Smoke Limit
The smoke limit is the limiting of the fuel quantity on a diesel engine according to the amount of air that can be drawn in at that moment. Without the limit, more fuel than air is delivered at the moment of loading, part of the fuel leaves unburned, and black smoke comes out of the exhaust. The limit also prevents overheating and soot build-up.
On a turbocharged diesel the amount of air depends on the intake pressure. At the moment load comes on, the turbo has not yet spooled up; air is scarce. The governor wants to increase fuel to recover speed, and the smoke limit temporarily restrains that demand. As the turbo speeds up, the limit rises and full power can be delivered.
- Brief smoke on sudden and full loading is normal; continuous black smoke is a sign of overloading, a blocked air filter, or faulty injection.
- The smoke limit is the job of the engine's own fuel system; opening the throttle lever faster from outside does not let you exceed this limit, it only increases the smoke.
The practical consequence: opening the throttle fully as a step brings no benefit. Because the GS740-3P's soft ramp opens the throttle lever in a controlled way, it reduces unnecessary smoke and fuel waste during loading. In drilling and irrigation applications, raising the speed gradually lowers both smoke and mechanical shock.
Context in which this term is used: Electronic speed and throttle control on a diesel engine