08. The Diesel Engine Flashcards
Diesel engine
Diesel engines produce heat through what means and which stroke
COMPRESSION
Heat generated during compressiong stroke
Pg 184
Diesel engine
Another name given to Diesel engines based on them creating heat during compression is what
COMPRESSION IGNITION ENGINES
Pg 184
Diesel engine
As ignition occurs spontaneously, which 3 components are not needed in a diesel engine
- Spark Plugs
- Distributors
- Magnetos
Pg 184
Diesel engine
Why is there no need for a mixture control on a diesel engine
DIRECT FUEL INJECTION
Diesel engines use direct fuel injection into the cylinder
Pg 184
Diesel engine
What method do diesel engines use to get fuel into the cylinder
DIRECT FUEL INJECTION
Pg 184
Diesel engine
Operating at a higher compression ratio ensures a sufficiently high enough what
TEMPERATURE
Pg 185
Diesel engine
The typical compression ratio is from ____ : ____ to ____ : ____
14:1 < > 28:1
Pg 185
The maximum compression ratio of a petrol engine compared to a diesel engine is what
9:1
Pg 185
Diesel engine
What is increased as a result of a higher compression ratio of the charge
POWER OUTPUT
Pg 185
Diesel engine
As power output is improved given a higher compression ratio of the charge, what benefit does this have to the engine in terms of temperature
THERMAL EFFICIENCY
Pg 185
Diesel engine
What fuel is used in a diesel engine
JET A1
(Kerosene)
Pg 185
Diesel engine
Why can’t gasoline be used in a diesel engine
DETONATES UNCONTROLLABLY
Detonates uncontrollably at such high compression ratios
Pg 185
Diesel engine
What is the specific gravity range for Jet A1
0.8 - 0.9
Pg 185
Diesel engine
Jet A1 compared to AVGAS is;
1. MORE or LESS viscous
2. More or LESS volatile
3. HIGHER or LOWER flash point
- MORE
- LESS
- HIGHER
Pg 185
Diesel engine
As Jet A1 is more viscious, the main disadvantage is what
POOR LUBRICANT
Pg 185
Diesel engine
Since Jet A1 is more viscious and makes a poor lubricant, which component needs to be specifically designed for a diesel engine
FUEL PUMP
Pg 185
How are Kerosene fuels sometimes categorised
CETANE NUMBER
Pg 185
Diesel engine
What is a cetane number
KEROSENE CATEGORISATION
HIGHER the cetane number, SHORTER the ignition period
Pg 185
Diesel engine
A high cetane number means a LONGER or SHORTER ignition time
SHORTED
Pg 185
Diesel engine
Select which of the following are advantages of a diesel engine
1. Fuel Efficient [ ]
2. Light Weight [ ]
3. Robust [ ]
4. Ideal for Supercharging [ ]
5. Ideal for Turbocharging [ ]
6. Cheaper to run than AVGAS engine [ ]
7. Larger engine size than petrol engine gives more power [ ]
8. Lower power to weight ratio [ ]
9. More reliable than petrol engine [ ]
- FUEL EFFICIENT
- ROBUST
- TURBO
- RELIABLE
- CHEAPER
- POWER RATIO
1, 3, 5, 6, 8, 9
- More fuel efficient
- Heavier build makes them more robust and ideal for turbocharging
- No ignition system, makes them simplier and more reliable
- Jet A1 is cheaper than AVGAS
- Compared to similar size AVGAS engine, power to weight ratio is better
Pg 186
Diesel engine
What are the 4 strokes of a diesel engine
- Induction
- Compression
- Power Exhaust
Suck, squeeze, bang, blow
Similar operation to a petrol engine
Pg 187
Diesel engine
During the induction stroke, what is drawn into the cylinder, and how does this differ to a petrol engine
- Air
- Petrol engine draws in mixture i.e. air AND fuel
Pg 187
Diesel engine
What position and in during which stroke is the piston in when fuel is introduced into the cylinder
- TDC
- Very end of compression stroke
Compression ratio is so high, flash point would be reached very quickly during compression strok.
Fuel is subsequently injected at the very last moment
Pg 187
Diesel engine
What is the force exerted in a power stroke so much greater than a petrol engine
VOLUME
Compression is so much greater, volume is compressed greatly
Pg 187
Diesel engine
Given that there is no risk of detonation, what benefit does this have regarding the stoichiometric ratio of the fuel
MUCH LEANER
Pg 187
Diesel engine
How is power output controlled
CONTROL AMOUNT OF FUEL INJECTED
Control the amount of fuel injected into the cylinder.
This differs to a petrol engine where the amount of mixture is controlled that is introduced to the cylinder
Pg 817
Diesel engine
What pressure (in bar and PSI) must a direct fuel injection system cope with
1600 BAR
24,000 PSI
Pg 188
Diesel engine
What 2 types of injection system are used in an aero diesel engine
- Direct Injection
- Common Rail
Diesel engine
What is the difference in terms of fuel delivery to the cylinder between a direct injection system and a common rail system
DIRECT INJECTION - High pressure fuel pumped directly into each cylinder
COMMON RAIL - Pressure pump suppliers a common rail where fuel is distributed to the cylinders evenly
Pg 188
Diesel engine
Most common diesel engines use a DIRECT INJECTION or COMMON RAIL system
COMMON RAIL
Pg 188
Diesel engine
What 4 things must the pump of a direct fuel injection system be able to do in order to deliver an exact meterd amount of high pressure fuel to the injector
- RPM
- DENSITY
- TIMING
- PULSES
- Sense the engine RPM
- Sense air density
- Advancing and retarding the timing of fule pulses
- Generate fuel pulses of sufficient pressure
Pg 190
Diesel engine
How does the fuel injector port open when the pressure is correct
SPRING LOADED POPPET
Spring loaded poppet opens momentarily when the fuel line pressure exeeds the opposing force
Pg 191
What are the 4 key components that make up a common rail injection system
- PRESSURE PUMP
- COMMON RAIL
- INJECTORS
- ECU - Engine Control unit
- High pressure pump - also with a pressure regulator and metering valve
- Common rail acts as an accumulator of high pressure fuel
- Injectors - electro-magnetically operated
- Engine Control Unit - monitors engine conditions and controls pressure in common rail, and timing of injectors opening and closing
Pg 192
When can diesel engines be difficult to start
COLD DAY
Pg 194
Why are diesel engines difficult to start on a cold day
FLASHPOINT TEMPERATURE NOT REACHED
Compression stroke may not be enough to raise temp above flash point
Pg 194
To overcome the issues of flash point of fuel not being reached by the compression stroke on a cold day, what is fitted into diesel engines to increase the temperature
GLOW PLUGS
Pg 194
What is the purpose of a glow plug
INCREASE TEMPERATURE in COMBUSTION CHAMBER
Pg 194
What are the 2 types of glow plug
- Sheathed
- Ceramic
Pg 194
A sheathed glow plug contains an ____.
A ceramic glow plug contains a ____.
- Electrically heated coil
- Heating element
Pg 194
Where do glow plugs obtain their power
BATTERY
Pg 195
Compared to an equivilant petrol engine, in regards to temperature, what does a diesel engine require more of
COOLING
Pg 196
What is the most common method of cooling a diesel engine
LIQUID
Pg 196
What is the cooling liquid in a diesel engine comprised of typically
WATER & ANTIFREEZE
Pg 196
What component located in the intake of the cooling system helps disperse heat absorbed by liquid coolant
AIR COOLED HEAT EXCHANGER
Pg 196
