I have an engine cycle in mind looking for it's name

In summary, the conversation revolves around trying to identify a particular engine cycle that is described as a square on a Pressure-Volume Diagram. It is similar to the Ericsson cycle and consists of four steps: isothermal compression, isobaric heat addition, isothermal expansion, and isobaric heat rejection. However, it is pointed out that this cycle is not possible as it requires constantly increasing and decreasing temperatures without a work retrieving phase in between. The maximum efficiency of this cycle is also discussed.
  • #1
shanesworld
28
0
This is a simple question I have because I am looking at a particular engine cycle, and I can't seem to think of its name...thus it is very difficult to search for discussions of something you don't know the name of. I'll describe the cycle, if anyone knows the name of the cycle please let me know, or remind me of what it is called. This is neither the Carnot cycle, nor the Otto Cycle,( aguable even more simlpe minded)

In four steps on a Pressure-Volume Diagram it goes

1) Gas in piston (or the likes) expands at a constant pressure P1
2) Heat is allowed to escape, but volume is held fixed at V1
3) Gas in piston contracts at constant lower pressure P2
4) Heat is added while volume is held fixed at V2. (V2<V1)

It looks like a square drawn on the P-V diagram. What is it's name?
 
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  • #2
Sounds similar to the Ericsson cycle.
isothermal compression - isobaric heat addition - isothermal expansion - isobaric heat rejection
so it's a P-V square.
 
  • #3
EWH said:
Sounds similar to the Ericsson cycle.
isothermal compression - isobaric heat addition - isothermal expansion - isobaric heat rejection
so it's a P-V square.

Thanks for the reply...

...well, I don't actually think that is a P-V square though, but it's interesting in itself.
 
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  • #4
shanesworld said:
Thanks for the reply...

...well, I don't actually think that is a P-V square though, but it's interesting in itself.

If all the phases are isobaric or isothermal, then it can be a square on the P-V diagram. If any phase is other than isobaric or isothermal, it can't be a square on the P-V diagram.
 
  • #5
EWH said:
If all the phases are isobaric or isothermal, then it can be a square on the P-V diagram. If any phase is other than isobaric or isothermal, it can't be a square on the P-V diagram.

Isothermal usuall does not generally correspond to a straight line on P-V diagram. For instance for an ideal gas nRT=PV. At a constant temperature (i.e isothermal) this means that PV=constant; if the volume changes, the pressure must also change. So in a step where pressure is changed and the volume is held fixed, this would not be isobaric in general... there is at least one major case where your statement is not true. That is why I said the cycle you mentioned is not a square on the P-V diagram.
 
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  • #6
I don't think someone bothered naming such a cycle as its existence is pointless.

The problem lies in your isobaric expansion phase followed by a isochoric cooling phase. The only way to achieve the isobaric expansion is by constantly increasing the temperature (like in a brayton or a diesel cycle). And right after that, you are cooling the gas ... without a «work retrieving» phase in between! You absolutely need an adiabatic phase, worst case scenario, an isothermal phase to convert the heat you added into work.

The same goes for your isobaric compression where you need to constantly drop the temperature in order to achieve that, hence removing heat ... followed immediately by a heat addition!

If I didn't make any mistake, the maximum efficiency ([itex]\eta[/itex]) you can get with the cycle you described is:

[itex]\eta = \frac{k-1}{k}[/itex]

where k is the specific heat ratio for the gas. For air, the max efficiency turns out be 29%. And that is assuming infinite pressure and compression ratios!
 
  • #7
"Isothermal usuall does not generally correspond to a straight line on P-V diagram. "

Quite right, my mistake.
 
  • #8
jack action said:
I don't think someone bothered naming such a cycle as its existence is pointless.

The problem lies in your isobaric expansion phase followed by a isochoric cooling phase. The only way to achieve the isobaric expansion is by constantly increasing the temperature (like in a brayton or a diesel cycle). And right after that, you are cooling the gas ... without a «work retrieving» phase in between! You absolutely need an adiabatic phase, worst case scenario, an isothermal phase to convert the heat you added into work.

The same goes for your isobaric compression where you need to constantly drop the temperature in order to achieve that, hence removing heat ... followed immediately by a heat addition!

If I didn't make any mistake, the maximum efficiency ([itex]\eta[/itex]) you can get with the cycle you described is:

[itex]\eta = \frac{k-1}{k}[/itex]

where k is the specific heat ratio for the gas. For air, the max efficiency turns out be 29%. And that is assuming infinite pressure and compression ratios!

Wow, hadn't checked on this thread in a while but thanks for the post. ...appreciate it.
 

Related to I have an engine cycle in mind looking for it's name

1) What is an engine cycle?

An engine cycle is a series of events that occur in an engine to convert fuel into mechanical energy, which can be used to power machinery or vehicles. It is a continuous process that repeats itself in order for the engine to continue functioning.

2) How does an engine cycle work?

An engine cycle works by using a fuel source, such as gasoline, to create a controlled explosion within the engine. This explosion creates pressure, which then moves the pistons and turns the crankshaft, ultimately producing the mechanical energy needed to power the engine.

3) What are the different types of engine cycles?

There are several types of engine cycles, including the Otto cycle, Diesel cycle, and Atkinson cycle. These cycles differ in the way they intake and compress fuel and air, as well as how they ignite and exhaust the resulting gases.

4) What is the purpose of determining the name of an engine cycle?

Determining the name of an engine cycle is important for understanding its specific characteristics and how it operates. This information can be useful in designing and improving engines, as well as in troubleshooting any issues that may arise.

5) How do scientists name engine cycles?

Engine cycles are typically named after the person who invented or discovered them. For example, the Otto cycle is named after Nikolaus Otto, who developed the first four-stroke internal combustion engine. The Diesel cycle is named after Rudolf Diesel, who invented the diesel engine. Other engine cycles may be named after the type of fuel they use or their specific characteristics.

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