Eg101-Otto and Diesel Cycles quiz 4
In a two-stroke engine, what processes occur with each stroke?
In a two-stroke engine, intake, exhaust, and power delivery all happen in a single stroke. During the second stroke, compression of the air-fuel mixture happens.
How many volume states are involved in the Diesel cycle? Name them.
Three volume states are involved in the Diesel cycle; they are the minimum, maximum, and intermediate volume.
What type(s) of energy transfer are involved in process 2-3 of a Diesel cycle?
Heat and work transfer are involved in process 2-3 of a Diesel cycle.
Describe the four processes of a Diesel cycle.
1-2. isentropic compression 2-3. constant pressure heat addition 3-4. isentropic expansion 4-1. constant volume heat rejection
Describe the four process of an Otto cycle.
1-2. isentropic compression 2-3. constant volume heat addition 3-4. isentropic expansion 4-1. constant volume heat rejection
Describe the four processes that occur in one cycle of a piston engine.
1. intake: air and fuel are drawn into the cylinder 2. compression: the air-fuel mixture is compressed to a high pressure and combusts 3. power delivery: expanding combustion gases apply force to the piston, delivering power to the crankshaft 4. exhaust: the combustion products are expelled from the cylinder
A greater compression ratio and greater displacement will do what to power delivered by an engine?
A greater compression ratio and displacement increases the power delivered by an engine.
What cycle do compression ignition engines operate on?
Compression ignition engines operate on the Diesel cycle.
How many revolutions are needed for one cycle in a two-stroke engine?
One revolution of the crankshaft completes one cycle of a two-stroke engine.
What are the two assumptions (one or the other) that can be made when analyzing Otto cycles?
The air standard assumption with variable specific heats or the air standard assumption with constant specific heat.
What is the main difference between the Diesel cycle and Otto cycle?
The main difference between the Diesel cycle and Otto cycle is that process 2-3 occurs as a constant pressure heat addition instead of a constant volume heat addition.
How many revolutions are needed for one cycle in a four-stroke engine?
Two revolutions of the crankshaft completes one cycle of a four-stroke engine.
How many volume states are involved in the Otto cycle? Name them.
Two volume states are involved in the Otto cycle; they are the minimum and maximum volumes.
What are the costs and benefits of two-stroke engines?
Two-stroke engines deliver twice the power of a four-stroke engine of the same displacement; however, they tend to eject unburned fuel with the exhaust gases.
four-stroke engine
four separate motions (strokes) of the piston are required to execute the four processes of a piston engine
What is another name for the air standard assumption with constant specific heat?
sometimes called the cold air assumption.
bottom dead center
the closest distance to the crankshaft that a piston can go
bore
the diameter of a circular cylinder
total displacement
the displacement volume of one cylinder multiplied by the number of cylinders
stroke
the distance between top dead center and bottom dead center
top dead center
the furthest distance from the crankshaft that a piston can go
displacement volume
the maximum volume with the piston at bottom dead center
compression ratio
the ratio between the maximum volume to the minimum valume
cutoff ratio
the ratio of combustion chamber volume at the end of fuel injection/combustion and the combustion chamber volume at the beginning of fuel injection/combustion.
Otto Cycle
the thermodynamic model for spark ignition engines
two-stroke engine
two separate motions (strokes) of the piston are required to execute the four processes of a piston engine
spark ignition engine
uses a spark to ignite the gasoline-air mixture inside a cylinder or combustion chamber
compression ignition engine
uses compression of the fuel-gas mixture to such a high temperature to ignite