Engineers put a lot of hours into making the 2014 Chevrolet Cruze Clean Turbo Diesel a segment leader in EPA-estimated highway mileage. And one of the tricks they used to get there was something called “variable swirl,” which occurs in the intake manifold.
Variable swirl increases the mixture-motion of air and fuel in low-speed, low-load driving, such as when in traffic. In doing so, the method helps give drivers the optimal combination of torque for the least amount of fuel at the lowest emission and noise levels. In the case of the Cruze Diesel, each cylinder has two separate valve-controlled intake ports, with one of them controlled by a valve. During variable swirl, each throttle valve varies how much it opens to create mixture-motion of air and fuel within each cylinder.