# Valve lift & variable air flowrate in compressed air

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1. May 8, 2015

### Chotai Nikhil

How we can incorporate valve lift and variable flow rate in compressed air engine

Mechanical power = air power
torque * angular velocity = pressure * flow rate

2. May 12, 2015

### Randy Beikmann

There's a lot to your question. Are you asking how to calculate the flow into the cylinder as a function of valve lift?
I don't believe your second expression is that useful. The power produced by the motor (it's not an "engine" because it doesn't run on heat) will be equal to the force on the piston times the piston speed (p*A*dx/dt), but not equal to the rate of energy coming in with the fluid. This is because some of the enthalpy of the incoming flow, through turbulence, will be converted to heat.
You'll need to calculate the mass-flow into the cylinder to get pressure as a function of crank angle theta, and calculate torque from T = p*A*dx/dtheta.

3. May 12, 2015

### Chotai Nikhil

Thank you sir

1) I used the Word Engine because i modified the 4 stroke petrol engine to 2 stroke engine

2) how does i incorporate flow rate instead of Pressure "P" because i have flow through valve here and i dont have exact value of Pressure of P incise the cylinder which we call as mean pressure in petrol engine.