What is simple carburetor and how it works? >>engineering explained<<
In this post I am going to explain what a simple carburetor is and how it works, not going in deep calculations so a non-technical person can also understand easily.
What is carburetor?
It is a device which is used in spark ignition engine or you can say petrol engines for proper mixing of air and fuel. As oxygen is needed for combustion so in petrol engine mixing of fuel and air is done through carburettor and then this mixture is sent into the cylinder.
Basic layout and working of a simple carburettor
Above shown a basic layout diagram of a carburetor, now what I am explaining further you can match it with this diagram to get a proper image of how it works.
Basic components
A basic carburetor consist of a venturi, a float chamber, a nozzle with metering orifice from float chamber to venture, on the other end of float chamber here is a needle valve to control the fuel supply coming from fuel tank.
Working
In suction stroke, when piston moves from top-dead centre to bottom-dead centre a low pressure zone is created inside the cylinder and as the inlet valve opens the air is drawn inside the carburettor and then this air passes through venturi.
Venturi is basically a tube with lesser cross-section area, thus velocity increases and we know that P1.V1 = P2.V2 so pressure decreases, thus a low pressure zone created in venturi which is far below than atmospheric pressure in float chamber thus fuel flows from float chamber to venturi and due to nozzle connected at the end of the tube which creates a spray of fuel in form of tiny droplets thus atomisation, evaporation and mixing takes place in the venturi. The size of jet is designed very carefully according to required performance of the engine.
Useful equations for calculation
What is vent and what is its requirement?
Vent is necessary to maintain atmospheric pressure inside the float chamber, thus the float chamber is vented through a small hole in the cover.
Does air-fuel mixture depends on the load on engine?
Yes, on different load conditions different ratio of air fuel mixture is required for proper working of the engine. For no load (0% to 20% of maximum load) also called idling condition or for maximum load (80% to 100% of maximum load) rich mixture is fed to the cylinders.
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