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These 10 free Fuel Oil Combustion questions are organized by exam domain, so you can see how each part of the Fuel Oil Combustion Certification blueprint is tested. Reveal the answer and explanation under each question.
An oil burner already has clean combustion and the required reserve air. Opening its air shutter substantially farther raises O2 and lowers CO2 while fuel flow remains constant. Why can this adjustment reduce efficiency?
Correct answer: B - More unused air leaves the appliance carrying sensible heat.
Correcting a smoky burner brings its smoke number to 0, but the boiler's stack temperature remains well above its clean-condition baseline. Fuel input, flue O2, inlet-water temperature, and water flow match that baseline. Which condition most likely accounts for the remaining temperature increase?
Correct answer: C - Residual soot insulating the heat-transfer surfaces.
After a cold night, an outdoor oil supply develops a filter restriction. The delivered fuel has a cloud point of -5°C and a pour point of -20°C; oil at the filter is -11°C. A sample still pours from its container. What does that observation tell the technician?
Correct answer: C - Wax can plug the filter even though the bulk oil is still fluid.
A laboratory heats an oil sample under a prescribed ignition test. At 56°C, applying the test flame produces the first momentary flash, but burning does not continue. The reported 56°C identifies the sample's:
Correct answer: A - Flash point.
A commercial burner approved for No. 6 oil loses its fuel preheater. Oil arrives at the nozzle colder than specified, and the spray becomes coarse even though nozzle differential pressure is unchanged. Which change in the oil best explains this result?
Correct answer: D - Higher viscosity resists breakup into fine droplets.
An appliance permits a pump pressure of 150 psi but limits actual oil delivery to 0.85 US gal/h. Its installed simplex nozzle is rated 0.75 US gal/h at 100 psi. With unchanged fuel properties and negligible combustion-chamber pressure, how does delivery at 150 psi compare with the appliance limit?
Correct answer: C - About 0.92 US gal/h; above the limit.
An oil burner locks out after failing to ignite. The owner has already pressed reset twice. With the burner now off, the technician finds accumulated unburned oil in the combustion chamber. What must take priority before another ignition attempt?
Correct answer: B - Isolate power and fuel, then clear the accumulated oil and correct the ignition fault.
A properly performed smoke test gives a Bacharach number of 0, but an undiluted flue-gas sample shows 160 ppm carbon monoxide. Both instruments pass their checks. Which assessment belongs in the service record?
Correct answer: A - Incomplete combustion is occurring even though the smoke test shows no visible deposit.
While an oil-fired furnace runs steadily, moving the analyzer bends its sample hose. O2 abruptly rises from 4.5% to 11.8%, and raw CO falls from 65 to 35 ppm. The probe remains upstream of the barometric regulator; blower speeds, flame appearance, draft, and stack temperature do not change. What is the most appropriate next step?
Correct answer: A - Check the sample hose and connections for room-air leakage, then repeat the measurements.
On a windy day, a single-acting barometric regulator swings farther inward as chimney suction increases. Overfire pressure stays at -0.015 in. w.c. relative to the room, within the appliance's specified -0.020 to -0.010 range. Combustion results meet the appliance's requirements, and there is no spillage. How should the technician respond to the regulator's movement?
Correct answer: B - Keep the regulator setting and document the verified overfire draft.
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