Are you asking about my take on the use of LPG and bio-diesel in a diesel engine? If so it's basically a non-starter. Unfortunately diesel engines won't run on pure LPG, so it has to be in addition to the use of DERV or bio-diesel. There are a couple of advantages to this:
1) The engine can be persuaded to produce more horsepower and/or torque, but at the expense of a higher total fuel useage.
2) LPG is cheaper than DERV and can give a lower overall fuel costs.
In practice most diesels converted to LPG are tuned to give a combination of both - a slight improvement in power output combined with a small reduction in running costs. Unfortunately you come across the problems inherent in most modern direct injection or common rail diesel engines in that they do not react well to the use of high percentages of bio-diesel or veggy oil (SWVO or WVO). You also have to take into account that many modern diesel engines are merely modified petrol engines and aren't capable of taking the higher stresses of more power than they were designed for.
Personally I prefer one option or t'other. Run and older diesel engine on veggy or convert a petrol engine to run on LPG. I've done both.
LPG is not the only environmentally friendly fuel. This area is for discussing the alternatives.