The normal work of the diesel engine exhaust should be close to colorless or slightly short of the gray, if the exhaust can be detected with the naked eye color, it shows that diesel engines do not work normal. But how much exhaust smoke is allowed to work? At present, China has not explicitly provided for temporary, but also to exhaust smoke and no determination of a unified approach. Therefore, the smoke was assessed by direct observation and practical experience-based.

Not only smoke pollution in the atmosphere, the deterioration of working conditions, and diesel will increase the temperature, severe coking coke in order to shorten the life of diesel engines. Therefore, in order to eliminate as much as possible.