Principles of Carburetion Automotive Technology 1 Mr Wasacz
Principles of Carburetion Automotive Technology 1 Mr. Wasacz
Objectives l You will be able to list and explain the principles of carburetion l Identify the types of carburetion l Explain the float carburetor system l Define manual throttle controls l List the basic functions of a governor l Describe the purpose of an air cleaner
Introduction l In order for an engine to work, what must happen to the fuel? ? l Liquid form gasoline will not allow the engine to run!
Carburetors function l The primary function is to produce an air fuel mixture to operate the engine n This process can be done by using a simple mixing valve, however it is not as efficient l The carburetor is a much more complex system that allows for the operation of the engine during these conditions
Carburetion Con’t l Cold or Hot Starting l Idling l Part Throttle l Acceleration l High Speed Operation
The Intake of Air l Remember, atmospheric pressure draws air/fuel through the carburetor and into the cylinder l This drawing in of air takes gasoline atoms with it creating an air fuel mixture
Air / Fuel Mixture l The amount of air needed for combustion is far greater than the amount of fuel needed l The usual weight ration is 15 parts of air to 1 part of fuel l For example, if we had 1 cubic foot of gasoline, it would require 9000 cubic feet of air to meet this ratio l This ration will change depending on engine operation
Pressure differences l. A carburetor is a device that is operated by pressure differences l These terms refer to those pressure differences n Vacuum n Atmospheric pressure n Venturi Principles
Vacuum l An absolute vacuum is an area that is completely free of air or atmospheric pressure l This is difficult to obtain and never reached within an engine l Any pressure that is less than atmospheric pressure is referred to as a vacuum l Basically, a vacuum is an empty space
Atmospheric Pressure l This is the weight of air molecules above earth l This varies with altitude because they higher up you go, the less atmosphere is on you! l If a vacuum is created, an equilibrium will want to be established, so the atmospheric pressure will fill that space (this is how engines work)
Venturi Principles l The carburetor creates a partial vacuum itself by using this principle l By restricting the passage that the air is flowing through, the velocity of the air will increase l This increase in velocity will decrease the pressure behind the venturi l This low pressure will be filled by fuel l Basically, a venturi is a restriction in an air flow passageway
Venturi
Types of Carburetors l There are three different types of carburetors l These carburetors are named after the direction of airflow from the outlet to the engine manifold l They are as follows n Natural (Side) n Updraft n Downdraft
Natural Draft Carburetor l Used to when there is little space in top of the engine l Air flows horizontally into the manifold l This type will be the most common on the small engines that we are working on.
Updraft Carburetor l l l Placed low on an engine Use gravity feed fuel supply Air / Fuel Mixture must be forced upward into the engine Needs high air pressure Uses smaller passages
Downdraft Carburetor Operates with lower air velocities l Uses larger passages l Gravity assists the air fuel mixture flow into the engine l Can provide large volumes of fuel for high speed and high power operation l
Float Carburetors l. A Float is a small sealed vessel made of brass or plastic. l It maintains a constant level of fuel in the float bowl. l The float rises and falls with the fuel levels l As the float rises to the top, it pushes a needle valve closed l This needs then shuts off fuel flow to the carburetor
Float Bowl Carburetors
Choke System l Since cold fuel is hard to vaporize, the choke is used during cold engine starts to provide a rich mixture to the carburetor in order to get the engine started. l The choke is a round disc mounted on a shaft located at the intake end of the carburetor.
Throttle System l The throttle is a round disc mounted on a shaft beyond the main fuel nozzle in the carburetor. l It regulates the amount of air-fuel mixture entering the cylinder. l The throttle can be connected to a governer l The governer will open and close throttle to regulate engine speed
What it looks like all together
Load Adjustment l The amount of fuel entering the main discharge nozzle is sometimes regulated by a load adjusting needle. l In some carburetors, there is no adjustment needle. These have a fixed flow that is designed for that specific engine
Primer l Many small engines have hand operated plunger called a primer. When depressed it forces additional fuel through the main nozzle prior to starting a cold engine.
Diaphram carburetors l This type does not have a float, rather the difference between atmospheric pressure and the vacuum created in the engine pulsates a flexible diaphragm l The pulsation of the diaphragm takes place on every intake and compression stroke.
Air Cleaners / Filters l As an engine operates, it needs an enormous amount of air passing through the carburetor into the combustion chamber l This incoming air needs to be clean (this means that all particulate needs to be removed!) l If this grit were to enter the combustion chamber, it would cause rapid wearing and scoring of the precision machined parts
Air Cleaners / Filters l Under severe dust conditions, engine life can be reduced to minutes l To keep this dust from entering the engine, we use different types of cleaners / filters n Oil wetted n Dry types n Dual element
Oil Wetted Air Cleaner l Uses a filtering element (crushed aluminum and polyurethane foam) dampened with engine oil l Air is drawn through the oil wetted filter l The filter in return removes any debris or particulate l This type of filter can be reused! n Clean n Dry n Re-oil with soapy water
Dry Type Air Cleaner l Air passes through n Treated paper n Felt n Fiber n Flocked screen l These are designed for 1 time use! l You can only clean large particulate from the filter l Most dust however will stay in between the fibers of the filter
Dry Type Cleaner Cont l. A new style is the pleated paper design. l This style uses a porous paper filter material to allow air flow to the engine, while allowing the filtration of debris l This design provides great surface area to collect particles l This is common to most automobiles
Dual Element Air Cleaners l These filters are used on engines that operate in dustier than normal conditions l Can you guess why its called a dual element air cleaner?
Dual Element Air Cleaners l l l Its because they use both an oil wetted cleaner foam filter, and a dry type filter This offers more protection to dust and particulate The oil wetted filter acts as a pre cleaner The paper cartridge then cleans out any missed debris These come in many shapes and sizes, the most common is a cylidrical filter
Summary l What is the main point of the carburetor? l The average weight ration of air to gasoline is 15: 1. What does this mean? l How do carburetors operate? (think of the venturi!) l What are three types of carburetors, and what is the difference?
Summary l What are the two ways of regulating gasoline within the carburetor? l What is the function of the throttle? l What is the function of the choke? l What is the function of the primer? l What is the main purpose of a filtering system?
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