When you boil a kettle of water, you will shut off fire or electric power when water comes to a boil.

No so with a steam boiler. Generation of steam is a continuous process. Once a boiler is generating steam, it may take quite a long while before it is stopped. When steam is evaporated from water, new water has to be added in to replace water given out.

As more and more steam is evaporated, water becomes more and more concentrated with salts and other impurities. If you use your kettle for a long while, you will see some chalky deposits inside it.

The fresh water supplied to replenish those lost through evaporation cannot be pure and free from salts. Even minute quantities of salt in water will eventually become so concentrated as to form scales or deposits. The deposits are usually calcium or magnesium salts.

When fuel oil is sprayed as a fine mist in boiler burners, it is able to burn at a relatively slow rate. When fuel is sprayed into cylinders of diesel engines, fuel burns in such a rapid rate that explosions occur. Fortunately, these explosions are protected from persons as these engines are called internal combustion engines.

Whatever type of combustion, it is a chemical reaction between carbon, hydrogen, sulphur and oxygen.

C + O2 = CO2 2CO + O2 = 2CO 2H2 + O2 = 2H2O S + O2 = SO2 2S + 3O2 = 2SO3

Air consists of 77% Nitrogen and 23% Oxygen by mass. For a particular design of combustion air, theoritical oxygen multiplied by 100/23 will give theoritical air required.

How do you measure a good combustion. The percentage of Oxygen or Carbon Dioxide will tell us whether combustion is good or not good.