Variable Geometry Combustion Chamber

I ran across this in while reading Pounder’s Marine Diesel Engines and Gad Turbines by Doug Woodyard:
Author describes it as “an ingenious combination” of direct injection and precombustion chamber systems. It is cute, obviously.

What I wonder is: when the area exposed to the pressure suddenly changes as the piston drops, wouldn’t there be a shock to all the components between the crown and the crank? Have any of you worked on this kind of set-up? What do you think?

1 Like

This has been around for years. Cat IH John Deere ect…makes for a more efficient and longer burn of the fuel injected.

I know it isn’t new, but I’ve never seen one before. I was just wondering about the possibility of increased shock loading versus conventional combustion chambers.

Not applicable in this case but my eng dept uses Diesel Doctor


They can print out a diagram of pressure vs time of each cylinder. It’s turned out to be very helpful to figure out what’s happening. One of my regular chiefs discovered that some of our main engine cylinder heads were being overhauled to the wrong template (my understanding) and the volume was slightly more than specs. The resulting lower pressures could be seen on the pressure graphs on only the cylinders that the heads had been overhauled in one particular shop.

1 Like

What makes you think more of the piston crown suddenly becomes exposed to pressure? Certainly the volume is a different shape at TDC but the surface area is always there. To the extent the small passage from the chamber to cylinder proper acts like an orifice and to the extent press rise in the small chamber rises more rapidly (which I’m not sure of) - it would seem the orifice would act to more gradually raise the pressure in the main cylinder acting on the piston crown.

Is this anything like the older truck engines with IDI like the old International 7.3 liter?


Precombustion chambers have been part of diesel design for a century, they were originally “hot bulbs” to enable fuel vaporization and later became a means to increase turbulence in the cylinder to produce more complete combustion. There were all kinds of weird designs of piston bowls and crowns to enhance turbulence and even at least one that had a deep pocket that acted like moving prechamber.

Nothing new here folks.

1 Like

Thinking more carefully about it, I think you’re idea is more likely than mine. Thanks!

Works a charm, donnit? My instructor handed me something like this:

…expecting that I could puzzle it out. I couldn’t at that time. But its the traditional way to do what that pretty yellow pelican case does. Actually a very powerful tool, as it turns out. I would like to learn to use the old one, someday, just for kicks.


The end of this clip shows one operating.