Yea, pure gas is no good in a diesel. The gas would ignite off before the piston hit near the top as a very bad pre-detonation/spark knock. A gas engine can't get anywhere near 17:1 because of those problems, I think the highest is around 13:1 and that's with very high octane fuel.
Also, diesel doesn't fire off with a spark very easily but it can run in a spark ignition engine as a mix. I looked for a video of a gas car being filled with diesel, but a PF video came up so I knew it would be interesting. Besides some cold start issues, a 50/50 mix of diesel and gas runs in a lawnmower, way more than I'd suggest. Also keep in mind, push mowers generally are pretty low compression, so have a low octane requirement.
I don't know what the mix was, but my dad's friend had his son fill his diesel up and he put gas in, instead of diesel. Truck did run, but very poorly. For fun I looked for a video of the opposite effect, gas in a diesel. They don't say what the mix was in either case, just the tank was low on fuel and they added 5L in of the wrong fuel which I suspect is over 50% of the wrong fuel.
This is more inline with the story I was told. My dad's friend moved to GA from MI using the same truck. It was an F250 or F350, 7.3L diesel, can't remember the year, I was like 14 at the time, probably mid 90's (it was a newer truck at the time).
The contract issue is interesting, the guy that I talked about lived way up north and he got 2x 55gal barrels filled with used fryer grease from a restaurant that serves beef and other meats deep fried. His wife was the manager there, but she left before they got the oil, but maybe she had some connections yet with the workers. I'm not one to sign a contract unless I read it, so if it's a mandated I must take the oil, I'd want to find out how much oil they need removed per year.
I do understand the cracking a bit, basically taking a complex molecule and breaking it down into a simpler one. I watch a lot of science based youtube channels and such so I hear and see the context of that term somewhat often.
Here's a channel that does a lot of things against "common sense", like who fills a container with propane and "burn" oxygen, but if you understand the process of burning, it's quite safe if done right. Below is the video, way off topic but still burning related so slightly engine related. I've had training on a gas that combusts with oxyegen with no spark or heat source. If I remember the figures right, if it's 90% or more pure, it will not react, and below 30% it won't. The gas I'm talking about is the man made gas called silane... byproduct of the fire is sand.
Here's a quick silane video. The plant I worked at made it as a secondary main product. They stored silane under high pressure to have it in tanks as a liquid (takes up much less space). However, trucking it, they have to transport as a compressed gas due to the high risk of the material. I was told a figure that each semi tank full is worth well over $1m and it's not even in liquid form. I was responsible for fixing their computers, printers, and very basic networking (patch cables, computer to wall box, etc).
For propane, I've read a little on them, and the ideal compression ratio is somewhere around 13:1 and is about 104 octane (race fuels can go over that but extremely expensive). Diesels are higher compression than ideal (atleast for spark ignition). I've heard of people running propane in their diesels, but I never asked the question if it's pure propane, or if it's mixed. I suspect a diesel could run on pure propane though, just not sure if the ignition point is too early or not via compression. It's an interesting alt fuel to look into as well. Bulk LP is cheap, even if there's a degrade in power the price difference is nearly 50% cheaper than diesel, should be cleaner burning, no fuel gel problems (extreme cold), etc.
This all makes me want to get a cheap (and old) VW diesel to experiment with. I have been wanting to get a generator for the house as a backup power source (one with electric start and such), I figured converting a gas engine to LP would be a smart move since I plan to have a pretty large tank on hand so in the event of an extended power outage, I could have reliable power for quite some time. With a battery bank, I could effectively P&G the system to extend the fuel usage. I've had power outages a lot this year and last year, probably 7 full outages in the last year where the power actually went off completely. For power flickers that can make a computer die, I've had countless of those events, it was so bad nearly daily my internet would drop out. I put everything on a large UPS and now my internet and computers have been nearly fault free. There's a lot of power related work being done because of the dam washing out so I guess it's kind of expected to have unreliable power. If batteries were cheaper, I'd be off grid with solar power + wind, but the costs are too high for my area currently to be a solid investment. It's getting close though.