Grand Central 180 with green stripe

[plugwash]

It is surely a basic requirement of a fuel that it will burn.

Sure, but some fuels require a lot more encouragement to burn than others.

 

[TRAX]

Presumably that would require a new engine - one with spark plugs - whereas this mixture probably only requires modifying the fuel injection system.

As I said in the message you quoted, there are a lot of gas engines available on the market that would be suitable for a railway application. So another engine yes, but not a new development.