A system of fuel supply developed by the late Dr. Diesel, a German chemist and engineer, is attracting considerable attention at the present time on account of the ability of the Diesel engine to burn low-grade fuels, such as crude petroleum. In this system the engines are built so that very high compressions are used, and only pure air is taken into the cylinder on the induction stroke. This is compressed to a pressure of about 500 pounds per square inch, and sufficient heat is produced by this compression to explode a hydrocarbon mixture. As the air which is compressed to this high point cannot burn, the fuel is introduced into the cylinder combustion chamber under still higher compression than that of the compressed air, and as it is injected in a fine stream it is immediately vaporized because of the heat. Just as soon as the compressed air becomes thoroughly saturated with the liquid fuel, it will explode on account of the degree of heat present in the combustion chamber. Such motors have been used in marine and stationary applications, but are not practical for airplanes or motor cars because of lack of flexibility and great weight in proportion to power developed. The Diesel engine is the standard power plant used in submarine boats and motor ships, as its efficiency renders it particularly well adapted for large units.
NOTES ON CARBURETOR INSTALLATION IN AIRPLANES
A writer in “The Aeroplane,” an English publication, discourses on some features of carburetor installation that may be of interest to the aviation student, so portions of the dissertation are reproduced herewith.
“Users of airplanes fitted with ordinary type carburetors will do well to note carefully the way in which these are fitted, for several costly machines have been burnt lately through the sheer carelessness of their users. These particular machines were fitted with a high powered V-type engine, made by a firm which is famous as manufacturers of automobiles de luxe. In these engines there are four carburetors, mounted in the V between the cylinders. When the engine is fitted as a tractor, the float chambers are in front of the jet chambers. Consequently, when the tail of the machine is resting on the ground, the jets are lower than the level of the gasoline in the float chamber.
“Quite naturally, the gasoline runs out of the jet, if it is left turned on when the machine is standing in its normal position, and trickles into the V at the top of the crank-case. Thence it runs down to the tail of the engine, where the magnetos are fitted, and saturates them. If left long enough, the gasoline manages to soak well into the fuselage before evaporating. And what does evaporate makes an inflammable gas in the forward cockpit. Then some one comes along and starts up the engine. The spark-gap of the magneto gives one flash, and the whole front of the machine proceeds to give a Fourth of July performance forthwith. Naturally, one safeguard is to turn the petrol off directly the machine lands. Another is never to turn it on till the engine is actually being started up.
“One would be asking too much of the human boy—who is officially regarded as the only person fit to fly an aeroplane—if one depended upon his memory of such a detail to save his machine, though one might perhaps reasonably expect the older pilots to remember not to forget. Even so, other means of prevention are preferable, for fire is quite as likely to occur from just the same cause if the engine happens to be a trifle obstinate in starting, and so gives the carburetors several minutes in which to drip—in which operation they would probably be assisted by air-mechanics ‘tickling’ them.
“One way out of the trouble is to fit drip tins under the jet chamber to catch the gasoline as it falls. This is all very well just to prevent fire while the machine is being started up, but it will not save it if it is left standing with the tail on the ground and the petrol turned on, for the drip tins will then fill up and run over. And if it catches then, the contents of the drip tins merely add fuel to the fire.
Reversing Carburetors
“Yet another way is to turn the carburetors round, so that the float chambers are behind the jets, and so come below them when the tail is on the ground, thus cutting off the gasoline low down in the jets. There seems to be no particular mechanical difficulty about this, though I must confess that I did not note very carefully whether the reversal of the float chambers would make them foul any other fittings on the engine. It has been argued, however, that doing this would starve the engine of gasoline when climbing at a steep angle, as the gasoline would then be lowered in the jets and need more suction to get into the cylinders. This is rather a pretty point of amateur motor mechanics to discuss, for, obviously, when the same engine is used as a ‘pusher’ instead of a tractor, the jets are in front of the floats, and there seems to be no falling off in power.