Assume an engine has a compression ratio of 9.5:1. It operates at BDC cylinder pressures up to 14.7 psia. Once compressed the pressure is 9.5 times that or 140 psia. Higher than this running regular gas causes preignition.
Now assume a similar engine is designed which operates with a maximum BDC pressure of 7.35 psia. It has a compression ratio of 19:1. In operation the max chamber pressure is still 140 psia. so there is no knocking at 19:1 compression.
If one is willing to operate an engine with less than atmospheric pressure, then one can use higher compression ratios, yes?
We operate most of our automobile engines at less than 7 psia mfld pressure. wouldn't this work?
larry, Iburnh20, mpgmike?