272 ENGINE TESTS. 



and increase the efficiency of the boilers a little less than 

 2%. If the temperature of the main feed- water was at a 

 higher point, the effect of the heat returned from the jackets 

 would be correspondingly less. If we make this for an aver- 

 age case, l-J-%, we should have the combined economy of the 

 jackets due to both causes about 3%. 



There is one test of a compound engine which was made to 

 determine the effect of shutting off the steam from the re- 

 heater, in a case where the cylinders were unjacketed. This re- 

 lates to Engine No. 48. Test A was made with the re-heater 

 on, and test B with the re-heater off. The figures show that 

 the engine was the most economical in the latter case, the 

 difference between .11 of a pound or .7 of 1%; so that in 

 this one instance it would seem that the use of the re- 

 heater produced a loss in steam consumption instead of a 

 gain. If allowance is made for the heat which could be re- 

 turned from the water of condensation to the boilers, the 

 advantage from this source would be nearly 1%, so that 

 there was a slight advantage in fuel economy due to the use 

 of the re-heater. 



Whatever the actual economy due to jacketing or to re- 

 heating or to both, which from the evidence of these tests 

 appears to be rather small, there is no question but that the 

 action of the jacket and the re-heater produces a powerful in- 

 fluence on the steam in its passage through the cylinders. The 

 effect upon the indicator diagrams is very marked. The use 

 of these appliances makes the engine more powerful in view of 

 the fact that it increases the work done by the low-pressure 

 cylinder for a given amount performed by the high-pressure 

 cylinder. In Knimie No. 47, the low-pressure cylinder de- 

 veloped 34 horse-power less than the high-pressure cylinder 

 when the jackets and re-heater were off, and 10 horse-power 

 more than the H. P. cylinder when the jackets were on. In 

 Engine No. 52, the low-pressure cylinder developed 24 horse- 

 power more than the H. P. cylinder when the jackets and re- 

 heater were off, and 92 horse- power more when the jackets 

 were on. In Engine No. 48, the low-pressure cylinder de- 



