🔍 Key Concepts

• Diesel combustion timing and how it affects pressure rise in the cylinder • Relationship between start of injection, peak firing pressure, and combustion duration • How injection timing influences exhaust gas temperature and mean effective pressure (MEP)

💭 Think About

• If fuel is injected earlier in the compression stroke, what happens to the time available for mixing and burning before and after top dead center (TDC)? • Think about when maximum useful pressure on the piston should occur for best efficiency: just before, at, or after TDC? How does early injection change this? • If combustion pressure builds up too early, what happens to peak firing pressure and to the average (mean effective) pressure during the power stroke?

✅ Before You Answer

• Be clear on the difference between peak firing pressure (instant maximum) and mean effective pressure (average over the stroke). • Consider how earlier injection affects where the pressure peak occurs relative to TDC: does it move pressure earlier or later in the cycle? • Recall that late injection tends to increase exhaust gas temperature; think about whether early injection does the same or the opposite.