SAE AIR 885-1965 The Spark Calorimeter《火花量热计》.pdf

1、A ER0 S PAC E SOCIETY OF AUTOMOTIVE ENGINEERS. Inc. 48s LEXINGTON AVENUE IN FO RM ATION REP0 RT NEW YORK 17, N.Y. Isaued 3-25-65 Revised THE SPARK CALORIMETER AIR 885 TABLE OF CONTENTS Section Fimre I II III rv V VI VII VIII IX X XI XII Introduction Theory of Operation Test Method Stabilization Proc

2、edure Calibration Procedure Operation Procedure Uses TABLE OF ILLUSTRATIONS Calorimeter and Associated Equipment Block Diagram Calorimeter Bomb and Bottle Assembly Calorimeter Head Assembly Bomb Assembled Sectional View of Spark Bomb Housing Protection Cap Protection Cap Igniter Tip and Threaded Ins

3、ulator Calibrating Resistor Assembly Typical Calibration Curve Pane Pane 8 9 10 11 12 13 14 15 16 17 18 19 CoDYrlrht 1965 by Soolotr of Automotivo Enelnoarm. Ino. Printed In U. S. A. COPYRIGHT SAE International (Society of Automotive Engineers, Inc)Licensed by Information Handling Services_- _ SAE A

4、IR*KB85 65 m 8357340 OOOOL2 3 I -2- 1. INTRODUCTION 1.1 A spark calorimeter is an instrument used to measure the average spark energy (joules/spark) of an ignition system across the igniter gap. 2. THEORY OF OPERATION 2.1 “Energy“ is defined as the capacity to perform work. In an ignition system the

5、 spark manifests itself as the rapid release of the stored or developed electrical energy at the igniter. This rapid energy release is in the form of thermal energy which the calorimeter measures. 2.2 When such an energy release (spark) is confined in a spark bomb, the heating com- ponent of the spa

6、rk warms the bomb air which in turn is transferred by radiation, convection, and/or conduction to the bomb walls. If this bomb is enclosed by a perfect thermal insulator, the bomb wall temperature will rise proportionally to the thermal energy dissipated internally. All measurements are made when te

7、mperature equilibrium is reached within the bomb. If all the thermal character- istics of the components are known, it is possible to calculate the generated thermal energy. However, there are many aspects of the components and the calorimeter which make direct calculations impossible. 2.3 A practic

8、al method, which provides precision results, is to place a resistor in the bomb through which accurately measured current and voltage can be passed. This resistor is a heating element which causes the chamber to be heated in a similar fashion to that of the spark. Since the current and the voltage c

9、an be measured accurately, then the power or energy dissipated in the chamber can be calculated very easily and accurately. By comparing the temperature rise (measured by thermocouples and a potentiometer) due to the spark against Cali- bration Lurves at various power levels, the energy released to

10、give this rise can be determined. If the number of sparks providing this rise is known, then the energy per spark can be computed very accurately. 2.4 Assume that housed internally in the calorimeter is a spark bomb consisting of masses M1, M2, M3, M4, etc. and associated with each mass are their re

11、sped- tive specific heats C1, C2, C3, C4, etc. When temperature equilibrium is reached, all components see the same temperature change ( A T). The heat therefore absorbed to provide this change, AT, is then given by the equations: Q = M1 C1 AT + M2 C2 AT + M3 C3 AT +. M4 C4 AT+ . . (1) or Q = Ml C1

12、+ M2 C2 + M3 C3 + M4 C4 i- . . . . . AT (2) COPYRIGHT SAE International (Society of Automotive Engineers, Inc)Licensed by Information Handling ServicesSAE AIR*885 65 m 8357340 00090L3 5 m -3- In the above equations - Q = quantity of heat in joules, M1, etc. = component masses in grams, C1, etc. = co

13、mponent specific heats in jouledgrams C, and A T = temperature change in C. If all components are equally insulated from the outside, then equation 2 shows that it is of little importance which element produces therefore, this eliminates the consideration of which component produced the heat. 2.5 2.

14、6 In actual spark bomb calorimeters all components are not equally insulated from the external surroundings. Under this condition, when heat is being produced, losses vary from component to component; therefore, errors will develop de- pending on which component is the heat producer. In most cases t

15、his error is considered negligible. 3. TEST METHOD 3.1 Figure I shows the calorimeter and associated equipment as used in spark energy measurements. 3.2 Figure II is a block diagram showing the arrangement of this equipment used in the measurements. 3.3 3.4 Figure III is a drawing of the calorimeter

16、. Figure TV is a cross sectional view of the calorimeter head assembly. 3.5 3.6 3.7 Figure V shows the assembled igniter spark bomb. Figure VI shows a cross sectional view of a spark bomb. Figures VII through XI are detail drawings of the bomb components. 3.8 Figure XII shows a typical calibration c

17、urve for a particular igniter tip configura- tion. 3.9 As described previously, the number of watts dissipated as heat energy may be accurately calculated if the amperage and voltage applied to the resistor is known. 3.10 A known quantity of heat energy, produced by the resistor, is compared with an

18、 unknown quantity of heat energy, produced by an ignition gap, provided condi- tions such as time of operation and characteristics of surroundings are unchanged. COPYRIGHT SAE International (Society of Automotive Engineers, Inc)Licensed by Information Handling Services- - SAE AIRx885 b5 = 8357340 00

19、0701i4 7 M -4- 3.11 The bomb, Figures V and VI, in this calorimeter contains a resistor which is used to-provide a known amount of heat energy. In the bomb, near the re- sistor, is an appropriate igniter tip to be operated by whtever system is being tested. The bomb is insulated and placed in an ins

20、ulating flask so that the thermal leakage is minimized. The flask also protects the bomb from sudden changes in temperature. 3.12 Supplying power to the resistor will result in an increase in millivolt reading of the two thermocouples located in the insulating flask. The Itbomb thermo- couple, attac

21、hed directly to the bomb, will show a fairly large increase in millivolt reading. The 1 ambient“ thermocouple , attached to the inside of the insulating flask but out of contact with the insulated bomb, will show a much smaller increase in millivolt reading. Hereafter, !ambient temperature“ -will me

22、an the ambient temperature of the flask, not the external temperature. This change in readings is proportional to the joules per second dissipated, or heat energy. As greater amounts of heat energy are released with increasing voltage and amperage, greater changes in millivolt readings will be produ

23、ced. This fact is useful for measurements only when each run is performed in the same manner as all others. . . 3.13 This means cycles of the same length, and always the same number of cycles per run. As the millivolt reading is directly proportional to temperature, the larger the millivolt reading,

24、 the higher the temperature. Large changes in millivolt readings indicate large changes in temperature. 3.14 The calorimeter calibration is obtained by several normal runs, This calibra- tion determines the change in millivolt reading that will be produced by a given amount of heat energy, or joules

25、/second, over a certain time in the bomb. After several runs a graph (Figure XII) may be plotted which will show clearly the simple relationship between the heat energy in joules/second and the total change in Ibombt millivolt reading. 3.15 After the calibration graph has been completed, the test ga

26、p comes into the operation. The spark measurements are made with no change in the bomb. An ignition unit is connected to the gap and operated for the same length of time, in the same set of cycles, as the resistor was for all the calibration runs. Obviously, the spark will heat the bomb. The heat wi

27、ll produce a change in the l1bornbfI millivolt reading as the heat from the resistor did, and this change will be proportional to the energy released. At the end of the run, the total change in “bombf millivolt reading is calculated and this change is compared with the curve on the calibration graph

28、 to determine the equivalent joules/ second dissipated by the spark. 3.16 One run is made for each measurement. The only change which occurs is the spark rate. Other controllable quantities are held constant. For the purposes of uniformity and accuracy all test run cycles and periods are held consta

29、nt. COPYRIGHT SAE International (Society of Automotive Engineers, Inc)Licensed by Information Handling Services- SAE AIR*885 65 8357340 OOOOL5 9 -5 - 4. STABILIZATION PROCEDURE O 4.1 4.2 4.3 4.4 Before each run, the bomb and flask temperatures must be equal. If they are not, the warmer one will cool

30、 off and the cooler one will warm up. These changes cannot be separated from the changes produced by the spark gap and will produce erroneous results, especially for low spark energies. If over a period of ten minutes the “bombl.and “ambientff millivolt readings remain unchanged within two microvolt

31、s , the bomb and flask are well stabilized. However, if not, the test results will be inaccurate by the resulting drift, and cannot be considered. The detailed directions described here assume the use of thestandard run, which consists of six cycles, each cycle consisting of a two-minute operating p

32、eriod followed by one minute off. It is necessary that the calibration of the potentiometer be checked before each test run. 5. CALIBRATION PROCEDURE 5.1 Connect all associated apparatus ; then set panel switch to calibrate. 5.2 5.3 Fill reference temperature vacuum bottle with cracked ice and water

33、. Adjust the rheostat for the required wattage, as read from the ammeter on the calorimeter panel. The first calibration run should be at O. 5 watt, later runs greater by O. 5 watt increments. For powers of over 6 watts use 1 watt increm- ents. With the apparatus and operating cycle described, the c

34、alorimeter has a maximum power rating of 20 watts. This rating is derived from the tempera- ture rise in the bomb, and the temperature gradient on the insulation and other fabricating materials. O 5.4 Set the timer for the desired cycle of operation, normally two minutes on, and one minute off. Set

35、to repeat cycles. Turn off the timer. 5.5 Allow 10 minutes minimum for lbombf and “ambient“ temperatures to stabilize. Flask must be closed and sealed. At the end of this period, the millivolt readings should agree within 2 microvolts. 5.6 Record bomb millivolt readings. 5.7 Set timer on “off“ cycle

36、, turn on heater power supply and switch. 5.8 Turn on all parts of the equipment, allow timer to start cycle. 5.9 At the end of a test run record the Ibombl temperature. COPYRIGHT SAE International (Society of Automotive Engineers, Inc)Licensed by Information Handling Services5.10 5.11 5.12 5.13 5.1

37、4 5.15 SAE AIR*5 65 357340 OOOOLb O U -6- After this reading is completed turn off the timer and heater switches. Bring temperature back to its initial value by circulating external air into flask Subtract from the initial millivolt reading the reading at the end of the test run. Record the resultin

38、g temperature rise and calculate the wattage producing the rise. Repeat steps 5.1 through 5.13 for other energy levels. Develop a curve with power (or joules/second) as the axis of the abscissa and temperature rise on the ordinate axis from the data obtained in steps 5.1 through 5.13. NOTE: A calibr

39、ation curve is good only for the set of timer cycles used in the calibration runs. If the timing periods are changed, then an entirely new curve must be plotted. 6. OPERATION PROCEDURE 6.1 Connect all associated equipment, including the ignition system, to be tested. Set the timer switch to operate.

40、 Follow Calibration Procedure exactly for steps 5.2 and 5.4 through 5.6. Set timer on “offf cycle, turn on all equipment including the ignition system to be tested. Allow timer to start the first cycle. Follow Calibration Procedure steps 5.9 and 5.10, Record number of sparks. Using the calibration g

41、raph, determine the watt value corresponding to the measured temperature rise. Calculate as shown in the following example: As a fypical example of spark energy measurements, assume that the tempera- ture rise due to sparking is equivalent to 2.5 watts for 12 minutes of operation. The energy (J) exp

42、ended in the calorimeter is 6.2 6.3 6.4 6.5 6.6 COPYRIGHT SAE International (Society of Automotive Engineers, Inc)Licensed by Information Handling ServicesJ = Pt where P = power in watts, and t = total operating time in seconds In the example cited, P = 2.5 watts and t = 920 seconds; therefore , J =

43、 2.5 watts x 720 seconds = 1,800 watt-seconds or 1,800 joules If 100,000 sparks caused this temperature rise, then the energy per spark is 1,800 joules/100,000 sparks or . O18 j oule/spark . 7.1 The calorimeter has been used extensively in evaluation programs. Typical evaluation programs in which th

44、e spark calorimeter has been and is being used are: a. Energy release by various spark igniter configurations, b . Energy transfer through leads, c. Comparison of ignition units , and d. Comparison of component parts affecting energy release. 7.2 The calorimeter produces excellent results where the

45、required duty cycle for operation is not beyond the design limits of the apparatus. However, for some systems the duty cycle may exceed the operational limits at room temperature, so that a modified cycle would be required or a different method used with a possible shift in accuracy. Prepared by the

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