Gas-Engine Indicator-Diagram. 71 



stroke, and if p m is the mean value of p, then 



1*2 q m = 169-5 + 1*2 p m , 

 or 



g m = 141*25 +p m . 



We find from the diagram that p m =94*5, so that # m = 235*75. 



Now 1*2 A# TO is H, the total heat given to the fluid to alter 

 its volume and pressure until the exhaust-valve opens ; 



1*333 Ax 61*52 is the indicated work W of the cycle, as 

 calculated from the total indicator-diagram, including 

 the dismission and suction parts not shown in fig. 1. 



Hence h =fSiSS w > ot3 - 45W - 



As we know that combustion, about the period of opening 

 of the exhaust-valve, is just sufficient to supply the loss by 

 radiation to the cylinder without having much effect on the 

 volume and pressure of the fluid, we can assume that any 

 combustion after that time produces heat which is radiated to 

 the cylinder. We are told that there is no combustion in the 

 exhaust. For the small amount of combustion after the 

 exhaust-valve opens we do not see our way at present to the 

 basis of any but the very roughest assumption, and we think 

 that attention ought to be paid to this matter in future inves- 

 tigations. What complicates the question is the fact that the 

 mass of the fluid which radiates heat to the cylinder rapidly 

 gets less after the exhaust-valve opens. To obtain a first 

 approximation, we may assume that the heat of combustion 

 after the exhaust-valve opens is equal to the work done in the 

 forward stroke after that time — that is, 0*14 W. 



The heat retained by the fluid is 141*25 x A x 1*2, or 1*94 W. 



The gases in the exhaust-pipe close to the cylinder are 

 known to have a temperature not much greater than 400° 0. 

 Hitherto it has been customary to calculate the amount of 

 heat carried off by the gases through the exhaust-pipe from 

 the heat-capacity multiplied by the difference of temperature 

 from that of the atmosphere. It must be remembered, how- 

 ever, that the total heat of combustion of coal-gas contains the 

 latent heat of the steam produced, and that the exhaust gases 

 carry off this heat. Hence the amount of about 0*95 W, de- 

 ducible from the experiments of Messrs. Brooks and Steward, 

 must be increased by two thirds of itself, giving 1*57 W as the 

 energy carried off by the gases in the exhaust-pipe. 



Hence (1*94— 1*57) W, or 0*37 W, is the amount of energy 

 which is lost by the fluid from the opening of the exhaust- 

 valve until the fluid is passing along the exhaust-pipe outside 



