At the core of your oven operation and performance is a constant spark ignition system (CSI) or a direct spark ignition system (DSI). For those of you that have CSI systems we are going to address the advantages of upgrading to DSI and for those of you with DSI this will be a refresher on why you chose DSI and ensure that you are leveraging the DSI system in your baking operations to full advantage.
A Brief History
The direct-fired gas oven became popular with the baking industry following World War II. These ovens consist of numerous pipe ribbon burners arranged in sections, or “zones”, to provide flexible temperature control for the oven. The first style was a tunnel oven with either a grid or solid hearth. This style of oven had burners arranged above and below the hearth. Similar to the tunnel oven are single-lap, double-lap and multi-cycle tray ovens, which have their burners below the trays, although some do have burners above.
The gas valve train, which provides fuel to the burners, was a manual or semi-automatic system. Because of the small amount of gas consumed per burner, and with the large number of burners, it was not then economical to provide individual flame sensing or proving. Instead, the burners utilized constant spark ignition transformers to light the burners, with all burners lit at all times. The temperature was controlled by modulating the air/fuel supply to the burner. This type of burner control resulted in temperature over-rides during breaks in production.
During the late 1970’s, the Joseph M. Day Company of Saginaw, Michigan developed the Banner-Day ISPU (Ignitor/Sensor Proving Unit) Ignition Module to not only ignite the burner, but to prove the continuing existence of flame.
This solid-state device was quite radical at the time and is still the ignition module of choice around the world. This device is designed in such a way that it replaces the ignition transformer by providing the spark for ignition. At the same time, it provides the safety feature of modern flame supervision. In order to deliver maximum flexibility and safety under a variety of baking conditions, one ISPU Module is used for each burner. This system has come to be referred to as DSI – Direct Spark Ignition. Each burner has a dedicated ignition source combined with a flame safety monitor.
The DSI system replaces all existing ignition transformers and a solenoid gas valve is installed in the gas fuel line to each burner. When electricity is applied to the ignition module, typically through a switch located on the system control panel or via automatic PLC control, a 30,000 volt spark is applied to the burner ignitor, the solenoid fuel valve opens and the burner is ignited. Once a flame is present, the spark is shut off and the ignitor acts as a flame rod to monitor the continued presence of the flame.
The heart of the system is the solid state ignition module that provides both the high voltage spark to ignite the burner, and then the means to monitor the flame. Once the burner is lit, a small electric current flows from the ignitor to the burner through the flame. The ignition module generates and monitors this electric current. The presence of the DC current indicates that flame is present. The ignition module keeps the burner solenoid fuel valve open as long as the flame is present. Should the burner flame fail, the ignition module reinitiates the high voltage ignition spark for typically up to 11 seconds (for standard modules). If the flame is not reestablished within the trial period, the ignition module closes the solenoid fuel valve, shutting off gas to the burner. In order to reset the ignition module and burner, power must be interrupted and restored to the burner.
Constant Spark Advantages
- Simpler technology – Easily understood and maintained
- Very few “specialty” parts
Constant Spark Disadvantages
- Time consuming to light oven – The manual gas cock at each burner must be closed before purging the oven, then opened when purge is complete
- Fuel waste – In a typical constant spark ignition system, 10-20% of the burners are not lit, but fuel continues to flow through them. The vast majority of this fuel is simply exhausted out of the oven and completely wasted.
- Electricity waste – A constant spark system typically consumes 100 Watts/burner more than the equivalent DSI system. On an oven equipped with 50 burners running 24 hours/day, this equates to a waste of 120 KWH per day.
- Safety – Constant spark ignition systems are no longer allowed by current code on new or upgraded ovens. This change primarily stems from the fact that unburned fuel is injected into the oven by burners that have failed to light.
- Imprecise temperature control – With a constant spark system, all burners are lit at all times (in theory). The only temperature control provided is through modulating the strength of the flame. In most cases, when the oven runs empty due to a break in production, even the minimum flame strength is too much and the temperature overrides.
- More wiring and controls required, since there is one module per burner
- Ignition module required, not just an “off the shelf” transformer
- Faster oven lighting – Since each burner is equipped with a solenoid valve, it’s no longer necessary to manually close the gas cock at each burner during purge, then reopen to light. It’s all done electrically and automatically.
- Gas savings – If a burner isn’t lit, the solenoid fuel valve is closed. Only burners that are lit have fuel supplied to them.
- Electricity savings – A typical DSI system saves approximately 100 Watts/burner/hr. vs. a comparable constant spark system.
- Safety – Unburned fuel is never vented into the oven, except during the ignition trial.
- Vastly improved temperature control – When connected to a properly designed control system, DSI provides the ability to turn specific individual burners on and off at any time. In conjunction with burner flame modulation, this gives the ability to control temperatures to a much higher degree than constant spark systems, greatly reducing overrides.
- Simpler maintenance – When connected to a properly designed control/monitoring system, the status of each burner can be monitored via feedback from the ignition modules. If a burner fails to light, this information can be indicated to the operator/maintenance personnel at the main control panel. This means the maintenance personnel no longer have to go through the headache of checking each and every ignitor individually.
If you are operating your ovens using constant spark ignition you may want to consider upgrading to DSI. A consideration in this upgrade, beyond the benefits and advantages stated above, is reduced labor resulting from the elimination of manual control of the CSI system.
For those of you already taking advantage of DSI systems, we hope this will provide additional insight and a refresher on its operation. Are you having problems with your current DSI system?
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