SAE AIR 825 4A-2002 Chemical Oxygen Systems《化学氧系统》.pdf

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1、_ SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising there

2、from, is the sole responsibility of the user.” SAE reviews each technical report at least every five years at which time it may be revised, reaffirmed, stabilized, or cancelled. SAE invites your written comments and suggestions. Copyright 2016 SAE International All rights reserved. No part of this p

3、ublication may be reproduced, stored in a retrieval system or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of SAE. TO PLACE A DOCUMENT ORDER: Tel: 877-606-7323 (inside USA and Canada) Tel: +1 724-776-497

4、0 (outside USA) Fax: 724-776-0790 Email: CustomerServicesae.org SAE WEB ADDRESS: http:/www.sae.org SAE values your input. To provide feedback on this Technical Report, please visit http:/www.sae.org/technical/standards/AIR825/4A AEROSPACE INFORMATION REPORT AIR825/4 REV. A Issued 2002-01 Revised 200

5、2-08 Reaffirmed 2016-06 Chemical Oxygen Systems RATIONALE AIR825/4A has been reaffirmed to comply with the SAE five-year review policy. FOREWORDThis document is one of a set of related documents. These documents comprehensively address the “Introduction to Oxygen Equipment for Aircraft“, and are ref

6、erred to as slash (/) documents, rather than chapters. The documents may be obtained as a set or individually. As the field of oxygen systems for aircraft has evolved, it became cumbersome for one document to cover the full range of subject matter. The reader who is seeking overall familiarity with

7、oxygen systems for aircraft should read all of these documents that combine to form a general reference to oxygen systems. The reader who is familiar with oxygen systems for aircraft may want to obtain only the slash documents that pertain to topics that are of specific interest.The document set is

8、written as an introductory level, suitable for anyone who would like to understand the basics of oxygen systems in aircraft, and specifically for the engineer who has just recently been assigned to aircraft oxygen systems. Many of these documents point the reader toward more detailed treatments loca

9、ted in other SAE documents.TABLE OF CONTENTS1. SCOPE .32. REFERENCES .32.1 Applicable Documents .32.2 Definitions33. PRINCIPLE OF OPERATION.44. CHARACTERISTICS OF CHEMICAL OXYGEN SYSTEMS54.1 Hardware Configuration.54.2 Maintenance 64.3 Oxygen Flow Rates .6SAE INTERNATIONAL AIR825/4A Page 2 of 8 TABL

10、E OF CONTENTS (Continued)4.4 Heat Evolution64.5 Purity64.6 Reliability75. CONSIDERATIONS IN SPECIFYING SYSTEMS 76. PORTABLE OXYGEN SUPPLIES 87. NOTES87.1 Key Words .8SAE INTERNATIONAL AIR825/4A Page 3 of 8 1. SCOPE:This SAE Aerospace Information Report (AIR) provides an orientation regarding the gen

11、eral technology of chemical oxygen generators to aircraft engineers for assistance in determining whether chemical oxygen generators are an appropriate oxygen supply source for hypoxia protection in a given application and as an aid in specifying such generators. Information regarding the details of

12、 design and manufacture of chemical oxygen generators is generally beyond the scope of this document.2. REFERENCES:2.1 Applicable Documents:The following publications form a part of this document to the extent specified herein. The latest issue of SAE publications shall apply. The applicable issue o

13、f other publications shall be the issue in effect on the date of the purchase order. In the event of conflict between the text of this document and references cited herein, the text of this document takes precedence. Nothing in this document, however, supersedes applicable laws and regulations unles

14、s a specific exemption has been obtained.2.1.1 SAE Publications: Available from SAE, 400 Commonwealth Drive, Warrendale, PA 15096-0001.AIR825/8 Continuous Flow Oxygen SystemsAIR825/11 Closed Cycle Breathing ApparatusAIR1133 Chemical Oxygen General InformationAS1303 Portable Chemical OxygenAS1304 Con

15、tinuous Flow Chemical Oxygen GeneratorsARP1894 Useful Life Determination for Chemical Oxygen GeneratorsAS8010 Aviators Breathing Oxygen Purity Standard2.2 Definitions:CHEMICAL CORE: An object, composed of sodium chlorate or an analogous alkali metal chlorate or perchlorate, formulated with fuels, ca

16、talysts, and other modifiers and additives as required by the particular design, which evolves oxygen by a controlled chemical decomposition reaction, when actuated. Also sometimes called a chlorate candle.CHEMICAL OXYGEN GENERATOR: A device comprising a chemical core and its surrounding mechanical

17、enclosure, insulating material, actuation means for the chemical core, and any necessary filtering means. A means of conveying evolved oxygen to the masks is also frequently included, although that function can also be fulfilled by an external manifold.CHLORATE CANDLE: An alternate term sometimes ap

18、plied to a chemical core, possibly because the progress of the organized decomposition reaction along the length of the core can be likened to the burning of a candle. This term is also sometimes loosely applied to the entire chemical oxygen generator.SAE INTERNATIONAL AIR825/4A Page 4 of 8 2.2 (Con

19、tinued):DESCENT PROFILE: A curve relating altitude to elapsed time following a decompression, which can be utilized in determining the flow rate of oxygen which should be supplied by a chemical oxygen generator at each point in time following initiation of an emergency descent. This curve is establi

20、shed by the aircraft designers, based on the performance features of the aircraft under various operating conditions. It sometimes is modified to reflect assumptions about height of local terrain which might be encountered in operating the aircraft over a given route.OXYGEN GENERATOR: Generally, any

21、 device or system which generates oxygen. For the purposes of this document, the term is a shortened form of chemical oxygen generator, unless the context clearly implies the more general meaning.OXYGEN MODULE: A structure or assembly, frequently in the form of a box or container, in which an oxygen

22、 generator is installed. Such containers typically contain the oxygen mask assemblies and a solenoid latch which is employed to deploy the masks in the event they are needed. In some cases, oxygen generator installations do not include a distinct, separate oxygen module, but rather the generator and

23、 other components are installed directly into an integrated Passenger Service Unit.PASSENGER SERVICE UNIT (PSU): A structure or assembly frequently mounted above a row of passenger seats, which typically includes individual reading lights and fresh air vents for the use of the passengers, and a door

24、 behind which the passenger oxygen mask assemblies are stowed. Passenger information signs are often included, as well.REACTION ZONE: The area or region of a chlorate candle within which oxygen is being released at a given point in time. Typically, this region is somewhat molten, while the unreacted

25、 material ahead of this region and the residue behind it are solid. As the candle operates, this region travels along the length of the candle.3. PRINCIPLE OF OPERATION:A chemical oxygen generator produces oxygen when actuated by means of a chemical reaction involving the decomposition of sodium chl

26、orate (or an analogous compound) to evolve oxygen. A solid chemical residue is left behind. The basic chemical reaction is shown in Equation 1.(Eq. 1)This chemical reaction is exothermic, meaning that there is net evolution of heat.The melting point of pure sodium chlorate is about 260 C and the dec

27、omposition reaction occurs at about 500 C. Thus, if a chemical core were made of pure sodium chlorate, it would melt and run into a puddle at a temperature far below that at which oxygen would be produced, and no organized reaction zone could form. Practical chemical cores contain a variety of addit

28、ives, such as fuels, catalysts, and modifiers, which enable the decomposition reaction to take place in an organized manner, so that a reaction zone can travel along the chemical core in a steady way.NaClO3 NaCl 3/2 O2+SAE INTERNATIONAL AIR825/4A Page 5 of 8 3. (Continued):The chemical reaction is i

29、nitiated by input of thermal energy to the end of the chemical core. This is frequently accomplished by use of a percussion primer, as would be used in small arms cartridges. It can also be accomplished electrically.The flow rate of oxygen from a chlorate candle can be controlled by proper selection

30、 of additives, in combination with selection of a suitable physical size and shape. This flow rate is normally programmed to change as a function of time following actuation, to match the rate of oxygen production which is needed for each point in the aircraft descent profile.The rates of chemical r

31、eactions vary as a function of reaction temperature. For this reason, the rate of oxygen production from a chemical core depends on the environmental temperature under which the chemical core is operated. Because the flow rate is lower under colder conditions, the nominal flow rate at ambient must t

32、ypically be higher than the specified requirement. Because the duration is shorter under hotter conditions, the nominal duration at ambient temperature must typically be longer than the specified requirement. AIR1133 gives added information about the operation of chemical oxygen generators.Another c

33、hemical technology which can be employed to produce oxygen is the reaction of potassium superoxide (KO2) with moisture and carbon dioxide exhaled by the user.Use of this technology requires the use of a closed rebreather type of apparatus. While such equipment lies outside the scope of this document

34、, it is discussed in AIR825/11, and the chemistry is reviewed in AIR1133.4. CHARACTERISTICS OF CHEMICAL OXYGEN SYSTEMS:4.1 Hardware Configuration:A typical chemical oxygen system is made up of a set of boxes which each contain an oxygen generator and from one to five constant flow phase dilution pas

35、senger mask assemblies, along with an electrically operated latch which is operated to open the door of the box and allow deployment of the masks following a decompression. These oxygen modules are installed adjacent to each group of seats in the passenger cabin, and at flight attendant stations, an

36、d in galleys and lavatories. The electrically operated latches are usually connected to the central control system on the flight deck.When an increase in cabin pressure altitude beyond a preset value occurs, an aneroid switch sends a signal which causes power to be supplied to the latched, opening t

37、he doors of the boxes. The masks are then presented within reach of the passengers. Each generator may be actuated by means of a lanyard, when a passenger grasps any one of the masks and pulls it towards his face. Alternatively, actuation may be accomplished by an electrical current, as the masks ar

38、e presented. The performance requirements for chemical oxygen generators are addressed in AS1304.SAE INTERNATIONAL AIR825/4A Page 6 of 8 4.2 Maintenance:Chemical oxygen generators are sealed, single use devices. They require no maintenance during their stated useful life which is typically in the ra

39、nge of 12 to 15 years or more. ARP1894 furnishes a basis for determining useful life and evaluating the possibility of extending useful life.4.3 Oxygen Flow Rates:One limitation of a chemical oxygen generator is its lack of flexibility in oxygen flow rates. Once the generator is actuated, flow will

40、continue until the core is completely reacted. The rate of oxygen production has been previously programmed at the time of design. To change duration or conform to a different descent profile, one must change the generator to a different model. Since oxygen flow requirements at a given altitude also

41、 depend on mask efficiency, changing the type of mask used may also require a change in generator performance. AIR825/8 gives some information about nominal flow requirements.4.4 Heat Evolution:Because the oxygen producing reaction is exothermic, chemical oxygen generators emit heat, and their exter

42、nal surfaces are hot enough to burn unprotected human skin. Depending on the design, external temperatures of as much as 250 to 300 C (482 to 572 F) are sometimes observed when a generator is operated in the open air at 21 C (70 F) ambient temperature. Manufacturers of chemical oxygen modules use va

43、rious types of shields, insulating materials, and design features to control the heat which is released. It is also necessary to consider the heat dissipation capabilities and thermal tolerance of adjacent structures when designing chemical oxygen installations.Over time, installed generators someti

44、mes become coated with dust, residues from cigarette smoke, and similar contaminants. When the generator is operated, the heating of these contaminants may result in a noticeable odor, somewhat similar to the “hot“ odor experienced when an electrical heater is operated after a long period of storage

45、. Crew training should include an awareness of this possibility so that passengers can be reassured this odor is not a cause for alarm.Since oxygen has a relatively small heat capacity, the gas which reaches the passenger is cooled sufficiently between the generator outlet and the mask so that it is

46、 safe to breath. Typically the inhaled gas temperature is within 5 C (9 F) of the surrounding environmental temperature.4.5 Purity:Chemically produced oxygen may contain traces of other gases which are produced by the chemical reaction. However, these impurity levels are below the values considered

47、hazardous in the physiological literature, and conform to the required purity levels stated in oxygen source standards. AS8010 establishes purity requirements for oxygen sources, including chemical sources.SAE INTERNATIONAL AIR825/4A Page 7 of 8 4.6 Reliability:Chemical oxygen generators offer high

48、dispatch reliability because the generators are inert, sealed units which do not require servicing. These units have also displayed high actuation reliability and performance reliability under the conditions encountered in the field over many years of useful life.5. CONSIDERATIONS IN SPECIFYING SYST

49、EMS:In specifying a chemical oxygen system, there are certain basic design decisions which should be made, and communicated to potential vendors, in order to obtain the most suitable equipment for the intended application, with minimum weight and volume.a. Determine the emergency descent profile, in terms of cabin altitude versus time, considering the operational capabilities of the airframe design. This information may then