DUNN'S PATENT CALORIC ENGINE.

(Patent dated December 26, 1850. Specification enrolled June 26, 1851.)

Specification.

THIS invention consists in producing motive power by the application of caloric to atmospheric air, or other permanent gases or fluids susceptible of considerable expansion by the increase of temperature, -the mode of applying the caloric being such that, after having caused the expansion or dilatation which produces the motive power, the caloric is transferred to certain metallic substances, and again retransferred from these substances to the acting medium at certain intervals, or at each successive stroke of the motive enginethe principal supply of caloric being thereby rendered independent of combustion or consumption of fuel. Accordingly, whilst in the steam engine the caloric is constantly wasted by being passed into the condenser, or by being carried off into the atmosphere, in the improved engine, the caloric is employed over and over again, enabling me to dispense with the employment of combustibles, excepting for the purposes of restoring the heat lost by the expansion of the acting medium, and that lost by radiation also, and for the purpose of making good the small deficiency unavoidable in the transfer of the caloric.

Having thus stated the object and general character, I will now proceed to describe the structure of the improved engine for producing motive power, reference being had to the engraving. Figs. 1 and 2 represent longitudinal sections of the engine, both being alike in all essential points, differing only in part of the detail, as will be clearly seen by the following description. I will first describe fig. 1:-A and B are two cylinders of unequal diameter, accurately bored and provided with pistons a and b, the latter having air-tight metallic packing rings inserted at their circumferences. I call A the supply cylinder, and B the working cylinder; a' piston rod attached to the piston a, working through a stuffing box in the cover of the supply cylinder. C is a cylinder with a spherical bottom attached to the working cylinder at cc: I call this vessel the expansion heater; DD rods or braces connecting together the supply piston a and the working piston b. E is a self-acting valve opening inwards to the supply cylinder; F a similar valve opening outwards from said cylinder, and contained within the valve box f. Gis a cylindrical vessel, which I call the receiver, connected to the valve box f by means of the pipeg; H a cylindrical vessel with an inverted spherical bottom: I call this vessel the heater. Ja conical valve supported by the valve stem j, and working in the valve chamber J', which chamber also forms a communication between the expansion heater C and heater H by means of the passage h. K is another conical valve supported by the hollow valve stem k, and contained within the valve chamber k. Land M two vessels of cubical form, filled to their utmost capacity, excepting small spaces at top and bottom, with discs of wire-net or straight wires closely packed, or with other small metallic substances, or mineral substances such as asbestos, so arranged as to have minute channels running up and down. I call these vessels L and м, with their contents, regenerators. Il, mm, pipes forming a direct communication between the receiver G and the heater H, through the regenerators. NN two ordinary slide valves arranged to form alternate communications between the pipes Il and mm and the exhaust chambers O and P, on the principle of the valves of ordinary high-pressure steam engines. nn valve stems working through stuffing boxes n'n'. p pipe communicating between the valve chamber k and exhaust chamber P. o' pipe leading from exhaust chamber O. Q pipe leading into the receiver G, provided with a stop-cock 9. RR fire-places for heating the vessels H and C. r,r,r, r, flues leading from said fire-places, and terminating at r'. S a cylindrical vessel attached to the working piston b, having a spherical bottom corresponding to the expansion vessel C. This vessel S, which I call the heat-intercepting vessel, is to be filled with fire clay at the bottom, and ashes, charcoal, or other non-conducting substances towards the top, its object being to prevent any intense or injurious heat from reaching the working piston and cylinder. TT brickwork or other fireproof material surrounding the fire-places and heaters. I now proceed to describe fig. 2. All corresponding parts in this figure are marked by similar letters of reference as in fig. 1; it will, however, be well briefly to repeat the description of the same: -A supply cylinder; a supply piston; B working cylinder; b working piston; C expansion heater; C junction of working cylinder and expansion heater; D rods connecting the supply and working pistons; E inlet valve of supply cylinder; e valve chamber of the same, Foutlet valve of supply cylinder, and fits chamber; G receiver, g pipe connecting the same to outlet valve chamber f; L regenerator, I passage between the same and receiver; l' passage between the regenerator and the expansion heater; N' slide valve, n stem or spindle for working the same; O exhaust chamber under the slide valve; O' outlet pipe; Q pipe leading into receiver, q stop-cock in the same; R fire-place; r, r, r, r, flues leading from said fire-place; exit of said flues; T brickwork surrounding the fire-place and flues; U rock shaft, supported at both ends by appropriate pillar-blocks; uu' crank lever or arm attached to the said rock shaft; u' link connecting said arm to the working piston b; V another crank lever or arm attached to the extreme end of the rock shaft; a crank shaft or axle, having a crank Y firmly attached; v connecting rod connecting the arm V to the crank pin y of crank Y; y' pillar blocks supporting the crank shaft æ; ZZ represent the circumference of a fly-wheel, paddle-wheel, propeller, or other rotary instrument to be worked by the engine. Fig. 3 represents a sectional plan of the fig. 1, and fig. 4 a sectional plan of fig. 2. Before describing the operation of the improved engine, it will be proper to observe that the piston rod a' only receives and transmits the differential force of the piston b, viz.,

the excess of its acting force over the reacting force of piston a': it will also be proper to observe that this differential force imparted to said piston rod may be communicated to machinery by any of the ordinary means, such as links, connecting rods, and cranks; or it may be transmitted directly, for such purposes as pumping or blowing. I have further to observe that the conical valves K and J may be worked by any of the ordinary means, such as eccentrics or cams, provided the means adopted be so arranged that the valve K will commence to open the instant that the piston b arrives at the full up-stroke, and be again closed the instant the piston arrives at full down-stroke, whilst the valve J is made to open at the same moment, and to close shortly before or at the termination of the up-stroke. In like manner the slide valve N' is to open and close as the piston b arrives respectively at its up and down stroke, similar to the slide valve of an ordinary high-pressure engine. It will be seen that the link u", like the piston rod a', only transmits the differential or useful force of the piston b.

Having thus described the construction of the engine, I will now proceed to describe the manner in which the same is to be put into operation, reference being first had to fig. 1. Before starting, fuel is put into the fireplaces RR, and ignited, a slow combustion being kept up until the heaters and lower parts of the regenerators shall have been brought to a temperature of about 500°. By means of a hand pump, or other similar means, atmospheric air is then to be forced into the receiver G, through the pipe Q, until there is an internal pressure of some eight or ten pounds to the square inch. The valve J is then to be opened, as shown in the engraving, the pressure entering under the piston b will cause the same to move upwards, and the air contained in A will be forced through the valve F into the receiver. The slide valves NN being by means of the two stems nn, previously so placed that the passages 11 are open, the air from the receiver will pass through the wires in L into the heater H, and further into C, the temperature of the air augmenting, and its volume increasing as it passes through the heated wires and heaters. The smaller volume forced from A will in consequence thereof suffice to fill the larger space in C. Before the piston arrives at the top stroke, the valve J will be closed, and at the termination of the stroke the valve K will be opened; the pressure from below being thus removed, the piston will descend, and the heated air in C will pass through k, p, P, and m into the regenerator M and in its passage through the numerous small spaces or cells formed between the wires part with the caloric, gradually falling in temperature until it passes off at O', nearly deprived of all its caloric. The commencement of the descent of the piston a will cause the valve F to close, and the valve E to open, by which a fresh charge of atmospheric air is taken into the cylinder A. At the termination of the fall down stroke, the valve K is closed and the valve J again opened, and thus a continued reciprocating motion kept up. It will be evident that after a certain number of strokes the temperature of the wires or other matter contained in the regenerators will change,-that of M will become gradually increased, and that of L diminished. The position of the slide valves NN should therefore be reversed at the termination of every fifty strokes of the engine, more or less, which may be effected either by hand or by a suitable connection to the engine. The position being by either of these means accordingly reversed to that represented in the engraving, the heated air or other medium passing off from C, will now pass through the partially cooled wires in L, whilst the cold medium from the receiver will pass through the heated wires of M, and on entering H will have attained nearly the desired working temperature. In this manner the regenerators will alternately take up and give out caloric, whereby the circulating medium will principally become heated independently of any combustion after the engine shall have been once put in motion. Having thus with special reference to fig. 1, described the manner of putting the improved engine into operation, I have now to notice that the said engine, as represented in fig. 2, is operated precisely in the same manner, excepting that the regenerator is arranged in a single vessel, and that the metallic substances therein take up the caloric from the circulating medium that leaves the working cylinder or vessel C, and returns the same to the circulating medium that enters the working cylinder at each stroke of the engine, instead of transferring and retransferring the caloric at intervals, as shown in fig. 1. The manner in which the differential or useful upward force of the working piston b (fig. 2) in conjunction with its descending power, caused by gravity, are made to impart rotary movement to the crank-shaft z becomes selfevident on examining the disposition of the working gear of the engine, as shown in the engraving. It is particularly worthy of notice that the relative diameter of the supply and working cylinder will depend on the expansibility of the acting medium employed; thus in using atmospheric air or other permanent gases, the difference of the area of the pistons may be nearly as two to one, whilst in using fluids (such as oils, which dilate but slightly), the difference of area should not much exceed one-tenth. I have next to notice that in employing any other medium than atmospheric air, it becomes indispensable to connect the outlet pipe O', and the valve-box e of the outlet valve E, as indicated by dotted lines in both-figures, these dotted lines representing the requisite connecting pipe. The escaping air or fluid at O' will, when such a connecting pipe has been applied, furnish the supply cylinder independently of other external communication, and the acting medium will perform a continuous circuit through the machine under this arrangement, the operation being in other respects as before described. It is evident that the several parts composing the improved engine may be arranged in various ways, and that the external form thereof may be greatly changed whilst its principle of operation remains substantially as I have ascertained and described. It is also evident that the working cylinder may be placed horizontally or otherwise, and that it may be made double acting, and that a heat-intercepting vessel may be applied at each end of the working piston, and also an expansion heater at each end of the working cylinder. I do not, therefore, confine myself to the exact form represented in the engraving, but I claim as the invention the substantial features of the devices I have described as new, and by which I secure great and beneficial results; and particularly I claim as the invention :

First. I claim the structure which I call the regenerator, by which I effect a transfer of the caloric contained in the air or other circulating medium that passes off from the working cylinder to a series of discs of wire net, or to other minute metallic or mineral substances, for the purpose of being again retransferred to the air or other circulating medium that enters the working cylinder, whether said structure be arranged that the metallic or mineral substances are made to take up and again return the caloric at each successive stroke of the working piston, as in fig. 2; or whether it is so arranged that the transfer and retransfer of the caloric takes place at intervals, as in fig. 1; or whether said structure is arranged in any other manner for the purpose of accomplishing substantially the purposes hereinbefore mentioned.

Second. I claim the combination of the expansion heater with the working cylinder, by which the fall of temperature consequent upon the expansion of the air or other circulating medium during the upward movement of the working piston becomes restored, and by which also the force of said piston becomes augmented beyond what it would be if the acces sion of caloric effected by the expansion heater did not take place.

Third. I claim the heat intercepting vessel attached to the working piston, by which any injuriously high temperature is prevented from reaching the packing of said piston and by which also the very desirable end is attained of presenting at all times surfaces of uniform high temperature to the acting medium under the working piston.

Fourth. I claim the inverted position and open ends of the working and supply cylinders, as represented in the engraving.

Fifth. I claim the direct attachments of the working and supply pistons by which not only the acting and re-acting forces may be uniformly distributed over the area of each piston, but by which also the entire differential power of the working piston is rendered available, less only the friction of the packings.

ON THE CONSTRUCTION OF STEAM BOILERS AND THE CAUSES OF THEIR EXPLOSIONS. BY WM. FAIRBAIRN, ESQ., C.E., F.R.S. (Concluded from page 30.)

Under such circumstances what could be expected but a blow up? A madman rushing with a lighted match into a powder magazine could not act with greater insanity. Such, however, has been the case, and that arising from want of thought, or, what is worse, from the total absence of knowledge which it was the duty of his employer as well as himself to have possessed.

I have on former occasions stated that I am not an advocate for Legislative interference either in the construction or management of boilers; but seeing the dangerous tendency of these vessels when placed under the control of ignorance and incapacity, I would forego many considerations to encourage a more judicious and intelligent class of men than has hitherto been employed in the care and management of steam and the steam engine. The reforms necessary to be introduced may be done by the owners of steam engines, steam boats, railways, and others engaged in the use and application of this important element. A desire to enforce more judicious and stringent regulations, to remunerate talent, and to employ only those whose good conduct and superior knowledge entitle them to confidence, is the only sure guarantee of public safety and the prosperity of the employer.

Lastly. The remedies applicable for the prevention of accidents arising from explo. sion.

Having noticed in the foregoing remarks most of the causes incident to boiler ex

plosions, it now only remains to draw such inferences as will point out the circumstances which it is desirable to cultivate, and others which it is desirable to avoid. These circumstances I have endeavoured to class in such way as to bring the subject prominently forward, and to point out under each head; first, the causes which lead to accident; and secondly, the means necessary to be observed in avoiding it. In a general summary it may not be inexpedient briefly to recapitulate these statements, in order to impress more forcibly upon the mind of those concerned the necessity for care and consideration in the use of one of the most powerful agents ever placed at our disposal.

One of the most scientific nations of Europe places the greatest confidence, as a means of safety, on the use of a fusible metal plate over the furnace. These plates are alloys of tin and lead with a small portion of bismuth, in such proportions as will ensure fusion at a temperature something below that of molten lead. In France, the greatest importance is attached to these alloys, and in order to ensure certainty as to the definite proportions, the plates are prepared at the royal mint, where they may be purchased duly prepared for use. In this country these alloys are not generally in use; but in this respect I think we are wrong, as boiler explosions are not so frequent in France as in this country, and high-pressure steam, from its superior economy, is more extensively