(1) It should have high "calorific value" or heat content.
(2) It should have "moderate ignition temperature". (lgnition temperature is the minimum temperature at which it stars burning). The fuel having low ignition temperature catches fire easily and it is difficult to store or transport. High ignition temperature causes difficulties in combustion of fuel i.e. large amount of heat energy is requires.
(3) It should have "low moisture content" since it reduce the heat value.
(note : it takes away appreciable amount of the liberated heat in the form of latent heat of vaporization. It increases the transport costs. Surface moisture causes difficulty in handling of solid fuel. Anyway, presence of 5-10% moisture is desirables as it produces a uniform fuel bed and less fly ash).
(4) It should have 'low ash or non combustible matter'.
(Note: high percentage of ash is undesirable as it does not contribute to the calorific value Ash i.e., Non-combustible matter causes reduction in heat value, increase the cost of storage and disposal, increase the cost of fuel and also causes environmental problems. In furnace grate, the ash may restrict the passage of air and lower the rate of combustion.
(5) It should have "harmless products on combustion". (I.e. it should not liberate harmful gases like SO2, CO, H2S, PH3 etc.)
(6) It should have "moderate velocity of combustion".
(Note: if velocity of combustion is slow, high temperature required cannot be attained. If velocity of combustion is high, major part of energy will be radiated to atmosphere.)
(7) Fuel should be readily available at low cost.
(8) Storage cost should be low.
(9) Size of fuel should be uniform in case of a solid fuel.
(10) Storage and transportation should be easy.
(11) It should not burn with long smoky flame and combustion should be controlled.