Chapter 15 Ignition and Transient Considerations Flashcards
what are three types of burner ignition systems used
Standing pilot burner
Intermittent spark igniters
Hot surface ignition
benefits of hot surface ignition
best at lighting large gas flow rates
has the most customer appeal
disadvantages of hot surface ignition
longest delay period from “on signal” to “gas ignition”
can cause damage if not installed properly
highest initial cost
least rugged
benefits of intermittent spark ignition
flame sensing often included
consumes least energy
disadvantage of spark ignition
noisiest system
benefits of standing pilot burner ignition
most rugged and durable design
lowest initial cost
does not require electrical power
disadvantage of standing pilot burner ignition
consumes the most energy
What are key factors for good ignition location
securely mounted
close enough to the flame kernel so that when gas and air start flowing it will quickly ignite
Must be hot enough to ignite
Must not be located so that it overheats the burner or tube
explain the steps leading up to a burnable air/fuel mixture
initial push is pure air for 50-100ms
then the slug of pure gas comes but is too rich for 100-150ms
primary air starts to flow at 40-60 percent aeration taking 100-150ms
after another 300-400ms the mixture is in the combustible range
pressure/flow steps to combustion
inside the burner must be higher than atmospheric so that a combustible mix can flow out
velocity of fuel turned into pressure through the burner ports
the combustible gasses move towards the burner inlet and ignition ports
summarize a typical gas burner start transient
- mixture is pure air
- short time too rich
- settles to combustible mixture range
- far end of burner tube pressurizes first
- ignition ports are pressurized and gas starts flowing
- ignition takes place
