Abstract:
An environmental control system for ground vehicles and low flying aircraft that supplies purified and conditioned ambient air to the vehicle&#39;s crew compartment is provided. The system integrates catalytic and particulate filters, that remove nuclear, biological, and chemical warfare agents from ambient air, with a source of compressed ambient air, and an air cycle refrigeration unit.

Description:
TECHNICAL FIELD 
     This invention pertains to environmental control systems for ground vehicles and low flying aircraft that supplies purified and conditioned ambient air to the vehicle&#39;s crew compartment, and more specifically to an environmental control system that integrates catalytic and particulate filters for removing nuclear, biological, and chemical warfare agents from ambient air with a source of compressed ambient air, and an air cycle refrigeration unit. 
     BACKGROUND OF THE INVENTION 
     Veltman et al., U.S. Pat. No. 4,732,578 discloses an air purification and temperature control system for combat vehicles that incorporates a pressure swing adsorbent system for filtering nuclear, biological and chemical warfare agents. This adsorbent system is comprised of two tanks each of which has an adsorbent bed. As described in column 4, lines 5-45 of Veltman compressed air from the control system enters the first tank through a four way inlet purge valve. Water, hydrocarbons, and chemical agents are adsorbed in the bed and purified so that dry air exits the tank. A portion of the purified air is expanded through an orifice an then passed through the second tank in the direction opposite the flow in the first tank. This flow purges contaminants from the adsorbent bed in the second tank, and is then dumped over board. After a period of time the process is reversed and the second tank receives the compressed air and the first tank is purged. 
     The Applicants have found that pressure swing adsorbent systems have a number of disadvantages. First, the portion of air required for purging can be as large as half of the air entering the system. By dumping this purging air over board a large amount of energy is lost reducing the system&#39;s overall efficiency. Second, if the temperature differential between the air entering the system and the purge air becomes too large, the adsorbent system ability to purify the air starts to degrade. 
     Accordingly, a need exists for an environmental control systems for ground vehicles and low flying aircraft, that includes a means for filtering nuclear, biological, and chemical warfare agents that does not have the deficiencies associated with pressure swing adsorbent systems. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an environmental control system that integrates a source of pressurized ambient air, a catalytic filter, a particulate filter and an air cycle refrigeration unit. 
     Another object of the present invention is to provide a method for providing clean air at a desirable temperature free of nuclear, biological and chemical warfare agents to the compartment of a ground vehicle or low flying aircraft. 
     The present invention achieves the above-stated objects by providing an environmental control system for mounting aboard a ground vehicle or aircraft that integrates a source of compressed ambient air, a catalytic filter, a particulate filter and a refrigeration unit. 
    
    
     These and other objects, features and advantages of the present invention are specifically set forth in or will become apparent from the following detailed description of a preferred embodiment of the invention when read in conjunction with the accompanying drawing. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic of one embodiment of the environmental control system contemplated by the present invention. 
     FIG. 2 is a schematic of another embodiment of the environmental control system contemplated by the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An environmental control system, generally denoted by the reference numeral 10, is schematically depicted in FIG. 1. Integrated within the system 10 are a catalytic filter 12, a source of compressed ambient air 20, and an air-cycle refrigeration unit 40. 
     In the following, the refrigeration unit 40 is described as a three-wheel, boot strap type unit, however, as one of ordinary skill in the art would appreciate a two-wheel bootstrap unit or a simple cycle unit is interchangeable with the three-wheel unit within the system 10. 
     High pressure and high temperature air enters the refrigeration unit 40 through a venturi 42 which is sized to be not quite choked when the refrigeration unit 40 is running on a hot day. This air passes through a primary, air-to-air heat exchanger 44 which employs ambient air as the heat sink. Within the heat exchanger 44 the air is cooled to near ambient temperature with very little pressure drop. The air exits the heat exchanger 44 and enters a compressor 46 where it is pressurized and heated. The reheated air is again cooled, with only a slight pressure drop, to a temperature near ambient in a secondary, air-to-air heat exchanger 48 which also uses ambient air as a heat sink. 
     At this point the processed air is at a pressure level above its inlet pressure and is at a temperature near ambient. This air is then passed through a condenser 50 where it is cooled while undergoing only a slight pressure drop which results in condensation of almost all the moisture that may have been in the air stream. This condensed moisture is mechanically removed from the air stream by a water extractor 52 which centrifuges the water droplets out of the air stream and then drains the water. 
     The cooled, dried air exiting the water extractor 52 then passes to an expansion turbine 56 in which the air is expanded to near atmospheric pressure and further cooled to well below ambient temperature. This cold air is circulated through the condenser 50 where it is used to cool the turbine inlet air and is heated in return. This air than passes through a high efficiency particulate air (HEPA) filter 54 for removing nuclear and biological particles, and then to the crew compartment of the vehicle. 
     The expansion turbine 56, compressor 46, and a cooling fan 62 are all mounted on a common shaft 64 so that the energy extracted from the air exiting the condenser 50, by the expansion turbine, is used to drive the compressor 46 and the fan 62. The cooling fan 62 draws ambient air through the primary and secondary heat exchangers 44,48 and discharges this air back to ambient. 
     The source of compressed ambient air 20 includes a shaft driven compressor 22 which is driven by any suitable means such as the vehicle&#39;s engine, or an electric motor or a hydraulic motor mounted aboard the vehicle. The compressor 22 inducts ambient air, compresses it to about 53 psia, and heats it to a temperature of about 450° F. for an ambient air temperature of 125° F. To maintain a constant 450° F. discharge temperature, a thermocouple 24 mounted downstream of the compressor 22 senses the compressor exit air temperature and when it falls below 450° F signals a modulating valve 26 to open and divert a portion of the hot air discharged by the cooling fan 62 to the inlet of the compressor 22 where it is mixed with the ambient air until the compressor discharge temperature returns to 450° F. 
     Disposed downstream of the compressor 22 and upstream of the venturi 42 is the catalytic filter or reactor 12. In this position the catalytic filter is always receiving a high pressure and high temperature air. The constant high pressure minimizes the size of the filter, while the constant high temperature ensures proper catalytic action independent of changes in ambient conditions and changes in the temperature of the air exiting the fan 62. Within the filter 12, chemical agents are mixed with air and oxidized, thereby altering their chemistry and rendering them harmless. Also, the filter 12 kills the biological agents. 
     The temperature of the air entering the crew compartment is preferably controlled by bypassing hot supply air from between the venturi 42 and the primary heat exchanger 44 to just upstream of the HEPA filter 54. The amount of air bypassed is controlled by a modulating valve 58 and a thermocouple 60 disposed immediately downstream of the HEPA filter 54. 
     In an alternative embodiment 10a, schematically illustrated in FIG. 2, a source of compressed ambient air 20a is configured as a recuperated turbogenerator comprising in flow series arrangement a compressor 70, a recuperator 72, a combustor 74 and a turbine 76. The compressor 70 and the turbine 76 are both rotatably mounted on a shaft 78. Surrounding the shaft 78 between the compressor 70 and the turbine 76 is a 3-phase alternator winding 80 which generates an AC voltage. A 3-phase rectifier/inverter 82 receives this AC voltage and converts it to DC voltage. To start the source of compressed ambient air 20a, DC voltage is applied to the rectifier/inverter 82 which converts this voltage to 3-phase voltage having a variable frequency that generates a corresponding electro-magnetic force that causes the shaft 78 to rotate. 
     Air ingested by the compressor 70 first passes through an air filter 84 and is then compressed to a pressure of about 45 psia. This compressed air is then heated in the recuperator 72 to about 700° F. A portion of this compressed, hot air is sent to the catalytic filter 12. The remainder of this air is sent to the combustor 74 where it is mixed with fuel and ignited. The hot gas exiting the combustor 74 is expanded across the turbine 76 which extracts energy from the gas and converts this energy into mechanical energy in the form of the rotating shaft 78. The hot, expanded gas exiting the turbine 76 passes out through the recuperator 72 and then over board. Compressed air can be bled upstream of the catalytic filter 12. A surge control valve 86 is provided to allow the amount bleed air to be rapidly changed without surging the compressor 70. 
     A thermocouple 88 measures the temperature of the air entering the catalytic filter 12 and sends a signal to an electronic control unit 90 which governs the source of compressed ambient air 20a. Should the temperature measured by the thermocouple 88 drop below 650° F. then the unit 90 either changes the operating condition of the source of compressed ambient air 20a to maintain the 650° F. or sends a signal to the crew compartment indicating that NBC protection is not available, (not shown). 
     Additionally, the source of compressed air can be configured to include a non-recuperated gas turbine auxiliary power unit, a free piston power unit, or an automotive turbocharger. With each of these devices, the waste heat from the refrigeration unit can be used to heat the inlet air so as to maintain a constant discharge temperature. 
     Thus, the integrated environmental control system of the present invention is able to filter nuclear, biological, and chemical warfare agents without the efficiency degradation associated with pressure swing adsorbent systems. 
     Various modifications and alterations to the above described system will be apparent to those skilled in the art. Accordingly, the foregoing detailed description of the preferred embodiment of the invention should be considered exemplary in nature and not as limiting to the scope and spirit of the invention as set forth in the following claims.