Presentation

1. Fuel Systems
1

2. Fuel Systems
1. Carburetors
2. TBI
3. PFI
4. CPFI
5. DFI
6. Diesels
7. Forced Induction
2

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. 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. 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. TBI
6

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. 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. PFI
9

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
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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. 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. CPFI
13

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. 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
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16. DFI
16

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. 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. Diesels
19

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. 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. 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. Diesels
23

24. Diesels
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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
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26. Superchargers
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27. Turbochargers
Exhaust driven turbine forces air into intake
manifold
Same operating principles as supercharging
Usually found on inline engines
Plumbing complexity
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28. Turbochargers
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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
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30. Intercoolers
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