It works by forcing fuel directly into the combustion chamber of each cylinder to mix air and gas simultaneously at the point of combustion, rather than mixing air and gas in a separate chamber like more conventional engines.

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This chamber contains a slightly eccentric cylinder which can be rotated to make either the upper or the lower slots bigger.

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The EPA pulled off the feat by sharply increasing the amount of oxygen-poor exhaust that is recirculated into the combustion chamber and increasing the pressure of the fuel being forced into the cylinder.

FORBES: EPA, Inc.