Quote:
Originally Posted by Daox
Does anyone know why they've been decreasing the CR of diesels in recent years? I'd figure you want a higher CR to increase efficiency.
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The trend to lower compression ratios (Mazda Sky-D, 14:1) is the convenient engineering solution to reduce temperatures = required lower NOx numbers. The observed fuel mix had less hot spots and locally rich areas that creates telltale exhaust soot. Mazda also claims the lesser compression also mitigate heat expansions thus less friction. Improvements and gains in fuel economy. Less internal stresses also let the engineers to make the crankshaft, rods & pistons much lighter for beneficial weight savings.
Again the lower operating temps mean some difficulty in colder climes.