Which braking system slows a vehicle by diverting compression in diesel engines?

The correct answer is that the engine brake slows a vehicle by utilizing the engine's compression to create resistance, thereby reducing speed. In diesel engines, when the driver releases the accelerator pedal, the engine's throttle closes, and the engine acts as a pump. The pistons still move, creating a vacuum during the intake stroke and compressing the air during the compression stroke. This process generates resistance against the engine's pistons, effectively slowing the vehicle down without using the traditional friction-based braking systems.

The engine brake is particularly useful in heavy vehicles, such as those used in firefighting or transportation, allowing for smoother and controlled deceleration, especially when going downhill or in situations requiring reduced speed without overusing the service brakes, which can lead to brake fade.

While the exhaust brake also helps in slowing down a diesel engine by redirecting exhaust flow to create back pressure, the primary mechanism at play here is the engine’s compression, making "engine brake" the more direct answer to the question. Hydraulic brakes and disc brakes, on the other hand, rely on friction to slow down the vehicle and do not utilize the engine's compression characteristics.