45
THE BOILER TEST
53
The average pressure of steam at the boiler during the various runs was 595 lb. The average degree of
superheat at the boiler was 298
0
. The mean temperature of feed water was 78
0
. The average evaporation was l0.34 lb.
of water for 1 lb. of gasoline. From this data, by consulting Buel's steam tables, we find
B.T.U. per lb. of steam above
212
0
=
1051
B.T.U. per 1b. for raising feed to
212
0
=
l44
By producing lines in Fig. 12, the
specific heat is found to be 0.69.
Heat required to superheat 298
0
=
298x69 =
206
Total. . . . . . .
140l
Equivalent evaporation from and at 212
0
per sq. ft. of heating surface per hour, was 13 lb. for highest result.
54
In the above calculation the heat required for superheating is extremely approximate as the pressures in my
test were about three times as high as those in the Sibley College test for specific heat of steam. In this last calculation
I have obtained the specific heat as 0.69 by extending the lines in Fig. 12. This quantity gives the value of the heat in
one lb. of steam above 212
0
as 1257 B.T.U., which averages about 29 B.T.U. per lb. higher than that which I
calculated as supplied to the engine, and is I believe too high since the loss of heat between the points where the two
observations were made was small and in my opinion must have been less than 1% or about 14 B.T.U. in this case. If
the heat required for superheating were calculated by using 0.48 for the specific heat the above results would have
been 1339 B.T.U. per lb. which is 62 B.T.U. or 4.4% less than the above.
55
The heat absorbed by the steam for one lb. of gasoline burned would be, in accordance with the above
calculation, 14,486 B.T.U., corresponding to an equivalent evaporation from and at 212
0
F. of 14.9 lb. per lb. of
gasoline, and made on the supposition that the specific heat of steam is constant and equal to 0.48, it would be equal
to 13,845 B.T.U. corresponding to an equivalent evaporation from and at 212
0
of 14.3 lb. of water per lb. of gasoline.
56
If the heating value of the gasoline be 18,482 B.T.U. per lb., the respective boiler efficiencies of these 2
cases would be 78.4% and 75.0%.
If the heating value be assumed at 20,400 B,T.U. per lb, the respective efficiencies
become 71.2 and 67.3%.
THE EFFICIENCY OF THE ENTIRE PLANT
57
The engine developed a horse power on the brake at its highest load during the various tests with a
consumption of 11.96 lb. of feed water per hour. The evaporation under actual running conditions with the feed water
heater in operation was 11.5 lb. of water for one of gasoline. This would show that l.04 lb. of gasoline would be used
under best conditions per developed HP
58
If the engine friction be considered as 1.6 HP, the water per IHP per hour would be as calculated under best
conditions, 11.54 lb. and the gasoline per IHP per hour, l.004, which is practically one lb. of gasoline per IHP per
hour.
59
If the gasoline has a heating value of 18,482 B.T.U. per lb., we find a heat efficiency for the whole plant on
the basis of total heat supplied, compared with that converted into useful work on the brake, of l3.25%, and compared
with that indicated of 13.35%. If the heating value for gasoline be 20,400 B.T.U. per lb. the per cent of efficiency for
these two cases becomes respectively 12.1 and l2.45%.
60
The above calculations are made to cover the extreme results of he heating values of gasoline, in order to
make the results accord with either method of calculation.
SUMMARY OF TESTS MADE BY PROF. C. H. BENJAMIN
61
The test made of the White steam system by Prof. C H. Benjamin in 1903 has already been referred to and a
summary of the results is given here for comparison with the tests which I made.
62
The engine tested by Prof. Benjamin was of the vertical cross
compound type with high pressure cylinder 3
inches in diameter, low pressure cylinder 5 inches in diameter, and with a stroke of 3
½
inches. Its general
construction was in many respects similar to the 1907 engine, which has been fully described; it was not however,
provided with ball bearings. The test was made by essentially the same method as described in the paper. During the
