Simon and Ravel. The Simon motor, of which only a very small number were constructed, was very interesting from the economy point of view. The explosion of the mixed gas was not allowed to take place suddenly, but proceeded gradually as the piston moved forward, and the heat which in the Otto engine is carried off by the water jacket, was made use of, as in the old Hugon motor, to vaporize a spray of cold water, and thus adding to the total force behind the piston. This process was so effective, that on shutting off the supply of gas the motor continued to revolve for a considerable period by means of the vaporized water. About 800 litres of gas were consumed and four litres of water per horse-power hour, a very good result. The Ravel motor used even less, about 500 or 600 litres only, but owing to the bad arrangement of the parts the mechanical efficiency was very low.
Such was the position of the gas engine in 1878. A standard type had been adopted and worked excellently. It merely required to be perfected in detail and simplified in order to make it still more economic, and capable of holding its own against its powerful rival the steam engine.
Many modifications of the Otto gas engine have appeared since that date, among the most important being those by—Dugald-Clerk, in 1879, a motor which compressed and exploded the gases once in every revolution; Lenoir, in 1833, the cylinder being cooled by currents of air; and in the same year appeared the Griffin gas engine, with a complete cycle of operations every three revolutions.
At the Antwerp Exhibition of 1884 several new types appeared, among them the Stockport engine by Andrews, and others by Koerting, Bénier, and Benz. In the same year a very good motor appeared, called the Simplex, constructed by Powell of Rouen (now Matter et Cie.), according to the plans of MM. Delamare-Deboutteville and L. Malandin. This engine was the subject of some litigation, the Otto people considering it an infringement of their patents, but the improvements in the design of the working part and the novelty of several details being apparent, the Simplex gas engine gained the day. In 1885, after the appearance of the Simplex and the new Lenoir motors, most makers made use of the Otto cycle, and about this time appeared the first carburetted gas motors, that is to say, using volatile spirits and products of petroleum for their source of energy. Such motors have been devised by Tenting, Koerting-Boulet, Diedrichs, Gotendorf, Noël, Forest, Ragot, Rollason, Atkinson, etc.
At the International Exhibition in 1889 there were thirty-one exhibitors and fifty-three machines, with a total power of 1000 horse-power. All except four used the Otto cycle, and for the first time a motor was to be seen using a gas other than coal gas, namely a poor gas produced at a very low cost in a special gas-producing plant. The motor itself was of the single-cylinder Simplex type of 100 horse-power, opening up a new horizon to inventors, and demonstrating the possibility of using large gas engines supplied with poor gas.
This short history of the gas engine will be seen to consist of three distinct periods—firstly, from 1700 up to 1860, during which time many inventors tried and failed to produce anything practical; secondly, from 1860 to 1889, during which the gas engine became something really practical; thirdly, from 1889 up to the present date. In this period gas engines have grown in size, and large units of 200 to 400 horse-power are now constructed, worked by poor gas produced from special gas plants, and enabling the gas engine to successfully hold its own against the steam engine, which it may one day entirely supplant.
CHAPTER II
THE WORKING PRINCIPLES OF THE GAS ENGINE
Assuming that the earth once formed part of the sun, the whole of the energy at our command for commercial purposes can be traced back to the sun as source. This energy we have received from it in the form of heat, and under certain circumstances the heat is stored up in a latent form in chemical compounds such as coal, petroleum, etc. With our present knowledge it is exceedingly difficult to extract the latent energy from coal and petroleum in any other form but heat, and in order to do so to our greater benefit, it is necessary to study the laws of heat and heat engines. The law which states the relation between heat and other forms of energy such as electricity, mechanical work, is called the principle of the conservation of energy, and forms the first law of thermodynamics. It is enunciated as follows. Whenever a body does work or has work done upon it, there is a disappearance or an appearance of heat, and the amount of heat thus produced or used up is always exactly proportional to the work which is done. The ratio of the amount of work which a certain quantity of heat can produce has been therefore termed the mechanical equivalent of heat.
It has been found by experiment, taking the calorie (C.G.S. unit) as the unit of heat and the kilogramme metre as the unit of work or energy, that the mechanical equivalent is 424. That is to say, the heat necessary to raise the temperature of one kilogramme of pure water at 0° Centigrade through 1° C. (the calorie) is equal to the work done in raising 424 kilogrammes to a height of one metre.
In nearly all commercial heat engines the heat is converted into the energy of movement (kinetic energy) by using some body such as water vapour, gas, or air as an intermediary agent. We do not, however, know at present how to transform heat into mechanical work without losing a greater part of it in the process. Even in the most perfect heat engines at least 70% of the heat is lost, only about 30% being converted into mechanical energy. This is as yet the most perfect result which engineers have obtained even with the most elaborate precautions. As a rule the loss is greater; for instance, many good machines which we consider efficient burn one kilogramme of coal, giving out 8000 calories, equivalent to 3,400,000 kilogramme-metres, and transform only about 400,000 kilogramme-metres into work, the rest, forming nearly 80%, is lost.
It has been the aim of engineers for many years past to reduce this extravagant waste by every means possible, and the very fact that such a waste exists, clearly shows that our vaunted engines are hopelessly wrong in their principle. There is reason, however, to hope that one day we may, by converting the chemical energy of coal direct into electricity, and thereby avoiding the wasteful heat altogether, reclaim at least 80% of the latent energy which nature has so bountifully supplied to us.
It can be shown mathematically that the ratio of the quantity of heat actually converted into work to the total heat used by an engine depends on the temperature at which the heat was absorbed and on the temperature at which the waste heat was discharged. For instance, in a gas engine the efficiency depends on the temperature of the gases directly after the explosion, and on the temperature of the exhaust gases after the work has been done. The exact relation is as follows: the above stated ratio, which is called the theoretical or thermal efficiency, is equal to the difference between the temperature of the hot gases immediately after explosion, and the temperature of the gases of the exhaust divided by the temperature of the hot gases after explosion. This somewhat cumbrous statement may be expressed more clearly in algebraic symbols—
W
T2–T1
—
=
———
H
T2
where W is the amount of work done by an engine supplied with a quantity of heat, H, and T2 is the temperature of the heated gases which expand doing work, and are thereby cooled to the temperature T1, at which they are exhausted.
It is therefore evident, that to make an engine work perfectly efficiently we must obtain an amount of work from it exactly equivalent to the heat put in. That is to say, W must equal H in the above equation. We therefore have the efficiency of such a perfect engine
T2–T1
W
=
———
=
—
=
1.
T2
H