Fig. 15.—Crossley Gas Engine.
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. Two or three other features call for special notice, especially the device for lubricating the cylinder. In the illustration (Fig. 14) will be seen a small bell-shaped receptacle. This vessel contains oil, and also a small crank inside driven by a belt off the valve-shaft. As this crank rotates it dips into the oil at the bottom of the vessel, and at the top of its path it wipes off the oil which it has gathered on to a cup which allows it to flow into the cylinder.
The water jacket is cast separately from the cylinder, and not, as in many engines, in one piece with it. There is an advantage in this, because there is less likelihood of flaws or blow-holes in the cylinder wall passing unobserved when the engine is leaving the maker’s hands. The governor in some of the sizes is centrifugal, and in others of the inertia type similar to that described in the Fielding gas engine.
Pygmée motor (Lefebvre).—This motor, shown in Fig. 16, gives one the idea of solidity and compactness. It possesses the peculiar property of working equally well in any position, either horizontal or vertical. This is due to the fact that it is particularly well balanced, and when running does not vibrate at all. Easily started, these engines run at a very constant speed, and their power in relation to their size is truly remarkable, hence the name Pygmée. They have been especially designed for self-propelled vehicles, and are not affected by the worst running conditions, such as inclement weather or bad roads. In this type they are constructed with two cylinders in order to obtain a more constant torque, and also have an arrangement by which the speed can be changed. For stationary purposes the motor is mounted on a cast-iron stand (Fig. 16). In virtue of their exceedingly small dimensions and reduced weight they are specially suitable where small-power motors are required for home industries or small workshops, and also for driving private electric installations and pumping water. They have economically replaced steam engines in agricultural operations, both on a large and small scale. The working parts being entirely enclosed they stand a good deal of rough usage, and will work in positions in which other motors would be useless. Where it is necessary to bring the motor to the work it is required to perform they are bolted to a carriage instead of a cast-iron base.
Fig. 16.—Pygmée Gas Engine.
The “National” gas engine.—As a gas engine this machine is constructed in all sizes, from one horse-power up to large units requiring a gas plant of their own. As petroleum motors they range from one to ten horse-power. They are all provided with two fly-wheels, which keep them well balanced and steadies their speed. They have besides been especially designed with a view to economy of coal gas or petroleum. An idea of the general arrangement of the parts will be obtained by glancing at Fig. 17. The petroleum motors are provided in addition with a vaporizer and a petroleum lamp placed at the front end of the machine, and the oil reservoir is situated immediately above the cylinder. M. Herckenrath has specially devoted himself to simplifying the mechanism and making it more self-contained and less unsightly. Up to 50 horse-power only one cylinder is found necessary, and for larger powers two are provided. The patent governor is centrifugal and rather novel in construction, and to it is partly due the high efficiency of these engines. The large sizes are as easily started as the smaller ones, and the lubrication is perfectly automatic. Besides these advantages they require a minimum of attention, in fact, a skilled attendant can be dispensed with, a few explanations and instructions being all that is necessary to enable a boy or labourer to take competent charge of them.
Fig. 17.—Herckenrath National Gas Engine.