10 exam-style questions with answers and explanations, straight from our 1,030-question bank. Tap an answer to check yourself. When you're ready, take the scored version in the free practice test.
These 10 free DDE questions are organized by exam domain, so you can see how each part of the National Designated Duty Engineer Steam/Motor/GT (DDE) blueprint is tested. Reveal the answer and explanation under each question.
After an individual fuel-injection pump is replaced, one cylinder of a propulsion diesel has a higher exhaust temperature than the others at the same engine load. Its indicator diagram shows normal compression pressure, but the combustion-pressure rise begins later and peak firing pressure is lower. The other cylinders are unchanged. What fault best accounts for this combination?
Correct answer: C - Retarded fuel-injection timing on the affected cylinder.
A propulsion diesel's duplex lubricating-oil filter has a changeover limit of 0.8 bar differential pressure and a bypass-opening setting of 1.4 bar. Differential pressure has risen to 1.0 bar at unchanged oil temperature and engine load. Bearing-oil pressure remains normal, no other alarms are present, and the clean standby chamber is ready. The filter is designed for on-load changeover. What should the engineer do next?
Correct answer: A - Change over to the clean chamber while monitoring bearing-oil pressure.
A large steam consumer comes on line. Boiler drum pressure falls, steam flow briefly exceeds feedwater flow, and both the gauge glass and level transmitter show a rising level. The trainee suggests closing the feedwater valve because the boiler appears to be gaining water. How should the engineer interpret this brief level rise?
Correct answer: B - Steam bubbles are expanding; indicated level can rise while water inventory falls.
At steady steam load, condenser absolute pressure rises from 8 kPa to 15 kPa. Circulating-water inlet temperature, circulating-water flow, and hotwell level remain normal. Condensate conductivity is unchanged, but sealing-steam pressure at the low-pressure turbine glands has fallen sharply. Where should the investigation focus?
Correct answer: D - Air leaking inward through the low-pressure turbine shaft glands.
A gas turbine's starting instructions require at least 55% gas-generator speed within 40 seconds after fuel admission; failure to reach that speed requires an abort. The start-temperature limit is 700°C. At 45 seconds, flame is established, temperature is steady at 560°C, and speed has remained at 38% for the last 15 seconds. The starter itself is rated for 90 seconds of continuous operation. Classify the start and select the appropriate response.
Correct answer: D - A hung start; abort because the speed-and-time requirement was not met.
An engine-room fire is to be attacked with the fixed total-flooding CO2 system. The alarm has been raised, everyone is accounted for outside the space, fuel supplies are isolated, and ventilation fans are stopped. One supply-air damper has failed to close, but its external manual operating mechanism is safely accessible. Which action must be completed before the authorized CO2 release?
Correct answer: B - Close the damper using its external manual operating mechanism.
A centrifugal pump takes hot water from a tank open to the atmosphere. At its operating flow, atmospheric-pressure head is 10.2 m, the liquid surface is 2.0 m above the pump centerline, suction-line losses are 1.4 m, and vapor-pressure head is 6.0 m. All heads are meters of the pumped liquid; tank-surface velocity is negligible. The pump requires 3.0 m NPSH, and the installation requires an additional 1.0 m margin. Which assessment of suction conditions is correct?
Correct answer: D - NPSH available is 4.8 m; the required margin is met.
An R-134a provision refrigeration plant has poor cooling despite normal evaporator airflow. At the expansion-valve bulb location, suction pressure corresponds to a saturation temperature of -8°C, while the suction-line temperature is +10°C. At the condenser outlet, condensing saturation temperature is 40°C and liquid temperature is 28°C. Across the liquid-line filter-drier, temperature drops from 28°C to 16°C, and bubbles appear downstream. Which diagnosis fits both the evaporator and liquid-line readings?
Correct answer: C - Superheat is 18 K; a restricted filter-drier is starving the evaporator.
Two identical synchronous generators are paralleled with manual reactive-load sharing. Each carries 220 kW, but No. 1 supplies 150 kVAR and No. 2 supplies 50 kVAR. Bus voltage and frequency are normal, and both generator currents are below their ratings. To equalize reactive loading without changing the kW split, the engineer should:
Correct answer: A - Reduce No. 1 excitation and increase No. 2 excitation.
A ship's diesel-generator set is rated for 400 kW and 500 kVA continuous output under the present ambient conditions. A proposed balanced three-phase load would draw 360 kW at 0.60 lagging power factor. Consider steady operation only, with starting transients excluded. Can the proposed load be carried continuously?
Correct answer: C - No; apparent power is 600 kVA, above the alternator rating.
The full bank has 1,020 more DDE questions with explanations.
Continue in the free practice test →
View plans