A V-12 four-stroke/cycle 500 horsepower diesel engine is operating under a normal load, the firing pressures are low and the exhaust temperatures are high. Which of the following problems is the most probable cause of this condition?
• Effect of fuel rack setting on combustion pressure and exhaust temperature in diesel engines • How restricted air flow or exhaust flow affects firing pressure and exhaust temperature • Normal indicators of overfueling vs. underfueling in a four-stroke diesel
• If firing pressures are low but exhaust temperatures are high, what does that tell you about how completely the fuel is burning and how much air is available? • Which of the listed problems would most likely reduce the engine’s ability to get fresh air in or exhaust gases out, and how would that show up in cylinder pressure and temperature? • How would moving the fuel pump rack "too far in" versus "too far out" typically change firing pressures and exhaust temperatures on a diesel under load?
• Match low firing pressure with the most likely cause (less fuel vs. less air vs. more restriction). • Match high exhaust temperature with the most likely cause (overfueling vs. poor scavenging vs. restricted flow). • Eliminate any choice that would be expected to cause both high firing pressure and high exhaust temperature, as that does not fit the question.
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