Natural and Fan-Assisted Draft Appliances - Part A 080205aA Flashcards
Natural draft burners are often called what?
Atmospheric burners
What burner do all natural draft appliances use?
Inspirated burner
Definition of Primary Air
That portion of the combustion air that is supplied for the initial stages of the combustion process and is supplied upstream from the point of ignition
Definition of Secondary Air
That portion of the combustion air that is supplied for the intermediate and final stages of the combustion process and is supplied downstream of the point of ignition
Definition of Excess Air
Air supplied to the combustion zone in excess of the quantity of air to assure complete combustion of the fuel but is theoretically not required
What type of burner does an atmospheric burner use?
Inspirated
The pressure in the Venturi of the burner will be higher or lower than atmospheric pressure?
Lower (below 14.7psi)
The quantity of air a burner entrains increase as what increase?
Fuel pressure and velocity
Natural draft atmospheric appliances rely on the _____ _____ of the warm air escaping through the combustion chamber vent opening and rising up a chimney to create a ___ pressure area which draws in a new supply of air to the firebox and the effects of ______ creates an air flow into the combustion chamber
stack action, low, buoyancy
What are you 3 types of air supply for combustion?
Primary air
Secondary air
Excess air
The burner on a hot water tank is an example of what kind of burner?
Upshot Inspirated burner
What creates the need for an induced draft fan on an appliance?
Resistance in the heat exchanger (bends and dimpling create more surface area)
What are the 2 main burner classifications?
Atmospheric
Power burner
What is the main difference between power burners and atmospheric burners?
Power burner is fan assisted
A pilot that burns continuously?
Standing pilot (continuous pilot)
A pilot which is automatically lit and burns each time there is a call for heat until main burner flame is established
Interrupted pilot (remains lit until burner is lit)
A pilot that is automatically lit and burns when the main flame is established and shuts off when main flame is extinguished
Intermittent pilot (lights main burner with call for heat and shuts off when main burner shut off)
How is stack action created?
Difference in buoyancy between lighter warm air rising through the appliance venting and heavier cold air flowing into the combustion chamber
How does flame lift off occur?
Quantity of primary air is too high for a given quantity of fuel
Fuel pressure is higher than the burner can handle
Fuel moves too quickly through the burner for a given quantity of primary air
How is burner flashback created?
Fuel/air mixture moves through the burner ports at a rate slower than combustion burning the fuel
Too low gas pressure
Excessive primary air for a given quantity of fuel
How does a yellow flame burner operate and where is it used?
Burns almost entirely with secondary air
Used is some gas fireplaces with simulated logs in firebox
What are 2 dangerous compounds that may be created as products of combustion if fuel is not completely burned?
CO (carbon monoxide)
Aldehydes
What is the basic difference between an aspirated burner and an Inspirated burner?
Aspirated burners entrain fuel with air
Inspirated burners entrain air with fuel
What does the term stack action refer to?
The flow of products of combustion through the appliance and up through the vent
What are the products that result from the complete combustion of fuel and air?
CO2 and H2O
A 2 stage furnace uses what kind of fan speed?
Staging
Appliances with variable firing rates require a burner design with a good turndown ratio. This can be described as what kind of fan speed?
Modulating
The burners on a furnace are what kind of burners?
Inshot burners
The heat exchanger must not scrub too much heat from the products of combustion for what reason?
There will not be enough heat left for adequate stack action
In general, ______ the ______ of fluid flowing through a closed channel ______ the ______ of the channel to the flow of fluid through it
Doubling, volume
Quadruples, resistance
How is static pressure created by a centrifugal fan counteracted by discharge housing design?
Increasing the size of the outlet / sudden enlargement
The amount of air a natural draft burner entrains increases as what other factor or factors increase?
Fuel pressure and velocity
