Fuels and Combustion

  Fuel may be chemical or nuclear. Here we shall consider briefly chemical fuels only.

A chemical fuel is a substance which releases heat energy on combustion. The principal combustible elements of each fuel are carbon and hydrogen. Though sulphur is a combustible element too but its presence in the fuel is considered to be undesirable.

·         In chemical thermodynamics the study of systems involving chemical reactions is an important topic. A chemical reaction may be defined as the rearrangement of atoms due to redistribution of electrons. In a chemical reaction the terms, reactants and the products are frequently used. ‘Reactants’ comprise of initial constituents which start the reaction while ‘products’ comprise of final constituents which are formed by the chemical reaction. Although the basic principles which will be discussed in this chapter apply to any chemical reaction, here main attention will be focused on an important type of chemical reaction—combustion.

CLASSIFICATION OF FUELS

Fuels can be classified according to whether:

1. They occur in nature called primary fuels or are prepared called secondary fuels 

2. They are in solid, liquid or gaseous state. The detailed classification of fuels can be given in a summary form as follows 

Type of fuel                        Natural (Primary)        Prepared (Secondary)

Solid                                      Wood                       Coke

             Peat                          Charcoal

             Lignite coal                Briquettes

Liquid                                    Petroleum                 Gasoline
                                                                               Kerosene
                                                                               Fuel oil
                                                                               Alcohol
                                                                               Benzol
                                                                               Shale oil

Gaseous                              Natural gas                Petroleum gas
                                                                               Producer gas
                                                                               Coal gas
                                                                               Coke-oven gas
                                                                               Blast furnace gas
                                                                               Carburetted gas
                                                                               Sewer gas