DON'T - repeat DON'T - use it in any HDi.
And what about the non-turbo 1.9?
I used to regularly use veg oil in my 1.5 diesel Citroen AX, with no issues. Only problem was when it was really cold (ie below -5) and I had a 50/50 mix or greater. In fact it always kept the emissions nice and low, even over 120k miles...
I used it up to a 50/50 maximum in my XUD Xantia for a coupel of years without problem. Every so often I filled with neat Diesel and injector cleaner and gave it an Italian tune up just to shift any deposits. I imagine yours would be the same, but I would recommend some research first.
1.9 is old technology, indirect injection so more veg oil friendly than hdi engines.
Is the DW8 basically an XUD with a partly electronic fuel injection system? I might try a few litres of veg oil in the next tank, every little helps.
I think it depends on the injector pump type I remember reading on a veg oil sites that the Bosch diesel pump was okay but the other wasn't