5 stroke engine

[Steamchick]

Good stuff! Thanks all - as I find this very interesting. But my mind boggles when I read such things as the "Water gas shift reaction" - Water-gas shift reaction - Wikipedia - it is beyond my brain processing ability!
I am aware (from working alongside the engineers that explained how the various components of "modern" car engine design contribute to efficiency and emissions improvements - some of only less than 1% taken individually).

• To reduce detonation, a key was the re-design of combustion chambers to reduce squish... 2 inlet valves, plus the intake tract to valve shape causes adequate swirl without complex squish zones, that would generate cold zones where incomplete combustion could occur, and hotter zones more prone to detonation. Thus "unleaded" fuel - with different additives to reduce detonation - that are generally lower octane than the higher octanes used in the 1970s with lead additives - can be run at relatively high compression compared to engines from the 70s with the same octane fuel. Also electronic ignition delay with direct feedback sensor-triggered retardation eliminates any odd knock that may occur, thus allowing the ignition to be relatively "more advanced" than traditionally. In other words, the "anti-knock" retardation safety margin of pre-1980s engines was much greater than the margin applied today. Wikipedia explains this quite well, but on "modern" engines this would be much less useful as we have electronics and computer aided design that means manufacturers have countered problems that water injection was doing 70 years ago.
• Reduction of the space above the top piston ring, and corners of combustion chambers (e.g. around valves) where un-burned fuel can occur, has been applied to reduce hydrocarbon emissions.
• Introduction of Exhaust gas (EGR) to slow combustion rates and reduce high peak temperatures also reduces knock at the higher compression with lower octane fuels, and reduces NOx formation (keeping peak temperatures below 900 deg. C). I guess that as the Exhaust gas introduced by the EGR system has a percentage of water, mixed with CO2 and NOx, then it is in fact a form of "gaseous" water injection? - Which will aid the "water-gas shift reaction"? - Although I am aware that excessive EGR will generate excessive Hyrocarbons and CO in the exhaust that cannot be catalysed so cause emissions test failures - so MUST be avoided.
• Efficiency improvements in where to cool the engine - and where to not cool it - so minimising cooling water heat losses. I think this energy "saving" - by not throwing away too much excess heat - is the industry's way of trying to redress some of Ved's Q=E1+E2+E3 balance? - Combined with the reduction of friction losses, etc.
• Use of minimal contact pistons to reduce oil-shear drag losses...
• Minimal crank bearing size to reduce oil-shear drag losses.
• Finite element and fatigue analysis studies to minimise the materials everywhere. - Thus reducing dynamic loads and losses due to friction. (e.g. Reducing valve stem diameter reduces heat losses up the valve stem, and friction in the valve guide).

Many of these ideas Model Makers adopt "almost without thinking" when designing their own models... and some are very appropriate on models due to the scale problem - and the low power of model engines being more prone to "High" friction problems.
I hope some of my musings are helpful?
K2