All About Engines

Power and Its Measurement 3*9 Fourthly, the bottom line represents the pressure of the steam during exhaust. It should be fairly straight, and in a non-condensing engine it will be at or above atmospheric pressure. In a condensing engine it will, of course, be below this. The exhaust port is closed just before the end of the stroke and cushioning occurs. This causes a rise of pressure, and is represented by the upward curve at the left- hand bottom corner. It is always more pronounced in high - speed than in slow - speed engines, be- cause of the great neces- sity there is of bringing I'lg. 178.—Indicator diagram of gas engine the reciprocating parts of the engine to rest smoothly, and avoiding all jerks. Under various conditions the indicator diagram exhibits curious forms, but every curve and bend in the line corresponds to something which has occurred in the cylinder, and is capable of being interpreted by the engineer. From the information which can be gleaned from it, it is often possible to readjust the valves so that a diagram of larger area is obtained ; for if the area can be increased without altering the steam consumption, the power put into the engine is increased in the same ratio. Exactly the same methods are applied to gas and oil engines as to steam engines, but special springs are used. The diagram of an internal combustion engine is markedly different from that of a steam engine, as will be seen from Fig. 178 ; but it must