Dugald Clerk

“ Most engines at certain speeds discharge considerable quantities of carbonic oxide into the atmosphere with their exhaust gases, and some discharge so much as to give rise to danger in a closed garage. Carbonic oxide is an extremely poisonous gas which should be reduced to the minimum in the interests of the health of our large cities. The enormous increase of motor traffic makes it important to render the exhaust gases as pure and innocuous as possible. ”

“ The heavier petrol is not so easily converted into vapour. The great modern development of the motor car gives the light oil engine a most important place as one of the leading sources of motive power in the world. The total petrol power now applied to cars on land and to vessels on sea amounts to at least two million H.P. The petrol engine has also enabled aeroplanes to be used in practice. ”

“ The outer sleeve acts really as a distributor; the inner sleeve supplies the pressure tightness required to resist compression and explosion. The idea of working exhaust and inlet by two sleeves within which the main piston operates is very daring and ingenious; and for these small engines the sleeve valve system works admirably. There are many advantages; the shape of the compression space is a most favourable one for reducing loss by cooling. All the valve ports required in ordinary lift valve engines are entirely dispensed with ”

“ To start the engine a hand pump is worked until the pressure is sufficient to force the oil through the spraying nozzle, and oil spray is formed in the starting lamp; the spray and air mixed produce a blue flame which heats the vaporizer. The fly-wheel is then rotated by hand and the engine moves away. The eccentric shaft is driven from the crank-shaft by means of toothed wheels, which reduce the speed to one-half the revolutions of the crank-shaft. The charging inlet valve is automatic. Governing is effected by throttling the oil and air supply. ”

“ Throttle control is very effective, and it has the great advantage of diminishing maximum
pressures to which the piston and cylinders are exposed while the engine is running at the lower loads. This is important both for smooth running and good wearing qualities. Theoretically, better results could be obtained from the point of view of economy by retaining a constant compression pressure, constant charge of air, and producing ignition, somewhat in the manner of the Diesel engine. ”

“ H is a short platinum tube, which is always open to the compression space. It is rendered incandescent by the burner I, fed with petrol from the pipe supplying the vaporizer. The open incandescent tube is found to act well for small engines, and it does not ignite the charge until the compression takes place, because the inflammable mixture cannot come into contact with the hot part till it is forced up the tube by the compression. The engine is started by giving the crank-shaft a smart turn round by means of a detachable handle. The exhaust is alone actuated from the valve shaft. ”

“ It is a curious fact that with heavy oils ignition is more easily accomplished at a low temperature than with light oils. The explanation seems to be that, while in the case of light oils the hydrocarbon vapours formed are tolerably stable from a chemical point of view, the heavy oils very easily decompose by heat, and separate out their carbons, liberating the combined hydrogen, and at the moment of liberation the hydrogen, being in what chemists know as the nascent state, very readily enters into combination with the oxygen beside it. ”

“ On the compression stroke of the piston A the charge of air is forced into the combustion chamber B and the vaporizer chamber C, where it mixes with the oil vapour, and the mixture is ignited at the termination of the stroke by the ignition tube H. This tube is isolated to some extent from the vaporizer chamber C, and so it becomes hotter than the chamber C and is relied upon to ignite the mixture when formed at times when C would be too cold for the purpose. E is the exhaust valve, which operates in the usual way. ”

“ It has been found, however, that many petrol engines having jet carburettors will operate with the heavier oils if the jet carburettor is suitably heated by means of the exhaust gases. In some engines it is customary to start with petrol, and then when the parts have become sufficiently heated to substitute paraffin or heavy petroleum oil, putting the heavy oil through the same spraying process as the petrol and evaporating the spray by hot walls before entering the cylinder. ”

“ The same effect is produced by devices which alter the area of the petrol jet or increase or diminish the number of petrol jets exposed as required. Although engine designers have succeeded in proportioning mixture through a considerable range of speed and charge demand, so as to obtain effective power explosions under all these conditions, yet much remains to be done to secure constancy of mixture at all speeds. ”

“ The earlier inventors often expressed the idea that an explosive mixture could be prepared without any vaporization whatever, by simply producing an atmosphere containing inflammable liquid in extremely small particles distributed throughout the air in such proportion as to allow of complete combustion. ”

“ Experiments by Callendar, Hopkinson, Watson and others have proved that the thermal efficiency obtained from these small engines with the throttle full open is very high indeed; 28% of the whole heat in the petrol is often given as indicated work when the carburettor is properly adjusted. As a large gas engine for the same compression cannot do better than 35%, it appears that the loss of heat due to small dimensions is compensated by the small time of exposure of the gases of explosion due to the high speed of rotation. ”

“ The majority of petrol motors are provided with water jackets around their cylinders and combustion spaces. As only a small quantity of water can be carried, it is necessary to cool the water as fast as it becomes hot. For this purpose radiators of various constructions are applied. Generally a pump is used to produce a forced circulation, discharging the hot water from the engine jackets through the radiator and returning the cooled water to the jackets at another place. ”

“ Sometimes the same ignition plugs are adapted to spark from either source, and in other cases separate plugs are used. The magneto systems have the great advantage of generating current without battery, and by their use noise is reduced to a minimum. All electrical systems are now arranged to allow of advancing and retarding the spark from the steering wheel. In modern magneto methods, however, the spark is automatically retarded when the engine slows and advanced when the speed rises, so that less change is required from the wheel than is necessary with battery and coil. ”

“ Shortly after the introduction of the "Otto" gas engine in 1876, a motor of this type was operated by an inflammable vapour produced by passing air on its way to the cylinder through the light oil then known as gasolene. A further air supply was drawn into the cylinder to form the required explosive mixture, which was subsequently compressed and ignited in the usual way. The Spiel petroleum engine was the first Otto cycle motor introduced into practice which dispensed with an independent vaporizing apparatus. ”

“ The device in this form works quite well when the range of speed required from the engine is not great; that is, within limits, the volume of petrol thrown by the jet is fairly proportional to the air passing the jet. When, however, the speed range is great, such as in modern motors, which may vary from 300 to 1500 revolutions per minute under light and heavy loads, then it becomes impossible to secure proportionality sufficiently accurate for regular ignition. ”

“ The shaft Q is operated by pinion and a spur-wheel Q' at half the rate of the crank-shaft. The governing is accomplished by cutting out explosions as with the gas engine, but the governor operates by preventing the exhaust valve from opening, so that no charge is discharged from the cylinder, and therefore no charge is drawn in. The cam R operates the exhaust valve, the levers shown are so controlled by the governor (not shown) that the knife edge S is pressed out when speed is too high, and cannot engage the recess T until it falls. ”

“ Light and heavy oils are used; light oils may be defined as those which are readily volatile at ordinary atmospheric temperatures, while heavy oils are those which require special heating or spraying processes in order to produce an inflammable vapour capable of forming explosive mixture to be supplied to the cylinders. Of the light oils the most important is known as petrol. ”

“ The radiators consist in some cases of fine tubes covered with projecting fins or gills; the motion of the car forces air over the exterior of those surfaces and is assisted by the operation of a powerful fan driven from the engine. ”

“ The cylinders in the 35 H.P. motor are no mm. bore X 120 mm. stroke. The speed of rotation is usually 1200 revolutions per minute. The total weight of the engine complete is 180 lb, or just over 5 lb per brake horse-power. The subject of aeroplane petrol engines is a most interesting one, and rapid progress is being made.
So far, only 4-cycle engines have been described, and they are almost universal for use in motor-cars and aeroplanes. Some motor cars, however, use 2-cycle engines. Several types follow the "Clerk" cycle (see Gas Engine) and others the "Day" cycle. ”

“ I, but alterations have been made to allow of the production of uniform mixture in the cylinder under widely varying conditions of speed and load. The original form of carburettor was not well adapted to allow of great change of volume per suction stroke. Tube ignition has been abandoned, and the electric system is now supreme. The favourite type at present is that of the high-tension magneto. Valves are now all mechanically operated; the automatic inlet valve has practically disappeared. Engines are no longer controlled by cutting out impulses ”

“ His little engines contained nothing new in their cycles of operation, but they provided the first step in the startlingly rapid development of petrol motive power which we have seen in the last twenty years. The high speed of rotation enabled motors to be constructed giving a very large power for a very small weight.
Fig. I is a diagrammatic section of an early Daimler motor. A is the cylinder, B the piston, C the connecting rod, and D the crank, which is entirely enclosed in a casing. ”

“ The amount of heat obtained for a given monetary expenditure is only about half that obtained by means of petrol. On the continent of Europe, however, alcohol motors have been considerably used for public vehicles. ”