Diesel Engine Flashcards
Diesel fuel.
Kerosene ( Jet A1 / Jet A)
Specific gravity of 0.8-0.9
Less volatile, higher flash point than AVGAS.
Poor lubricant.
Advantages and disadvantages of diesel engines.
More fuel efficient
Less schedule maintenance
Suited to turbocharging
Simpler and more reliable without ignition system
Kerosene is cheaper and safer than AVGAS
Higher operating pressures requires stronger, heavier designs.
Compression.
Air is compressed much further than in spark ignition engine.
Just before TDC a precisely metered fuel quantity is injected into cylinder.
Immediately ignited due to cylinder temp.
Power
At point of ignition the charge is much more compressed and contained in a smaller volume hence more pressure generated.
No risk of detonation so operate much leaner.
No mixture control lever required.
Exhaust.
Same as petrol engine.
Diesel fuel injection system.
Up to 24000psi.
Two types:
Mechanical injection
Common rail
Most common is common rail as it gives more efficient combustion, cleaner emissions and quieter operation.
Mechanical injection.
High pressure fuel is fed to each injector from a dedicated fuel pump (crankshaft driven).
Common rail.
High pressure pump supplies fuel to a common rail from where the fuel is distributed to each electronic injector.
Direct injection.
Uses 2 pumps due to high pressure.
Injectors.
Mechanically operates spring loaded poppet valve which opens when fuel pressure exceeds spring force.
Metering system.
Sends timed pulses of pressurised fuel to each injector.
Glow plugs.
Contains an electrically heated coil encased in a sheath filled with magnesium oxide powder.
Powered from the battery.
Used to warm the cylinder pre start.
Power to weight ratio.
Diesel engine has lower power to weight ratio
Diesel engine cooling.
Water cooling galleries in the free spaces.
Mixture of water and anti freeze.
An air cooled heat exchanger disperses the heat energy absorbed by the coolant.
