A diesel injection system is primarily a mechanical system that forces diesel fueldirectly into the combustion chambers. Unlike the gasoline engine, the diesel engine doesnot use wpark plugs to ignite the air-fuel mixture. Instead, it uses the extremely highpressure produced during the compression stroke to heat the air in the combustionchamber. The air is squeezed until it is hot enough to ignite the fuel, shown as Fig. 4. 11.
When the mechanical pump sprays the diesel fuel into a combustion chamber, the hotair in the chamber causes the fuel to begin to burn. The burning fuel expands and forcesthe piston down on the power stroke. Electronic devices are commonly used to monitorand help control the operation of today's diesel injection systems.
Fig. 4.10 shows a basic diesel injection system.
．Injection pump一high pressure，mechanical pump that meters the correct amountof fuel and delivers it to each injector nozzle at the proper time
．Injection lines一high-strength steel tubing that carries fuel to each injector nozzle
．Injector nozzles一spring-loaded valves that spray fuel into each combustionchamber
．Glow plugs一electric heating elements that warm air in pre-combustion chambersto aid starting of cold engine
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