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A History of Aeronautics by Marsh and Vivian

Charging of the cylinder occurs


There

was also a Nieuport two-cylinder air-cooled horizontal engine, developing 35 horse-power when running at 1,300 revolutions per minute, and being built at a weight of 5.1 lbs. per horse-power. The cylinders were of 5.3 inches diameter by 5.9 inches stroke; the engine followed the lines of the Darracq and Dutheil-Chambers pretty closely, and thus calls for no special description.

The French Kolb-Danvin engine of the horizontal type, first constructed in 1905, was probably the first two-stroke cycle engine designed to be applied to the propulsion of aircraft; it never got beyond the experimental stage, although its trials gave very good results. Stepped pistons were adopted, and the charging pump at one end was used to scavenge the power cylinder at the other ends of the engine, the transfer ports being formed in the main casting. The openings of these ports were controlled at both ends by the pistons, and the location of the ports appears to have made it necessary to take the exhaust from the bottom of one cylinder and from the top of the other. The carburetted mixture was drawn into the scavenging cylinders, and the usual deflectors were cast on the piston heads to assist in the scavenging and to prevent the fresh gas from passing out of the exhaust ports.

VI. THE TWO-STROKE CYCLE ENGINE

Although it has been little used for aircraft propulsion,

the possibilities of the two-stroke cycle engine render some study of it desirable in this brief review of the various types of internal combustion engine applicable both to aeroplanes and airships. Theoretically the two-stroke cycle engine--or as it is more commonly termed, the 'two-stroke,' is the ideal power producer; the doubling of impulses per revolution of the crankshaft should render it of very much more even torque than the four-stroke cycle types, while, theoretically, there should be a considerable saving of fuel, owing to the doubling of the number of power strokes per total of piston strokes. In practice, however, the inefficient scavenging of virtually every two-stroke cycle engine produced nullifies or more than nullifies its advantages over the four-stroke cycle engine; in many types, too, there is a waste of fuel gases through the exhaust ports, and much has yet to be done in the way of experiment and resulting design before the two-stroke cycle engine can be regarded as equally reliable, economical, and powerful with its elder brother.

The first commercially successful engine operating on the two-stroke cycle was invented by Mr Dugald Clerk, who in 1881 proved the design feasible. As is more or less generally understood, the exhaust gases of this engine are discharged from the cylinder during the time that the piston is passing the inner dead centre, and the compression, combustion, and expansion of the charge take place in similar manner to that of the four-stroke cycle engine. The exhaust period is usually controlled by the piston overrunning ports in the cylinder at the end of its working stroke, these ports communicating direct with the outer air--the complication of an exhaust valve is thus obviated; immediately after the escape of the exhaust gases, charging of the cylinder occurs, and the fresh gas may be introduced either through a valve in the cylinder head or through ports situated diametrically opposite to the exhaust ports. The continuation of the outward stroke of the piston, after the exhaust ports have been closed, compresses the charge into the combustion chamber of the cylinder, and the ignition of the mixture produces a recurrence of the working stroke.


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