To know Heat energy (Engine)

 

Fuel Engine

Heat is a form of  energy transfer. As an Energy  , its unit is joule. Becouse any energy's unit to be  joule. So its unit is joule. 

Heat is denoted by Q letter. Sometime its denoted by H, Where it tell enthalpy( H). 

From the 1st law of thermodynamics, we get 

dQ = du + dw ------------(1)

Where, dQ is the  change of heat energy,  du is the change in internal energy and dw is the work done by gas.  Hare work done equal to pressure into volume expansion.  

 dw =pdv  

We discuss a heat energy of Hydrocarbon fuel:

When thr air fuel ratio and composition of a fuel are known  it is a simple matter to estimate the total heat energy per unit volume of mixture. That shown in combustion of Hydrocarbons fuel.

It can be shown that all hydrocarbon fuels suitable for petrol and C.I engine give the same heat energy, namely 45 ft. lb. per square in. within a margin of about 2 per centimetres. Expressed differently, it can be estimated that for hydrocarbon fuels, from 1275 to 1335 B.T.U  per lb.  of air used, are  liberated ; an average value of 1300 B.T.U is usually taken for calculation purposes.

Combustion of Hydrocarbon fuels. 

Hydrocarbon fuel can be regarded,  for combustion calculations, as mixures of hydrocarbons, represented by the general chemical notation as CxHy, so that the air-fuel propertion for complete combustion can be calculated on this assumption. The reaction is expressed,  

CxHy + (x + y/4) O2 = x CO2 + y/2 H2O 

This expression shows that 1 volume of CxHy fuel requires (x + y/4)  volume  of oxygen. x volume of carbon dioxide and y/2 volumes of water vapour are formed. Quantitatively, it can be show that 12x +y weight unit of the hydrocarbons fuel, CxHy will required 32 (x+y/4) unit of air. It will be seen that 1 lb. of CxHy fuel will required  (32+8y)/(12x+y) lb. of oxygen for complete combustion, and the products of combustion will be consist of 44x/(12x+y)lb of corbon dioxide and 9y/(12x+y) lb of water (vapour).