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. We shall proceed to describe the best known of these.

Mille carburetted gas.—In this system air is drawn into a reservoir containing a petroleum spirit by the volatilization and fall of the petroleum vapour, this vapour being heavier than air. The reservoir is placed on a higher level, and an indiarubber tube connected to its base leads the explosive mixture to the cylinder. The success of this arrangement encouraged inventors to perfect it. One of the earliest carburators by Lafroque was provided with a tiny hot-air engine, which helped to obtain a more perfect saturation of the air with the volatile spirit. In the Eclipse motors, and also in the Phoebus motors of Pluyer and Muller of Birmingham, the air and spirit vapour are mixed by an injector. The vapour is first obtained by heating the liquid spirit in a small still; it then passes by a fine nozzle across a space drawing air with it after the manner of the Giffard injector. The explosive mixture thus obtained passes into a reservoir.

Faignot apparatus.—The air is drawn in by a revolving pump and forced into a vessel, divided into several compartments, one above the other, separated by porous partitions and containing gasoline; several taps or valves cause the compartments to be alternately opened or closed, so that the mixture can always be drawn off rich in hydrocarbon vapour. This apparatus appeared in 1885 at the Antwerp Exhibition, and supplied a BÉnier motor with carburetted air. It is suitable for lighting villages, country houses, etc., in fact, any places where coal gas is not laid on. The apparatus has been imitated by Polack of Hamburg and others.

Lenoir carburetted air motor.—Carburators for producing fuel for motive power have been carefully studied during the last ten years by reason of the rapidly extended use of gas motors. One of the most ingenious is due to M. Lenoir, constructed for a special motor designed by himself and constructed by Messrs. Rouart frÈres. This carburator consists of a horizontal cylinder rotated by a pinion wheel, and performing five or six revolutions a minute. Vertical perforated partitions divide the cylinder internally into several compartments, and the interior wall of the cylinder has attached to it a number of small buckets which draw up the spirit like a water-wheel, and pour it out again when they reach the summit of their path. The air and vapour are thus thoroughly mixed, and pass from thence into the cylinder. Motors supplied by such carburators have been used for agricultural operations, and also for driving small pleasure vessels, the cost of maintenance per horse-power hour being about 2½d.

Schrab carburator.—The idea of this apparatus is quite original. The jacket for cooling the motive cylinder is filled not with water but with the hydrocarbon to be vaporized. From thence it passes at a temperature of about 180° F. into a carburator containing several compartments, and through which pass part of the products of combustion; these gases passing through the already boiling liquid hydrocarbon become saturated with its vapour, but require admixture with air before they are capable of being exploded. The inventor states that the waste gases only take up ¹/₁₆th part of that which pure air would in passing through the hot liquid fuel, and thus explains the extraordinary economy of fuel which is obtained by these motors, only 1/16th of a litre of gasoline being necessary to produce one horse-power hour. This is a very remarkable result, and if it is correct places this combined plant in the foremost rank of carburetted air engines.

Meyer carburator.—This apparatus has the advantage of allowing heavier and cheaper oils to be used, at the same time completely volatilizing them. The heavy hydrocarbons are allowed to fall drop by drop into a steel chamber about eight centimetres diameter and four centimetres in height, heated by a flame. The vapour is produced at a high pressure, and escapes through a fine nozzle at high speed drawing the necessary air with it. Entering a reservoir this explosive mixture is prevented from returning by a check-valve. The apparatus is so arranged, that when the pressure in the reservoir has reached a certain point, the flame heating the vaporizer is turned down and prevents further explosive mixture being formed. The apparatus is therefore self-regulating, the supply of carburetted air being always proportional to the demand.

Delamare carburator.—M. Delamare-Deboutteville has devised a very compact carburator for use with his Simplex motor. Gasoline is contained in an upper vessel, from which it flows in a fine stream from a tap on to a horse-hair brush, and is there met by a similar stream of warm water coming from the water jacket of the cylinder. The heat obtained from this source tends to vaporize the hydrocarbon, and the two liquids fall together into a closed vessel. The gasoline rids itself of its impurities and floats on the surface of the water, which is withdrawn from underneath it by a siphon. The hydrocarbon vapour produced during the fall, and afterwards by the heat of the substratum of water, passes by a check-valve to the motor. It is found that the cleansing effect of the water renders the cylinder much less liable to become fouled by tarry products.

Lothhammer carburator.—Experience has shown that vapour of petroleum when mixed with air soon separates out; the vaporizer must therefore be placed as close to the engine as possible. In this motor it has been the aim of the inventor to obtain an exceedingly perfect mixture of the explosive gases. In order to do this the air enters the vaporizer near its base, and passes through it in a number of exceedingly fine streams of bubbles. The petroleum spirit is at the same time heated by a flame, and the result is a very close mixture of the gases. The inventor claims that he thereby obtains much more complete combustion.

Tenting motor.—M. Tenting has arranged his gas engine, which we have already described on page 57, for use also as an oil engine. The carburator is composed of three superposed vessels, through each of which the oil flows in turn. The upper vessel acts as a reservoir and will hold a day’s consumption of oil, and the lower one is traversed by the exhaust pipe, which supplies the heat necessary to obtain the change of state of the oil from liquid to gas. Although this carburator is rather crude it gives a very fair practical result.

Durand carburetted air engine (Fig. 27).—M. Durand has set himself to produce a motor which should work equally well with gas or petroleum, and which should require a minimum of attention at the same time, keeping in view such points as regularity of speed, rigidity, economy of space, and above all low price. This ideal he has, however, failed to reach, although his engine has many good points. He fails chiefly because the mechanism is too complicated. The motor works with an Otto cycle, and the ignition is by an electric spark generated by a small magneto machine. The regulation of the speed is obtained by throttling the admission, and the air is drawn through a tube heated by the waste gases; this arrangement allows a slight economy to be effected. The carburator is automatic, consisting of a closed cylinder placed vertically over the motor cylinder. Within it is placed the oil fuel, and also a spongy mass of cork which soaks up the heavier impurities found in the oil, and thereby allows cheaper oils to be used. Air is drawn through the spongy mass, becoming carburetted in the process; these gases are mixed with a further quantity of pure air in a distributing chamber before entering the cylinder.

Such a Durand motor sins only by the number of its parts, the inconvenience of which is noticeable not only by the amount of lubrication they require, but also by their rapid deterioration.

Daimler motor.—This motor, constructed by Panhard and Levassor, has become especially famous for its application to power-driven road vehicles. It gained nearly all the best prizes in the automobile races organised in 1894 between Paris and Rouen, and again in 1895 between Paris and Bordeaux. MM. Panhard and Levassor also construct their motors as fixed engines, but except for slight modifications, the mechanism is the same in both; we shall therefore describe the automobile type.

There are two single-acting cylinders working on the same crank-shaft. A central valve allows compressed air to be admitted which completely drives out the products of combustion. The admission and exhaust valves are enclosed in a chest also containing the incandescent tube which ignites the mixture. The governor on the crank-shaft prevents the exhaust gases from escaping when the normal speed is exceeded. The gases remaining in the cylinder prevent a fresh charge from entering, and during the next revolution no explosion takes place. The whole mechanism of the engine, together with the fly-wheels, are enclosed in an air-tight case communicating with the outside air by a valve opening inwards. The pistons during the backward stroke draw in air through this valve and compress it during the forward stroke; this forms the supply of compressed air for the explosive mixture. The carburetted air is obtained by the suction of heated air through oil placed in a vaporizing vessel. The motor cylinder is kept cool by a stream of water, which is itself cooled by travelling through a long annular pipe which runs completely round the carriage. The heat which it has absorbed from the cylinder is rapidly extracted from it by the circulation of the air on both the inside and outside of the tube.

Brouhot gas and carburetted air engine.—The firm of Brouhot of Vierzon construct an engine capable of working either by coal, gas, or petroleum, and which has been especially designed for agricultural operations. The general appearance of the engine is of the usual type; the cylinder projects over the bed-plate and is cooled by a water jacket. 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 at a constant level. The whole machine, though not presenting any novel features, is strongly constructed and thoroughly suitable for the work it has to perform.

Carburetted air motors for horseless carriages.—Although not to such a great extent in England, self-propelled vehicles have within the last two years come rapidly into favour on the Continent, and the success which has attended them has caused inventors and makers to concentrate their efforts on building the motors as light and as practicable as possible, as much for purposes of locomotion as for a host of other uses. We have already spoken of the Daimler motor, which is used to drive several different types of motor cars; we will now speak of more recent developments in the same direction. Among many of the same character, the most noticeable is the high-speed motor of MM. de Dion and Bouton, who have applied them with great success to the propulsion of tricycles (Fig. 28).

The cooling is effected by radiating cast-iron ribs offering a considerable surface to the air. The ignition is obtained by an induction coil and accumulator with a contact mechanism, invented by Captain de Place. The rotation of the crank-shaft is transmitted to the wheel-shaft of the tricycle by a reduction gear.

Among other motors we must mention the benzoline engines for self-propelled vehicles of Lepape, Gautier, the Gladiateur tricycles and quadricycles constructed by the SociÉtÉ des Voitures sans Chevaux; also the exceedingly light motors of the Kane-Pennington type; and lastly, the voiturette-tandem of M. Leon BollÉe, some of whose vehicles have shown a remarkable speed with a very small consumption of fuel.

A few monstrosities have also appeared in the shape of a five-cylinder motor driving a bicycle called the “bicyclette Soleil Millet,” and a heavy and complicated mechanism by WolfmÜller, also driving a bicycle and using petroleum. These motors have not, however, obtained any success, nor will they at a future date, by reason of their complication and weight. It is almost unnecessary to state, that any of the above types may be equally well used for driving a dynamo and producing electric energy or light.