greasemonkee |
06-03-2009 01:45 PM |
WOW! How about stepping back to the thirties?
IF an auto manufacturer were attempting to create an economy engine via high compression, seems like the most logical thing to do would be to properly design a combustion chamber that would withstand 12-13:1 static compression on pump fuel alone, it is a fact that as static CR #'s increase, maximum cylinder pressures greatly increase. Over the long run this is probably not desirable.
For starters, ethanol has a low calorific value - the stoichiometry is 9:1, so obviously not the most potent fuel for extracting mechanical energy. The only thing beneficial to ethanol as a fuel supplement is its high latent heat absorbs massive amounts of heat before the intake valve closing resulting in a higher volumetric efficiency, (more power). However, this may only be true to an extent, under certain conditions and there is a point of diminishing returns. The slight gain in thermal efficiency is likely at best, negligible for this company's approach.
Reducing flame temps increases thermal efficiency. This has been commonly accomplished by operating at leaner than stoichiometric ratios with a super homogeneous intake charge. There is a catch though, flame speed decreases and more ignition timing is required, ultimately defeating the purpose. The static CR could be increased to offset the difference, I find it a curiosity as to why this hasn't been done. The civic VX is likely operating in that sweet spot somewhere between 16-17:1. Nearly every mass produced powerplant after that engine which attempted to achieve ultra high economy is severely lacking.
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