a) Engine brake
When the fuel supply is cut off, the engine provides a braking moment which is created by pumping work. The negative area of brake power in the pi-V-diagram of the engine can be extended by two different measures:
-      Exhaust Brake
In this case, the free cross-section of the exhaust manifold is partly or totally blocked by a throttle. As a result, the exhaust pressure increases, thus causing the surface area of the gas exchange loop to increase.