in summer when the shearing resistance of the oil has slight influence on engine starting. The approximate temperature cycle encountered by the oil in its passage through a modern aircraft-engine is discussed.
Technical Paper

High-Output Aircraft Engines

INDIRECT or liquid-cooled aircraft engines fit into the picture of future aircraft types better than do the direct or air-cooled engines, the authors contend. As reasons for their belief they draw attention to the small frontal area of this type; the heat capacity of the liquid in equalizing temperatures; and greater freedom in cylinder design because large heat-transfer surfaces are unnecessary. Rolls-Royce has been producing liquid-cooled aero engines for 23 yr, they announce, and has concentrated a large staff on installation problems. One of the results of this work, they report, has been the development of the interchangeable powerplant in which the engine-mounting auxiliaries and bulkhead form a complete detachable unit. These units, the authors explain, are interchangeable within 48 hr, and provide interchangeability between air-cooled and liquid-cooled engines.
Technical Paper


The development of air-cooled engines for aircraft never made much progress until the war, when the British attempted to improve the performance of existing engines by a series of experiments leading eventually to the development of aluminum cylinders with steel liners and aluminum cylinder-heads with a steel cylinder screwed into the head. The advantages of these constructions and the disadvantages of other types are discussed. Results are reported of tests at McCook Field on a modern cylinder-design of this type showing good results, that lead to the belief that large air-cooled engines will be produced in the near future, equal in performance to water-cooled engines of the same power.
Technical Paper

Ice Formation in Aircraft-Engine Carburetors

ICE formation in the carburetor must depend on, at least, the factors (a) volatility and heat of vaporization of the fuel; (b) mixture ratio; (c) humidity, pressure, and the temperature of the intake air; and (d) heat transfer between the carburetor and its surroundings, especially the engine, according to the authors. Small-scale and full-scale tests were made, descriptions of the seven fuels used and of the testing apparatus being given. The procedures for both sets of tests are outlined and the results are analyzed. Other subjects treated are the heat necessary to melt ice, and correlation with the A.S.T.M. distillation. Five conclusions are stated. Appendix 1 refers to calculation of the relation between intake and mixture temperatures when ice formation occurs. Appendix 2 treats of the construction of equilibrium-air-distillation curves for a series of supplied mixture ratios. Appendix 3 is concerned with engine operation near the danger zone and definition of border conditions.
Technical Paper

Fin and Cylinder-Baffle Design for Air-Cooled Engines

THE National Advisory Committee for Aeronautics has undertaken a research to determine the effect of the fundamental factors influencing the cooling of air-cooled radial engines. This paper presents some of the results of an investigation made to obtain information that can be used in the design of fins for the cooling of heated cylindrical surfaces in an airstream. An equation has been developed for calculating the quantity of heat dissipated by a given fin-design, using experimentally determined heat-transfer coefficients. The agreement between the quantity of heat dissipated, as determined by experiment and calculated by the equation, was found to be sufficiently close to justify its use. A method has been developed for determining the fin dimensions, utilizing a minimum of material for a variety of conditions of heat transfer, airflow, and metals.
Technical Paper

The Design of Metal Fins for Air-Cooled Engines

THIS paper gives the results of an analysis made to determine the proportions of aluminum and steel fins to dissipate maximum quantities of heat for several pressure differences across a finned cylinder. The power required to force the cooling air between the fins and the relative weights of the various designs are presented. The calculation of the heat flow in the fins is based on an experimentally verified, theoretical equation and the surface heat-transfer coefficients and pressure differences were taken from previously reported experiments. In particular, the analysis concerns fin proportions for minimum pressure drop, minimum power, and minimum weight.