Why does the car's exhaust pipe turn black?

[Parker]

Car exhaust pipes turn black due to incomplete combustion of the combustible mixture in the engine. This is a very common occurrence, especially in China where road congestion is frequent. During traffic jams, the engine operates at idle speed, resulting in incomplete combustion. When the combustible mixture in the engine doesn't burn completely, it produces carbon particles in the exhaust gases. These carbon particles accumulate on the exhaust pipe, causing it to turn black over time. The exhaust pipe is part of the engine's exhaust system, which mainly includes the exhaust manifold, exhaust pipe, and muffler. Typically, the three-way catalytic converter for controlling engine pollutant emissions is also installed in the exhaust system. The exhaust pipe generally consists of a front exhaust pipe and a rear exhaust pipe.