TO UNDERSTAND DIESEL ENGINES, WE MUST FIRST START WITH INTERNAL COMBUSTION ENGINES.INTERNAL COMBUSTION ENGINE, ALSO KNOWN AS INTERNAL COMBUSTION ENGINE, IS A DEVICE THAT CONVERTS THE CHEMICAL ENERGY OF FUEL INTO THERMAL ENERGY, AND THEN CONVERTS THE THERMAL ENERGY INTO MECHANICAL ENERGY THROUGH A SET OF MECHANISMS (CRANK CONNECTING ROD MECHANISM) AND OUTPUTS POWER TO THE OUTSIDE WORLD. AND THE COMBUSTION AND CONVERSION PROCESS OF THIS ENERGY IS COMPLETED INSIDE THE POWER UNIT (CYLINDER), SO IT IS CALLED AN INTERNAL COMBUSTION ENGINE.RELATIVELY SPEAKING, IF THERE IS AN INTERNAL COMBUSTION ENGINE, THERE MUST BE AN EXTERNAL COMBUSTION ENGINE. THE COMMONLY USED STEAM LOCOMOTIVES IN THE RAILWAY SYSTEM WERE EXTERNAL COMBUSTION ENGINES. A STEAM LOCOMOTIVE RELIES ON A BOILER TO BURN COAL AND HEAT WATER TO PRODUCE STEAM. THE STEAM ENTERS THE CYLINDER AND DRIVES THE PISTON TO RECIPROCATE, GENERATING POWER AND DRIVING THE WHEELS TO ROTATE. BECAUSE COMBUSTION OCCURS OUTSIDE THE CYLINDER, IT IS CALLED AN EXTERNAL COMBUSTION STEAM POWERED LOCOMOTIVE.A DIESEL ENGINE IS AN INTERNAL COMBUSTION ENGINE, ALSO KNOWN AS A COMPRESSION IGNITION PISTON ENGINE. IT IS A DEVICE THAT RELIES ON THE HIGH TEMPERATURE AND PRESSURE GENERATED BY THE PISTON DURING THE COMPRESSION PROCESS TO IGNITE AND BURN THE FUEL ON ITS OWN, AND CONVERT THE CHEMICAL ENERGY OF THE FUEL INTO MECHANICAL ENERGY TO OUTPUT POWER EXTERNALLY. ITS WORKING MEDIUM IS DIESEL, SO IT IS CALLED A DIESEL ENGINE.RELATIVELY SPEAKING, GASOLINE ENGINES ARE CALLED SPARK IGNITION PISTON INTERNAL COMBUSTION ENGINES, AND THEIR WORKING MEDIUM IS GASOLINE, SO THEY ARE CALLED GASOLINE ENGINES.THE MAIN DIFFERENCES BETWEEN DIESEL ENGINES AND GASOLINE ENGINES ARE:① THE WORKING MEDIUM IS DIFFERENT. DIESEL ENGINES BURN DIESEL, WHILE GASOLINE ENGINES BURN GASOLINE;② THE IGNITION METHOD IS DIFFERENT. DIESEL ENGINE - COMPRESSION SPONTANEOUS COMBUSTION. GASOLINE ENGINE - COMPRESSION IGNITION.③ THE COMPRESSION RATIO IS DIFFERENT.THE COMPRESSION RATIO OF DIESEL ENGINE IS LARGE, WITH Ε=12-22THE COMPRESSION RATIO OF GASOLINE ENGINES IS SMALL, WITH Ε=6-11④ THE DIMENSIONS OF THE COMPONENTS ARE DIFFERENT.DIESEL ENGINES REQUIRE A HIGHER COMPRESSION RATIO DUE TO THE USE OF COMPRESSION SELF IGNITION. THEREFORE, ALL COMPONENTS HAVE TO WITHSTAND MUCH HIGHER EXPLOSIVE PRESSURE THAN GASOLINE ENGINES (UP TO 13.0MPA). THIS PLACES SPECIAL REQUIREMENTS ON THE STRUCTURE AND STRENGTH OF THE COMPONENTS. SO AT THE SAME POWER, THE VOLUME AND WEIGHT OF A DIESEL ENGINE ARE MUCH LARGER THAN THOSE OF A GASOLINE ENGINE.⑤ DIFFERENT USESDIESEL ENGINES ARE SUITABLE FOR VARIOUS PURPOSES. IN THE FIELDS OF HEAVY-DUTY VEHICLES, CONSTRUCTION MACHINERY, LUXURY BUSES, PUBLIC BUSES, GENERATOR SETS, INTERNAL COMBUSTION LOCOMOTIVES, AND MARINE USE, DIESEL ENGINES DOMINATE THE WORLD. GASOLINE ENGINES ARE WIDELY USED IN THE FIELD OF SMALL CARS.⑥ FUEL CONSUMPTION VARIES. DIESEL ENGINES ARE FUEL-EFFICIENT AND HAVE BETTER OPERATING COSTS THAN GASOLINE ENGINES.⑦ THE OIL AND GAS MIXING METHODS ARE DIFFERENT.DIESEL ENGINE - CYLINDER MIXING; GASOLINE ENGINE - INTAKE MIXING (OR CYLINDER MIXING).