How to set loading(resistance) when i try to simulation Darlington pair limit current between Voltage 9 to 36

Hi All

could anyone know how to set my loading (R13) value for simulating darlington limit current between Voltage 9 to 36 ?

if there is no loading(R13),the result of Q1 current(C to E) would not show correctly. but placing fixed resistance that might 1k does not simulate how much current darlington will be limited in this circuit when changing Voltage range.     i think current should increase as voltage is decreased 

thnaks in advance