Heat Calculations in IC Engine / Heat Balance Sheet

The complete record of heat supplied and heat rejected during a certain time by an I.C Engine is entered in a tabular form known as heat balance sheet. All the heat energy supplied to an engine can not be converted into useful work. Some of the heat energy may be lost by means of some sources. The source of heat losses are given below,

i) Heat rejected to the cooling water.

ii) Heat Carried away by exhaust gases.

iii) Unaccounted heat losses by means of radiation , incomplete combustion and errors in observations etc.

The Following Valves should be calculated for tabulating heat balance sheet.

i) Heat Supplied by the Fuel (Qs) :

Q s = m f * CV kJ / hr

ii) Heat absorbed in B.P. Produced ( Qip) :

Brake Power Q bp = 2 (3.14) N T kJ / hr (N in rev / hour )

Q bp = 2 (3.14) N ( W - S ) kJ / hr

iii) Heat Rejected to the cooling water (Qw) :

Qw = mw Cw ( T2 - T1 ) kJ / hr

Where, mw = Mass of the cooling water circulated in kg / hr .

Cw = Specific heat capacity of water in kJ / kg K.

T1 = Inlet Temperature in K.

T2 = Outlet Temperature in K.

iv) Heat Carried away by exhaust gas ( Qg ) :

Qg = mg Cg ( Tg - Ta )

Where mg = mass of exhaust gases in kg / hr

Cg = Specific heat capacity of exhaust gas in kJ / kg K

= 1.005 kJ / kg k

v) Unaccounted Heat Losses (Q ua ) :

Qua = Qs - (Qip + Qw + Qg + ...) kJ / hr .

Find out all the above heat losses into percentage ,

% heat loss = (Heat loss / Qs ) * 100

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