27 February 2018

Factor affecting carburetion

The process of carburetion is influenced by various factors following below :
  • The engine Speed 
  • The vaporization characteristics of the fuel 
  • The temperature of the incoming air 
  • The design of the carburettor 
Since modern engines are of high-speed type, the time available for mixture formation is very limited. 

For example, An engine running at 2500 RPM has only about 10 milliseconds for mixture induction during the intake stroke. When the speed become 5000 RPM the time available is only 5 millisecond.
therefore in order to have high-quality carburetion, the velocity of the airstream at the point where the fuel is injected has to be increased. This is achieved by introducing a venturi section in the path of the air. The fuel is discharged from the main metering jet at the minimum cross-section of venturi. 

Other factors which ensure high-quality carburetion within a short period are the pressure of highly volatile hydrocarbons in the fuel. Therefore, suitable evaporation characteristics of the fuel indicated by its distillation curve are necessary for efficient carburetion, especially at high engine speeds. 

Also, another parameter like the temperature and pressure of the surrounding area has a large influence on efficient carburetion. Higher atmospheric air temperature increases the vaporization of fuel and produces a more homogeneous mixture. An increase in atmospheric temperature leads to a decrease in power output of the engine when the air-fuel ratio is constant due to reduces mass flow into the cylinder or in other words reduced volumetric efficiency. 

The design of carburetor, the intake system and the combustion chamber have influence on uniform distribution of mixture to the various cylinders of the engine. proper design of carburetor elements alone ensures supply of desired composition of the mixture under different operating condition of the engine.