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

• Engineering
• lee123456789
In summary, the 2-stroke engine would have a compression stroke and an ignition stroke, while the 4-stroke engine would have a power stroke and heat rejection.

#### lee123456789

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Would two stroke spark ignition PV digram be same as 4 stroke spark ignition. both have otto pv diagrams.

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?

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

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.

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

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:

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.

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.

jack action said:
Thank u and sorry for being that dang at it
Diagram helped.

jack action

## 1. What is the difference between a two stroke and a four stroke engine?

The main difference between a two stroke and a four stroke engine is the number of strokes required for one complete cycle. In a two stroke engine, the piston moves up and down twice in one revolution, while in a four stroke engine, the piston moves up and down four times in one revolution.

## 2. How does the spark ignition process differ in two stroke and four stroke engines?

In a two stroke engine, the spark plug fires once every revolution, while in a four stroke engine, the spark plug fires once every two revolutions. This is because the spark plug ignites the fuel-air mixture on every stroke in a two stroke engine, while in a four stroke engine, the spark plug only ignites the mixture on the power stroke.

## 3. Are the pressure-volume diagrams different for a two stroke and four stroke engine?

Yes, the pressure-volume (PV) diagrams are different for a two stroke and four stroke engine. In a two stroke engine, the PV diagram shows a single loop, while in a four stroke engine, the PV diagram shows two loops. This is due to the difference in the number of strokes required for one complete cycle.

## 4. Is the efficiency of a two stroke engine the same as a four stroke engine?

No, the efficiency of a two stroke engine is typically lower than a four stroke engine. This is because in a two stroke engine, some of the fuel-air mixture can escape through the exhaust port before it is fully burned, resulting in lower efficiency compared to a four stroke engine.

## 5. Can the same PV diagram be used for both two stroke and four stroke spark ignition engines?

No, the PV diagram for a two stroke spark ignition engine will be different from that of a four stroke spark ignition engine. This is because the combustion process and the number of strokes required for one complete cycle are different between the two types of engines.

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