Would the two stroke spark ignition PV digram be same as for a 4 stroke?

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Discussion Overview

The discussion centers on the comparison of the pressure-volume (PV) diagrams for two-stroke and four-stroke spark ignition engines, specifically focusing on the differences in their respective diagrams and the phases represented within them.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants question whether the PV diagrams for two-stroke and four-stroke engines are the same, noting that both utilize Otto cycle diagrams.
  • Participants identify various strokes in the PV diagram, with some suggesting that the stages of compression and expansion can be identified, while others discuss the inclusion of intake and exhaust phases.
  • There is a proposal that the two-stroke engine has only a compression stroke and an expansion stroke, with intake and exhaust phases included within the compression stroke.
  • Some participants clarify that the intake and exhaust phases do not appear on the PV diagram for a two-stroke engine, contrasting it with the four-stroke engine diagram which has distinct phases.
  • One participant outlines a sequence of phases for a two-stroke engine, including ignition and heat rejection, while others challenge the clarity of this sequence.
  • There is a request for clarification on the layout of strokes in the diagrams, indicating some confusion regarding the representation of phases.

Areas of Agreement / Disagreement

Participants express differing views on the representation of strokes in the PV diagrams, with some asserting that the two-stroke engine has fewer distinct strokes than the four-stroke engine. The discussion remains unresolved regarding the exact representation and sequence of phases in the diagrams.

Contextual Notes

Participants mention the absence of certain lines in the PV diagram for two-stroke engines, indicating a potential misunderstanding of how the intake and exhaust phases are represented. There is also uncertainty regarding the specific points and transitions within the diagrams.

lee123456789
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Homework Statement
write about engines
Relevant Equations
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Would two stroke spark ignition PV digram be same as 4 stroke spark ignition. both have otto pv diagrams.

1623567900237.png
 
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What research have you done on this so far?
 
Chestermiller said:
What research have you done on this so far?
ive write about everything just getting confused on the PV diagrams pics to put into the document. i think its otto pv diagram.
 
How many strokes can you identify on the diagram in the OP?
 
jack action said:
How many strokes can you identify on the diagram in the OP?
I was thinking on the diagram
stages 1 -2 - 3 compression and 3 -4 - 1 was expansion
 
A stroke is a displacement ##V_s##. From 2 to 3 and 4 to 5, there are no displacements (constant volume), so let's forget about those for the moment. But you are correct with 1-2 for compression and 3-4 for expansion. But what about 0-1 and 5-0?
 
jack action said:
A stroke is a displacement ##V_s##. From 2 to 3 and 4 to 5, there are no displacements (constant volume), so let's forget about those for the moment. But you are correct with 1-2 for compression and 3-4 for expansion. But what about 0-1 and 5-0?
would 2 -3 be ignition phase and 4 - 5 would heat rejection?

0 - 1 Intake Stroke?
5 - 0 Exhaust Stroke?
 
2-3 would be combustion and 4-5 would be heat rejection (or cooling), but that doesn't have anything to do with our strokes.
lee123456789 said:
0 - 1 Intake Stroke?
5 - 0 Exhaust Stroke?
So now you have identified a total of 4 strokes. I guess this is good for a 4-stroke engine PV diagram.

How would a 2-stroke engine PV diagram differ?
 
jack action said:
2-3 would be combustion and 4-5 would be heat rejection (or cooling), but that doesn't have anything to do with our strokes.

So now you have identified a total of 4 strokes. I guess this is good for a 4-stroke engine PV diagram.

How would a 2-stroke engine PV diagram differ?
There would just be a compression stroke and expansion stroke and the exhaust would be in included in the compression stroke and intake would be included in compression stroke?
 
  • #10
lee123456789 said:
There would just be a compression stroke and expansion stroke and the exhaust would be in included in the compression stroke and intake would be included in compression stroke?
jack action said:
2-3 would be combustion and 4-5 would be heat rejection (or cooling), but that doesn't have anything to do with our strokes.

So now you have identified a total of 4 strokes. I guess this is good for a 4-stroke engine PV diagram.

How would a 2-stroke engine PV diagram differ?
I think this would be the sequence of 2 stroke

0 to 1 intake phase
1 to 2 compression stroke
2 to 3 ignition phase
3 to 4 expansion stroke
4 to 5 heat rejection phase
5 to 0 exhaust phase
 
  • #11
Post #9 is good, post #10 is wrong, or at least confusing. The intake phase (0-1) and exhaust phase (5-0) will not appear on the PV diagram as they will be included in the compression and expansion strokes. They are only 2 strokes.
 
  • #12
jack action said:
Post #9 is good, post #10 is wrong, or at least confusing. The intake phase (0-1) and exhaust phase (5-0) will not appear on the PV diagram as they will be included in the compression and expansion strokes. They are only 2 strokes.
I think this is it

0 to 1 to 2 to 3 compression stroke - included intake phase, compression stroke and ignition phase.

3 to 4 to 5 to 0 power stroke - includes power stroke, heat rejection, and exhaust phase
 
  • #13
There are no 0 to 1 nor 5 to 0 lines drawn on the PV diagram. That is the difference between the 2-stroke and the 4-stroke PV diagrams. The 2-stroke has only 4 points:

-assignment-help-with-two-stroke-engine-pv-diagram.jpg
Both the intake & exhaust phases will begin somewhere between 3 and 4 and end somewhere between 1 and 2.

Versus a 4-stroke engine PV diagram:

23ae3f3d-8f23-488a-b17e-f7f95ac1d435.jpg
 
  • #14
jack action said:
There are no 0 to 1 nor 5 to 0 lines drawn on the PV diagram. That is the difference between the 2-stroke and the 4-stroke PV diagrams. The 2-stroke has only 4 points:

Both the intake & exhaust phases will begin somewhere between 3 and 4 and end somewhere between 1 and 2.

Versus a 4-stroke engine PV diagram:

Sorry could u layout the strokes eg 1 to 2 to 3.
Sorry for being thick.1 to 2 to 3 I take, compression stroke and ignition.

3 to 4 to 1. Power stroke, heat rejection and exhaust.
 
  • #15
If you look at the 4-stroke engine PV diagram in my last post, a downward stroke is from TDC (top dead center) to BDC (bottom dead center) and an upward stroke is from BDC to TDC. The same limits applied to a 2-stroke engine.
 
  • #17
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