In my fluid mechanics class, I've learned that a fluid traveling in a pipe will generate a force when the exit area is smaller then the entrance area. Suppose a pipe is attached to a car that will use the kinetic energy of the air passing over the vehicle. Assuming that the car is moving at a constant velocity and the pipe is straight and the exit area is 1/4 the size as the frontal area, is it feasible for a moving vehicle to generate enough force from the air to reduce energy use?
No, you can not create energy or a force from nothing. It would break the laws of thermodynamics.
Specifically addressing your question in a simplified way; the large area on the front multiplied velocity equals the small area on the back multiplied by the higher velocity. In practice, the losses are quite high and it would waste lots of energy.
Imagine holding a cup out the window with a small hole cut in the bottom. With the top of the cup facing the direction of travel, the air traveling into the cup would act to force the cup rearward, so it would actually increase the drag on the vehicle. In your example, the force acting on the pipe would add to the drag not decrease it.