1、SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and enginee ring sciences. The use of this report is entirelyvoluntary, and its applicability and suitability for any particular use, including any patent infringement arising therefr
2、om, is the sole responsibility of the user.”SAE reviews each technical report at least every five years at which time it may be reaffirmed, revised, or cancelled. SAE invit es your written comments and suggestions.Copyright 1998 Society of Automotive Engineers, Inc.All rights reserved. Printed in U.
3、S.A.QUESTIONS REGARDING THIS DOCUMENT: (724) 772-8510 FAX: (724) 776-0243TO PLACE A DOCUMENT ORDER: (724) 776-4970 FAX: (724) 776-0790SAE WEB ADDRESS: http:/www.sae.org400 Commonwealth Drive, Warrendale, PA 15096-0001AEROS PACE INFORM ATION REPORTSubmitted for recognition as an American National Sta
4、ndardAIR951 RE V. AIssued 1968-06Revised 1998-08S park E nergy M easuremen t , A l ternative M ethodsFOREWORDThis revision contains format/editorial changes only.INTRODUCTIONThe subject of spark energy measurement for the user of gas turbine engine ignition systems has been cautiously approached in
5、that no one method has been developed that is readily usable outside the system designers laboratory. Also, there is a lack of agreement as to the most desirable and informative method or methods to be used in establishing the system integrity except that it will effect an engine start when called u
6、pon. Periodic inspections during the used life of the ignition system crudely consist of (a) visual evidence of a spark and (b) sound level of the spark resounding within the caverns of its operating environment. Both of these depend primarily on human judgment which varies considerably with the ind
7、ividual.This document is prepared in an effort to acquaint and summarize, for the user, the available methods, over and above those stipulated for overhaul agencies, for possible refinement and use as periodic inspection media.1. SCOPE:Parameters to consider and various methods of measuring spark en
8、ergy of aviation ignition systems.2. 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 of other publications shall be the issue in effect on the date of the purchase orde
9、r. 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 unless a specific exemption has been obtained.AIR951 Revision A- 2 -2.1 SAE Publication
10、s:Available from SAE, 400 Commonwealth Drive, Warrendale, PA 15096-0001.See Appendix I.3. SPARK DISCHARGE AS RELATED TO IGNITION:At the present time there is little agreement on what characteristics of spark discharge are critical to ignition of various fuel-air mixtures. Spark discharge parameters
11、which are known to affect ignition include:a. Peak temperatures created by the spark,b. Time vs. power of the spark,c. Spark rate,d. Spark shape (resulting from electrode shape and gap geometry),e. Temperature, pressure, and velocity of the ignitable mixture,f. Type of spark igniter, i.e., air gap,
12、surface gap, shunted surface gap,g. Total energy discharged per spark.The above parameters are all controllable by the ignition system designer, or (item e) are capable of reasonable reproduction. Not included as spark discharge parameters are such engine parameters as spark location in the combusto
13、r, spark location vs. fuel spray quality, etc.3.1 Peak Temperatures Created by the Spark:Every commonly used hydro-carbon fuel has what is known as a spontaneous ignition temperature. This temperature is the lowest at which ignition will occur in an environment where temperature is the only variable
14、. The spontaneous ignition temperature may vary as a value depending on the particular test method and fuel or fuel mixture used. It is generally accepted that the temperature created by the spark must exceed a certain value which either is or is related to the spontaneous ignition temperature of th
15、e mixture to be ignited. 3.2 Time vs. Power of the Spark:With continuing advancement in engine and ignition technology, it has become common practice to measure and sometimes specify spark duration, peak power, and total discharge energy of a spark. (See Reference 1, Appendix I). Average spark power
16、 is also of some interest. It should be noted that peak spark temperatures are related to the power vs. time function.3.3 Spark Rate:There are at least two functions of spark rate related to successful ignition. One of these is to provide a spark at the proper time to coincide with earliest ignitabl
17、e fuel-air mixtures. Another function of spark rate may be to control the rate of energy transfer to the ignitable mixture, in a manner allied to that provided by spark duration.AIR951 Revision A- 3 -3.4 Spark Shape:This parameter relates to the physical shape of the luminous part of the spark, or p
18、lasma. Spark shapes may, through constriction of the arc, be related to peak temperatures developed. Many interesting spark shapes can be recorded photographically, and for a particular design ignition system these shapes are quite similar. The spark shape results primarily from electrode size, shap
19、e, and gap geometry of the spark igniter, but can also be influenced by the system energy level.3.5 Temperature, Pressure, and Velocity of the Ignitable Mixture:These parameters, while basically a function of engine design, influence the discharge characteristics of a spark. In can be readily demons
20、trated that an inductive type spark changes in color and intensity as a function of pressure and velocity. Increasing ambient pressure will tend to reduce the effective arc length of a capacitive spark to a minimum. Temperature and pressure variations influence the ionization voltages necessary to p
21、roduce a spark, and depending on the spark igniter, these variations may result in a significant portion of discharge energy being consumed as heat loss internal to the igniter.3.6 Type of Spark Igniter:Air gap, surface gap, shunted surface gap (See Reference 2, Appendix I) - The effect on ignition
22、of type of spark igniter is related to both the ease of creating a spark (voltage level) and the resistance to fouling (discharge energy losses). Shunted surface gap igniters are generally more resistant to external fouling than other types, but may incorporate semiconductor materials which in thems
23、elves tend to be too conductive and dissipate significant discharge energy as internal losses.3.7 Total Energy Discharged per Spark:This definition may be interpreted in two ways: (1) stored energy of the ignition system at the instant prior to discharge, and (2) energy dissipated at the spark ignit
24、er electrode location. This AIR is concerned with the second definition. The term, “total spark energy”, is a better definition, but not consistently applicable among the various measurement methods to be discussed.4. OPTICAL METHODS:A measurement of the light produced by a jet igniter spark dischar
25、ge has a relationship to the corresponding electrical measurement of spark energy made by oscilloscopic methods. Optical methods have the advantage of simplicity, and can be done in a very small fraction of the time required to accomplish referenced oscilloscopic methods.4.1 One optical method of sp
26、ark energy measurement is to take time exposure pictures of the spark discharge. This method provides a good comparative evaluation of competing igniter designs on a total discharge energy basis. The results, of course, depend on the sensitivity of photographic film and equipment. Some typical resul
27、ts relative to spark shape are shown in Figure 1.AIR951 Revision A- 4 -FIGURE 1 - Some Typical Spark Plasma Shapes from Photographic Measurements4.2 Another optical method of spark energy measurement, designated as the photoelectric method, consists of sensing the light output of the spark discharge
28、 with a photocell or light sensitive device. By reading the output of such a device on an oscilloscope, a relationship of light emission vs. time may be established. Figure 2 illustrates a circuit and set-up as practiced by one igniter manufacturer. The instrumentation used in this method consists o
29、f a special photo-electric fixture as illustrated, and a stable calibrated cathode-ray oscilloscope of average sensitivity. Peak light measurements have proven most consistent, but measurements of duration and area under the curve may also be of interest. Figure 3 illustrates typical response. It wi
30、ll be seen that the shape of the energy waveform is quite similar to that obtained by oscilloscopic methods in References 3 and 4 of Appendix I.Calibration of the light signal in terms of electrical energy has not yet been done, but the method has been particularly useful in making direct comparison
31、s where absolute values of energy are not required. For example, igniter design changes have been quickly evaluated to determine their effectiveness.5. PRESSURE METHODS:Pressure methods of spark energy measurement, which have been attempted, are designed as total pressure measurement, peak pressure
32、measurement, and instantaneous pressure measurement.AIR951 Revision A- 5 -FIGURE 2 - A Test Set Up for the Photo Electric MethodAIR951 Revision A- 6 -FIGURE 3 - Typical Waveforms form Set Up of Figure 2 (Photo-Electric Method)AIR951 Revision A- 7 -5.1 Total Energy Method:The term total energy as use
33、d herein designates a net effect relation, irrespective of time. Total energy pressure method is based on theoretical relations of perfect gases which state that, (Eq. 1) = Change in total energy at constant volumeV = Chamber volume = Ratio of specific heatsP = Change in maximum pressureBy confining
34、 the spark in a closed volume container of low thermal conductivity, it can be seen that an increment of energy added by a spark will produce a corresponding rise in temperature and pressure of the confined gas. The quantity and duration of the pressure rise are dependent on the gas tightness and th
35、ermal loss characteristics of the container and igniter assembly, and on the number of energy increments (sparks) added. Experimental programs have yielded good correlation between total energy measured by the pressure pulse method and that measured by oscilloscopic methods. (See Reference 5, Append
36、ix I). Figures 4 and 5 illustrate one construction of the pressure bomb and the type of pressure output response obtained. It will be noted that the bomb type of construction is closely akin to that utilized in a calorimeter type measurement. (See Reference 6, Appendix I). It is conceivable that a s
37、ingle vessel could be constructed to serve both types of measurements.5.2 Peak Pressure Method:The peak pressure method is actually a kind of acoustic energy measurement, i.e., how big a “bang”. At least two variations of this method have been used with some degree of success.5.2.1 One peak pressure
38、 measurement method has been demonstrated using a microphone pick up positioned at a fixed distance from the igniter. The result is read on a meter, as with a circuit described in Figure 6.E V 1-P()=AIR951 Revision A- 8 -FIGURE 4 - Typical Pressure Bomb Construction for Spark Energy MeasurementAIR95
39、1 Revision A- 9 -FIGURE 5 - Typical Pressure Response Curve from Bomb of Figure 4AIR951 Revision A- 10 -FIGURE 6 - A Circuit for Acoustic Spark Energy Measurement Using Microphone Pick-UpAIR951 Revision A- 11 -5.2.2 Another spark energy pressure method has been devised based on the impact force gene
40、rated by the spark shock wave. In this method the spark is confined in a very small container, at least one wall of which is movable with application of a certain force. The size of the container is established experimentally so that the force of the shock wave will lift off the movable weight and m
41、ove it through a finite distance. The work thus performed is proportional to spark energy. The mass moved can be connected to a dial indicator of various types; for direct read-out.Repeatable results have been obtained with this method, and the method will differentiate between systems of various en
42、ergy levels. It is important with this method that no air leakage exists between the igniter shell and the movable weight prior to firing. This necessitates an accurate self-return feature and soft but firm gasket material at the interface. Figure 7 illustrates the concept.6. OSCILLOSCOPIC METHOD IM
43、PROVEMENTS:Chief among objections to electrical energy measurements based on voltage-current relations (See References 3 and 4, Appendix I) are the expense, time, and attendant operator inaccuracies involved in reducing the data obtained as photographic voltage and current waveforms. Instantaneous e
44、lectrical multiplication and integration of voltage and current waveforms have been accomplished. (See Reference 7, Appendix I). By use of appropriate digital read-out equipment, immediate results of improved accuracy can be obtained. As the art of solid-state devices advances, the economic and phys
45、ical size aspects of equipment necessary for such operations are expected to improve.7. OTHER POSSIBLE METHODS:The foregoing sections of this document have covered methods of energy measurement which have yielded, at least experimentally, results of some value. The foregoing methods are all based on
46、 forms of energy release which are generally regarded as having possible effect on ignition. There are additional measurement method possibilities which may or may not be of value.7.1 It has been observed that for an exciter and lead of a particular design, arc current is relatively constant regardl
47、ess of spark igniter design. Thus, when oscilloscopic energy measurement is used, igniter energy evaluation for a particular exciter and lead design can be based largely on measurements of arc voltage.7.2 Other measurement methods might be based on one or more of the following phenomena associated w
48、ith spark discharge: electric and magnetic fields, wave length spectra of luminous discharge, peak temperature of the arc.AIR951 Revision A- 12 -FIGURE 7 - Spark Shock Wave Measurement DeviceAIR951 Revision A- 13 -8. APPLICATION CONSIDERATIONS:Much controversy and confusion has developed regarding s
49、park energy and measurement thereof. There is not, nor is there likely to be, any one method or approach which can assure 100% ignition reliability. Neither is there any single method which is “best”. For use of all concerned, a listing of pros and cons for each method is included in Appendix II.Certain precautions are necessary in use of all methods. Care must be taken to minimize erratic readings caused by varying amounts of carbon, fuel, or other contaminants on the igniter firing ends. The most consistent results have been obtained when the firing ends have been cleane
