Fuel Systems

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Fuel Systems

  1. 1. Fuel Systems 1
  2. 2. Fuel Systems 1. Carburetors 2. TBI 3. PFI 4. CPFI 5. DFI 6. Diesels 7. Forced Induction 2
  3. 3. Carburetors Mechanical devices that use pressure differential to meter and vaporize fuel for engine demands Contains 6 circuits designed to deliver air/fuel mixture for different operating modes Float/choke/idle/acceleration/main/power Mounted on top of intake manifold Receives fuel from mechanical pump driven by camshaft 3
  4. 4. Carburetors Low fuel pressure: 3-5 psi Fuel is vaporized inside venturis and travels through intake manifold to cylinders 4 cyls: 1-2 venturis (barrels) 6 & 8 cyls: 2-4 venturis 80’s & 90’s: Higher fuel costs Increasingly tight emission laws Onboard computers 4
  5. 5. TBI (Central Fuel Injection) 1 or 2 injectors mounted inside throttle body on top of intake manifold Injector is a simple on/off valve controlled (pulsed) electronically by onboard computer (ECM) Fuel is sprayed into intake stream above throttle plate- vaporization takes place inside throttle body Uses tank mounted electric fuel pump Low pressure: 10-15 psi Eliminates possibility of vapor lock 5
  6. 6. TBI 6
  7. 7. TBI Advantages: Simplicity Low manufacturing cost Low cost of maintenance Disadvantages Fuel traveling through intake manifold Difficult to meter mixtures to individual cylinders 7
  8. 8. PFI One injector per cylinder Injector is mounted in intake port in manifold or cylinder head Injectors are connected by fuel rail Injectors can be controlled as groups or individually Higher pressure: 30-50 psi Necessary to break up fuel particles Vaporization takes place in front of intake valve 8
  9. 9. PFI 9
  10. 10. PFI Electric fuel pump mounted inside fuel tank Fuel pressure in fuel rail is regulated and excess is returned to fuel tank Fuel filter is usually mounted under body of car Throttle body controls air only 10
  11. 11. PFI Advantages: Precise control of fuel mixtures to cyls No fuel traveling through intake manifold Disadvantages: Higher cost of manufacturing: complexity Higher cost of maintenance Injector location causes deposits 11
  12. 12. CPFI Designed as a “hybrid” system Allows for precise fuel control of PFI Simplicity of TBI Uses central injector mounted inside intake manifold Injector connects to nozzles that feed individual cyls Injector is electronically actuated Nozzles are activated by pressure 12
  13. 13. CPFI 13
  14. 14. CPFI Advantages Simplicity allows for low production cost Low cost of maintenance While unit is located inside intake manifold, fuel is injected at intake port Disadvantages Extremely sensitive to pressure changes Plastic lines that connect injector with nozzles are prone to breakage 14
  15. 15. DFI Injector sprays fuel directly into combustion chamber Uses much higher pressure: 2000-3000 psi Fuel must overcome compression pressures Vaporization must take place during injection Uses electric feed pump inside fuel tank Uses mechanical high pressure pump to increase fuel pressures 15
  16. 16. DFI 16
  17. 17. DFI Advantages: Allows for complete air fuel mixture control Better atomization from higher pressures Vaporization process cools combustion chambers allowing higher compression ratios Disadvantages Complexity High cost of manufacture and maintenance High pressure fuel pump 17
  18. 18. Diesel Systems Diesel fuel is heavier and requires much higher temperatures to ignite Engine is designed to create high heat with compression Fuel is injected once air is heated from compression Ignition occurs once fuel is injected into chamber “Compression ignition engine” 18
  19. 19. Diesels 19
  20. 20. Diesels Fuel is injected directly into combustion chamber with precise timing Uses very high pressures to overcome compression pressures and to provide atomization of fuel Most systems use electric in-tank pumps to supply high pressure injection pumps Injection pressures can be created by pumps or injectors themselves, both driven by engine camshaft 20
  21. 21. Diesels Pressures: Supply pressures: 5 to 75 psi Injection pressures: 3000-40000 psi Injection timing is critical for: Power Noise Smoke Air is unthrottled Engine speed is controlled by fuel delivery alone Engine acceleration is slower than spark ignition engine 21
  22. 22. Diesels Advantages Extremely high engine output (torque) Higher energy content of fuel allows for better economy Disadvantages Higher emissions caused by high combustion chamber temperatures High compression ratios require expensive internal engine components Fuel systems components are precision and expensive Different operating characteristics: slower acceleration 22
  23. 23. Diesels 23
  24. 24. Diesels 24
  25. 25. Superchargers Uses engine power to pressurize intake manifold Boost pressures on stock engines: 7-10 psi Forces more air into engine creating more power Usually found on V-type engines Simplified plumbing 25
  26. 26. Superchargers 26
  27. 27. Turbochargers Exhaust driven turbine forces air into intake manifold Same operating principles as supercharging Usually found on inline engines Plumbing complexity 27
  28. 28. Turbochargers 28
  29. 29. Intercoolers Cools compressed air going into intake manifold Cooler air= more dense charge More air= more power Cooler is mounted in front of radiator and transfers heat to ambient air 29
  30. 30. Intercoolers 30

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