Question

Which of the following actions will help to reduce the black smoke emission of a diesel engine?

1. Run at lower load, i.e. derating

2. Have regular maintenance of the diesel engine, particularly of injection system

3. Use diesel oil of higher cetane number

Select the correct answer using the code given below.
1. 1 and 2 only
2. 1 and 3 only
3. 2 and 3 only
4. 1, 2 and 3

Answer 1

Correct Answer - Option 4 : 1, 2 and 3

Black smoke at the exit of the diesel engine is due to the soot component of the diesel, particulate matter. Under normal operating conditions, this soot is oxidized in the cylinder and is not visible. The visible black smoke is generally due to injecting too much fuel for the amount of air available in the cylinder or due to poor mixing between fuel and air. This black smoke emission can be avoided by the proper design and maintenance of the injection system.

Cetane Number: Centane number is the measure of the fuel's ignition capacity under the combustion chamber temperature and pressure conditions. Cetane number is determined by comparing its ignition quality with the blend of two standard reference fuels, the straight-chain-paraffin n-cetane which ignites very quickly and a branched paraffin heptamethyl nonane which has a long ignition delay. Higher cetane number fuel is associated with improved combustion, improved emissions. Black smoke emission increases with lower cetane number fuels especially when it is below 45. 

Derating: Derating of the engine means a reduction in power output compared to the most efficient power output, to match the ambient air conditions. Derating reduces the power output, therefore, there will be a lean mixture of fuel and air, the combustion of fuel will be proper and there will be lesser black smoke emissions.