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Fuel Systems

Fuel Systems. AF115 M. Westerman. Fuel System Components Common to both A/C. Fuel Tanks Vents Lines Measuring device Fuel Gauges Fuel tank selector Fuel Strainer. Fuel System Components Specific to N model A/C. Primer Carburetor. Fuel System Components Specific to S model A/C.

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Fuel Systems

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  1. Fuel Systems AF115 M. Westerman

  2. Fuel System Components Common to both A/C • Fuel Tanks • Vents • Lines • Measuring device • Fuel Gauges • Fuel tank selector • Fuel Strainer

  3. Fuel System Components Specific to N model A/C • Primer • Carburetor

  4. Fuel System Components Specific to S model A/C • Fuel Reservoir • Auxiliary Fuel pump • Fuel Shut off valve (separate from selector) • Engine Driven Fuel Pump • Fuel/Air Control Unit • Fuel distribution valve • Fuel Flow Indicator

  5. Fuel tanks • S Model • Integral tanks (part of the wing) • Riveted together with sealant between • Can hit the rib when checking fuel quantity giving inaccurate reading • N Model • Aluminium tanks strapped into wing between ribs

  6. http://www.youtube.com/watch?v=dye_ibjPY0g

  7. Fuel tanks cont’d… • Attached to fuel tanks: • Fuel caps • Fuel lines • Fuel quantity indicating system • Fuel caps • Both models have vented caps for each tank. • Allows air in or out?

  8. Fuel Lines • Some carry air, others carry fuel • Fuel lines exit the tanks at the wing root, and there are two per tank • Extending from the front and back of the fuel tank, and going down through each door post • Venting lines extend overhead in the cabin and join the two tanks

  9. Fuel lines Cont’d… • Air is drawn in from the vent located behind strut on left wing • S model has an additional vent line extending to the fuel reservoir • Before fuel leaving the tanks there is a coarse mesh to filter out any large particulate

  10. Fuel Quantity • Both have a float and gear assembly to measure fuel • Float position is converted into an electrical resistance that can be used by a fuel gauge to determine fuel level

  11. Tank Selector • Simply allows you to select which tank to feed fuel from to the engine • Both models have a Both, Left and Right position • N model there is an off position incorporated into this selector

  12. Fuel Strainer • At the lowest point of the fuel system • Used to collect water and sediment from the system • Has a fine mesh screen inside to filter out larger debris • Is drained before each flight to rid the system of contaminants

  13. N Model Components • Primer • Essentially a cylinder and a piston that only go through the intake and exhaust stroke • As you pull primer out, fuel is drawn into cylinder • As you push primer back in, fuel is ejected from cylinder and driven into three of the four cylinders • Why only three you ask!

  14. Carburetor • Main principle fuel metering devices work from is Bernoulli • As speed increases, pressure decreases • Pressure decrease= vacuum • Venturi‘s are used to create this area of low pressure • How does air pass through venturi?

  15. Float type carb • A small reservoir of fuel the metering unit draws from • The amount of fuel in the reservoir is controlled by a float (just like a toilet)

  16. Carburetor cont’d… • Systems within a carburetor • Main metering • Idling • Mixture control • Accelerating

  17. Main Metering • Comprised of • Venturi • Main metering jet • Butterfly valve • Fuel at tip of metering jet is level with that of the fuel chamber • As air flows past the venturi the vacuum draws fuel out of the metering jet

  18. Idling • When butterfly valve is closed there is little if any pressure diff in venturi • At idle there will be a small idle metering jet that is above the butterfly valve • It can be adjusted to allow more or less fuel in while idling • If your a/c is idling too high or too low, it can be changed

  19. Mixture control • A small valve is installed inline with the main metering jet • Allows you to control how much fuel is being allowed to enter the main metering jet

  20. Accelerator Pump • When you increase throttle rapidly main metering jet can’t keep up with initial airflow • Similar to a primer • When you reduce throttle to idle cylinder fills up • When you increase throttle piston drives the fuel out of a secondary discharge nozzle

  21. Problems • Cold Air and accelerating quickly • Accelerator pump and flooding • Carb ice • Can’t go upside down • Less efficient than fuel injection

  22. http://youtube.com/watch?v=tOM7lzSwY8g

  23. S Model • Fuel Reservoir • Auxiliary Fuel pump • Fuel Shut off valve (separate from selector) • Engine Driven Fuel Pump • Fuel/Air Control Unit • Fuel distribution valve • Fuel Flow Indicator

  24. Fuel Resevoir • Located under the floor of the passenger’s feet • Vented through the fuel tanks venting system • Allows for a continuous reliable source to draw from

  25. Auxiliary Fuel Pump • Located beside of the reservoir • Providing required fuel pressure through lines for starting • Helps prevent vapour lock • A backup source for the engine driven pump

  26. Aux Pump Cont’d… • Vane type is most commonly used however it does vary • Vanes offset so fuel gets in one side and forced out the other • Has a relief valve so over pressurization doesn’t occur

  27. Engine Driven Fuel pump • Same idea as the electric pump but more regulated as it turns in time with the engine

  28. Fuel Air Control Unit • RSA type continuous flow fuel injection system used • Meaning fuel is continuously flowing through nozzles and put in the stream of metered air just before the intake port

  29. Fuel air control unit cont’d… • From the engine driven fuel pump fuel flow into the fuel metering unit • Fuel metering unit consists mainly of mixture control valve, and an idle valve • First fuel is metered past the mixture valve (you control) • Second flows through the idle valve controlled by a mechanical linkage with the throttle

  30. http://youtube.com/watch?v=46FuNqyTIDk

  31. Fuel regulator • Uses both air metering forces and fuel metering forces to regulate the fuel to the divider • Ram air pushes the valve open while the venturi sucks the valve open • Pressure diff between inlet fuel pressure and metered fuel pressure will allow more fuel to flow through the main metering jet and through to the metered fuel

  32. Fuel regulator cont’d… • Therefore the more the throttle is open, the more ram air there is and the lower the pressure is across the venturi

  33. Flow divider • Once fuel is regulated it is sent to the fuel divider via a steel tube • Fuel divider has a spring loaded diaphragm that shuts the fuel off to the injectors is fuel pressure is not present • Fuel is split evenly to each injector • There is one injector per cylinder

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