Modern pre combustion chamber engines

I recently came across an Italian company who seem to still be in business and are making common rail Diesel engines with pre-combustion chambers and master/slave connecting rods.

In addition to V12's, they also make W18's (three banks of 6 at a 40° angle). I've never seen anyone else continue to make three-bank engines.

I also would have never thought that anyone these days would still be making indirect injection engines outside of very small displacement ones, let alone indirect injection engines (old technology) with a common rail fuel system (latest & greatest technology). I also didn't think anyone these days would be putting master-and-slave con rods into a V engine.

This got me thinking: What would a modern 15L truck engine with common rail or electronic unit injection be like? What kind of fuel economy would it get if it ran, say, (and this is probably going to be sound very silly at first) 25:1 static compression ratio? I heard that the old PC 3406A's got only like 3 to 3.5 MPG while the 3406B's and DI 3406A's got about 4 MPG. But I'm not sure about the figures on newer engines.

If anyone here is still familiar with old IDI engines, that would be great.

I'm aware of the PCTA 3406A's, and it also appears that Cat did make PC 3408's and 3412's as well. But did Cummins or Detroit make any pre-chamber engines in the past?

 

In PC engines, the fuel begins burning in a pre-combustion chamber and then the combustion spreads into the cylinder. DI engines spray the fuel directly into the cylinder.

 

IDI engines were somewhat infamous for being fuel hogs. That's because the pre-chambers increase the surface area that the fuel and air are exposed to, which means more of the combustion heat is wasted instead of being used to drive the piston down in the cylinder. To make up for this you need to run a higher compression ratio, which is why many IDI engines ran 20:1 CR or higher.

For example, the C13, C15, C18, C27, and C32 all run 16:1 CR in stock form today, but they are DI. PC versions of those engines could run as high as 25:1 CR, assuming the same fuel system.

Theoretically, you could convert these engines to PC if you really wanted to, but that would require:

• Glow plugs
• Different cylinder heads with different injector bores
• Shorter injectors to accommodate the pre-chambers
  
• Different gear trains
  
• Different valvetrain arrangements
  
• High compression pistons (as running stock pistons would lower the compression)
  
• Different fuel mappings depending on the application

and a whole host of other modifications. There are probably even more things that would have to be modified if one of these was going into an on-highway truck compared to off-highway industrial applications.