Stirlingengineforum.com

Is stiring engine directly proportional to temperature difference? theoretically?
I mean, if the temperature difference doubled, the rpm of the engine will be doubled ?

or is there any additional folmula of this...

The speed is mainly a function of the pressure differential (both sides of working piston). Under ideal conditions, if you double the presssure then both speed and output double, but only when load per rpm remains constant. In this case (and ideal Stirling) 2x T = 2x P = 2x rpm = 2x work.