The JFS (Jet Fuel Starter) on the F-16 is basically an APU that runs on jet fuel, but started by compressed air, from what I understand.
As an aside: Please correct this too, preferably with some reference. Is it correct that it is started on compressed air? And that it gets refilled, compressed again, when the engine runs above a certain RPM?
Why doesn't the F-16 JFS keep running? If it runs on jet fuel, couldn't it keep running as long as the F-16 has fuel? I believe the JFS is shut down automatically once the engine is running, but if it weren't for this feature, it would just keep running. Is that correct?
Edit addressing some comments:
Why am I asking this? Why would I want to have the JFS running?
It is simply a question to help me understand how the JFS works. It is unclear to me why it has an inlet and exhaust port. This indicates to me it runs like a normal APU. Yet, I find various information indicating it runs on compressed air, some sources say it runs on hydraulic fluid. If it runs on compressed air or hydraulic fluid, why would it need both an inlet and an exhaust port?
It isn't that I would like to keep the JFS running on the low-mileage F-16 I have in my garage, rather that I don't understand the mechanics of the JFS and how it differs from a regular APU.