A portion of the heat is also expended in the performance of work, and a loss of heat is sustained by radiation from those portions of the cylinder not protected by the jacket. The amount of heat remaining after the steam has passed through these operations is that which is rejected by it through the exhaust valve to the atmosphere or to the condenser.
In the case of an internal combustion engine, the total heat of combustion expended in the working of the engine may be divided into three parts: (1) Heat converted into work and represented by indicated or brake horse power. (2) Heat carried away by the cooling water circulated through the water jacket. (3) The heat lost in the exhaust gases, and through incomplete combustion and radiation.
15.. Heat Converted into Indicated or Brake Horse Power.—The number of foot pounds of work done by one pound or one cubic foot of fuel divided by 778, the mechanical equivalent of one British Thermal Unit, will give the number of heat units desired.
16. Heat Carried Away by the Jacket Water.— This is determined by measuring the quantity of cooling water passed through the waterjacket equivalent to one pound or one cubic foot of fuel consumed, and calculating the amount of heat rejected by multiplying that quantity by the difference of the tempera ture of the water entering and leaving the jacket.
17, Heat Rejected in the Exhaust Gases, or Total Heat Unused.—The sum of the heat converted into brake horse power and the heat carried away by the jacket water, subtracted from the total heat supplied, will give the total heat rejected or unused.
In order to determine the cost of each horse power hour in thermal units, the gas consumed and the air supplied should be reduced to the conditions of temperature and pressure corre sponding to some adopted standard. This may
be done as stated under gas meters in rule 7, or more conveniently by the formula t v=- X V in which v=volume of gas reduced to standard; F., absolute standard temperature; p=29.92 inches of mer cury; vl=volume of gas registered by meter; pi=pressure of gas at meter measured by manometer in inches of water; temperature of gas.
Since t and p are constants tapl lir.= JOAN -9 and as and ti are practically constant dur ing a given test. v= Ev , in which E=18.00--, and height of barometer + (0.073 X read ing of manometer) ; and e=temperature of gas at meter+461.
For example: Assume the heights of the barometer as 29.40 inches; the reading of the manometer as 6 inches; the temperature of the gas F.; and the volume of the gas regis tered by the meter 350 cubic feet; the, for determining (v) the equivalent volume of gas for standard conditions: 29.40}(0.073X 6) =29.84 0=80+461=541; E =0.976; then v=0.976 X 350=341.6 cubic feet.
The air supplied should be entered and re duced to standard conditions in the same manner.
If the rate method is employed to ascertain the amount of gas consumed, the number of cubic feet for a ten-minute interval may be found by dividing the number of cubic feet registered by one revolution of the small dial by the time in seconds elapsed at the completion of that revolution and multiplying the result by 6,000.
18. Indicated Horse Power (I.H.P.).— This factor is expressed by the formula —