Table of Contents
The colour of exhaust smoke is a direct clue to engine condition: white smoke indicates water vapour in the fuel, blue smoke indicates lubricating oil, and black smoke indicates inefficient combustion. This page lists the causes of black smoke and how to find the faulty unit.
Colors of Smoke
- The white color indicates the presence of water vapor in the fuel.
- Blue-colored smoke indicates the presence of lubricating oil in the smoke.
- The dark black color indicates inefficient combustion or the lack of air. It could also be due to scavenging fire or economizer fire or boiler problems.
Causes of Black Smoke
The air-related problems in marine diesel engines may be due to the following reasons:
- The turbocharger air filter is choked.
- The turbocharger turbine blades are fouled and damaged; therefore it is giving insufficient air to the engine.
- The turbocharger inlet grid in the exhaust manifold is choked, and therefore the turbocharger is running at low speed.
- The compressor blades are dirty or damaged.
- The scavenge ports of the engine may be dirty and choked.
- The scavenge valves may be faulty or damaged.
- The nozzle ring of the turbocharger is soiled.
- The engine room blowers are not supplying sufficient air as the filters are choked.
The fuel-related problems that could cause black smoke are as follows
- A low temperature of the fuel causing poor atomization and penetration.
- The fuel injectors may be dripping causing after-burning.
- The timing of the fuel pumps may be wrong.
- The holes of the fuel injectors may have become large by wear.
- Incorrect spring pressure of the fuel injectors.
- Wrong grade of fuel or low fuel quality.
- Incorrect valve lift of the fuel injection valves.
- Unbalanced engine. Thermal and power balancing needs to be done.
- Overloaded engine due to governor malfunction.
- Some units may not be firing leading to overloading of the other units.
- Scavenge fire has taken place
Finding the Source of Black Smoke
- The engine must be checked for overloading and the exhaust temperatures of the individual units must be checked. The difference in temperature of the individual unit and the average temperature must not exceed 50 degrees C.
- The engine must be checked for scavenging fire and the under-piston temperature must be checked of all the units.
- The fuel racks of all the fuel pumps must be checked and must be within limits.
- The air filter of the turbocharger blower must be checked for choking.
- The turbocharger speed must be checked and the temperature drop across the turbocharger must be checked.
- The fuel temperature must be checked and it must be within the range 120 to 140 degrees C for heavy fuel oil.
- In the case the problem is only due to a particular cylinder, the units must be cut off one by one and for about two-three minutes any change in exhaust must be observed.