I read about this on the University of Wisconsin's website. They claim much lower combustion temperature from either a normal gasoline or diesel engine. That is what gives the better thermal efficiency. They used what looks like an older Cat 1 or 2 cylinder diesel (from a picture I found). They inject the gasoline into the intake and the diesel through the normal diesel injectors. My best guess on how they are able to make this work is by keeping the gasoline relatively lean (greater than 18:1). It is extremely hard to make an lean gasoline air mixture ignite, so they use the diesel to create a widespread ignition source.
My dad has an old Isuzu diesel pickup that my brother rolled. The engine still runs. I am putting plans together to try to validate their test results. It seems that there wouldn't be much variation in the amount of diesel actually injected since it there to support the function of the spark plug. I think that I could drill in a gasoline injector or two, add a throttle position sensor, a crank position sensor, and a megasquirt EFI controller to be able to run the motor. When I got done I could put the megasquirt on my boat. I have been wanting to do that anyway. I thought about using a carburetor but I don't know how I could control it because I can't use the throttle plate. Maybe a needle valve on the fuel flow to a venturi, but that would be hard to connect to a pedal. Does anybody have an old Chevy TBI around?