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Hi > Gas - Products of Combustion and the Combustion Process > Flashcards

Gas - Products of Combustion and the Combustion Process Flashcards

1
Q

List the three basic requirements of combustion?

A

Fuel.

Heat.

Oxygen.

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2
Q

What percentage of oxygen does air contain?

A

20%.

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3
Q

Name three possible sources of the initial heat required for combustion.

A

Hot surface igniter.

Pilot flame[][][][][][][][]

Spark igniter[][][][][]]

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4
Q

When we completely burn a hydrocarbon fuel, such as natural gas or propane gas, the products of combustion will contain:

A

CO2.

H2O.

N2[][]

Heat.

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5
Q

Which type of combustion has been created if carbon monoxide is found in the products of combustion?

A

Incomplete.

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6
Q

Theoretical volume of air that must be mixed with fuel gas is the definition of?

A

Perfect combustion.

Stoichiometric combustion.

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7
Q

Supplying air in excess of perfect combustion to ensure all atoms of carbon and hydrogen are united with enough oxygen atoms is the definition of?

A

Complete combustion.

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8
Q

Not enough oxygen is available to burn the fuel gas completely. Carbon monoxide is produced. CO not completely burned. Is the defintion of?

A

Incomplete combustion.

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9
Q

The combustion air mixed with the fuel gas before ignition is the defintion of?

A

Primary air.

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10
Q

The combustion air supplied from around the flames is the defintion of?

A

Secondary air.

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11
Q

The air required in addition to theoretical combustion air to ensure complete combustion is the definition of?

A

Excess air.

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12
Q

Why must excess air be kept to a minimum?

A

It absorbs heat and carries it off to the venting system. This causes the appliance to become less efficient.

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13
Q

The room air entering the venting system at a draft control device. It cools hot vent gases and controls the draft influence on the combustion chamber is the definition of?

A

Dilution air.

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14
Q

Primary air is equal to:

A

1/3 of combustion air.

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15
Q

Secondary air is equal to:

A

2/3 of combustion air.

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16
Q

Excess air is equal to:

A

Rating plate / 1000.

Then times 5[][][][][][]

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17
Q

Combustion air is equal to:

A

Rating plate / 1000.

Then times 10[][][][][]

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18
Q

Dilution air is equal to:

A

Rating plate / 1000.

Then times 15[][][][][]

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19
Q

Describe the type of equipment that requires a flue gas analysis in order to adjust the air openings properly.

A

Fan-assisted or power burners.

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20
Q

Name two products of incomplete combustion that are life threatening?

A

CO - Carbon Monoxide.

Aldehydes - Complex chain of toxic alcohols.

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21
Q

The % of CO2 at perfect combustion with no excess air is the definition of?

A

Ultimate % CO2.

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22
Q

If two flue samples were taken, the first with 25% excess air and the second with 50% excess air, which would contain the higher CO2 reading?

A

The increase in excess air is directly proportional to the decrease in CO2. Therefore 25% excess air has a higher CO2 reading.

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23
Q

Explain the relationship between the % values of CO2 and O2 in the flue gas when you adjust the air shutter on a fan-assisted burner during setup.

A

The greater the amount of excess air, the higher the % of O2 and the lower the % of CO2

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24
Q

Free hydrogen is a sign of incomplete combustion, but is not normally present unless the level of carbon monoxide reaches a level of at least __ %.

A

2.

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25
Q

List three types of flue gas analyzers.

A

Continuous sampling (Bacharach)

Liquid type (Drager, Gastec)[][][][][]]

Tube type (Orsat, Fyrite)[][][][][][][][][]]

26
Q

The difference between the ambient (room) temperature and the flue gas temperature is the definition of?

A

Net stack temperature.

27
Q

List three conditions that will reduce the efficiency of the heating equipment and increase the temperature of the flue gas.

A

Dirty heat exchanger.

High draft[][][][][][][][][][]]

Overfiring of the burner.

28
Q

Do you require all three components that make up the combustion triangle in order for combustion to occur?

A

Yes.

29
Q

Explain why the % CO2 may be an indicator of the efficiency of the combustion process.

A

The addition of minimum excess air for complete combustion will result in higher CO2 readings.

30
Q

What are the two main components that make up air and how much of each is in the air?

A

20% Oxygen.

80% Nitrogen.

31
Q

What is the formula for the perfect combustion of Natural Gas?

A

(1)CH4 + (2)O2 + (8)N2 = (1)CO2 +(2)H20 + (8)N2 + Heat

32
Q

What is the formula for the perfect combustion of Propane?

A

(1)C3H8 + (5)O2 + (20)N2 = (3)CO2 + (4)H20 + (20)N2 + Heat

33
Q

What are the three main categories that air supply is divided into?

A

Combustion air.

Excess air[][][][][]

Dilution air[][][][]]

34
Q

What are the two categories that theoretical air can be split into?

A

Primary air: The combustion air which is mixed with the fuel gas before ignition.

Secondary air: Required to complete the combustion process[][][][][][][][][][][][][][][][]]

35
Q

Where does primary air enter the combustion process?

A

Primary air shutter.

36
Q

Where does secondary air enter the combustion process?

A

From the outside in.

37
Q

How much excess air is generally required for a high efficiency power burner?

A

20-30%.

38
Q

Does dilution air contribute to the combustion process and is dilution air always needed?

A

Dilution air is only required when there is draft control.

39
Q

The volume of air required to allow the appliance to operate safely and efficiently is the definition of?

A

Total air.

40
Q

What happens to the efficiency of an appliance as more excess air is added?

A

Efficiency decreases as more excess air is added.

41
Q

How is the efficiency of an appliance calculated?

A

Efficiency = Output ÷ Rated Input

42
Q

What is the ultimate percentage of C02 levels for Natural Gas?

A

Natural Gas = (1)CO2 +(8)N2

(1)Part CO2 ÷ (9)Total Dry Parts

1 ÷ 9 = .1111 x 100 = 11.11% (12%)[]]

Theoretical perfect comubstion[]

43
Q

What is the ultimate percentage of C02 levels for Propane?

A

(3) CO2 + (20)N2
(3) Parts CO2 ÷ (23) Total Dry Parts

3 ÷ 23 = 14%[][][][][][][][][][][][][][][][][][][]]

Theoretical perfect combustion[][][]

44
Q

What happens to the percent of carbon dioxide in the products of combustion as we add more excess air?

A

The percentage of carbon dioxide is decreased.

45
Q

What four conditions could lead to carbon monoxide being produced?

A

Lack of air.

Overfiring of the burner.

Poor mixing of the burner.

Quenching or chilling of the flame.

46
Q

How much excess air is added for a natural draft atmospheric burner?

A

50%.

47
Q

When dealing with the combustion of hydro carbon gases, why is stoichiometric combustion of fuel and air not a viable option for most burners?

A. This will produce an unacceptable luminous flame.

B. Burners are not capable of perfectly mixing air and fuel.

C. This type of combustion produces unacceptable flue gas components.

D. Stoichiometric combustion is unstable and unsuitable for heating applications.

A

B. Burners are not capable of perfectly mixing air and fuel.

48
Q

It is important to add excess air to the combustion chamber to:

A. Provide cooling for the heat exchanger.

B. To ensure perfect combustion occurs[][]]

C. To provide an adequate amount of dilution air.

D. To ensure complete combustion occurs[][][][][][]

A

D. To ensure complete combustion occurs.

49
Q

Which of the fuel air ratios show below is for Natural Gas?

A. 20ft³ to 1ft³.

B. 20ft³ to 100 Btu’s.

C. 10ft³ to 1000 Btu’s.

D. 2ft³ to 100 Btu’s[][]

A

C. 10ft³ to 1000 Btu’s.

50
Q

Why do air requirements differ for appliances with and without draft control?

A. All units require air to be supplied at a ratio of 30:1

B. Units with draft control require more combustion air

C. Units with no draft control require more excess air[][]

D. Units with draft control require dilution air[][][][][][][][][][]

A

D. Units with draft control require dilution air.

51
Q

How much excess air is added to the combustion process in order to achieve the ultimate percentage of CO2?

A. 1/3 the volume of combustion air.

B. 2/3 the volume of combustion air.

C. 50% combustion air[][][][][][][][][][][][]]

D. None is required[][][][][][][][][][][][][][][]]

A

D. None is required.

52
Q

What percent of excess air will produce equal percentages of O2 and CO2 in the flue products?

A. 25%.

B. 33%.

C. 50%.

D. 100%.

A

C. 50%.

53
Q

Analyzing the flue products after servicing a burner shows acceptable levels of CO2 and O2 but unacceptable levels of CO. What type of circumstances could cause this to happen?

A. Lack of combustion air.

B. Lack of excess air[][][][][]

C. Excessive dirt on fan blades.

D. Poor mixing ability of burner system.

A

D. Poor mixing ability of burner system.

54
Q

If a gas hot water tank was 100% efficient, what would the temperature of the flue products be?

A. Same as ambient.

B. 100°F above ambient temerature.

C. 100°C below ambient temperature.

D. Minimum 127° to maintain draft[][][]]

A

A. Same as ambient.

55
Q

The theoretical perfect combustion of Natural Gas requires an air/gas ratio of:

A. 10:1.

B. 15:1.

C. 25:1.

D. 30:1.

A

A. 10:1.

56
Q

The complete combustion of Propane in air (include 50% excess air) requires an air/gas ratio of:

A. 10:1.

B. 15:1.

C. 25:1.

D. 37:1.

A

D. 37:1.

57
Q

A furnace operating at the rated input on Propane is converted to Natural Gas. The total air requirements for the furnace will:

A. Increaase by 5%.

B. Increase by 10%[]

C. Decrease by 15%.

D. Remain the same.

A

D. Remain the same.

58
Q

Some flue gas analyzers can test for combustables. Which of the following could not be detected?

A. Carbon.

B. Hydrogen.

C. Carbon Monoxide.

D. Carbon Dioxide[][]]

A

C. Carbon Monoxide.

59
Q

A fan assist burner operating at its rated input is producing flue gas with 8.6% CO2. In order to increase the CO2 level you must:

A. Increase the air supply.

B. Decrease the air supply.

C. Increase the fuel supply[]

D. Decrease the fuel supply.

A

B. Decrease the air supply.

60
Q

The CO2 content for a power burner should not be higher than approximately:

A. 8 1/2%.

B. 10 1/2%.

C. 12%[][][]]

D. 14%[][][]]

A

B. 10 1/2%.

61
Q

When taking a flue gas analysis for an appliance where should the flue gas sample be taken from?

A. Downstream of the draft control device.

B. Upstream of the draft control device[][][]

C. Upstream of the heat exchanger[][][][][][]]

D. At the burner[][][][][][][][][][][][][][][][][][][][][][][][]

A

B. Upstream of the draft control device.

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