The Romance of Modern Mechanism / With Interesting Descriptions in Non-technical Language of Wonderful Machinery and Mechanical Devices and Marvellously Delicate Scientific Instruments

by Archibald Williams

THE DIESEL OIL ENGINE,

on account of some features peculiar to it, is treated separately. In 1901 an expert wrote of it that "the engine has not attained any commercial position." Herr Rudolph Diesel, the inventor, has, however, won a high place for his prime-mover among those which consume liquid fuel, on account of its extraordinary economy. The makers claim—as the result of many tests—that with the crude rock-oil (costing in bulk about 2d. a gallon) which it uses, a horse-power can be developed for one hour by this engine for one-tenth of a penny. The daily fuel bill for a 100 h.p. engine running ten hours per day would therefore be 8s. 4d. To compete with the Diesel engine a steam installation would have to be of the very highest class of triple-expansion type, of not less than 400 h.p., and using every hour per horse-power only 1 3 / 4 lbs. of coal at 9s. per ton. Very few large steam-engines work under conditions so favourable, and with small sizes 3-4 lbs. of coal would be burnt for every "horse-power-hour."

The Diesel differs from other internal combustion engines in the following respects:—

1. It works with very much higher compression.

2. The ignition is spontaneous, resulting from the high compression of the charge alone.

3. The fuel is not admitted into the cylinder until the power-stroke begins, and enters in the form of a fine spray.

4. The combustion of the fuel is much slower, and therefore gives a more continuous and elastic push to the piston.

The engine works on the ordinary Otto cycle. To start it, air compressed in a separate vessel is injected into the cylinder. The piston flies out, and on its return squeezes the air to about 500 lbs. to the square inch, thus rendering it incandescent.[11] Just as the piston begins to move out again a valve in the cylinder-head opens, and a jet of pulverised oil is squirted in by air compressed to 100 lbs. per square inch more than the pressure in the cylinder. The vapour, meeting the hot air, burns, but comparatively slowly: the pressure in the cylinder during the stroke decreasing much more gradually than in other engines. Governing is effected by regulation of the amount of oil admitted into the cylinder.

In spite of its high compression this engine runs with very little vibration. The writer saw a penny stand unmoved on its edge on the top of a cylinder in which the piston was reciprocating 500 times a minute!