I'm not sure how a newer diesel would like it, but older mechanically injected diesels are quite OK with having propane or NG introduced into their airstream. I've seen diesels around town that also have a natural gas system installed. This partially replaces the diesel, depending on the system settings. I have read that the diesel can end up being as little as 5% of the total fuel load and is really only there in order to commence combustion as the NG or propane won't auto ignite.
1989 E30 - M50B28 Turbo - ZF 8 Speed
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