🔍 Key Concepts

• diesel combustion process timing from start of injection to start of combustion • effect of fuel properties (like cetane number) on ignition delay • difference between hydraulic delay in the injector and chemical ignition delay

💭 Think About

• Think about what physically happens between the instant the pump/plunger begins to deliver fuel and the moment pressure in the cylinder actually rises due to combustion. • Which option describes something that would always be present in any liquid fuel system, and which describe conditions that may vary but are not the fundamental cause? • Consider which factor is directly related to the time needed for pressure to build and the injector nozzle to start spraying fuel.

✅ Before You Answer

• Distinguish between injection lag (mechanical/hydraulic delay) and ignition delay (chemical delay); the question is about injection lag, not combustion quality. • Check which option represents an inherent property of the fuel system rather than an operating condition like flow rate or turbulence. • Ask whether cetane value affects the pump/nozzle mechanical response or the fuel’s chemical ignition characteristics.