1. 52 RCACS Ground School Engines PO 407 EO 3 “Carburetor and Exhaust System”

2. Introduction Teaching Points Teaching Points Carburation Carburation Components of the Carburetor Components of the Carburetor Mixture Mixture Mixture control Mixture control Reasons to Lean the Engine Reasons to Lean the Engine Carburetor Icing Carburetor Icing Prevention of Carburetor Icing Prevention of Carburetor Icing Exhaust System Exhaust System Review Review Reference: Reference: FTGU Chapter 3 FTGU Chapter 3 Section C Pages 61-68 Section C Pages 61-68 Section D page 69 Section D page 69

3. Carburation The function of the carburetor is to vaporize the liquid fuel and to mix it with the proper proportion of air. The function of the carburetor is to vaporize the liquid fuel and to mix it with the proper proportion of air.

4. Components of the Carburetor Venturi: Venturi: Air is drawn into the venturi Air is drawn into the venturi Because of the smaller area, speed is increased and pressure is reduced. Because of the smaller area, speed is increased and pressure is reduced. Nozzle: Nozzle: Provides a passage for fuel from the float chamber to the venturi. Provides a passage for fuel from the float chamber to the venturi. The reduced pressure draws fuel into the venturi where it is vaporized. The reduced pressure draws fuel into the venturi where it is vaporized. Throttle Valve: Throttle Valve: Regulates the volume of air/fuel mixture. Regulates the volume of air/fuel mixture.

5. Components of the Carburetor Intake Manifold: Intake Manifold: This distributes the air/fuel mixture from the carburetor to the cylinders. This distributes the air/fuel mixture from the carburetor to the cylinders. Float Chamber: Float Chamber: This contains a constant level of fuel in order to keep the air/fuel mixture constant. This contains a constant level of fuel in order to keep the air/fuel mixture constant. Needle Valve: Needle Valve: Opens and closes the fuel line that is controlled by the float. Opens and closes the fuel line that is controlled by the float. Vent: Vent: Allows tank pressure to be equal to the changing outside air pressure. Allows tank pressure to be equal to the changing outside air pressure. Idle Jet: Idle Jet: Used to keep the engine going when there is insufficient airflow to draw fuel from the nozzle. Used to keep the engine going when there is insufficient airflow to draw fuel from the nozzle.

6. Mixture Engine temperature is greatly affected by the ratio of fuel to air. Engine temperature is greatly affected by the ratio of fuel to air. An engine will run hotter with a lean mixture than with a rich mixture because the lean mixture is faster burning. An engine will run hotter with a lean mixture than with a rich mixture because the lean mixture is faster burning. Lean mixture Lean mixture fuel/air ratio that is less than a rich mixture. fuel/air ratio that is less than a rich mixture. Too lean a mixture causes rough operation, sudden cutting out, detonation and possible engine failure. Too lean a mixture causes rough operation, sudden cutting out, detonation and possible engine failure. Rich mixture Rich mixture Has a lower combustion temperature. Has a lower combustion temperature. Wastes fuel and contributes to fouled spark plugs and combustion chamber deposits. Wastes fuel and contributes to fouled spark plugs and combustion chamber deposits. Can result in engine failure. Can result in engine failure. The mixture ratio is measured by relative weight of Fuel and Air. The mixture ratio is measured by relative weight of Fuel and Air.

7. Mixture control Mixture control adjusts the fuel ratio between idle cut-off and a rich mixture. Mixture control adjusts the fuel ratio between idle cut-off and a rich mixture. Idle cut-off is reducing the fuel/air ratio to shut down the engine. Idle cut-off is reducing the fuel/air ratio to shut down the engine. The engine should be run lean under the following conditions: The engine should be run lean under the following conditions: When operating below 75% of the rated RPM it can be used for economy. When operating below 75% of the rated RPM it can be used for economy. At higher RPM the excessive heat from leaning can cause engine damage. At higher RPM the excessive heat from leaning can cause engine damage. For take-off at high altitude, and at normal settings the less dense air would cause a loss of power due to an over rich mixture. For take-off at high altitude, and at normal settings the less dense air would cause a loss of power due to an over rich mixture. When climbing to a higher altitude the mixture should be leaned due to less dense air (and enriched during descent). When climbing to a higher altitude the mixture should be leaned due to less dense air (and enriched during descent).

8. Reasons to Lean the Engine Fuel economy Fuel economy Smoother running engine Smoother running engine Better performance Better performance Extended range Extended range Longer spark plug life Longer spark plug life More desirable engine temperature More desirable engine temperature Cleaner engine Cleaner engine

9. Carburetor Icing Under moist conditions icing can occur between approximately -5  C and 30  C. Under moist conditions icing can occur between approximately -5  C and 30  C. Carburetor ice is usually indicated by a loss of power (RPM drop). Carburetor ice is usually indicated by a loss of power (RPM drop). There are three forms of carburetor ice: There are three forms of carburetor ice: Fuel ice Fuel ice Impact ice Impact ice Throttle ice Throttle ice

10. Prevention of Carburetor Icing Modern aircraft use a means of directing heated air into the carburetor. This air is heated by the exhaust system. Modern aircraft use a means of directing heated air into the carburetor. This air is heated by the exhaust system.

11. Exhaust System The exhaust system collects and disposes of the dangerous gases, preventing them from entering the cabin. The exhaust system collects and disposes of the dangerous gases, preventing them from entering the cabin. Two types of exhaust systems: Two types of exhaust systems: The short stack system The short stack system Each side has its own collector tube. Each side has its own collector tube. Collector system: Collector system: Exhaust is collected to drive the turbocharger. Exhaust is collected to drive the turbocharger.

12. Questions? ?