OPERATOR, FIELD AND SUSTAINMENT MAINTENANCE
LARGE CAPACITY FIELD HEATER (LCFH)
THEORY OF OPERATION
is a heating system that provides clean, heated ventilation air
in a military
environment and worldwide temperature extremes. The LCFH provides a minimum of 350,000 BTUH of
heat and a minimum ventilation airflow rate of 2000 CFM.
Operational Concept. An operational cycle of the Large Capacity Field Heater begins by placing the
power switch located on the control panel in the ON position. Once the power switch is engaged, 24VDC
power is drawn from the two batteries located in the interior of the LCFH and supplied to all heater
The LCFH can be operated from its internal fuel tank or from an external fuel source. The fuel source is
selected via a two-position switch located on the operator control box. Fuel for both the diesel engine and
the burner fuel pump is drawn through a 10-micron fuel filter which removes any impurities or sediment.
The LCFH utilizes what is referred to as a continuous fuel loop system. As fuel is drawn from the internal
fuel tank and supplied to the burner and the engine, some of the unused fuel returns to the internal fuel
When operating in external fuel mode, the LCFH is connected to a bulk fuel supply by means of the
external fuel hose. Fuel is drawn from the internal fuel tank until it reaches a low level as determined by
the fuel level switch in the fuel tank. At this time fuel will start to be drawn directly from the external fuel
source. As fuel from the continuous fuel loop returns fuel to the tank, the level inside the internal fuel tank
rises, eventually reaching a point where the fuel level switch triggers a solenoid valve which once again
begins drawing fuel from the internal fuel tank. This cycle of drawing fuel from the internal fuel tank and
external fuel source continues throughout the operation of the LCFH.
A self test is performed using built-in-test logic designed into the control board. Once all heater
subsystems are verified to be within nominal operating limits, the heater enters a startup sequence that
varies with outside ambient temperature.
When the startup sequence is complete, fuel is pumped to the diesel engine by the priming fuel pump.
Once fuel reaches the diesel engine, a START signal is sent from the control board. If the ambient
temperature is 400F or above, the diesel engine will start unassisted using the two onboard batteries. If
the ambient temperature is between 400F and 650F, the diesel engine requires additional power
supplemented by an external 24VDC source connected to the slave connector on the side of the heater.
Once the diesel engine starts, it drives a belt driven alternator which takes over internal power generation
and recharges the batteries for the next startup cycle.
The diesel engine crankshaft is directly coupled to the burner fuel pump which provides fuel to the burner
nozzle. A combustion fan provides air to the burner assembly for combustion. Fuel is atomized by the
burner nozzle and ignited by the two electrodes.
Heat generated by the burner assembly heats the interior of the heat exchanger which in turn heats fresh
air which is drawn into the sealed heated air compartment via a fresh air inlet fan which is connected to an
isolated rubber coupling.
All combustion gases created by the diesel engine or the burner assembly are exhausted out through a