High compression ratios produces high combustion temperatures. This leads to the formation of nitrous oxide (NOx).
We have a lot of techniques to improve mpg that increase NOx. If you can figure out how to easily inhibit NOx formation inside the combustion chamber you could be a rich man.
Incedentally this is one way direct gasoline injection can improve economy. The injector sprays directly into the cylinder, and can do so in a way that forms a little donut of air/fuel mix that is insulated from the walls by a layer of air. It is then ignited. The air barrier helps keep combustion temperatures down.
One last thing, really high compression tends to result in a chamber that is very flat and narrow, which can counterproductively cause hotspots and incomplete combustion because the flame front is restricted. This can be fixed with undersquare pistons with longer travel, but that leads to big, low-power, slow-revving engines, like diesels!
We have a lot of techniques to improve mpg that increase NOx. If you can figure out how to easily inhibit NOx formation inside the combustion chamber you could be a rich man.
Incedentally this is one way direct gasoline injection can improve economy. The injector sprays directly into the cylinder, and can do so in a way that forms a little donut of air/fuel mix that is insulated from the walls by a layer of air. It is then ignited. The air barrier helps keep combustion temperatures down.
One last thing, really high compression tends to result in a chamber that is very flat and narrow, which can counterproductively cause hotspots and incomplete combustion because the flame front is restricted. This can be fixed with undersquare pistons with longer travel, but that leads to big, low-power, slow-revving engines, like diesels!