I have owned a couple of VW Jetta (N. American Bora) TDIs.
My current car is an '04 Jetta TDI wagon with the new unit injection pump ("PumpeDüse") engine. My previous one, a '99, had the older rotary injection pump.
I would be worried about using Jet A1 in a car with a high pressure injection pump due to lack of lubricity of the fuel (namely, from sulphur). The pumps aren't cheap, they go for around $3,000 CDN, I believe. In Europe though, I believe diesel fuel is low-sulphur. So perhaps European diesels are set up to handle it. N. American fuel is high-sulphur, which is great for the pump, but not so great for meeting emissions regulations, hence the paucity of diesels over here (for cars, VW only until this year, the Merc is coming back with diesels).
You need to save a lot of money to risk a $3k injection pump!
VW will void the warranty if you use N. American biodiesel in a TDI, presumably due to the possible effects on the injection pump (or pumps on the unit-injector models).
For those of you who drive VW TDIs, a great resource is
www.tdiclub.com, somebody there has probably tried it or researched it. Incidentally don't many airport diesel vehicles run off the dregs of Jet A1 that doesn't make into the air?
Mike
C-GTLM