🔍 Key Concepts

• Diesel combustion process – how air is compressed and how fuel normally ignites in a diesel engine • Difference between preignition (before intended start of combustion) and afterburn/overlong injection (continuing combustion) • Causes of hot spots or abnormal ignition sources in the combustion chamber

💭 Think About

• Think about what could cause the fuel-air mixture (or fuel spray) to start burning before the fuel is supposed to ignite from normal compression heat • Which option would most likely create hot particles or surfaces in the cylinder that could light off the charge early? • For each choice, ask: does this condition tend to delay, prevent, or advance the start of normal combustion?

✅ Before You Answer

• Be clear on the term preignition = ignition that occurs too early, not delayed ignition • Eliminate any options that mainly lead to poor combustion, misfiring, or delayed ignition rather than early ignition • Focus on the option that can create abnormally high local temperatures or combustible deposits in the air charge before the normal injection point