ON LIQUID FUEL. 551 
<4 
air supply is equivalent to about 12 pounds of steam per pound of hydrogen burnt, and 
nearly one-half of this waste heat is consumed in heating the surplus air supply. 
Therefore, by dispensing with this surplus air, and cooling the furnace gas in a feed- 
water heater, a saving of something like one-fourth of the total available heat might be 
effected. A further advantage would also result from the increased temperature of 
combustion, viz. 4692° F. for carbon, and 4922° F. for hydrogen, and the consequent 
more ready transmission of heat from the combustion product to the water in the boiler. 
Combustion of Hydrogen. 
Furnace-gas 
from 1 lb. 
hydrogen. 
Quantities of heat in 
furnace-gas. 
Equivalent 
evaporation 
of water at 
212° F. 
lbs. 
Heat units. 
lbs. 
Water vapour. 
9-00 
600° x 4-3 = 2,580 
2-7 
Nitrogen gas. 
26-78 
600° x 6-6 = 3,960 
41 
Surplus air. 
34-78 
600° x 8-3 = 4,980 
5-1 
70-56 
11,520 
11-9 
Latent heat} 
of water > 8,695 
9-0 
vapour . j 
20,215 
20-9 
The combustion of the carbon and hydrogen of fuel presents another point of differ¬ 
ence, which is important as regards the extent to which the available heat is, under ordi¬ 
nary conditions, capable of being rendered effective in producing steam. This difference 
is due to the presence of water-vapour in the furnace gas, resulting from the combustion 
of hydrogen. As a consequence of this circumstance, a large amount of heat is absorbed 
and rendered ineffective for producing steam. From the foregoing table, representing 
the disposition of heat amongst the furnace gas, it will be seen that every pound of 
water-vapour in the furnace gas corresponds to a waste of heat sufficient to produce 
rather more than lj pound of steam; and hence it will be evident how great is the dis¬ 
advantage resulting from the presence of water in the furnace gas, whether originating 
from hydrogen burnt or from damp fuel or otherwise. 
The volumes of the air supply and combustion products for the extreme cases of 
carbon and hydrogen are as follows:— 
Air supply at 60° F. 
Combustion products 
at 660° F. 
Pound. 
Pounds. 
Cubic feet. 
Pounds. 
Cubic feet. 
Carbon . 
1 
24 
320 
25 
630 
Hydrogen. 
1 
69 
960 
70 
2,044 
In the combustion of carbon there is no expansion of volume in the combustion pro¬ 
duct, except that due to the heat generated, which would render the volume at the 
temperature of combustion (2522° F.) rather more than six times that of the air supplied. 
By the transfer of heat to the boiler, to such an extent as to reduce the temperature to 
660° F., the volume would be reduced again to about 630 cubic feet per pound of carbon 
burnt. 
In the combustion of hydrogen the supply of air required is about three times as large 
as that required in the combustion of an equal weight of carbon. There is also an ex¬ 
pansion of the combustion products, independent of the heat generated, and amounting 
to one-half the normal volume of the hydrogen burnt. The expansion due to beat is 
also greater than in the combustion of carbon, on account of the greater amount of heat 
generated, so that the volume of the furnace gas at the temperature of combustion 
(2791* F.) would be about six and a half times that of the air supplied, and the volume 
