ACS Combustion & Flues

Question 1

What is the product of complete combustion of natural gas (methane)?

Accepted Answer

Carbon dioxide and water vapour

Answer

Carbon monoxide and water vapour

Answer

Carbon dioxide and nitrogen

Answer

Carbon monoxide and carbon dioxide

Question 2

What is carbon monoxide (CO) and why is it particularly dangerous?

Accepted Answer

An odourless, colourless, tasteless gas that binds to haemoglobin with far greater affinity than oxygen, causing rapid incapacitation and death

Answer

A visible yellowish gas with a strong smell that alerts occupants to danger

Answer

A gas that causes respiratory irritation but is rarely fatal

Answer

A combustion by-product that is lighter than air and disperses quickly

Question 3

What does a high CO/CO2 ratio (Wobbe index deviation) in flue gas analysis indicate?

Accepted Answer

Incomplete combustion is occurring, likely due to insufficient air supply, a dirty burner, or flue restriction

Answer

The boiler is operating at peak efficiency

Answer

The flue temperature is too high

Answer

The gas pressure is above the required operating range

Question 4

What is the primary air/secondary air function in a gas burner?

Accepted Answer

Primary air mixes with gas before the burner to support combustion; secondary air provides additional oxygen around the flame to complete combustion

Answer

Primary air cools the burner; secondary air ignites the flame

Answer

Both primary and secondary air cool the heat exchanger

Answer

Secondary air is only used in condensing boilers

Question 5

What does a 'balanced flue' on a gas appliance mean?

Accepted Answer

The appliance draws its combustion air from outside and expels flue gases to outside through a co-axial terminal, making it room-sealed and unaffected by internal air quality

Answer

The flue is balanced between two buildings sharing a party wall

Answer

The flue passes through a balancing chamber before exhausting

Answer

The flue is shared between two appliances

Question 6

What is the function of a flue gas analyser in gas engineering?

Accepted Answer

It measures the concentrations of CO, CO2, and O2 in the flue gases to verify that combustion is complete and the appliance is operating safely and efficiently

Answer

It measures the gas pressure at the meter

Answer

It detects gas leaks in the pipework

Answer

It measures the temperature of the heat exchanger