Howard Prize Essay 1967: STEAM ENGINES THAT WORK WITHOUT BOILERS

Howard Prize Essay 1967: STEAM ENGINES THAT WORK WITHOUT BOILERSAuthor(s): CLIFFORD HALLSource: Journal of the Royal Society of Arts, Vol. 116, No. 5137 (DECEMBER 1967), pp. 61-66Published by: Royal Society for the Encouragement of Arts, Manufactures and CommerceStable URL: http://www.jstor.org/stable/41371803 .

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Howard Prize Essay 1967

STEAM ENGINES THAT WORK

WITHOUT BOILERS*

by CLIFFORD HALL

For 200 years the steam engine has served mankind. It still continues to do so as it forms the link between heat energy and rotational or electrical energy.

I refei to electrical generating plants, be they nuclear, or coal or oil fired. These large applications make use of the steam turbine, which for big plants is

unrivalled. The position is not so distinct for the lower powers, say below 250 h.p. At these

lower powers the reciprocating steam engine can operate as efficiently as the steam turbine and has advantages such as speed range, cost and maintenance.

Steam engines of all types, reciprocating and turbine, have a big disadvantage -

they all need boilers. Boilers can be efficient devices, but at the best, they are costly, bulky, and above all, dangerous, unless made of the best materials and given expert maintenance and operation. In large plants elaborate safety devices and skilled operatives make the boiler hazard tolerable, but in small units it is a serious problem, as boiler insurance costs demonstrate.

I believe that for certain applications the reciprocating steam engine, divorced from the boiler hazard, has still a part to play in the world to-day. With this object in mind, means by which a steam engine could run, without á boiler, were sought and found, and I now propose to describe the broad principles of such an engine.

If water is converted into steam at atmospheric pressure, one unit of water will produce 1,700 units of steam or, in other words, a cubic inch of water will produce a cubic foot of steam. Under certain conditions this expansion can be extremely rapid and violent, and it is this 'explosive' expansion that is used in what I will now describe as the Hall engine.

From the outset it must be emphasized that the Hall engine does not require a boiler of any description and that the steam is generated inside the working cylinder; the boiler hazard is thus eliminated.

For a steam engine to be efficient it must be capable of reasonably high speed, and the Hall engine (which can exceed 3,000 r.p.m.) was designed to accept water, convert it into steam, utilize the expansion on the power stroke and eject the spent steam on the exhaust stroke in one revolution. This means that at 1,500 r.p.m. the above mentioned processes must take place twenty-five times per second.

How has this been achieved? The problem was one of heat exchange and, in order to explain this, it would help if 1 described the problem in reverse, that is the problem of getting rid of heat from water instead of accepting heat, the same principle applying. *Patent No. 923,235. Sec November Journal for announcement of this award.

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JOURNAL OF THE ROYAL SOCIETY OF ARTS DECEMBER 1 967 The first car I ever drove was a 6 h.p. De Dion Bouton 'Populaire' made around

1903. This car had a single cylinder petrol engine of 90 mm bore and no mm stroke and was reputed to develop its 6 h.p. at about 1,700 r.p.m. To cool this one cylinder required the following :

A bulk head mounted water tank holding about 3 gallons (I quote from memory). At least 12 ft. of f-in. diameter gilled copper tube, which formed the radiator. A centrifugal water pump. Several feet of copper connecting pipes.

Most people would agree that this was a lot of water and equipment to cool one cylinder, and the reason, I believe, is that the water was at all times in a large mass moving at a low speed. As car engine speeds and pressures (with consequent higher temperatures) rose, the honey-comb radiator was introduced. This gave large surface area for small volume. In other words, the water was in the form of a thin film over a large area. The modern film core radiator achieves the same object.

From the foregoing it is apparent that for the rapid dissemination or assimilation of heat, water must be in a thin film over the largest practicable area.

There is another aspect that is relevant to the problem. It is known as the 'Spheroidal Phenomenon' and is a characteristic of water in contact with a hot surface.

If water is sprayed on to a very hot surface it does not immediately form steam and disappear as such, but forms bubbles of steam that dance and dither about the hot surface and take an appreciable time to vanish as steam. Steam is a bad conductor of heat and a hot surface covered with bubbles of steam is, in effect, thermally insulated.

It was therefore decided that in order for an engine to operate efficiently these things were essential:

(a) The injected water ßhould be squeezed into a narrow, heated cavity of high internal area but low volume.

( b ) The injected water should be ironed out to break the bubbles and, given a high degree of turbulence, to deform the bubbles and minimize bubble formation.

Bearing the above points in mind an engine was designed to incorporate them. The practical layout will now be given.

The Hall engine to be described is a single acting, single cylinder horizontal type with a poppet type exhaust valve mounted in the head. (See Figure 1.)

The piston, which may be domed or flat -topped has a very small clearance from the cylinder head at the extremity of its stroke, and water, wet steam or bubbles, trapped between the piston and the cylinder head, will be ejected or squeezed out radially at high speed. A cavity is placed to receive the displaced water. As the metal forming the cylinder head is heated externally to a high temperature (say 400°C.), the water forced into the cavity forms superheated steam which expands and drives the piston away from the cylinder head, this

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DECEMBER 1967 HOWARD PRIZE ESSAY

Figure i

being the power stroke. Just before the piston reaches the limit of its outward stroke the exhaust. valve opens and the piston ejects the spent steam and continues to do so until just before the piston reaches T.D.C, (the point at which the piston is closest to the cylinder head). This is the end of the exhaust stroke. Water is injected towards or in the path of the piston and is timed to occur from 50 to 45o before T.D.C. , the exact point depending upon the engine speed. The faster the engine is running the earlier the moment of injection.

It will thus be seen that the Hall engine has: (a) A power impulse every revolution. (Ò) That no inlet valve is required as no steam is admitted. (c) That the steam is used 100 per cent expansively. ( d ) That the steam is generated as required and can expend its energy upon

the piston. There is, therefore no hazard as is the case with a boiler under pressure.

(e) That as the head is heated externally, any form of heat (oil, gas, solid, solar, chemical, nuclear, etc.) is suitable.

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JOURNAL OF THE ROYAL SOCIETY OF ARTS DECEMBER 1 967

(/) That as the water is injected near the end of the exhaust stroke, the back pressure is low and the energy absorbed, by the injection pump, is very small compared with that necessary for the feed pump of a conventional steam engine, that has to pump water into a boiler against full boiler pressure.

( g ) That the temperature of the head (up to 500°C.) is very high, producing superheated steam and preventing condensation in the cylinder.

In regard to the crankshaft, connecting rods, crank base, etc., the Hall engine is conventional ; the parts that do not follow general practice are as follows :

(1) The cylinder or cylinders are of stainless steel or cast iron with a hard chrome cylinder bore. This is because of the use of superheated steam and also to obtain compatibility with the piston material.

(2) The piston has metallized carbon lands and rings, as the running temperature precludes the use of conventional lubricants. This material has been used for many years in connection with high duty air compressors, where the use of oil is dangerous. Cylinder lubrication of the Hall engine is, therefore, 'built in'.

(3) The cylinder head is made of metal with high thermal conductivity, such as clad copper or bronze. It is provided with external finning to increase the heat intake.

(4) The Patent covers the thermal insulation of the cylinder head from the cylinder barrel. This is not necessary on small engines.

(5) All positive displacement engines using steam are liable to hydraulic lock from condensed steam. The Hall engine incorporates an automatic pressure relief valve; also, the same valve is designed to break any . vacuum that might be formed if the engine was rotated with the cylinder head cold.

(6) Valves are either poppet or balanced pressure piston valves. Poppet valves may be mounted in the head or on the cylinder side. Piston valves are located on the cylinder side. The cavity necessary, with side mounted valves, is masked by the piston at the extremity of the stroke. This is to isolate the valve cavity during the 'squeeze' period at T.D.C, (the time of steam generation).

(7) The injection pump is of the 'jerk' ram type and is of variable stroke. The engine speed is governed by the amount of water injected and also by the heat input. The water injection and the heat input controls may be coupled, as it is obvious that the larger the amount of water injected, the more heat will be required to evaporate it.

(8) As the engine is single-acting, a flywheel is required, but as there is no compression, this need not be of excessive weight or size.

(9) The injection nozzle or nozzles are plain jet with a check valve, although the latter item is not essential. Thermal insulation of the injection nozzles is desirable, as it is very important that the water injected is not too near boiling point. A coarse jet is preferable. There is no need to provide a fine atomized spray as in a diesel type of engine.

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DECEMBER 1967 HOWARD PRIZE ESSAY

HALL ENGINE TIMING DIAGRAMS Figure 2

The engine so far described has been of the single cylinder type. There is, of course, no reason why the principle should not be applied to multi -cylinder engines. If multiple expansion (compound) engines were required, it is suggested that the first stage or cylinder should be according to my invention, followed by further expansion in conventional cylinders and finally exhausting to a condenser. In such a lay-out, the hot heating gases leaving the first stage could be utilized to reheat the later stages operating at lower pressures and temperatures.

Because it is economic to carry out initial experiments on a small scale and owing to limitations of equipment, the engines so far made have been small. As a basis of comparison, a conventional model steam engine of say f-in. bore by i ¿-in. stroke (double-acting) will, at a steady boiler pressure of 30 p.s.i., give an electrical output of 2 watts.

One of the engines I have made, according to my invention, has a bore of f -in. and a stroke of § in. (single-acting) and will give 2 watts output. Both engines have a similar heat input.

It should be mentioned that the engines I have made will, if provided with heat and water, run for long periods. At a recent exhibition one of my small engines, driving a four-way display rig, ran continuously for hours on each of two days.

Of the Hall engines I have made, some are of the 'Uniflo' pattern. In the conventional 'Uniflo' steam engine, steam is admitted at T.D.C, and exhausts by means of ports in the cylinder wall. As the Hall engine does not require inlet ports or valves, no valves at all are required other than the ports in the cylinder wall controlled by the piston. This makes a very simple engine with few working parts.

There is, however, a disadvantage in the small 'Uniflo' engine, as follows. As the cylinder exhaust ports are uncovered by the piston at approximately 75 per cent of the outward or power stroke, it follows that there will be compression of the cylinder contents on the inward stroke. This raises the pressure in the cylinder

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JOURNAL OF THE ROYAL SOCIETY OF ARTS DECEMBER 1 967 and that puts up the boiling point and more heat is required than in a normal valved engine.

It is interesting to note that in small internal combustion three port two strokes (the I.C. counterpart of the steam 'Uniflo' engine) any exhaust gases left in the cylinder dilute and lower the quality of the charge being compressed. In steam ('Uniflo') engines any residuum is still steam that has done work and lost heat and only requires re -heating.

In large 'Uniflo' engines a relieving valve may be used to drop the pressure, but this is hardly warranted in small engines.

A Hall engine that I have made on the 'Uniflo' principle, with a bore of ̂ in. and a stroke of § in. (single-acting), will give an output of 1 watt from a small toy alternator.

It is thought that the Hall engine is suitable for small industrial applications, especially in under -developed countries, by virtue of its extreme simplicity and the suitability of any form of fuel. If solar heat is to be exploited, the Hall engine is particularly suitable, as the heat is required in a local area and not spread over the bulky heating surface of a boiler.

The engine is already developed as a toy or model that is quite safe and easy to manufacture.

Experts have calculated that at the present and anticipated rates of consumption, fuel oil will only last another thirty to forty years, and as scarcity approaches, prices will inevitably increase. Some form of prime mover that is not particular regarding the type of fuel or heat it requires, will have to be found. It is suggested that the Hall engine is a possible answer.

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Howard Prize Essay 1967: STEAM ENGINES THAT WORK WITHOUT BOILERS

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