Have You Guys Seen This One?

[Big Dave]

A spark-ignition engine with the efficiency of a diesel.

https://www.youtube.com/watch?v=u0uPmrSRM7w

https://www.youtube.com/watch?v=-yo6xuVS7tg

It’s rather like taking the Atkinson engine to the next level. A great deal more expansion than compression.

Back in the late 40s, aircraft engine designers played with turbocompounding – using expansion turbines to wring every last bit of work out of a pound of hot exhaust gas. And it worked, sorta. The engines of Shackleton bombers and B-29s were marvels of thermal efficiency. But they weren’t reliable. They relied on gear reduction to match turbine RPM with engine RPM. Those stressed out gear trains were more of a danger to B-29 crews than Zeros.

Even earlier steam locomotives used compounding. The exhaust steam from one cylinder was ducted into another (larger diameter) cylinder and allowed to expand some more. This worked but they were tricky to operate using 1920s controls.

But this uses the older idea to make an engine that does not have a stressed out system.

Ilmor is highly respected in the auto world.

[RustyLugNut]

I'm not sure it is going to be a market success but their mention of it's use in hybrid drives and stationary power applications shows they understand the limitations of the engine.

[solarguy]

Ferdinand Porsche tried something similar, with some pistons super charging other pistons.

I think it was given up as overly complex and had overheating problems.


I just bought a Mazda 3 with the Skyactiv system. Instead of typical gasser compression ratio of 9:1 or 10:1, the US version has 13:1, and the euro or japanese version is 14:1.

To prevent engine destroying pre-ignition, they use active changes in the cam timing.

So far, it works a treat.

[darcane]

Hmm... That looks very familiar, but not from the same company. I can't remember where, but I'd put money on this not being a new idea.

[redpoint5]

Seems a good idea. What are the limitations?

[darcane]

Originally Posted by darcane

Hmm... That looks very familiar, but not from the same company. I can't remember where, but I'd put money on this not being a new idea.

There we go. Nearly identical design circa 1879:
The Deutz compound engine: 1879


Patent issued to a Gottlieb Daimler (yes, that Daimler). Link above has a variety of other similar designs for compound engines. I believe these were popular back then since metallurgy wouldn't allow for the high compression of modern engines, so alternatives were needed to harness more energy from the fuel.