Mechanical Progress - Tesla's Steam Engine

Much has appeared in technical journals concerning this engine, and considerable speculation has been indulged in regarding its practicability. The engine is a vibratory direct-generating one, or steam dynamo. The scheme is to produce electric current without rotary movement, friction or moving joints even, except of a steam piston, which directly vibrates or reciprocates — an armature between magnets. Mr. Tesla gives out the following particulars of his direct steam engine:

"I had gone considerably into the study of the practical aspects of the work which I was to present, and my notion was that I was touching upon something which would lay the foundations of a novel industry, perhaps of more than one industry. I dwelt chiefly on those features which possessed a purely scientific interest, my desire being to present the subject very modestly, as I was not quite sure of some of the questions involved. A prominent engineer came to me and said: 'Mr. Tesla, I want to tell you something, but I fear I may offend you.' I knew what was coming, and so I asked what it was. He said: 'Well, don't you work on steam engines. You have done some work in electricity. If you stick to it you will do some good work, but if you work on steam engines you are bound to fail.' Another, to whom I showed the advantage of doing away with complicated mechanism, and generating electricity directly, said, after he had watched it for a long time, 'Couldn't you apply this to rotating motion?'

"One of the first impulses which guided me was to produce an absolutely constant motion, which would be independent of any friction losses, or gravity, or temperature changes within very minute limits. I wanted to produce a positive motion, so that I might operate what I called a disruptive discharge coil. With a device which I invented, I was able to maintain a vibration with perfect constancy. The device consisted of a spring which required several tons of force to spring a certain distance, and which was constantly kept in vibration by steam pressure or air pressure. In the beginning I used springs of tempered steel. These steel springs would break, though they had a section of two or three square inches. So I resorted to air springs. The air springs would not break, but they had no constant resistance. Then I made the chambers of the air springs communicate with the outer air. This device yields a constant vibration; and as the force which is driving it is many tons, and the friction but a very small matter, it is unaffected by the pressure, so I have a constant vibration. This is the device which I believe will be used for many purposes — for instance, for governing all sorts of mechanisms, engines and so on. It contains much of interest for scientific men, because with it I am now able to produce currents of perfectly constant frequency. 

"When we look at a steam engine, and inquire where the power comes from that drives the steam engine, we will always find that the power comes from a little box, a cylinder with a piston in it, and all the other appurtenances are really but to keep it going. My first idea was to apply the motion of the piston, which is freely movable, to a magnetic field, to move a magnet or coil in a magnetic field, and so generate currents by this direct motion. We can reduce the weight of the engine for the same pressure and the same piston speed to 30 or if not of its weight. We do away with all mechanical frictions. 

"The engine designed according to my ideas has a mechanical efficiency of 99 per cent. In my construction the dynamo may consist of a simple coil of the magnet and a simpler coil, which is all immersed in the magnetic field. There is no useless wire, consequently dynamo and engine, if they are reduced considerably in weight, increase in efficiency. There is only one engine that can equal it in output, and that is the turbine. With the steam turbine we can obtain an enormous output, and that is the reason why the steam turbine, in my opinion, may be found a valuable adaptation for driving dynamos. In reciprocating mechanisms we can expand the steam at an enormous rate. It is perfectly practicable in these mechanisms, which I have been working up to obtain, if you want, a speed of 100 metres a second; and while do not contemplate producing such speeds, yet it is quite possible to do it. As I am enabled now to work without a packing, the expansion occurs at an enormous rate; and the engine being of such character that the exhaust can be readily reduced to pretty nearly the atmospheric pressure and the mechanical friction is reduced to such a small figure that we can raise the temperature of the steam very considerably.

"I am now preparing a boiler which will give me up to 350 pounds pressure. If we want to drive motors we must have a long stroke and a slow frequency; if we want to light lamps then we want a very short stroke and a very rapid motion. It is very important in this mechanism, in which the power depends on the square, to obtain as high a pressure as possible. It is more economical to produce rapid vibrations than low vibrations. But, so far as the economy of the dynamo and of the engine is concerned, it is better to produce a long stroke, because a long stroke means a high velocity. I think I am not mistaken in believing that we are going very shortly to have a means at hand of producing twice as much electricity from coal as we can produce at the present time. This is subject, of course, to a test, but I am quite confident it can be done."