[MBLLANBv] EFFICIENCIES OF MULTIPLE-EXPANSION ENGINES 137 



is by adiabatic expansion and which would be able to do the amount of 

 work stated. This motor is then looked upon as the perfect type of 

 engine for this case, and the efficiencies of the jacketed and unjacketed 

 trials found in this manner, may be compared. 



With so large a number of trials, and so much important data 

 •obtained, it would be impossible to give all the deductions that can be 

 drawn from them. It is hojied however that the results have been 

 j^resented in such a form, that the members will be readily able to draAV 

 their own conclusions. A few important points may be noticed. The 

 ^ain in economy of the triple-expansion engine over the compound is 

 clearly shown by the results given in table Xo. 1. The economy effected 

 by jacketing the cylinder, and by increased speed of revolution is also 

 well marked, although it will be noticed that at the high speeds the 

 mechanical efficiency of the engine decreases. In some cases the lowering 

 •of the brake horse power, more than counteracts any gain in economy 

 made in reference to indicated horse power. The gain in economy of 

 the qiiadruple expansion engine with an initial pressure of altout 210 lbs. 

 absolute, over the triple expansion, with initial pressure of about 160 

 (tables 1 and 3) is very small, even when compared in terms of the 

 thermal units used per I. H. P. per minute. "Whether the slight gam in 

 terms of the B. H. P. is worth the additional first cost, attending the 

 «xtra cylinder, and the stronger type of boiler required, together with the 

 extra trouble of maintenance, seems very open to doubt. It Avill be 

 noticed that the triple expansion trials at 210 lbs. pressure have a greater 

 <;onsumption in terms of the I. H. P. than those at 160 lbs. pressure, and 

 also that their mechanical efficiency is less. Trials 30 and 31 were carried 

 out in view of the suggestions that have been made of late, to use 

 cylinders with ratios of about 1 to 7 for compound engines. These trials 

 are the least efficient of the series, showing that this ratio of cylinders 

 is not at all a desirable one. The enormous drop after release in cylinder 

 No. 1 is very apparent, and it maybe mentioned that even ])y making the 

 cut-off in the L.P. cylinder as early as possible, the pressure in the steam 

 chest was onl}" raised a few pounds, a considerable fraction of the area 

 of the L. P. card being lost. The effect that the temperature range in 

 the first cylinder has upon the consumption, due to the varying amounts 

 of initial condensation is very marked, and presents an interesting study. 



In conclusion I have to acknowledge my deej) indebtedness to Mr. W. 

 A. Duff, B.A.Sc, for the great help he has rendered to me in working 

 out the trials, and for his assistance in preparing the diagrams. 



