Main Processes in Combustion of  Fuels

Solid Fuel Combustion Mechanism

• Solid fuel combustion comprises the pyrolysis of solid fuels followed by a reaction in solid fuel and air
• Devolatilization of coal is an example of the pyrolysis of coal.
• Homogenous and heterogeneous reaction:
  • Combustion is observed from the reaction of carbon in the volatile matter and char with air
• Unburned fuel can result in ash and carbon particles
• More pollution due to incomplete burning of fuel
• In rural areas, biomass from agricultural waste is used as fuel. Which is more affordable than LPG

• The basic steps for the combustion of cola are presented in the following diagrams

 Liquid  Fuel Combustion Mechanism

• The phase change from liquid to gas phase occurs followed by combustion
• For liquid fuel, the combustion has three steps:
  • evaporation of liquid fuel by absorbing heat,
  • mixing of fuel with air in the gaseous phase,
  • formation of flames or reaction zone
• Unburned fuel can result in soot particles
• Some kind of pollution due to soot particles

Here are some key aspects of liquid combustion processes:

1. Fuel Atomization:
   • In liquid combustion, the first step is often the atomization of the liquid fuel.
   • This process breaks down the liquid into small droplets to increase the surface area exposed to the oxidizer, facilitating a more efficient and complete combustion process.
   • Fuel atomization can be achieved using various methods, including mechanical injectors, pressure nozzles, or air-assist mechanisms.
2. Ignition:
   • Liquid fuels need an ignition source to initiate the combustion process.
   • This can be done using spark plugs (common in gasoline engines) or through compression (common in diesel engines). Once ignited, the fuel-air mixture starts to burn.Mechanism of liquid combustion
3. Stoichiometric Ratio:
   • Achieving the correct air-fuel mixture ratio is crucial for efficient combustion.
   • This ratio is often expressed as the stoichiometric ratio, which is the ideal proportion of air to fuel required for complete combustion.
   • Deviations from this ratio can result in incomplete combustion, leading to the production of pollutants such as carbon monoxide (CO) and unburned hydrocarbons.
4. Combustion Chambers:

• The design of the combustion chamber varies depending on the application.
• For example, in internal combustion engines, the combustion chamber is typically found within the cylinder.
• In industrial burners, it’s part of the combustion equipment. The design and geometry of the combustion chamber affect combustion efficiency, heat transfer, and emissions.

1. Flame and Heat Release:
   • Combustion results in the formation of flames, which are visible as a result of the release of heat and light energy.
   • The temperature of the flame and the rate of heat release are essential parameters to consider in many applications.
2. Emissions Control:
   • Controlling emissions, such as nitrogen oxides (NOx), particulate matter, and carbon emissions, is a significant concern in liquid combustion processes.
   • Advanced combustion technologies and emission control systems are employed to reduce environmental impacts.
3. Applications:
   • Liquid combustion processes are used in various applications, including internal combustion engines (e.g., cars, trucks, and airplanes)
   • Industrial furnaces, boilers, and power generation. Different fuels and combustion processes are used based on the specific requirements of each application.

• Understanding the characteristics of liquid combustion processes is essential for optimizing combustion efficiency, minimizing emissions, and improving the performance and environmental impact of systems using liquid fuels.
• Research and development in this field continue to focus on increasing efficiency, reducing emissions, and finding alternative and sustainable liquid fuels.