United States or Isle of Man ? Vote for the TOP Country of the Week !
The short-stroke enthusiasts pointed to the high piston speed of the long-stroke type, while those who favoured the latter design contended that full power could not be obtained from each explosion in the short-stroke type of cylinder.
This point is dwelt upon because it is observed that many engineers find difficulty in freeing themselves from early impressions made by long-stroke engines, express apprehensions at fifty and sixty revolutions, and stand ready to obviate the difficulty by gearing, which it is hoped may not henceforth be adopted in our national ships.
The piston in a long-stroke compressor travels through considerable space before the pressure reaches a point where the discharge valve opens, and after reaching that point it has to go on still further against a prolonged uniform resistance. This makes rotative speed difficult.
Long-stroke air compressors are evidently objectionable on the basis of greater expense of construction. All the parts must be larger and heavier. The fly wheels are increased enormously in diameter and weight, and the strength of bearings must be enlarged in proportion. It is difficult to equalize power and resistance in air compressors with long strokes.
It is now generally conceded that the long-stroke engine yields higher efficiency, and in addition to this, so far as car engines are concerned, the method of rating horse-power in relation to bore without taking stroke into account has given the long-stroke engine an advantage, actual horse-power with a long stroke engine being in excess of the nominal rating.
Evidence in favour of the long-stroke engine is afforded in this type as regards economy of working; under full load, working at 2,000 revolutions per minute, the consumption was 0.55 pints of fuel per brake horse-power per hour, which seems to indicate that the long stroke permitted of full use being made of the power resulting from each explosion, in spite of the high rate of speed of the piston.
This may have had some influence on aero engine design, but, however this may have been, the long-stroke engine has gradually come to favour, and its rival has taken second place.
Word Of The Day