Different Types of Air-Fuel Mixture in Carburation - Stoichiometric Mixture, Rich Mixture, And Lean Mixture

air-fuel mixture type
🔗What is Carburation? What are the factors affecting carburation?

Normally an engine will work on different load and speed condition. The required air-fuel mixture ratio will vary according to this operating condition. The proper air-fuel mixture is to be supplied to the engine cylinder for efficient working of engine. According to the amount (mass ratio) of fuel and air get mixed in carburation, the mixture classified into three

  • Chemically correct mixture or Stoichiometric mixture
  • Rich mixture
  • Lean mixture
🔗Design and working principle of simple carburetor
🔗Advantages and limitations of simple carburetor

What is Stoichiometric mixture or chemically correct mixture?

Stoichiometric mixture is the type of air-fuel mixture in which amount of air is just enough to complete combustion of fuel. The complete burning means that the all the hydrocarbon present in the fuel is getting converted to CO2 and H2O. The amount of air required is calculated from the chemical equation of burning of particular fuel.

What is Rich air-fuel mixture?

This type of mixture contains the amount of air less than the amount of air present in the stoichiometric mixture. There is no adequate amount of air for the complete combustion of fuel. The mixture has excess fuel.

What is Lean air-fuel mixture?

This the air-fuel mixture which has the more air than the stoichiometric requirement. The mixture has excess air. The lean mixture is more efficient than a stoichiometric mixture. The advantages of lean mixture include less heat loss, less engine knocking, Low throttling loss, and achieve higher compression ratio.

Consider a gasoline engine, in which the stoichiometric air-fuel ratio is 14.7: 1, then air-fuel ratio
14.7 : 1 – stoichiometric mixture
14 : 1 – Rich mixture
15 : 1 – Lean mixture

Not all range of this mixture won’t run the engine properly. There is a combustible range for air-fuel mixture for sustainable flame propagation. The mixture falls outside this range is known as either too lean mixture or too rich mixture. The carburetor should provide the proper air-fuel ratio according to the operating condition and this must be with in combustible range.



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