Fuel Systems

1
Fuel Systems

• Carburetors
• TBI
• PFI
• CPFI
• DFI
• Diesels
• Forced Induction

2
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
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
• 80s 90s
• Higher fuel costs
• Increasingly tight emission laws
• Onboard computers

4
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
TBI
6
TBI

• Advantages
• Simplicity
• Low manufacturing cost
• Low cost of maintenance
• Disadvantages
• Fuel traveling through intake manifold
• Difficult to meter mixtures to individual
  cylinders

7
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
PFI
9
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
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
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
CPFI
13
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
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
DFI
16
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
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
Diesels
19
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
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
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
Diesels
23
Diesels
24
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
Superchargers
26
Turbochargers

• Exhaust driven turbine forces air into intake
  manifold
• Same operating principles as supercharging
• Usually found on inline engines
• Plumbing complexity

27
Turbochargers
28
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
Intercoolers