F1&F2 Assignments

Question 1

list the three basic requirements of combustion

Answer 1

1. heat
2. oxygen
3. fuel

Question 2

what percentage of oxygen does air contain?

Answer 2

20% oxygen

Question 3

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

Answer 3

1. pilot flame
2. spark ignitor
3. hot surface ignitor (glow coil)

Question 4

Write the formula for the chemical reaction in the combustion of methane and air.

Answer 4

CH4 + 2O2 = CO2 + 2H2O + Heat

Question 5

When we completely burn a hydrocarbon fuel, such as natural gas or propane gas, the products of combustion will contain (4)

Answer 5

1. CO2
2. H2O
3. N2
4. Heat

Question 6

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

Answer 6

incomplete

Question 7

Describe perfect combustion.

Answer 7

Theoretical volume of air that must be mixed with fuel gas to achieve perfect combustion. 10 cu ft of air for every 1,000 Btu of gas. Only under theoretical conditions.

Question 8

Describe complete combustion.

Answer 8

Supplying air in excess of perfect combustion to ensure all atoms of carbon and hydrogen are united with enough oxygen atoms to produce complete combustion.

Question 9

Describe incomplete combustion.

Answer 9

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

Question 10

Name a product of incomplete combustion which is toxic and has a penetrating odour.

Answer 10

Aldehydes

Question 11

Explain primary air and give the number of cu ft required to mix with 1 cu ft of CH4 (natural gas).

Answer 11

Primary air is the combustion air mixed with the fuel gas before ignition. It occupies approximately one-third of a 10:1 ratio. 1 cu ft CH4 requires 3.33 cu ft primary air.

Question 12

Explain secondary air and give the number of cu ft required to mix with 1 cu ft of CH4 (natural gas).

Answer 12

Secondary air is the combustion air supplied from around the flames. It occupies approximately two- thirds of theoretical air ratio 10:1. 1 cu ft CH4 requires 6.66 cu ft secondary air.

Question 13

Explain excess air.

Answer 13

Excess air is the air required in addition to theoretical combustion air to ensure complete combustion. It occupies approximately 50% of theoretical combustion air.

Question 14

Why must excess air be kept to a minimum?

Answer 14

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

Question 15

Explain the purpose of dilution air.

Answer 15

Dilution air is 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.

Question 16

State the relationship of Btu of input to the volume of combustion air required.

Answer 16

For every 1,000 Btu of input, 10 cu ft of air is required for perfect (theoretical) combustion.

Question 17

How many cu ft of combustion air are required for an appliance firing on C3H8 (propane) with a calorific value of 2,500 Btu/cu ft burning 100 cu ft of fuel per hour?

Answer 17

2,500× 100 cu ft= 250,000 Btu/h

250,000btu/1000btu x 10cu ft = 2500 cu ft combustion air

Question 18

State the relationship between Btu of input and the volume of excess air required.

Answer 18

For every 1,000 Btu of input, 5 cu ft of excess air is required.

Question 19

Give the excess air requirement of the appliance mentioned in Question 7.

Answer 19

250 MBH input × 5 cu ft = 1,250 cu ft excess air

Question 20

State the relationship between Btu of input and the volume of dilution air supply.

Answer 20

For every 1,000 Btu of input, 15 cu ft dilution air is required.

Question 21

Referring to the appliance in Question 7, give the required dilution air supply. (250,000btu input)

Answer 21

250 MBH input × 15 cu ft = 3,750 cu ft dilution air

Question 22

State the relationship between Btu of input and the volume of total air supply.

Answer 22

For every 1,000 Btu of input, 30 cu ft of total air is required.

Question 23

Referring to the appliance in Question 7, give the total air requirements. (250,000btu input)

Answer 23

250 MBH input × 30 cu ft = 7,500 cu ft total air

Question 24

Calculate the combustion and excess air requirements to burn 1 cu ft of C4H10 (butane).

Answer 24

3,260 Btu / cu ft

326btu/1000btu x 15cu ft = 48.9 cu ft combustion and excess air

Question 25

Calculate the air requirements for a boiler with an input of 350,000 Btu/h, firing on CH4, with a calorific value of 1,000 Btu/cu ft.

1. Combustion air:
2. Primary air:
3. Secondary air:
4. Excess air:
5. Dilution air:
6. Total air:

Answer 25

1. 3,500 cu ft
2. 350 MBH x 3.333 cu ft = 1,166.56 cu ft
3. 350 MBH × 6.667 cu ft = 2,333.45 cu t
4. 350 MBH × 5 cu ft = 1750 cu ft
5. 350 MBH × 15 cu ft = 5250 cu ft
6. 350 MBH × 30 cu ft = 10,500 cu ft