11 March 2018

Modern carburetor | Requirement of vehicles

There are some new systems used in the modern carburettor for meeting the requirement of vehicles so now in this article, we will discuss those systems.

  • Anti-dieseling system :
A spark-ignition engine sometimes continues to run for a very small period even after the ignition is switched off. This phenomenon is called dieseling. 

It may take place due to one or more of the following factors below :
  • High engine idling speed
  • Compression ratio increase due to the carbon deposits 
  • Low octane rating
  • Engine overheating
  • Spark plug heat range too high
  • Incorrect adjustment of idle fuel-air mixture
  • Sticking of throttle 
  • Engine tune-up required
  • Oil entry into the cylinder
So as we discuss above modern carburettor use an anti dieseling system to prevent dieseling system. This system has a solenoid valve operated the idling circuit. With ignition key turn on current flow in the solenoid coil of the solenoid while generating force. This force opens the passage for a slow mixture when the ignition key is turn off the magnetic force disappears. The needle valve is brought to original by the action of the spring in the solenoid valve. By this way, the slow mixture passage is cut off and hence the engine stops. This reduces hydrocarbon emissions.

  • Richer coasting system :
This system is incorporated in some modern cars. When the car is travelling at high speed and when the accelerator pedal is suddenly released, the wheel will motor the engine at a high speed. Consequently, the vacuum in the inlet manifold and the combustion chamber increased too much and cause incomplete combustion. This system is designed to overcome this problem by supplying a proper mixture to the intake manifold for stable combustion. 

  • Acceleration pump system :
It is a transient phenomenon. To accelerate the vehicle and consequently its engine, the mixture required is very rich and the richness of the mixture has to be obtained quickly and very rapidly. So when the situation arise of the acceleration this requires an increased output from the engine in a very short time. If the throttle is suddenly opened there is a corresponding increase in the airflow. But because of the inertia of the liquid fuel, the fuel flow doesn't increase in proportion to the increase in airflow. This results in a temporary lean mixture causing the engine to misfire and a temporary reduction in power output. To prevent this condition, all modern carburettor is used in this system in carburetion. 

  • Economizer or Power enrichment system :
At the maximum power range of operation from 80% to 100% load, a rich air-fuel ratio is required. It is about 12 to 14. Is a valve which remains closed at normal cruise operation a gets opened to supply rich mixture at full throttle condition. It regulates the additional fuel supply during the full-throttle operation. so economizer is supplied economy mixture. It also called a power enrichment system.