US2536238A - Method of heat-recuperative power generation and apparatus therefor - Google Patents

Description

Jan. 2, 1951 A. M. THOMSEN METHOD OF HEAT-RECUPERATIVE POWER GENERATION AND APPARATUS THEREFOR Filed June 10, 1946 IN VEN TOR.

Patented Jan. 2, 1951 METHOD OF HEAT-RECUPERATIVE POWER GENERATIONAND APPARATUS THEREFOR Alfred M. Thomsen, San Francisco, Calif. Application J line 10, 1946-, Serial No. 675,657

2 Claims.

In general terms my process consists of a way of obtaining greater thermal efliciency in a reciprocating internal combustion motor by returning through heat recuperative functions a portion of the heat now lost in the exhaust gases to the power generating phase of the engine cycle. The general concept is, of course, not new, but until the advent of the gas turbine it has not come into general use. This latter device, through the absence of cooling water has concentrated such a large proportion of the heat waste in the exhaust that heat recuperation therefrom has become accepted practice.

Unfortunately, the standard types of heat recuperators, consisting of tubes within a shell with the hot gases passing counter-current to one another on opposit sides of the tube wall, are exceedingly inefficient per square foot of heat transmitting area. This means that the first cost of such a system is too great for the gain achieved when one-half of the total heat waste is represented by jacket water, such as is common practice in the reciprocating engine with its lubricated cylinder.

An entirely different aspect is presented when heat recuperation is introduced into the engine cycle itself. Manifestly, the only recuperator feasible under such a system is the heat accumulator, i. e., a large surface of conducting material which absorbs heat from the exhaust gases as they leave on the exhaust stroke, and in turn communicate this heat to the new air of combustion when aspirated on the initial or suction stroke. In this case there is no conduction of heat through a metallic wall, but a purely surface phenomenon of heat absorption and emission from the same surface traversed in turn by gases losing heat and absorbing heat.

Such a heat recuperator can be made a part of the engine assembly and is conveniently placed as a prolongation upon a cylinder head, or as an integral part of said cylinder head, the exhaust and suction valves being placed in the relatively cool gases that leave or enter the combustion chamber, by way of said accumulator. This assembly is represented in the drawing where I is the cylinder and 2 is the piston of an orthodox reciprocating engine. 3 is a tube packed with axial rods constituting the accumulator. 4 and 5 are the suction and exhaust valves respectively.

In operation the hot spent gases discharged through 5 must first pass through the accumulator 3 where most of their heat is retained. On the next stroke of the cycle the air entering through 4- must now pass through the heated packing of the accumulator and thus abstract the heat'stored on the exhaust stroke. Becoming heated it will expand and the weight of air in the working cylinder would becom correspondingly reduced; To avoid this undesirable feature the entering air, the arrow 6, must be pre-compressed so that the density in the working cylinder is enhanced instead of diminished.

The energy resident in said compressed air would manifestly be restored in expansion in the engine cylinder so there would be no change in the volume of gas leaving, the arrow 1, unless compression were raised to such a degree as to supercharge the engine.

Other arrangements of valves than that repre-. sented on the drawing would manifestly be possible but would have no special advantage. To have the valves situated at the coolest part of the assembly would seem most desirable, hence the present illustration. The salient feature of my invention is that the spent gases'drop their heat in an accumulator before they are discharged into the atmosphere, and that said heat is in turn communicated to the air entering the working cylinder in the succeeding cycle. In this manner the heat accumulator becomes a portion of the engine cycle.

Such a heat recuperative engine can with equal facility operate on a two-cycle or on a four-cycle basis, but the admission of fuel must be directly into the working cylinder on the power stroke as in the Diesel engine. By the use of the heat accumulator the temperature within the cylinder will becom so high that any admixed fuel in the entering air would immediately ignite. As the Diesel type is admitted to be the one having the highest thermal efficiency at present such a limitation is no disadvantage.

It is essential that the packing of the accumulator be of relatively good conducting power in order to facilitate the heat exchange. The end contiguous to the cylinder will become very hot but any great strength is not required. The material can therefore be selected from any of the numerous types of stainless steel now available.

The outer surface should, of course, be insulated againstheat losses.

The figure s has been placed upon the fuel inlet. Such fuel may be gaseous or liquid and will ignite spontaneously upon entering the superheated atmosphere of the working cylinder. Said injection of fuel will commence substantially with the power, or firing, stroke and will be cut off as soon as compatible with the power demand of the engine. This observation applies whether the engine operates upon a two cycle or on a four cycle basis.

Owing to the high temperature within the working cylinder less fuel will be required than that required without the use of a heat accumulator. Combustion will be more perfect for any unburnt fuel and surplus air will combine in the passage through the accumulator, and the heat thus generated will be conveyed to the entering air on the succeeding cycle. It will manifestly be possible to supercharge this engine to any extent desired by smply raising the pressure of the entering air, the only limitation in this rcspect being inherent in the ability of the engine to resist the heat and pressure thus generated.

Control over the heat .gradient within the accumuiator is furnished by an injection of water into the pre-compressed air after it leaves the compressor and before it enters the accumulator. s uchinjected water will at once be evaporated and a consequent drop in temperature will be eifected. Regulaton may likewise be obtained bypermitting atomized water to enter the compressor, at the start of compression or at intervals during compression, the final product being a mixture of steam and compressed air which will have the same effect in reducing accumulator temperature at the low temperature end as would a; single injection of water where previously specified. In the latter case, however, some power gain would be achieved through a more nearly iso-thermal compression of the air. 'As the compressor can be any conventional type it is not illustrated in the drawing. The figure 9 has been placed upon a jet device wherebywater can be injected into the precompressed air just before it enters into the heat accumulator. Such injection may be continuous or intermittent, at will, as it is self-evident that no harm would result from commingling said water with the spent gases after said spent gases had passed through the accumulator, the actual amount of water entering the accumulator being the determining factor in the operation.

Having thus fully described my invention, I claim:

1. The method of regenerative internal combustion which comprises: Burning fuel in preheated, pre-compressed air within an internal combustion motor; converting a part of the heat thus generated into mechanical energy by expansion of the resultant products of combustion; storing heat still resident in said gases after expansion in a heat accumulator; preheating the pie-compressed air above specified by passing same through said heat accumulator thus returning stored heat to the engine cycle; and controlling the heat gradient Within said accumulator by the injection of water into the air of combustion prior to its entry into said heat accumulator.

2. In a reciprocating internal combustion motor, the combination of a combustion chamber closed by a movable piston, a heat accumulator so connected to said combustion chamber that it is traversed alternately in opposite direction by' the incoming air of combustion and by the out going spent gases remaining after said combustion, respectively, suitable Valves for the admis- S1011. of said air of combustion and for the discharge of spent gases, respectively, and means for injecting water into the air of combustion prior to its entry into the accumulator.

ALFRED M. THOMSEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,249,412 Joslyn Dec. 11, 1917 1,764,755 Skreen June 1'7, 1930 2,239,922 Martinka Apr. 29, 1941 2,439,379 Bergman Apr. 13, 1948'

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