Patent Publication Number: US-5255125-A

Title: Particulate obscurant disseminator air source

Description:
GOVERNMENTAL INTEREST 
     The invention described herein may be manufactured, used and licensed by or for the U.S. Government. 
    
    
     BACKGROUND OF THE INVENTION 
     Armies have used visual obscurants for centuries to protect their personnel from observation by their enemies. Presently, with the advent of laser rangefinders operating at near infrared and thermal imaging systems at mid and far infrared frequencies, the need for obscurant counter-measures at these wavelengths has become a primary protective requirement. The need for obscurants at even longer wavelengths is a necessity because of the recent development of &#34;smart&#34; munitions with millimeter wave seekers. 
     Known obscurants at these wavelengths are comprised of solid particles. Thin flakes are used for the infrared wavelength detection devices. Small high-aspect ratio fibers are used as an obscurant against millimeter wave detection devices. 
     The problem with aerosolizing these solid particles to form an obscurant cloud is that these obscurants require a large amount of propelling air. The basic rule of thumb developed by prior art experience with these materials is 10 pounds of air required for each pound of particulate dispensed. In the past, the use of an air ejector, such as the Rutstein AP-83, partially reduced the problem. Operating at about 30 psig, the Rutstein ejector acts as a venturi nozzle to induce about 5 pounds of air flow for every pound of air delivered to it. However, even with the AP-83, to generate an obscurant cloud at a flow rate of 10 pounds per minute requires a primary air source at 20  pounds per minute. 
     
         10 lb. air/1 lb. obscurant×10 lbs. obscurant÷5 (ejector induced-to-primary air ratio)=20 lbs./MIN. 
    
     Prior art conventional air compressor with this capacity would be huge and not practical for a mobile fighting vehicle. A blower with the flow capacity will not provide the aforementioned required pressure. 
     All smoke generators presently under development with the capability to disseminate infrared and millimeter wave obscurants use the bleed air from a turbine as the air source for the air elector. Usually these smoke generators are mounted on a host vehicle, such as a High Mobility Multipurpose Wheeled Vehicle or an Armored Personnel Carrier. The problem with these obscurant disseminators using turbines is that turbines are sophisticated, expensive engines requiring special skills for maintenance and repair. Their durability in today&#39;s mobile army battlefield environment is questionable. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a particulate obscurant disseminator which utilizes shaft power supplied by the vehicle to be obscured, mechanically connected through a clutch and fluid coupling to a high ratio gearbox whose output shaft drives a compressor of an automotive-type turbocharger whose air output is fed to the input of a venturi type ejector where it induces additional air flow and is mixed with particulates from a material supply bin to form an obscurant cloud. 
     An object of the present invention is to provide an obscurant disseminator which produces the air required for particulate dissemination with a simple device powered by the host vehicle engine. 
     Another object of the present invention is to provide an obscurant (disseminator which can generate an obscurant cloud with a primary air source of 20 pounds per minute. 
     Another object of the present invention is to provide a particulate obscurant disseminator air source which can meet the 20 pounds/min requirement with 30 horsepower and weighs less than 200 pounds. 
     A further object of the present invention is to provide an obscurant disseminator which utilizes the compressor half of an automotive-type turbocharger which has proven reliability of use. 
     For a better understanding of the present invention, together with other and further objects thereof, reference is made to the following descriptions taken in connection with the accompanying drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a schematic representation of the particulate obscurant disseminator air source. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     To calculate the power required to compress 260 cubic feet/minute of air from atmospheric pressure to 30 psig: 
     1. Assign a value for temperature: 
     
         Ta=80° F.=540°R 
    
     2. The formula for work per unit mass for a reversible, adiabatic compressor: ##EQU1##  where C p  =specific heat of air at constant pressure=0.25 
     ε=C p  /C v  =1.4 
     C v  =specific heat of air at constant vol.=0.17 Btu/lb °R 
     P 1  =atmospheric pressure=14.7 psia 
     P 2  =30 psig 44.7 psia 
      therefore: 
     W c  =0.25×540× ##EQU2## -1=50.5 Btu/lb. 3. Using an 80 percent efficiency factor for the compressor, the work becomes: 
     
         50.5 Btu/lb÷80%=63.1Btu/lb 
    
     4. Multiplying by the mass flow rates and converting to horsepower yields the following: ##EQU3## 
     A typical commercial 2-stage compressor has the following characteristics: 
     
         ______________________________________                                    
CFM @ 100 psig        140                                                 
Cost                  $3,000                                              
Weight                600 pounds                                          
Horsepower Required   25                                                  
______________________________________                                    
 
    
     It would take two of these units to meet the 20 pounds per minute requirement. 
     
         20lb/min×13.07cu ft/lb=260CFM 
    
     With mounting and power transfer apparatus, the prior art combination could easily weigh 1500 pounds and require 50 horsepower. The present invention would require only 30 horsepower and weigh less than 200 pounds. 
     In operation, referring to FIG. 1 the power is supplied by the vehicle engine (not shown) to an input shaft member 10 which rotates at 1500 RPM. Shaft 10 is mechanically connected to an electric clutch 12 which is used to engage or disengage the disseminator systems. A fluid coupling 14 is mechanically coupled to electric clutch 12. Coupling 14 is used to dampen impact loading of the disseminator system on the input shaft 10. A gearbox member 16 is mechanically coupled to the output side of the fluid coupling 14. Gear box 16 has an input to output ratio of 1 to 40 thus will step up the shaft 10 rpm from 1500 RPM to 60,000 RPM required by compressor 18 which is mechanically linked to the output of gear box 16. The air output of compressor 18 is supplied to the input 20 of venturi ejector 22, where it will induce additional air flow and is mixed with particulate from the material supply container 24 via supply line 26 to form an obscurant cloud 28. 
     While a specific embodiment of the invention has been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.