 Why is the air inside the machine not stale on the return trip like it had been on the prior trip?
You can see a sort of foggy nothing surrounding the cockpit; it is probably the field that prevents passage through time from affecting us. That means you either carry a small time field with you, or you are catching a small increment of time from the main field. You suddenly realize that everything in the machine is wide open, yet you haven't seen any effects of air loss. You feel a dankish sort of air replace the stale air, and you breathe easier, though we're in complete darkness, except for the weak light in the machine, which always burns, and a few feet of rough dirty cement floor around. There's no feeling of acceleration—some kind of false gravity they use in the future.
 Because there is only one Jerome smoking inside the machine.
 Because the generator is working and clearing the air.  Because there is a clearer air flow now with the retrieval of the generator.  Because no one is smoking inside the machine.  Because there is only one Jerome smoking inside the machine.