Thanks!
Do you mind if I ask what ratios you use for your propane fumigation? Is it mostly propane or mostly diesel, for an example? Looks like natural gas has a higher octane than propane so it sounds promising.
I found an article that suggests that 22.9:1 CR may be a bit too high for a CNG diesel engine. But maybe it won't be as bad as they calculated (e.g. maybe they didn't take into account heat absorption into engine during compression stroke??) or maybe all I'd need is water injection to go with it.
https://eprints.usq.edu.au/72/1/LIMPeiLi-2004.pdf
I thought of CNG because I saw a 24 hour station in town, whereas with propane I'm stuck with $20 partially filled 5 gallon tanks or seasonal RV parks at about $2.50 per gallon IIRC. Ideally I'd need something that can quickly refuel on the road. It seems what I've read about CNG home refueling is that it takes all night, kind of like charging the electric car itself, which would be cool, but not so helpful away from home, which is where I'd need it the most. Obviously I could and should get the diesel pusher trailer going and later switch to natural gas or propane.