Which of the indicator diagrams illustrated...

Which of the indicator diagrams illustrated depicts the condition that should be corrected by retarding only the timing? Illustration MO-0029

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🔍 Key Concepts

• Diesel engine indicator diagrams – understand that the dashed curve usually shows the normal or desired pressure vs. crank angle, and the solid curve shows the actual condition. • Fuel injection timing (advance vs. retard) – advancing moves the whole combustion portion of the curve to the left (earlier in crank angle), retarding moves it to the right (later), without changing the amount of fuel. • Peak pressure and its position – timing corrections mainly shift when peak pressure occurs, while fuel quantity/quality problems mainly change how high the pressure rises.

💭 Think About

• Compare the solid and dashed curves in each option: in which diagram is the shape and height of the curves nearly the same, but the whole combustion part is simply shifted earlier or later in relation to the dashed curve? • In which option does the peak pressure occur noticeably too early (before top dead center) or too late, yet the magnitude of peak pressure is about right – suggesting a timing change would fix it? • Eliminate any diagrams where the main problem looks like too high or too low peak pressure or a very different curve shape, which would usually require changing fuel quantity or injector condition, not just retarding timing.

✅ Before You Answer

• Be sure you can tell which line is the normal reference curve and which is the actual engine condition in each panel. • Check whether the height (peak pressure) of the actual curve is roughly the same as the reference; if it’s much higher or lower, timing alone is usually not the only correction. • Focus on the diagram where the only obvious difference is that the actual peak occurs too far to the left of the reference curve relative to top dead center, indicating that simply retarding the timing would align it correctly.

🔍 Key Concepts

💭 Think About

✅ Before You Answer