Objective 05: The Diesel Cycle Flashcards
What does the Diesel Cycle apply to?
Compression-ignition internal combusion engines
What characterizes the Diesel Cycle?
Heat addition occurs at almost constant pressure.
What is the main working fluid of the Diesel Cycle?
Air
How does the Diesel cycle differ from the Otto cycle in terms of how compression and heat addition occur?
The air is compressed to a higher pressure inside the cylinder, which increases the temperature, and the fuel ignites spontaneously when it enters the cylinder.
What occurs during the intake stroke of the Diesel Cycle?
Adiabatic compression causes both the pressure and temperature to increase while the volume decreases
How does heat addition occur in the Diesel Cycle?
Internal combustion occurs as the fuel is injected. Pressure remains almost constant since the piston is forced to the right (thus increasing the volume) for the first part of the power stroke.
How is work done in the Diesel Cycle?
During the second part of the power stroke, combusion gases expand adiabatically as the pressure decreases.
How does heat rejection occur in the Diesel Cycle?
Combustion gases are exhausted from the cylinder and pressure is reduced back to starting pressure while volume remains constant.
Are compression and expansion both isentropic in the Diesel Cycle?
Yes
Cut-off Ratio (R)
The ratio between the cut-off volume (V1) and the clearance volume (V2).
Why doesn’t a Diesel Engine have the same restriction on compression as the Otto Engine?
The compression is of the air only
What is an advantage of the Otto cycle over the Diesel cycle?
It is more efficient for the same compression ratio
What is an advantage of the Diesel cycle over the Otto cycle?
It can operate at substantially higher compression ratios which makes it more efficient.
What is the maximum compression ratio that mechanical considerations limit diesel engines to?
25:1
