🔍 Key Concepts

• Compression stroke and ignition delay in a diesel engine • Relationship between piston position (TDC/BDC) and cylinder pressure • Difference between compression pressure and maximum combustion pressure

💭 Think About

• Think about when fuel is injected and starts burning in a diesel engine relative to the piston reaching top dead center (TDC). Does this burning and rapid pressure rise happen instantly or over a short period of crankshaft rotation? • Consider what happens to cylinder pressure as the piston moves slightly before, at, and just after TDC on the power stroke. At which point would the combination of compression plus combustion produce the highest pressure? • Ask yourself: is the pressure during normal running higher or lower than the pressure during air starting, and is starting air meant to equal peak combustion forces?

✅ Before You Answer

• Be clear on the difference between compression-only pressure (no combustion) and combustion peak pressure (after fuel burns). • Recall that fuel injection in a diesel engine typically starts slightly before TDC on the compression stroke—how does that timing affect when the peak pressure actually occurs? • Verify whether starting air pressure is designed to match or be significantly lower than the maximum firing (combustion) pressure in the cylinder.