Automatic Ignition Systems
Topics Covered:
• Terminology Associated With Automatic
Ignition Systems and the Origin of.
• Direct Spark Ignition Systems
• Intermittent Pilot Systems
• Hot Surface Ignition Systems
• Integrated Furnace Control
Automatic Ignition Systems
• In the past automatic ignition systems were
mainly used on light commercial heating
equipment where access to the pilot was difficult.
• Environmental factors would cause frequent pilot
outages that would result in expensive service
calls.
• These automatic ignition systems were mainly
designed to re-light standing pilots.
Automatic Ignition Systems
• Today automatic ignition systems for residential
and light commercial gas appliances fall into one
of three categories.
• Direct Spark Ignition (DSI) in which the burner
flame is directly ignited by an ignition spark upon
each call for heat.
• Intermittent Pilot (IP) in which the burner flame is
ignited by a pilot flame that is established at the
beginning of each heating cycle.
Automatic Ignition Systems
• Hot Surface Ignition (HSI) in which the burner
flame is ignited by a hot surface igniter on each
call for heat.
• These modern electronic ignition systems employ
electronic flame sensing systems, which has
greatly reduced the flame sensing response time.
• Remote location applications still apply, but the
rising cost of fuel has greatly increased the
presence of Automatic Ignition Systems.
Terminology
• Trial for Ignition Time: Maximum time allowed for
the ignition module to the establish burner flame.
• Flame Failure Response Time: Time it takes the
ignition control module to react to the presence
or absence of the flame. (Standing pilot 90
seconds, 0.8 seconds Electronic Ignition)
• Lock-out or Safety Shut-off: The ignition module
shutting down upon failure to establish flame
during the ignition cycle.
Terminology
• Remote Reset: Resetting the ignition control
module by turning off the 24 volt power supply to
the module.
• Recycling: The process of the ignition control
module repeating the ignition sequence upon lost
flame detection during burner run cycle.
• Safe Start Check: Ignition prevention if a flame
signal is present prior to the call for heat.
Terminology
• Pre-purge: A process where the induced draft or
burner fan operate for a specific period of time
clearing the combustion chamber prior to the
ignition sequence.
• Post-purge: A process where the induced draft or
burner fan operate for a specific period of time
clearing the combustion chamber after the burner
cycle has completed.
Terminology
• Retry: The ignition control repeats the ignition
sequence, if the burner flame is undetected after
the first try for ignition.
• Ignition controls with a retry feature built-in
usually have a maximum number of retries before
a hard lock-out occurs.
• Often 3 retries is the maximum number of cycles,
with a 3hr re-cycle period before the ignition
control tries again.
Direct Spark Ignition Systems
• Direct spark ignition or DSI is a method of burner
ignition in which ignition is directed to the main
flame by a high voltage electrical spark, instead of
a pilot flame.
• System Control Module controls the system
operations.
• Spark Igniter consists of an inner electrode and
outer ground electrode, the spark arcs across the
two electrodes in front of the gas burner.
Direct Spark Ignition Systems
• Gas Control Valve consists of two in line main
valves that provide added protection against valve
failure.
• A flame sensor is used to detect the presence of
the flame using a principle called flame
rectification.
• Air and gas molecules between the flame sensor
and the grounded burner become ionized and are
able to conduct an electrical current.
Direct Spark Ignition Systems
• The current flow through the flame flows in one
direction because of the size difference between
the flame sensor and ground areas, resulting in a
pulsing direct current.
• The conversion of alternating current to direct
current results in the term Flame Rectification,
due the rectifying nature of the process.
Honeywell S87A DSI System
Intermittent Pilot Systems
• IP systems differ from DSI and HSI in that a spark
ignited pilot is established to ignite the main
flame upon each burner start-up.
• The electronic flame sensor continuously
monitors the pilot flame which remains on during
the burner cycle.
• This system utilizes a dual valve type gas control
valve, with a separate operated pilot valve, and
separate operated main valve.
Honeywell S8600 IP System
Natural Draft Appliance
Cycle Pilot Systems
• The White Rodgers cycle pilot system is an
intermittent pilot system, using a unique gas
control valve, a spark electrode and mercury
flame sensor.
• The cycle pilot system is an early style of
automatic ignition systems, the purpose of this
system was to automatically re-light the pilot
incase of outage.
• There are many variations of this system existing.
White Rogers 36C84
Cycle Pilot System
Cycle Pilot Systems
• The White Rodgers cycle pilot system is an
intermittent pilot system, using a unique gas
control valve, a spark electrode and mercury
flame sensor.
• The cycle pilot system is an early style of
automatic ignition systems, the purpose of this
system was to automatically re-light the pilot
incase of outage.
• There are many variations of this system existing.
White Rogers 36C84
Cycle Pilot System
Honeywell Intermittent Pilot
Ignition Systems
• The Honeywell S8600 ignition systems is a flame
rectification type intermittent pilot system that
provides 100% safety shut off and system
prepurge.
• Prepurge is accomplished by a combustion air
blower assembly clearing the heat-exchanger.
• Nominal flame current is approximately 1.0 uA DC
micro-amps, checked through the ground return
lead to the ignition control module.
Honeywell S8600 IP System with
Combustion Air Blower
Honeywell S8600 IP System
Heating and Cooling
Hot Surface Ignition Systems
• The hot surface ignition system like the DSI
system, provides direct ignition to the burner
flame.
• The HSI system like DSI system utilizes an
electronic flame sensing system, typically through
flame rod rectification circuitry.
• In some installations the hot surface igniter is
used as the flame sensing device, instead of a
flame rod rectification system.
Hot Surface Ignition Systems
• The igniter is a silicon carbide igniter which is
heated to give a hot surface that ignites the
burner flame.
• The relatively large surface area of the igniter
ensures that it is not position sensitive as an
ignition spark.
• The hot surface igniter is checked through the use
of an ohm meter, refer to the manufacturer for
specific resistance intervals for replacement.
Honeywell S8910U HSI
Integrated Furnace
Control System
• The integrated furnace control is an expanded
automatic ignition control, that contains a
microprocessor that governs the furnace
functions.
• The IFC controls all of the furnace functions from
burner functions, to the blower motor controls.
• These types of controls are often outfitted with
self diagnostic tools to aid the service technician.
White Rodgers Integrated
Furnace Control