1. Controlling steps for the three fuel types

Gaseous fuels: mainly gas-phase reactions; process = mixing + chemical reaction; control often by mixing rate (diffusion flame) or reaction kinetics (premixed flame).

Liquid fuels: atomize into droplets -> evaporate -> mix with air -> gas-phase combustion. Control often by atomization quality (droplet size) and evaporation rate.

Solid fuels (coal/coke):

• Volatiles release and burn (gas phase)
• Solid carbon (coke) surface reactions: $C+O_2\to CO_2$, oxygen-deficient: $2C+O_2\to 2CO$
  Control often by coupled heat/mass transfer (oxygen diffusion, ash-layer diffusion) and kinetics.

2. Typical reaction network (simplified)

• $C+O_2\to CO_2$
• $2C+O_2\to 2CO$
• $CO+\tfrac12 O_2\to CO_2$
• $H_2+\tfrac12 O_2\to H_2O$
• $S+O_2\to SO_2$

3. Complete vs incomplete combustion
   Complete combustion: all combustibles convert to stable oxides ($CO_2,H_2O,SO_2$). Incomplete combustion shows $CO$, unburned hydrocarbons, soot, and higher carbon in fly ash; corresponding heat losses increase.