🔍 Key Concepts

• Diesel combustion stages: ignition delay, rapid (uncontrolled) combustion, controlled combustion, afterburning • Relationship between piston position (before/after top dead center) and mechanical efficiency • Effects of peak cylinder pressure occurring too early vs. too late in the power stroke

💭 Think About

• Think about where in the stroke you want the highest rate of pressure rise so that it pushes the piston down most effectively. • What happens if the most rapid combustion is completed too far before top dead center? What happens if it continues too far after top dead center? • Which option best aligns the rapid combustion phase with the point where the crank and connecting rod can turn fuel energy into useful work most efficiently?

✅ Before You Answer

• Identify which choice matches the rapid (uncontrolled) combustion phase, not the entire burn period. • Check that the timing you pick gives maximum pressure slightly after top dead center, not well before or far after. • Make sure you distinguish between injection period, vaporization, and afterburning—they are not all the same part of the combustion process.