柴油机为什么冒黑烟？ Why do diesel engines emit black smoke?

5. Why do diesel engines emit black smoke?

Answer: Diesel engines easily emit black smoke from the exhaust at high loads. It is generally believed that when the load of the diesel engine is high, the amount of fuel injected into the combustion chamber increases, and the temperature in the combustion chamber is also high. In addition, the uneven formation of the diesel engine mixture can cause the combustion fuel with insufficient air in the local area of the combustion chamber to decompose and polymerize under high temperature and oxygen deficiency conditions, forming soot (carbon black). Charcoal is not pure carbon, but a polymer mainly composed of carbon (more than 85%) but also contains a small amount of oxygen Hydrogen and ash content, and their composition changes with the load of the diesel engine. By collecting the soot through a filter and observing it under an electron microscope, large soot particles with a diameter of about 0.05 μ m can be seen. The high-temperature cracking reaction of combustion in diesel engines is inevitable, especially in space mixed combustion diesel engines where high-temperature gases surround liquid oil droplets, creating the most favorable conditions for cracking reaction. High speed photography of the combustion process proves that a large amount of black smoke will appear around the top dead center, but in general, soot can find air in the subsequent combustion and completely burn without black smoke in the exhaust. However, if the air in the cylinder is insufficient and the mixing process is slow, the cylinder temperature will decrease due to expansion, and carbon cannot... Burning and aggregating into soot. The formation of soot makes incomplete combustion economical for diesel engines The carbon deposition on the surface area of the combustion chamber and the inability to further increase the load due to the decrease in exhaust temperature and the increase in exhaust smoke can cause faults such as piston ring or piston jamming, valve biting, etc. Therefore, it is not allowed for diesel engines to operate under long-term overload conditions