How is the power output of a diesel engine controlled as the driver presses the accelerator?
- By throttling the amount of intake air
- By changing the amount of fuel injected
- By changing the compression ratio
- By advancing the valve timing with load
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B. By changing the amount of fuel injected
A diesel takes in a full charge of air on every intake stroke and varies power by how much fuel is injected. Throttling the intake air is how a gasoline engine is controlled, which is the tempting wrong answer.
Reference: Diesel engine fundamentals, fuel metering
What does the cetane number of a diesel fuel describe?
- How well the fuel resists knock in a spark engine
- How much heat energy a gallon of fuel contains
- How cold the fuel can get before it stops flowing
- How readily the fuel ignites under compression
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D. How readily the fuel ignites under compression
Cetane rates ignition quality: a higher number means a shorter ignition delay and easier starting. Resistance to knock is what octane measures for gasoline, and it is roughly the opposite property.
Reference: ASTM D975 diesel fuel properties (cetane number)
An inline six-cylinder diesel has the firing order 1-5-3-6-2-4. Which cylinder is the companion (running mate) of cylinder 1?
- Cylinder 5
- Cylinder 4
- Cylinder 6
- Cylinder 2
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C. Cylinder 6
Companion cylinders have pistons that rise and fall together and fire 360 crankshaft degrees apart. In 1-5-3-6-2-4, cylinder 6 is three positions after cylinder 1, so the pairs are 1-6, 2-5 and 3-4. Cylinder 5 simply fires next; it is not the companion.
Reference: ASE T2 Diesel Engines task list, cylinder head and valve train (valve adjustment)