Fuel Properties and Combustion Explained

Fuel Properties and Combustion

Oil is formed by the decomposition of organic matter, primarily plankton, in marine environments. It contains the remains of animals and is a mineral found in sedimentary rock formations.

Soluble compounds begin to form, undergoing thermal decomposition into hydrocarbons (HC).

Gaseous Fuels

Gaseous fuels, also called hydrocarbons (HC), are designed for use in combustion. They are divided into natural gas fuels and manufactured gaseous fuels.

Advantages and Properties of Gaseous Fuels

The calorific value varies greatly depending on the type of gas and the presence of non-combustible components. Non-combustible components lower the heat efficiency of combustion.

Calorific value is the heat released during combustion.

Specific Heat

Specific heat is defined as the amount of heat required to raise the temperature of a unit mass of gas by 1°C.

For combustion to occur, fuel and oxidizer must be well mixed, and the temperature must be at or above the ignition temperature. Proper combustion requires sufficient air.

Ignition Temperature

Ignition temperature is the temperature at which combustion begins.

Flammable Limit

Flammable limit is the percentage range of air and gas within which combustion can occur.

Deflagration Speed

Deflagration speed refers to a stable flame propagation rate.

Combustion Air or Theoretical Air

Combustion air, or theoretical air, is the amount of air needed to ensure complete combustion.

Smoke

Smoke consists of all gaseous products generated during the combustion process.

Excess Air Index

Theoretical combustion with precisely the required amount of air is impossible. In practice, excess air is necessary, governed by a supply coefficient.

Advantages of Gas Fuels

• Ease of handling and transport via pipelines.
• No ash or extraneous matter.
• Fuel maintains a consistent temperature even with variable demands.
• Often derived from low-quality solid fuels.

Liquid Fuels

Liquid fuels are derived from tar or crude oil. Examples include gasoline, kerosene, and fuel oil.

Characteristics of Liquid Fuels

Calorific Value

Calorific value is the heat released when a fuel undergoes rapid oxidation (combustion). The calorific value of a fuel determines the amount of usable heat on an industrial scale.

Specific Gravity or Relative Density

The specific gravity or relative density of liquid combustibles varies. Lower densities correspond to a higher content of lighter atoms and less carbon. Gasolines have lower specific densities, while fuel oils have higher specific densities.

Viscosity

Viscosity measures the internal resistance of a fluid to the movement of its molecules.

Volatility

Volatility is determined by the distillation curve. Liquid fuel is a fraction obtained from the distillation of crude oil.

Types of Gasoline

Natural Gasoline

Natural gasolines are produced by the separation of natural gas components. The relative proportion of gas varies, with a lower hydrocarbon (HC) content compared to gasoline.

Direct Distillation Gasoline

Direct distillation gasoline is obtained by distilling crude oil. It contains atmospheric hydrocarbons. It comes from a high-cut fraction.

Octane Rating

Octane rating indicates the gasoline's resistance to detonation. It is used to classify gasolines.

Properties of Fuels

• Aniline Point
• Volatility
• Water and Sediments
• Flashpoint
• Freezing Point
• Viscosity
• Sulfur Content

Fuel Oils

Fuel oils are residual fuels, representing the residue remaining after atmospheric crude oil distillation.