[Jack of all Trades]

I worked on partial Propane injection for a while about 10 years ago.

A sensor that measures pressure in the cylinders plays a key part...

...aaaand there's one of the major technical hurdles, at least as I'm aware of. I haven't looked into it in a while. That pressure sensor is going to see on the order of 100 million pressure cycles over the life of the engine. That's a lot.

[The Antiyuppie]

“...aaaand there’s one of the major technical hurdles, at least as I’m aware of. I haven’t looked into it in a while. That pressure sensor is going to see on the order of 100 million pressure cycles over the life of the engine. That’s a lot.”

Piezo might be able to do it.