COMBUSTION CHAMBER GEOMETRY AND FUEL UTILIZATION 570261
Compression ratios ranging from 4:1 to 16:1 have been investigated in a special single-cylinder engine, as have quench or squish areas from 0 to 50 per cent piston coverage at each compression ratio. The following conclusions can be drawn from this work:
As compression ratios are increased, gains are subject to the law of diminishing returns. This is true of brake horsepower, as well as indicated power and thermal efficiency. At higher compression ratios, the only thing still increasing rapidly is the fuel antiknock requirement.
Quench area, in the range investigated, had no effect on power or thermal efficiency.
Quench area does have large and important effects on fuel antiknock requirements and engine severity. Fuel sensitivity, under certain conditions, can be a real asset instead of a liability.
High compression ratios bring on a host of new problems, including “run-away preignition,” extreme sensitivity to ignition timing, and intermittent brushes with so-called “engine roughness.”