# Thermo Question P-V diagram

1. Apr 21, 2010

### KCatBatt

If you were to combine a diesel cycle and a steam cycle (crower cycle) in 1 p-v diagram, what would it look like?

2. Apr 21, 2010

### Staff: Mentor

Welcome to PF.

Sorry, but the question doesn't make a whole lot of sense. What, physically, are you describing?

3. Apr 21, 2010

### KCatBatt

Thanks for the welcome.

I'm talking about a 6-stroke engine, more specifically a Crower cycle.

There will be a intake stroke, compression, combustion, exhaust... and at TDC of the exhaust stroke, water will be injected to harness the otherwise wasted heat and convert to steam... expanding and creating work, then exhausted again and the cycle starts over.

4. Apr 22, 2010

### jasc15

I would imagine it would simply be 2 superimposed cycles (otto/diesel, and rankine) analyzed separately, rather than one cycle since a cycle depicts what is done to a single working fluid. The duty cycles of each are reduced to producing power 1/6 of the time, which might or might not be enough to justify it.

In addition, I'm not sure you could create superheated steam in sufficient quantities in such a short period of time with those temperatures. Rankine cycle steam temperatures are roughly around 800* F, which will never occur in a typical IC engine.

Last edited: Apr 22, 2010
5. Apr 22, 2010

### KCatBatt

There will be 2 power strokes every 6 strokes.

The temps are there to phase change to steam at 1atm, but we can still play with the pressures by adjusting the timing at which it's injected, bringing down the pressure below 1atm.

Now the temps are not 800F, but I don't know what pressures you thinking of when you come up with that number. Are you saying that the steam will not be able to do work unless the temps are at 800F?

thanks,
Casey

6. Apr 22, 2010

### jasc15

The quality of steam goes down when pressure goes up (it wants to condense), so you need a higer temperature to maintain a superheated steam (>100% quality) at effective pressures.

And yes, you have 2 power strokes every 6 strokes for a duty cycle of 33%, whereas a 4 stroke has a duty cycle of 25%, so you are right there. However, It seems that the steam power stroke will not produce enough added benefit, not to mention the possibility of residual moisture during combustion since your condensing step is done in the cylinder (if i understand correctly).

Last edited: Apr 22, 2010
7. Apr 23, 2010

### jack action

It would look like two superpose traditional cycles (one smaller that the other).

Traditional heating by combustion of fuel