Carnot's cycle and a-like cycles

[Bassalisk]

Hello,

Lately I encountered thermodynamics. And all that world is very new to me, gas expansion etc etc.

I recently learned about Carnot's cycle. IT has 2 isotherms and 2 adiabatic processes.

Now, I understand what those processes in separation mean. Adiabatic processes don't exchange heat with the outside. I can coupe with that concept. But when you put all that together and pistons and all that stuff i come to confusion.

When you heat a gas inside the piston compartment, it expands isothermally. Now I understand what it means, temperature doesn't change. But why? How do you achieve this with gases? How do you control that variable, and after you expand it to some level, why does gas adiabatically continues to expand?

Can you explain this nature of gasses in these engines?

Thank you

 

[cgk]

Now, I understand what those processes in separation mean. Adiabatic processes don't exchange heat with the outside. I can coupe with that concept. But when you put all that together and pistons and all that stuff i come to confusion.

When you heat a gas inside the piston compartment, it expands isothermally. Now I understand what it means, temperature doesn't change. But why? How do you achieve this with gases? How do you control that variable, and after you expand it to some level, why does gas adiabatically continues to expand?

As you suspect, that variable cannot actually be controlled in reality, and the real processes occurring in engines have not much to do with the Carnot process or other idealized cycles. Go find a p/V diagram of a real combustion engine...

The cycles you learn are simplified abstractions. They are designed to be understandable and calculatable, and to graps the coarse idea behind the real processes. For example, if I remember correctly, the idea behind the adiabatic process was that the gas does not have enough time to equilibrate with the environment and thus no heat exchange occurs. Describing it in that way does not mean that really no heat is exchanged at all, it only means that other processes beside the heat exchange dominate the total behavior.

 

[Bassalisk]

I think i got it. Thanks