First.--Generators with internal vaporizers, such as the Otto Deutz and Wiedenfeld generators.

[Ill.u.s.tration: FIG. 92.--Old type of Winterthur producer.]

Second.--Generators with external vaporizers, such as the Taylor, Bollinckx, Pintsch, Kinderlen, Benz, Wiedenfeld, Hille, and Goebels generators.

=Cylindrical Body.=--The generator consists essentially of a mantle made of sheet-iron or cast-iron and containing a refractory lining which forms a retort, a grate, and an ash-pit. In the small size apparatus the cast-iron mantle is often used, whereas in large sizes the mantle is made of riveted sheet-iron so as to reduce its weight and its cost. In the latter case the linings are securely riveted or bolted.

The Winterthur generator (Figs. 92 and 93), the Taylor generator (Fig.

94), and the Benz generator (Fig. 97), are made of cast-iron; the Wiedenfeld generator (Fig. 95), the Pintsch generator (Fig. 96), are made of sheet-iron; the Bollinckx (Fig. 98) is made partly of sheet-iron and partly of cast-iron.

The different parts of a generator, if made of sheet-iron, are held together by means of angle-irons forming yokes, and a sheet of asbestos is interposed. If the parts are made of cast-iron, they are connected after the manner of pipe-joints and packed with compressed asbestos.

This latter way of a.s.sembling the parts presents the advantage of allowing them to be dismembered readily. Therefore, it allows the several parts to expand freely and facilitates the securing of tight joints. This last consideration is exceedingly important, particularly for the joints which are beyond the zone in which the distillation of the fuel takes place. Any entrance of air through these joints would necessarily impair the quality of the gas, either by mingling therewith, or by combustion. The air so admitted would also be liable to form an explosive mixture which might become ignited in case of a premature ignition of the cylinder charge during suction or through some other cause.

[Ill.u.s.tration: FIG. 93.--New type of Winterthur producer.]

[Ill.u.s.tration: FIG. 94.--The A. Taylor producer.]

[Ill.u.s.tration: FIG. 95.--Wiedenfeld producer.]

[Ill.u.s.tration: FIG. 96.--Pintsch producer.]

[Ill.u.s.tration: FIG. 97.--Benz producer.]

[Ill.u.s.tration: FIG. 98.--Bollinckx producer.]

[Ill.u.s.tration: FIG. 99.--Lencauchez producer.]

=Refractory Lining.=--The interior lining of the generator should be made of refractory clay of the best quality. It would seem advisable, in order to facilitate repairs, to employ retorts made of pieces held together instead of retorts made of a single piece. In the first case the a.s.sembling should preferably be made by means of refractory cement, and the inner surface should be covered with a coating so as to form a practically continuous stone surface.

[Ill.u.s.tration: FIG. 100.--Goebels producer.]

Some manufacturers, in order to allow for the renewal of the part most liable to be burnt, employ at the bottom of the tank a refractory moulded ring (Lencauchez, Fig. 99).

It is always advisable to place between the sh.e.l.l or mantle of the generator and the refractory lining a layer of a material which is a bad conductor of heat as, for instance, asbestos or sand, in order to avoid as much as possible loss of heat due to external radiation (Fig. 100).

[Ill.u.s.tration: FIG. 101.--Pierson producer.]

=Grate and Support for the Lining.=--These parts, owing to their contact with the ashes and the hot embers, are liable to deteriorate rapidly. It is therefore indispensable that they should be removable and easily accessible, so that they may be renewed in case of need. From this point of view, grates composed of independent bars would appear to be preferable. The clearance between the bars depends, of course, on the kind of ashes resulting from the different grades of fuel. It is advisable to design the grate so that the free pa.s.sage for the air is about 60 to 70 per cent. of the total surface.

In generators having a cup-shaped ash-pit, containing water (Fig. 95), the grate and the base of the retort are less liable to burn than in apparatus having dry ash-pits. Certain apparatus, such as those of Lencauchez (Fig. 99), Pierson (Fig. 101), and Taylor (Fig. 94), have no grates; the fuel is held in the retort by the ashes, which form a cone resting on a sheet-iron base, easy of access for cleaning and from which the fuel slides down gradually.

The Pierson generator (Fig. 101) is provided with a poker comprising a central fork, which is worked with a lever, in order to stir the fire from below without entirely extinguishing the cone of ashes.

In some apparatus in which a grate is used (Fig. 92), a s.p.a.ce is left between the grate and the support of the retort. This arrangement has the merit of allowing only finely divided and completely burnt ashes to pa.s.s to the ash-pit. Moreover, a large surface grate can be employed, thus facilitating the pa.s.sage of the mixture of air and steam.

[Ill.u.s.tration: FIG. 102.--Kiderlen producer.]

The s.p.a.ce above mentioned is provided with a cleaning-door through which cinder and slag may be removed.

In other apparatus the grate rests either on the support of the refractory lining, as in the old type invented by Wiedenfeld (Fig. 95), or upon a projection embedded in the lining, as, for instance, in the Kiderlen (Fig. 102) and Pintsch generators (Fig. 96).

In the Riche apparatus (Fig. 103) there is, besides the ordinary grate, a grate with tiers on which the fuel spreads. This grate consists of wide, hollow bars containing water. It should be noted that the apparatus is of the blower type.

[Ill.u.s.tration: FIG. 103.--Riche combustion-producer.]

An interesting arrangement is found in Benier's generator (Fig. 104).

This consists of a grate formed of projections cast around a cylinder which can be turned about its axis. The finely divided ashes which are retained in the s.p.a.ces between these projections are thus carried into the ash-pit, and those which adhere to the metal are sc.r.a.ped away by a metallic comb fastened to the lower part of the apparatus. The "Phoenix"

generator (Fig. 105) is fitted with a grate having a mechanical cleaning device, worked by a lever from the outside.

[Ill.u.s.tration: FIG. 104.--Benier producer.]

[Ill.u.s.tration: FIG. 105.--Phoenix producer.]

=Ash-Pit.=--The ash-pits are exposed to the destructive effects of heat and moisture, and should preferably be constructed of cast-iron, since sheet-steel is liable to corrode quickly.

[Ill.u.s.tration: FIG. 106.--Otto Deutz producer.]

In most apparatus the ash-pit is hermetically sealed, and the air for supporting combustion enters below the grate through a pipe leading from the heater or the vaporizer. This arrangement seems best adapted to prevent the leakage of gas which tends to take place by reaction after each suction stroke of the engine.

Ash-pits formed as water-cups, such as the Deutz (Fig. 106), the Wiedenfeld (Fig. 95), and the Bollinckx (Fig. 98), are fed by the overflow from the vaporizer. These ash-pits are themselves provided with an overflow consisting of a siphon-tube forming a water-seal.

Besides providing protection to the grate and other parts by this sheet of water, a larger proportion of the heat radiated from the furnace is utilized for the production of steam which contributes to enrich the gas. The doors of the ash-pits and their fittings are likewise exposed to a rapid deterioration.

For this reason these parts should be very strongly made, either of cast-iron or cast-steel. Furthermore, they should, at joint surfaces, be connected in an air-tight manner, which may be attained by carefully finishing the engaging surfaces of the frame and the door proper, or by cutting a dovetail groove in one of the sides of the frame which is packed with asbestos and adapted to receive a sharp edged rib on the other part.

The pintles of the hinges should also be carefully adjusted so that the joint members of the door shall remain true. Hinges with horizontal axes seem to be preferable in this respect to those having vertical axes. As a means of closing the door, the arrangement here shown (Fig. 107) seems to a.s.sure a proper engagement of the joint surfaces. It consists of a yoke which straddles the door, and which, on the one hand, swings about the hinge, and on the other hand engages a movable hoop. A screw, fastened to the yoke, serves to tighten the door by pressure on its center. This screw can also be fastened to the end of the yoke (Fig.

108).

[Ill.u.s.tration: FIGS. 107-108.--Fire-box doors.]

It is very advantageous to provide in each door a hole closed by an air-tight plug, so that in case of need a tool may be introduced for cleaning the grate. In this manner the grate may be cleaned without opening doors and without causing a harmful entrance of air.

The door of the furnace, particularly, should be provided with an iron counter-plate held by hinged bolts (Fig. 109); or, better still, this door should be so constructed that it can be lined with refractory material to protect it against the radiated heat of the fire.

=Charging-Box.=--Like the other parts of the generator the construction of which has been discussed above, the charging-box should be absolutely air-tight.

On account of their greater security, preference should be given to double closure devices, which form a sort of preliminary chamber, owing to which the filling of the generator is made in two operations. The first operation consists in filling the preliminary chamber after opening the outer door. Upon closing this outer door, the second operation is performed, which consists in moving the inner door so as to cause the fuel in the preliminary chamber to drop into the generator.

Stress has been laid on the greater safety of this type of charging-box for the reason that, with devices having a single charging-door, a sudden gust of air may rush in at the time of charging the furnace, and bring about an explosion very dangerous to the workman entrusted with stoking the furnace.

[Ill.u.s.tration: FIG. 109.--Door with refractory lining.]

The closure is generally simply a removable cover, or may be a lid swinging about a hinge having a horizontal or vertical axis.

As regards the inner door, which is of great importance, in order to insure an air-tight joint, there are three chief types of closure:

1. The Lift-Valve.

2. The Slide-Valve.

3. The c.o.c.k.