Improving Gas Oven Ignition
By CoorsTek, Inc.
Gas oven ignition systems used in residential cooking appliances have remained
essentially unchanged over the last three decades, until now. A novel design
combines the benefits of advanced materials and intelligent control modules to
improve safety, performance, and long-term reliability.
Spark-ignition systems range
from simple spark electrodes and
mechanical switches, with little or
no safety mechanisms, to flame
rectification or thermocoupleintegrated systems designed to
monitor the main burner flame.
Monitoring the main burner flame
provides an acceptable, though
not ideal, safety level for most oven
designs – providing shutdown of
the burner operation when it does
not initially light, or if the burner fails
during operation. However, this does
not prevent unlit gas from flowing into
the oven cavity in the event that the
spark ignition device fails to ignite the
gas at the burner.
Hot-surface oven ignition systems,
most common in North America, are
“proved” systems in which the gas
valve supplying the main burner(s)
will not operate until the igniter is
proved capable of lighting the gas
stream. This system design does
not monitor the main burner flame.
Instead, system safety is assured by
checking the ignition capability of the
hot-surface igniter prior to opening
the gas valve. In this design the flow
of unlit gas is prevented, so there is
no chance of unlit gas flowing into
the oven cavity.
Although both of these design
approaches have some merit, years
of real-world experience also reveal
weaknesses and vulnerabilities that
can be improved upon:
Improved Oven Ignition
System Design
A new oven ignition system design
improves on the current designs of
both the unproved spark and proved
hot-surface oven ignition systems. It
also complies with all existing safety
and design standards and is suitable
for use globally.
The ignition system combines
the best features of the existing
proved hot-surface igniter and
unproved spark-ignition systems.
It was developed to satisfy class
Characteristic
Spark electrode
Low spark energy
Spark Ignition
Noise
Failure
Hot
Surface
Ignition
Power
Fragile igniters
Amperage drift
Response time
Safety standards
C certification and ongoing
harmonization efforts to standardize
ANSI and IEC cooking and control
standards. The system provides for
rapid ignition when the oven is called
upon to operate as is found in sparkignition systems. The burner flame is
continuously monitored and burner
ignition performance is improved,
when compared to spark ignition
due to the higher energy and larger
surface area of the Mini-Igniter hotsurface igniter. The system utilizes a
“proved” igniter and thus the system
safety is improved in that no gas will
flow into the oven cavity until the
igniter is proven to be capable of
igniting the gas stream.
In addition to these design features
the Mini-Igniter-based ignition system
Weakness
Subject to wear and distortion – leading to poor or non-ignition of
the oven burner
Makes lighting of some burner designs (e.g., radiant wire mesh
and ceramic plaque) difficult, if not impossible
Electrical noise due to high voltage may require shielding to
protect electronic controls; audible noise is a nuisance,
especially for burner re-ignition
High-voltage spark generators have been prone to failure,
impacting long-term system reliability
Currently available only for 120V
Current igniters are somewhat fragile & damage-prone
Since gas valve is activated by igniter amperage output, current
drifts over time may limit system life
System response is somewhat slow and variable
No direct monitoring of the main burner flame. Does not comply
with some recognized safety and design standards outside North
America.
Improved Oven Ignition System Design
A new oven ignition system design improves on the current designs of both the unproved spark
and proved hot-surface oven ignition systems. It also complies with all existing safety and design
standards and is suitable for use globally.
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The ignition system combines the best features of the existing proved hot-surface igniter and
unproved spark-ignition systems. It was developed to satisfy class C certification and ongoing
harmonization efforts to standardize ANSI and IEC cooking and control standards. The system
provides for rapid ignition when the oven is called upon to operate as is found in spark-ignition
systems. The burner flame is continuously monitored and burner ignition performance is
improved, when compared to spark ignition due to the higher energy and larger surface area of
the Mini-Igniter hot-surface igniter. The system utilizes a “proved” igniter and thus the system
safety is improved in that no gas will flow into the oven cavity until the igniter is proven to be
utilizes an improved igniter design
— one with rugged construction
and stable long-term operating
characteristics. Combining the
improved igniter design with an
innovative electronic control system
improves performance even further
with operational adaptability, improved
reliability, and extended service life.
Mini-Igniter with electronic
control module applied to
tubular oven bake burner.
Source: CoorsTek
Superior System
Components
Mini-Igniter
The hot-surface
igniter utilized in the oven system
is composed of a unique ceramic
and intermetallic composite. This
composite is processed to be
fully dense through a hot isostatic
pressing (HIP) operation. The fully
dense material produces an igniter
with excellent mechanical strength.
Although smaller in size the MiniIgniter is more than 3 times stronger
than the traditional silicon carbide
igniters used in proved oven systems
today.
The ceramic and metallic material
system offers outstanding hightemperature performance capability
with an operating range up to 1500
ºC in application. The Mini-Igniter
processing and material system also
provides a product with very stable
electrical and thermal characteristics.
This is very important to the long-term
performance of a “proved” ignition
system where the igniter amperage
plays a key role in system operation,
safety and reliability, and service life.
Mini-Igniters are available in several
voltage ranges for use in system
designs worldwide. The typical
nominal voltages range from 12 to
240 volts. This makes the use of
Mini-Igniters a relatively simple task
for cooking appliance applications
regardless of the operating system
type used in the appliance design.
Electronic
control module
The oven ignition system operations
are controlled by a microprocessor
based integrated circuit design
produced to work specifically with
CoorsTek Mini-Igniter products. The
circuit can be produced as a standalone device or integrated into
existing electronic control systems
and is Class C certified to ANSI
and IEC standards. The electronic
control system is compatible
with any oven design utilizing an
electronically actuated gas valve.
The control module starts the
oven ignition sequences, monitors
and regulates the system voltage,
measures the igniter operating
characteristics, and detects the
presence of the gas flame at the
operating burner.
System Operation &
Functionality
“Proved” igniter operation
At the initiation of an oven operating
sequence the electronic control
monitors the amperage level of the
igniter. Only when the igniter reaches
the minimum amperage level defined
as an operating temperature adequate
to the igniter, will the control system
open the gas valve. No gas will flow
in the oven until the ignition source is
ready and able to ignite the gas!
Valve and
burner capability
The ignition system functions to control
multiple electronic valves and two gas
burner operations (bake and broil). The
system is fully programmable so that
various oven designs, burner types
and combinations, valve types and
capacities, and operating modes can
be accommodated without the ignition
system having to be modified beyond
simple programming.
Regulated voltage
The electronic control provides a
regulated voltage to the hot-surface
igniter. This supports igniter electrical
Figure 3
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stability (amperage) and temperature
stability leading to a long service life.
Operational and performance variations
associated with low line and highline
voltage conditions are eliminated with
the regulated voltage of this system.
The regulated voltage feature allows for
the easy adaptation of this system to
all nominal voltages and areas where
voltage variation is an issue.
“Jump Start” Ignition
Patented rapid ignition of the gas
burner is a feature that differentiates
this system from any other hotsurface oven ignition system. The
electronic control monitors the
incoming voltage to the appliance.
Based on this voltage the control sets
up a modulation sequence raising
the Mini-Igniter to a suitable ignition
temperature in less than 3 seconds.
Burner re-ignition – The ability of the
system to “jump start” the Mini-Igniter
in less than 3 seconds provides for
the safe re-ignition of the gas burner
in the event of a flame failure. This
allows for automatic, safe and silent
(no sparking noise) re-ignition of
the burner without the need to shut
down and re-start the oven operating
sequence. This rapid re-ignition
feature eliminates the safety issues
associated with the flow of unlit gas in
the oven cavity.
Continuous
burner flame monitoring
Once an ignition has been initiated
and the gas valve has opened the
control moves to monitor the burner
flame. The monitoring of the burner
flame is accomplished by flame
rectification between the igniter
assembly and the ground-referenced
gas burner. The monitoring of the gas
flame is continuous throughout the
entire operating sequence of the gas
burner by either sensing at the igniter
or with remote sensing.
Programmability
The MOS utilizes both the flame
monitoring, by flame rectification,
required by standard for un-proved
ignition systems as well as the
verification of the hot-surface igniter’s
temperature and therefore its ability
to ignite the gas burner prior to any
gas flow.
Safety
The issue of safety is a very important
aspect in the design of gas ignition
systems. While the long-standing, hotsurface igniter based “proved” system
used in North American for many
years has proven to be very safe it
does not monitor the burner flame
and is thus not acceptable to many
of the design and safety standards in
place throughout the world.
The unique “jump start” feature of the
electronic system control allows for
the safe re-ignition of the gas burner
without the need for a shutdown
of the oven operating sequence.
The gas burner will be re-ignited in
less than 3 seconds in the event of
a burner failure. If the burner is not
re-ignited in 3 seconds the flame
sensing circuit will activate and safely
shut down the system.
System designs that are not “proved”,
such as spark ignition systems, while
complying with required standards
have the potential to flow gas without
Mechanical strength
Igniter material
Igniter
Safety
Spark
+
Spark energy
Thermal performance
-
Electrical performance
Electrical noise
Audible noise
-
Proved ignition
Flame monitoring
Reignition
Yes
-
Hot Surface
+
Silicon
Carbide (SiC)
+
+
+
+
Yes
+
Safety standards
Mini-Igniter
++
Ceramic-intermetallic
composite
++
++
1500°C
++
+
+
Yes
Continuous
Auto – safe, silent
<3 sec jump start
Class C
ANSI, IEC
Controller configuration
Stand-alone or
integrated with existing
control system
Controller module
Programmable
- electronic valves
- 2 burner operations
- design compatibility
Functionality
Image/Captions:
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a resultant ignition. In gas ovens
operated from a cold start, there is no
flue to vent the unburned gas. There
is the potential, especially in systems
that incorporate multiple tries for
ignition, to build up the unburned gas
in the oven cavity.
The electronic control is fully
programmable to provide for
various operating parameters that
may be required by the OEM’s to
obtain the desired oven operating
characteristics. The system can be
programmed for such things as:
multiple tries for burner ignition, purge
cycles between operating sequences,
and safety shutdown sequences.
Voltage
Voltage regulation
+
-
120V only
Ignition time
Reignition
Service life
+
17-60 sec
12-240V options
monitor & regulate
(voltage fluctuations)
3 sec, jump start
+
++
Reliability
& Service Life
One of the major goals in designing
the Mini-Igniter-based oven ignition
system was to improve the reliability
and service life when compared
to other oven ignition systems.
Determined in long-term testing, the
stability of the Mini-Igniter (thermally
and electrically) is extremely good
when it is used in conjunction with the
electronic control module. To increase
the service life of the igniter, the new
system works as an interrupted
ignition system where the igniter
is de-energized once the system
receives a signal, through flame
rectification, that the main burner has
been lit.
Self-Clean
Range Life Testing
The chart in figure 3 shows the
“aging” data from bake and broil MiniIgniters tested with the Mini-Igniter
Oven System (MOS). The testing
was conducted using the reliability
test procedure and schedule of one
of the major North American range
manufacturers. The MOS was installed
in actual self-clean gas ranges just as
it would be on a production basis. The
ranges are cycled through bake, broil
and self-clean operations exposing
the Mini-Igniter to the harshest
operating conditions in the range.
The data shows the results for five
years of testing. The MOS control and
igniter performance in the testing with
minimal aging observed for both igniter
temperature and amperage, supports
the claim that the MOS will provide
an ignition system with exceptional
reliability and excellent functionality and
safety.
on the market today. Unique features
like the rugged Mini-Igniter design and
the “jump start” ignition and re-ignition
feature are part of the improvements.
The added safety benefit of both a
“proved” igniter and continuous main
burner flame monitoring are new to
oven ignition systems. Users never
have to worry about unlit gas in the
oven cavity. Reliability testing has
shown the potential for a long, trouble
free service life. Full system adaptability
to suit various valve types, burner
designs, and operating sequences
is readily accomplished through the
fully programmable electronic control
module. The control module also
regulates the input voltage to the
Mini-Igniter eliminating the nuisance
issues associated with voltage
fluctuations. Systems can be supplied
as stand-alone devices or integrated
into existing control electronics. The
CoorsTek MOS is Class C certified
and is in full compliance with ANSI and
IEC standards.
Conclusion
The CoorsTek MOS has been
designed to provide improved
performance, safety, and reliability
when compared to existing systems
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