Purpose of Carburetion A carburetor’s primary purpose is to produce a mixture of air and fuel for...
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Transcript of Purpose of Carburetion A carburetor’s primary purpose is to produce a mixture of air and fuel for...
Purpose of Carburetion• A carburetor’s primary purpose is to produce a
mixture of air and fuel for different engine operating conditions.
Purpose of Carburetion
• Store
• Deliver
• Filter
• Mix air and fuel
• Meter air and fuel
Carburetion Air-fuel
Requirements
• Ratio of air to fuel.
• Stoichiometric ratio of 14.7:1
• Example 14.7 lbs of air to 1 lb of fuel
• Fuel ratios– Rich / lean
Carburetor Operating Conditions
• Cold– Choke / prime
• Low speed– Idle
• Mid speed – Idle and high speed
• Acceleration– Accelerator pump
• High speed– Main discharge nozzle
Carburetion Pressure Differences
• Vacuum• Pressure less than atmospheric pressure
• Atmospheric pressure• Force of air on a surface at 14.7:1psi
• Venturi principle• A restriction in an air passage which causes an
increase in air speed and a decrease in air pressure
Carburetion Pressure Differences• Air horn
– Air enters at Atmospheric pressure
• Venturi– High vacuum is
created
• Engine side– Low vacuum
created on the intake stroke
Carburetion• Atomization
– Turning a liquid into little droplets
• Vaporization– Turning liquid
droplets into a vapor or gaseous state
Carburetion
• Types of carburetors - air direction– Side draft
Carburetion
• Types of carburetors - air direction– Up Draft
Carburetion
• Types of carburetors - air direction– Down draft
Carburetor Circuits• Float circuit
– To maintain proper fuel level
Carburetor Circuits
• Choke circuit– Provides a
rich air-fuel mixture for cold starts
Carburetor Circuits
• Throttle – Regulates
air –fuel mixture entering the cylinders
Carburetor Circuits
Idle circuit– Supplies air-
fuel mixture when the throttle is closed for low speed operation
Carburetor Circuits• High Speed
circuit– Full throttle– Maximum
air – fuel flow to develop full speed and power
Carburetor Circuits• Accelerator
circuit– Provides
additional fuel to maintain the air fuel ratio when the throttle is quickly opened.
Carburetor Circuits• Primer circuit
– Forces addition fuel into the engine prier to cold starting
Carburetor Circuits
• Diaphragm uses atmospheric pressure and vacuum to move fuel into a chamber of the carburetor to be used as needed
Carburetion / Governors
• Manual throttle controls
• Governor throttle controls– Limit low speed– Limit high speed– Maintain constant speed
Carburetor / Governor• Air vane governor
– Pneumatic
– Flywheel air pressure
Carburetion / Governors• Centrifugal (mechanical) governor
– Rotating mechanical force
Carburetion Air Filters
• Air cleaner purpose (3)– Filter air to remove dirt– Protect against back fire– Quiet engine operation
Carburetion Air Filters• Foam type air cleaners (reusable)
Carburetion Air Filters• Paper type air filters (replaceable)
Carburetor Adjustments
• Before making any adjustments clean and inspect parts for wear !!– Rough adjustment– Fine adjustment
• Idle mixture adjustment
• High speed mixture adjustment
• Rpm adjustment
Carburetor Adjustments• Before making any adjustments clean and
inspect parts for wear !!
Carburetor Exploded View
Running Conditions• Too Rich
– Air-fuel mixture with excessive fuel– HC and CO pollution– Exhaust black soot
• Too Lean– Air-fuel mixture lacking fuel– CO and NOX pollution– Engine overheating
• Just Right– Smooth engine operation– Rapid Acceleration– Low pollution / Clean Exhaust– Normal operating temperature
Carburetion• The purpose of the fuel system is store,
deliver, mix and meter air and fuel for the engine to function over a variety of operating conditions.
HAVE A NICE DAY