Basic Mechanical Fuel Injection System Flashcards
Regardless of design all Diesel engines must preform what five functions?
Timing Rate Atomization Metering Penetration
Fuel injection timing
Inject the fuel at the correct time, aiming for max pressure to be created when cylinder is at 20-25* after TDC.
What is retarded and advanced timing?
Retarded - timing that occurs after manufacturers spec.
Advanced - timing that occurs before manufacturers spec.
As engine speed increases when must the fuel be injected?
Earlier. A greater number of degrees before TDC
Rate of injection
How long it takes for a volume of fuel to be injected. Can be measured in 1/1000 of a second, or degrees of crankshaft rotation.
Atomization
To break up the fuel into tiny droplets small enough to vaporize readily with the heat of compression.
What to factors control atomization?
Injection pressure
Fuel injection nozzle design
Metering
Fuel systems must supply exactly the right fuel quantity for all speeds and loads. Two common pumps are port and helix (inline), opposed plunger
Penetration refers to what?
The ability of the fuel spray to reach all areas of the combustion chamber
Fuel pumps must be a minimum of how accurate?
Portions must not vary more then 5%
Timing of injections must also be within +- 1* of crankshaft rotation
What are the two basic currently used fuel injection systems?
Multi-plunger injection pump
Unit injection system
The basic fuel injection system is comprised of what two sections?
Fuel supply
Injection
The fuel tank serves a reservoir that must be of sufficient volume to?
Allow for continuos engine operation
Allow the return fuel to settle and cool before being pumped back to the injection system
Fuel filters must be:
If sufficient size and rating to remove contaminants from the fuel supply
Dirty fuel is ____ then no fuel
Worse
Function of transfer pumps?
Used to move fuel from the tank to the injection pump or unit injectors
What additional component may a unit injector system have?
A restriction device in return line. This will control pressure in supply circuit, as well as holding fuel in head when engine shut down
Injection pump and high pressure lines
The pump meters the fuel and generates the high pressure needed for injection. Pressure can reach 20,000 PSI. Lines are made from equal length heavy wall seamless steel tubing
Hydraulic injection nozzles
Used with multi plunger pump. Nozzles atomize and distribute the fuel in chamber. Nozzles are hydraulically actuated by the high pressure from the injection pump
Unit injectors
Must time, Atomize, meter, and pressurize fuel as well as distribute it to chamber. Pressures can reach 30,000 PSI
What two reasons would cause injection timing to vary from manufacturers specs?
Wear
Inaccurate adjustment
Five purposes of the fuel supply section?
Supply correct pressure fuel to higher pressure system Clean the fuel of contaminants Remove water Supply fuel at correct temp Remove air
Final Stage fuel filters remove ___________particles.
particles over 1 micron
Vane or blade type transfer pumps are most commonly used with?
distributor type injection pumps
Opposed plunger injection pumps are driven by the engines gear train and turns?
at camshaft speed
In an opposed plunger style injection pump the metering valve:
controls the amount of fuel that is loaded between the plungers
Air to fuel ratio control (AFRC) is used to?
limit max fuel metering until there is sufficient turbo boost
Fuel transfer pressure in most systems is approximately _________?
65 psi
Limiting speed governors control what?
high idle and low idle
Variable speed governors control what?
high idle, low idle and intermediate speeds
Primary fuel filter is designed to remove particles over ____________?
remove particles over 25 microns
The main cause of “knock” in a diesel engine is?
the ignition delay period
These type of fuel injection nozzles atomize, distribute, meter and pressurize fuel into the combustion chamber.
unit injectors
