If the diesel engine fuel injection timing is changed to delay the start of injection until the pistons are at top dead center, the engine will __________.
• diesel fuel injection timing and what happens with late injection (after top dead center) • relationship between combustion start, piston position, and pressure development in the cylinder • how engine power and cylinder pressure change with early vs. late injection
• Think about what happens to cylinder pressure if you start burning fuel when the piston is already beginning to move down instead of just before top dead center. • Which option matches the typical symptoms of retarded (late) injection timing in a diesel: power change, pressure change, or abnormal backfire? • Would late injection give combustion gases more or less time to expand on the power stroke, and how does that affect useful work on the crankshaft?
• Compare which choices are associated with very high peak firing pressures versus reduced effective pressure. • Consider whether backfire through the air intake is normally a diesel problem or more common with spark-ignition gasoline engines with intake manifolds. • Ask: with combustion starting late, is there more likelihood of lifting cylinder relief valves (excess pressure) or of not fully using the fuel energy for power?
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