I did a fair bit of work on it several years ago. Look up 'fumigation' on google. It's mainly done with LPG. You'll find that it will cause the engine to knock at high load, but works well for mid load. For vehicles, we turn off the gas completely to avoid knocking on over-run (no diesel to provide ignition, so presumably ignites when exhaust valve opens).
Ive done some looking on google, but am unsure where you are pointing me to : (
Can you give me a direct link?