Purpose of inspection
Inspect the diesel engine’s combustion condition based on the discharged smoke.
• With white smoke
White smoke is caused by combustion at a comparatively low temperature and is discharged when the injected fuel is not burnt. The cause of white smoke may be conditions where the fuel injection timing is retarded, or the after glow does not operate when it is cold, etc. For these reasons, checking the conditions when white smoke is discharged can determine the cause of the malfunction.
(1) White smoke is discharged regardless of the condition
• Internal malfunction of the injection pump
• Compression pressure is low
• Fuel cetane number is low
(2) White smoke is discharged when it is cold
Operational malfunction of the after glow
White smoke is sometimes discharged because engine oil or water enters the combustion chamber. In this case, checking the smell of the discharged gas will make it possible to judge whether engine oil or water has caused a fuel ignition failure. Check the smell by fanning the smoke by hand so as not to directly inhale it.
• With black smoke
When injected fuel particles are exposed to a high temperature and there is a lack of oxygen, the fuel becomes soot. Black smoke is this soot. Only the outside of the fuel drop is burnt, not the center. The following can be considered causes of black smoke: a large amount of fuel is injected, a small amount of air is taken in, the injection timing of the fuel is fast, atomization is poor, etc.