Why is the high pressure oil pipe hot when the diesel engine works?

Because the temperature is too high. The advantages of diesel engine are large power and good economic performance. Diesel engine work process and gasoline engine have many of the same place, each work cycle also goes through intake, compression, work, exhaust four stroke. But because the fuel used in diesel engine is diesel, its viscosity is bigger than gasoline, not easy to evaporate, and its spontaneous combustion temperature is lower than gasoline, so the formation and ignition mode of combustible mixture are different from gasoline engine. The main difference is that the mixture in the cylinder of a diesel engine is pressurized, not ignited. Diesel engine air into the cylinder is at work, at the end of the compressed air in cylinder, the temperature can reach 500-700 ℃, pressure can be up to 40-50 atmospheric pressure. Check point near the end of the piston, the engine of the high pressure pump with high pressure in the cylinder injection diesel, diesel form of subtle oil grains, mixed with high pressure high temperature air, diesel mixture combustion, violent expansion, produce explosive force, driving the piston downward to do work, the temperature can reach 1900-2000 ℃, pressure can reach 60-100 atmospheric pressure, the power is very big, so the diesel engines are widely used in large diesel cars. The advantages of diesel engine in energy saving and carbon dioxide emission are irreplaceable by all heat engines including gasoline engine.