H. de Graffigny

“ 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. ”

“ On page 21 we give a table embracing all the best known types of gas engines, which will also help to avoid the confusion arising from the fact that some motors exist which belong to neither one nor another, but are combinations of one or more groups. Such hybrid motors have been devised amongst others by Schweizer and Siemens. In the former the power of the explosion is used to compress a considerable volume of air, which is then used for working a compressed air engine. In the latter the gas heats a quantity of air which drives a hot-air motor. ”

“ Dugald-Clerk gas engine.—In the ideal motor we should have at least one explosion per revolution of the fly-wheel, which is not the case in the Otto cycle. For this reason many inventors have tried to construct gas engines with one cycle per revolution, but experience has taught us that though they may be mechanically more simple, they lose in efficiency what they gain in simplicity, and in spite of many eminent inventors attempting to solve the problem. Even the best-designed motors of this type have been unable to hold their own against the Otto cycle because they are not as efficient. ”

“ If, however, the speed of the engine be too great the sliding valve carries its knife blade forward too soon and it does not catch in the notch, with the result that no gas is admitted as the square end is too low. The speed of the engine, therefore, tends to remain adjusted to the rate of vibration of the pendulum, which is a fixed quantity. A self-starting arrangement is provided by stopping the engine half-way back along the compression stroke, so that it is only necessary to pass an electric spark across for an explosion to occur and give it the necessary starting impetus. ”

“ Hot-air engines using ordinary air as the expansible gas have been devised from time to time, but they have not met with much success owing to their weight and the large amount of space they take up, neither are they as efficient as a good modern gas engine. We will not, therefore, study the theory of hot-air engines, but further consider the details of gas engines, whose superiority over all other heat engines we think we have sufficiently pointed out. ”

“ The chemical operation of the production of the gas is a very delicate one, and requires skilled attendants if constancy in the quality of the gas is required. The Bénier gasogene has been designed to eradicate or circumvent these grave drawbacks. It presents many novel features, the most interesting of which is the device for absolutely ensuring no leaks. This is done by generating the gas below the pressure of the atmosphere. This low pressure is maintained throughout the plant right up to the valve which admits the explosive mixture to the motor cylinder. ”

“ The Otto gas engine is a marvel of simplicity from a mechanical point of view, very much more so than a Corliss steam engine for instance. The admission and exhaust valves are worked by cams, and the ignition takes place under pressure. The governor is sometimes of the centrifugal type, and at others of the inertia type, but in both it is a case of all or nothing, the supply being completely shut off if the engine is going too fast. The connecting rod joins the crank to the piston rod by a cross-head running into a bored out-guide. ”

“ As a matter of fact any person without previous knowledge is, with a few days’ practice, competent to take charge of a motor provided that he is intelligent and careful. Under these conditions a gas engine will last as long as a steam engine, and will be generally found much more satisfactory.
To stop the machine, the self-starting mechanism must first be allowed to operate, and then the supply of gas is shut off. After this the burner or electric ignition must be cut off, and the cooling water too, if it is not a circulating system. ”

“ The gases are ignited by means of a tube kept red-hot by a gas flame. This engine possesses the special advantage of being self-starting, that is to say, it is not necessary, as in many other motors, to start the engine by giving the fly-wheel a few rapid turns by hand. The motor is stopped with the crank in a position slightly in advance of the point corresponding to ignition. The gas is allowed to enter by a small auxiliary valve, which closes after the first explosion. This volume of gas entering the cylinder mixes with the air already in it, forming an explosive mixture. ”

“ The vaporizer is heated by the waste gas from the cylinder, and the oil falls drop 100 by drop on to the hot metal walls and becomes vaporized. The engine is of the ordinary four-cycle type, the most noticeable feature being the governing arrangement; a governor of the inertia pattern regulating the admission valve and the oil-pump. If the speed becomes too great the action of the governor on the valves ceases, and oil is no longer supplied to the vaporizer from the pump and the admission valve remains closed. Ignition is obtained by a red-hot tube heated by an oil lamp ”

“ It is, however, just as possible to turn all the heat supplied to a heat engine into work as it is to use up all the energy of a waterfall in a turbine, because the level from which the zero of the potential of the energy water is measured is the centre of earth, which is as inaccessible as absolute zero of temperature. ”

“ The air drawn in combines with the carbon during its downward journey, and then passes through a cooling tower surrounded by a water jacket which acts as a boiler. The heat extracted from the gas is therefore used to produce steam, which drives an engine working the pump which aspirates the air. The exhaust steam from this engine passes into the incandescent fuel and is decomposed, forming hydrogen and carbon monoxide. The valves which govern the supplies of air and steam are so arranged that producer gas or water gas, or both at once, may be generated at will. ”

“ 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 12 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. ”

“ Gas companies are, as a rule, heavily taxed, and if it were not for a vast amount of idle capital buried in the streets in the form of gas mains, they would probably supply gas at a very low price, especially as the sale of bye-products practically covers the cost of production. Some companies have even reduced the price of gas if used for driving gas engines, and have therefore slightly decreased the cost of production of power by this means. ”

“ It is necessary to have a heavy fly-wheel, because, as only one explosion takes place per two revolutions, the fly-wheel must store up enough energy during that explosion to carry it through the rest of the cycle. Many different types of Otto gas engines now exist, some having two cylinders and a single crank, and others two fly-wheels, in order to ensure constancy of speed for driving dynamos. ”

“ If cold air be saturated with the vapour of volatile spirits such as gasoline, or distillates of petroleum of about ·65 mean specific gravity, an explosive mixture is formed with similar properties to that produced by coal gas mixed with air. This carburetted air can be used as fuel for heat engines of the explosive type. About twenty different methods of carburating air are in existence, some of which are more practical than others. ”

“ Inventors have sought to still further lessen the cost of power by replacing the expensive coal gas by other gases of lower illuminating power, produced by special gas plants attached to the engine, and which can be used in places where there is no coal gas laid on. Other engines have been devised, as we have already shown, which get104 over the difficulty by consuming petroleum oil or distillates of same, such as benzoline and other light hydrocarbons. ”

“ This is due to the fact that if cost of coal gas in a particular district is high it is cheaper in the end to pay a higher price for an efficient engine than to buy a less expensive and at the same time less economical machine. ”

“ Admission and ignition are obtained by the action of a sliding valve and eccentric. The governor causes the gas admission valve to remain open for a shorter or longer time, so as to ensure constancy of speed. The exhaust gases escape by two valves actuated by a pair of cams, opening them at every turn and a half, so that the gases are alternately discharged from the back and front parts of the cylinder. The consumption of fuel for a 12 horse-power motor was about 792 litres of coal gas per horse-power hour in an official trial. The speed is very constant in spite of the long cycle. ”

“ 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. ”

“ Wilson gas-producer.—The generator is broader than it is high, and it is possible to use in it all sorts of cheap coal and coke. A window is provided, so that the attendant can see if the fuel is sticking and not settling down properly. The air is blown into the centre of the hearth by a steam injector at a low pressure of about two inches of water or less. Stoking is effected by turning spiral grate bars which rid the fire of clinkers and ashes. The air is heated by waste gases from the motor, a process which gives a slight gain in economy. ”

“ A reservoir of compressed air is used for starting the engine, and saves the trouble of turning the heavy fly-wheel round by hand to give it the necessary impetus.
The Brayton motors are constructed by an American firm from 1 to 10 horse-power. The cost of maintenance and fuel is moderate, rendering them exceedingly practicable where coal gas or the lighter petroleum are unobtainable. A later type than the one we have just described appeared in 1890 which is slightly more economic, single-acting, and uses the Otto cycle. The process 79 for obtaining a spray of oil is also much improved. ”

“ A number of analyses made by M. Witz show that Dowson gas consists on the average of 25% hydrogen, 16 to 25% carbon monoxide, and 50% of nitrogen. The heat of combustion of one litre varies according to the quality of coal used, but averages about 1400 calories. One kilogramme of anthracite will produce about four cubic metres of Dowson gas, the cost being one-tenth of a penny per cubic metre. It must not be forgotten that this gaseous mixture is only a quarter as rich as coal gas, but it costs 110 about one-tenth to produce, and is therefore cheaper on the whole. ”

“ There are no pressure or water gauges to attend to, because no more gas is ever produced than is absolutely wanted. A steam boiler may require to be stoked once every quarter of an hour, whilst a poor gas generator only requires charging about once every six hours, according to demand for power. The Simplex motor itself requires very little attention, and all bearing surfaces are made as large as possible to avoid the risk of heating. ”

“ The explosive mixture is ignited by an electric spark produced from a battery of cells whose charge lasts from 120 to 130 hours, or by a small magneto machine driven by the motor itself. When working with petroleum a carburator is attached filled with a very volatile mineral spirit. The air is carburetted by being sucked through it directly into the cylinder. A second vessel is provided, which serves as a reservoir for oil feeding the carburator automatically, and keeping the oil in it 75 at a constant level. ”

“ The petroleum is vaporized by passing through pipes coiled up in a vessel traversed by the heated products of combustion. The vapour thus formed has a high enough pressure to draw air along with it as it passes across an air space between two nozzles; an explosive mixture is therefore formed. The motor is started by carburating a small quantity of air by means of a reservoir containing a light oil, and this supplies sufficient energy to work the motor until the spiral coils are hot enough to vaporize the petroleum. ”

“ The valve chest is cylindrical and the valves themselves flat, and work off two eccentrics; ignition is effected by an electric spark from a Ruhmkorff coil, which passes through the gas in the cylinder when the piston is commencing the second half of the forward stroke. The exploded gases having done their work are driven out through the exhaust in the return stroke, during which work is being done by a similar explosion on the other side of the piston. ”

“ The pressure of the gases is raised during compression to about four atmospheres, and immediately after the explosion it rises to about 180 lbs. on the square inch; during the exhaust it averages about 10 lbs. per square inch. Ignition is obtained by a tube heated to a bright red incandescence by a Bunsen flame. At the right moment a valve is opened, placing the explosive mixture in contact with it and causing the explosion. When starting the machine the ignition is retarded or takes place a little after passing the dead point, so that the machine cannot start the wrong way by mistake. ”

“ If the machine is to remain stopped for some considerable period, turn the fly-wheel round till the piston is in its most forward position; this will prevent dust and grit from getting into the cylinder, and scoring the inside when the engine is re-started. These are the general 133 rules which must be obeyed in the maintenance of the gas engine. The attention they require is therefore small, and this quality has contributed not a little to their success. No stoker or engine-driver is required; any person can, with very little instruction, take charge of them. ”

“ If the engine is properly erected by skilled workmen, and has been running sufficiently long to have arrived at a condition of regular lubrication, etc., a person in constant attendance can be dispensed with, and it is sufficient to look in occasionally and see that everything is all right, that there is a sufficient supply of oil, and that the cylinder is cool, because if it became overheated it might bind and destroy the interior. ”

“ One explosion therefore occurs in every revolution.
The Bénier engine is constructed in sizes up to 100 horse-power, and also smaller ones of a few horse-power. A 5 horse-power motor consumes 800 grammes of anthracite per horse-power hour: this result is very remarkable, because great difficulty has been found in working these small engines at all with poor gas; the gas generator seems to work badly when its dimensions are so small. A 15 horse-power motor only consumes 600 grammes per horse-power hour. ”

“ The reservoir of fuel is situated in the bed-plate. The ignition is automatic, and an electric spark is unnecessary, in fact, the whole engine is of the simplest construction, in order that there may be no inconvenience due to breakdowns. Referring to Fig. 35, L is a special petroleum lamp situated at the back of the cylinder A. When starting this lamp is supplied with air from a rotary fan turned by hand; in a short space of time, by the help of this stream of high-pressure air, the cartridge C becomes sufficiently 91 heated to ensure the ignition of the explosive mixture. ”