424 FARM MOTORS 



565. Gasoline engine indicator diagram. The highest pressure 

 obtained in the average steam engine cylinder rarely exceeds 175 

 pounds to the square inch. In gasoline engines the average maxi- 

 mum pressure is about 300 pounds a square inch, and it often ex- 

 ceeds 400 pounds a square inch. Since the pressures are so high 

 in the gasoline engine, either the spring has to be made stiffer in 

 the indicator or else the piston made smaller. Either method is 

 utilized with success in indicator work. All parts of the gasoline 

 engine indicator, excepting the spring, are the same as those of the 

 steam engine indicator. In the steam engine the working fluid is 

 admitted to the cylinder ready to perform its work on the piston. 

 In the gasoline engine this is not the case. The working fluid enters 

 the cylinder in the form of a gasoline fuel, which has to be com- 

 pressed and burned before it is ready for use. Since these opera- 

 tions take place in the engine cylinder, the gasoline engine indicator 

 diagram is different from that of the steam engine. Fig. 312 is a 

 typical gasoline engine indicator diagram and can be followed out 

 thus: XY is the atmospheric line; ABC is the line produced by the 

 suction stroke of the piston ; CDE is the compression line ; E is the 

 point of ignition ; EFG is the line produced by the increase in pres- 

 sure as the gas burns; GHI is the expansion stroke line; / is the 

 point of release; 1C is the exhaust line and CJA is the exhaust 

 stroke line. If the inlet valve is opened automatically the suction 

 stroke line falls far below atmospheric pressure, but if it is opened 

 mechanically the line ABC will fall only a short distance below the 

 line XY. The indicator diagram shows as clearly what is the mat- 

 ter with a gasoline engine as it does with a steam engine. Fig. 

 313 shows cards from engines where ignition is too late; Fig. 314, 

 cards which indicate too early ignition. 



566. Losses in a gasoline engine. If it were possible 

 to utilize all the heat in the fuel in a charge of gasoline, 

 there would be no more economical method of producing 

 power, but the mechanical difficulties which have to be 

 overcome are so great that only about 25 per cent of the 

 fuel is converted into applicable work. The principal 

 losses of a gasoline engine are: radiation of heat, heat 

 passed off in the exhaust gases, and heat lost by leakages. 

 At the instant explosion takes place in the engine cylinder 

 the temperature at the center of this explosion is esti- 



