All About Engines

i84 All About Engines should be blown out of the top. This piston, more- over, was not connected to the shaft by a connect- ing rod and crank in the ordinary way. There was a connecting rod, but it was provided with teeth all the way along the upper half, forming a rack, and the shaft was provided with a toothed wheel into which the teeth of the rack fitted. When an ex- plosion occurred the piston rose rapidly, and the rack, acting on the toothed wheel, caused the shaft to spin round. Having arrived at the top of its stroke, the rack disengaged with the wheel, fell away from it, and allowed the piston to return to the bottom of the cylinder without affecting the rotating shaft. During this return stroke the exploded gases were swept out through the exhaust valve, and in the interval between the strokes a heavy flywheel kept the shaft in motion. Crude in design, cumbrous in action, and irregular in speed as the Lenoir engine was, a great many were made before, in 1876, Dr. Otto invented a far more perfect form—the parent of the gas engine of to-day. Its mode of operation is shown diagrammatic- ally in Fig. no. The first outward stroke of the piston draws in a mixture of air and gas, the valves being opened just long enough for the right pro- portion of each to enter. As the shaft continues to rotate the piston makes its return stroke, and as the gas and air valves are now closed the mixture is compressed. The efficiency of the engine increases with the degree of compression, but it must not be too high or the explosion will take place prema-