All you need to know about CARBURETOR
Introduction
All automobiles out there running on the roads, whether Light Motor Vehicles (LMV), Heavy Motor Vehicles (HMV), motorcycle, etc require fuel and air to produce power. Earlier we have studied how the air is supplied into the engine. Today we shall be discussing a major component for an automobile that forms a part of the fuel system and yet the most important one. Carburetors are the component that is responsible for the proper mixture of air and fuel which is then diverted into the combustion chambers for further process. Carburetors are used only in Spark Ignition also known as Gasoline Engines. The fuel from the fuel tank and air from the atmosphere is pushed into the carburetor where they are thoroughly mixed proportionately and passed into the engine.
Main parts of Carburetor are:
- Storage Chamber
- A Choke
- Slow-running (idling) jet
- Main Jet
- Venturi shaped air-flow restriction
- Accelerator Pump
Working
The quantity of fuel in the storage chamber is controlled by the valve, actuated by the float. The choke, a butterfly valve, reduces the intake of air so that only fuel-rich charge is drawn into the cylinders when the cold engine is started.
When the engine warms up, the choke is gradually opened either automatically by heat and engine speed responsive controllers or by hand.
The fuel flows out of the idling jet into the intake air due to reduced pressure near the partially closed throttle valve. The main fuel jet comes into action when the throttle valve is further opened.
Then the venturi-shaped air-flow restriction creates a pressure drop for drawing fuel from the main jet into the airstream at a rate related to the airflow so that a nearly constant fuel-air ratio is obtained. The accelerator pump injects fuel into the inlet air when the throttle is opened suddenly.
In Short
The air from the intake is sucked in and enters the carburetor from the top as shown as the upper valve after passing through the fuel filter.
This upper valve is called the starter circuit or choke which is used to restrict the airflow so that a large amount of fuel is supplied into the cylinder during cold engine startup and can be opened manually or electronically after the engine gets warmed up.
While the air is passing through the blue region, in the middle there is a change in the shape or narrower of the tube called venturi that is responsible for increasing the speed of airflow and decreasing the pressure ( pressure drop ).
The drop in air pressure creates suction on the fuel pipe (right), drawing in fuel (orange).
This pressure drop created a vacuum so that the fuel is sucked (orange color).
The throttle is the valve that is used to open or close the pipe. When the throttle is open, more air and fuel flow to the cylinders for more power production.
The mixture of air and fuel flow into the cylinders.
The float chamber is used to store the fuel which is later supplied through suction.
When the fuel level in the float chamber falls, it lowers the float valve with a spring action that earlier restricted the entry of fuel from the main fuel tank. Once the float chamber gets filled it again lifts up the valve with spring action and again restricts the fuel from the main fuel tank.
This cycle in carburetors keeps on going and the fuel is constantly supplied.
Originally published at https://www.carengineered.com on May 21, 2020.
