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SINCE Brayton used compressed air stored in a reservoir for starting purposes, which then, as now, was found unreliable owing to the difficulty of keeping up the pressure, the possibility of leakage, and also the reservoir being emptied before the engine was started, great strides have been made in the method of starting, and the development has gone on lines which may be classified as follows:
1. Pressure starter with a hand pump.
6. High-pressure single impulse with previous compression of air.
7. Steam from producer plant boiler.
Wells Brothers' Starter
The first application of the modern method of starter was introduced by Messrs Hamilton and Rollason, of the firm of Wells Brothers, in 1889. Fig. 124 is a part sectional elevation, fig. 125 end view, and fig. 126 a starting diagram.
At the extreme end of the combustion chamber is fixed a hand pump A fitted with a suction and delivery valve, the inlet of gas and air being through a three-way cock.
The action is as follows: The crank is placed on the firing stroke, and the timing valve kept closed by means of a catch. The combustion chamber being already filled with air, a proper charge of gas is pumped in, the threeway cock is then turned so as to admit air to the pump, which is then forced into the cylinder. The catch is released, and the charge ignites by means of the ordinary ignition tube.
In fig. 126 the starting is shown at 1, and the following ignitions (2, 3, and 4) take place in the same manner as when
the engine is working, but as the compression is relieved the impulses are small. In practice this starter works well, and is exceedingly simple.
A starter which has during the last few years made headway was introduced by Mr. Lanchester in 1890, some 600 of which are now at work.
Fig. 127 (No. 2) is a transverse section of a combustion chamber of an 11 x 18 inch stroke Robey engine fitted with a Lanchester self-starter. Fig. 128 is a facsimile of diagram taken from this engine.
A nozzle (1) opens to the explosion chamber of the engine, and connects it to a gas supply pipe by a valve (2). A cock (3) contains within it a valve (4) in the cylindrical space above the plug (5). The valve (4) rests upon the lower seat and has grooves or channels in it, so that while on the lower seat free communication is open between the compression space and the atmosphere. A pilot light (6) is lit when it is desired to start the engine, the crank is set over the centre and a little on the forward stroke (see fig. 128), and the gas valve (2) is opened by pressing the button (7). Gas then flows into the space as indi
cated by the arrows, and mixes with the air which was drawn in by the piston previous to stopping. Part of the air is displaced through the nozzle (8). At first air only passes out in this manner, but after a few seconds a mixture of gas and air is discharged; this mixture lights at the pilot light (6), and burns in the atmosphere more vigorously as the mixture becomes richer. Whenever it is rich enough in gas, which can be readily seen by the colour of the flame or by the characteristic roar made by it, the button (7) is released and the gas inlet shut off, and the cessation of flow allows the flame to strike back through the nozzle (8) into the compression space, and gives the starting impulse.
FIG. 128. -STARTING DIAGRAM ---LANCHESTER
On the return stroke the products of combustion are expelled, on the next forward stroke a charge of gas is drawn in, and on the return stroke (compression stroke) the exhaust valve is held open almost the whole length of the stroke so that sufficient compression is attained to force the remaining charge up through valve (8), lighted by pilot light (6), and before the piston has moved appreciably on its next forward stroke another impulse is given. This is repeated every other revolution until sufficient speed has been attained to start against full compression. In this engine about seven explosions are sufficient. With some sizes one impulse is sufficient to start with the ordinary relieving cam.
One great advantage this starter has is the small amount of shock with starting and successive impulses, for it should