"Most diesel engines do not have a throttle body, so regardless of throttle setting a full charge of air is always drawn into the cylinders (excluding the valve fitted to certain diesels, such as fire appliances and generators on oil and gas platforms, to prevent diesel engine runaway). Compressed air generated during the compression stroke acts as an air spring to push the piston back down. As such, even with fuel supply cut off and no power strokes taking place, a portion of the energy absorbed by the compression stroke within each cylinder is returned to the crankshaft. This results in very little engine braking being applied to the vehicle.
The typical compression brake consists of a hydraulic system using engine oil which transfers the motion of the fuel injector rocker arm to the engine's exhaust valve(s). When activated, the exhaust valve opens very briefly near the engine's top dead center, and releases the compressed air in the cylinder so that the energy is not returned to the crankshaft. If used properly, a compression release brake can assist a vehicle to maintain or even reduce speed with minimal use of the service brakes. The power of this type can be around the same as the engine power."
Basically, jake brakes vent the compressed air in the cylinders at the top of the cycle.
spookthesunset|4 years ago
"Most diesel engines do not have a throttle body, so regardless of throttle setting a full charge of air is always drawn into the cylinders (excluding the valve fitted to certain diesels, such as fire appliances and generators on oil and gas platforms, to prevent diesel engine runaway). Compressed air generated during the compression stroke acts as an air spring to push the piston back down. As such, even with fuel supply cut off and no power strokes taking place, a portion of the energy absorbed by the compression stroke within each cylinder is returned to the crankshaft. This results in very little engine braking being applied to the vehicle.
The typical compression brake consists of a hydraulic system using engine oil which transfers the motion of the fuel injector rocker arm to the engine's exhaust valve(s). When activated, the exhaust valve opens very briefly near the engine's top dead center, and releases the compressed air in the cylinder so that the energy is not returned to the crankshaft. If used properly, a compression release brake can assist a vehicle to maintain or even reduce speed with minimal use of the service brakes. The power of this type can be around the same as the engine power."
Basically, jake brakes vent the compressed air in the cylinders at the top of the cycle.