Thermo Cycle Analysis Flashcards
What is a polytropic relation?
It’s a process on a PV diagram where p*(v^n) = constant.
What is work?
Work = integral of p delta v
Usually this means using your polytropic relation to find p as a function of v and integrating.
What is an adiabatic process?
It’s a process where there is no heat transfer. It means all Win goes into internal energy.
Can be done either with insulation, or with isothermal conditions.
What is n for adiabatic?
n = Cp/Cv = gamma
Why do people want high octane fuels?
Higher octane fuels are less likely to autoignite. They’re good for performance cars with high compression ratios.
What’s the difference between gas and diesel engines?
Gas: fuel is added, mix compressed, spark plug ignites.
Diesel: Air is compressed, fuel is added, which auto-ignites.
Why would someone prefer a diesel engine?
Much higher compression ratios can be used.
What’s the difference between cetane and octane ratings?
Octane measures how resistant a fuel is to auto-igniting, whereas cetane measures how easily a fuel will ignite.
Higher numbers are better in both cases.
What’s the difference between a polytropic relation and the ideal gas law and the internal energy function?
Polytropic relations are a process equation.
Ideal gas and internal energy are equations of state.
Why is enthalpy a state function?
It’s made up of state variables.
