07-05-2013, 04:55 PM
Fuel Systems
Fuel Systems.ppt (Size: 927 KB / Downloads: 54)
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
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
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
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
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”
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