Why is the engine exhaust pipe black?

[StephenDella]

The reasons for the blackening of the exhaust pipe are as follows: 1. Poor fuel quality. The quality of fuel directly affects the working efficiency of the engine, and a large amount of impurities not only hinder the normal operation of the engine but also serve as a source of blackening. 2. Insufficient mixing of fuel and air. Inadequate mixing leads to uneven combustion, naturally resulting in incomplete combustion. 3. Turbocharged direct-injection engines are relatively more prone to blackening. Due to the high speed of the turbocharger in turbocharged engines, the mixture of fuel and air varies significantly before and after the turbo kicks in, making it difficult to control the concentration of the air-fuel mixture. Poor adjustment can cause some fuel to burn incompletely, leading to blackening. 4. Faulty catalytic converter. If the catalytic converter is damaged, its secondary oxygen sensor cannot provide accurate data to the engine control unit, causing the air-fuel mixture to become either too lean or too rich. Particularly when the mixture is too rich, symptoms such as increased fuel consumption, incomplete combustion, and severe carbon buildup in the cylinders and spark plugs may occur.