A practical means of varying an engine’s compression ratio has been a goal of automakers for ages. How hard the air—and sometimes fuel—is squeezed before ignition, plays a crucial role in overall efficiency. Varying the compression ratio in a running engine is daunting because the ideal ratio changes with speed and load. One expedient now in wide use is combining the Atkinson cycle—which separates the effective compression ratio from the expansion ratio—with variable intake-valve timing. But the current rise in global mileage standards is forcing every maker to search for additional means of curbing fuel consumption.

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Fuel Saving Car