North American Tempest® 4441 LNI Operation
— LNI Mode: Burners that use flameless combustion control techniques must run in conventional firing mode until the furnace temperature is above the autoignition temperature, generally above 1450°F (790°C). When operating in a flameless combustion mode there is no combustion inside the burner tile to monitor, so the flame supervision system must be put in a “bypass” state before switching to the flameless mode. It is important that the thermocouple used to bypass the flame supervision is installed in the coolest section of the furnace to insure the temperature is high enough everywhere in the furnace before switching into the flameless combustion mode. If the furnace temperature drops below the transition temperature the burner must be put back in conventional mode and the flame supervision system returned to conventional firing operation. When operating in conventional mode, combustion in the burner tile releases heat which causes the combustion air (and fuel) to expand. Because the tile exit has a reduced port, the expanding gases cause pressure in the tile to increase. This “tile pressure” reduces the amount of air that can pass through the burner at a given supply pressure. When the burner enters LNI mode, the fuel is moved to an injector in the furnace, so the combustion in the tile moves to the furnace outside the tile. When there is no burning in the tile the pressure in the burner tile is reduced. If the air supply pressure at the burner inlet is maintained the air flow through the burner will increase. The air flow conditions, including the “not burning” condition is documented in the engineering data section of the 4441 bulletin.
— Combustion Air: 0.3-41.6"w.c. (0.08-10.3 kPa) air pressure, max 350°F (177°C).
— Fuel: Natural gas for all burner sizes, The gas pressure in the conventional mode varies per size. See the main 4441 Bulletin for details. — Flame Supervision: Flame rod or UV detector Consult National Safety Standards and insurance underwriters for specific flame supervision requirements. Flame supervisory components must be ordered separately. See the parts list table for correct flame rod part number. — Ignition: Direct spark (no pilot) with 6000 V transformer. Lighting not recommended above 27.7"w.c. (6.9 kPa) main air pressure. Always energize the spark before the gas or with the gas as the flame lights most reliably in an excess air condition as the gas transitions from off to its set point. On systems that use UV flame supervision, UV radiation generated by the spark igniter can often be "seen" by the UV detector through reflection off the burner internals or the burner tile. Many flame relay controls turn off the spark when a flame (UV) is detected. This can be a problem when the controller responds to the spark but there is no actual flame. For this reason, it is often necessary to use additional timers and relays to prevent premature shutting off of the spark igniter. Halfwave ignition transformers will prevent UV sensing of the spark during trial for ignition, but they supply lower amperage to the igniter with produces a cooler spark that may not reliably ignite burners over as wide a range of inputs or air/fuel ratios as a conventional transformer.
— Relight: Tempest® burners require spark for re-ignition. They will not relight reliably from a hot tile or furnace.
— Control: Excellent performance with all control systems; StepFire™, and on-ratio. A limiting orifice valve that provides a pressure drop must be installed in gas supply line within 1 ft. (30 cm) of burner. A ratio regulator should be within 4 ft. (122 cm) of burner. — Piping: For cross-connected systems, the design, selection, and system installation must consider pressure drop through the components to avoid excessive pressure drop in the gas line between the ratio regulator and the burner. Consider the gas pressure required at the burner to achieve the desired heat release (i.e. gas flow). For more detailed information on cross- connected control systems, see Sheet 7218-2 Instructions, Bulletin 7216 and the Practical Pointers Book.
Bulletin 4441 LNI Page 3
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