Why do you get black smoke from a diesel engine?

Black smoke from your diesel generator occurs because of un-burnt fuel in the exhaust gas. It is a sign of poor combustion. Poor combustion leads to high fuel consumption and may be a sign of poor maintenance or engine damage. If you need help with your engine in the UK, try Regency Generators.

Smoke not black? See white smoke from your diesel generator, or blue smoke from your diesel generator. 

What are the common causes of black smoke from a diesel generator?

If the engine isn't able to combust the fuel effectively, black smoke shows the fuel/air in the cylinder is too rich with fuel in compared to the amount of air, the fuel doesn't combust fully and what ends up coming from the exhaust is black smoke - the black you see in the smoke is soot.

Dirty air cleaner, Faulty turbocharge, Restriction in induction system

If the engine isn't getting enough air from its air filter, due to a high restriction, there won't be enough oxygen in the engine cylinders. This will lead to un-burnt fuel. Check your air filter is free from restriction and change it. Also check all your pipes to the engine for blockages.

Injectors sticking Open, Incorrect valve clearances, Incorrect timing

An injector problem, timing problem or incorrect valve clearances can all cause black smoke. The engines injectors spray the fuel in very fine particles into the engine’s cylinders. These small particles of fuel find the oxygen and combust very easily. If the injector has a fault, it may not be able to spray finely combust as easily. It might be caused by poor fuel quality clogging the injectors or sulphur deposits building up. In this case all the injectors in the engine are likely to be affected. You should call a competent engineer to check your injectors.

If the valves or valve clearances aren't correct, this will also cause combustion problems in the chamber, leading to black smoke.

Excessive carbon build up in combustion and exhaust spaces

Common on very old engines, or those run on poor fuel. If other problems have caused black smoke and been solved, this one may need some extra attention to clean the system. It can often be fixed by running the engine on high load for a period to burn off the excess carbon.

Low cylinder compression

Often caused by worn components, but can also be caused by sticking piston rings. Its a sign that its time to do some potentially significant maintenance on the engine and get it back into good shape.

Poor quality fuel

Poor quality fuel is the cause of so many problems. If high in sulphur, it can clog injectors and damage the engine. Often poor quality fuel has a high water content which initially leads to white smoke from the engine, but this water can damage injectors and other components and lead to black smoke. Changing the fuel at this point won't solve the problem, you will need a generator engineer.