Study on the Multi-Spectral True Temperature Pyrometer for Explosion Transient of Thermo-Baric Explosives

ZHANG Fu-cai, SUN Xiao-gang*, XING Jian

1.Harbin Institute of Technology, Harbin 150001, China 2.Harbin Engineering University, Harbin 150001, China

Study on the Multi-Spectral True Temperature Pyrometer for Explosion Transient of Thermo-Baric Explosives

ZHANG Fu-cai1, SUN Xiao-gang1*, XING Jian2

1.Harbin Institute of Technology, Harbin 150001, China 2.Harbin Engineering University, Harbin 150001, China

The high temperature and destructive power, made it difficult to test the explosion temperature of thermo-baric explosive.To effectively assess heat damage effect of thermo-baric explosive, multi-spectral high temperature measurement system is applied to transient high temperature test of thermo-baric explosive.The emissivity and the true temperature of explosion flame are calculated by using the secondary measurement method.In the data acquisition system, the test instrument achieves data collection and transmission 500 meters away in combination with optical fiber sensing technology and under the precondition to guarantee the participants safety.The measurement results show that the designed measurement system has the advantages of simple operation, high safety and better application prospect.

Thermo-baric; Multi-spectral; True temperature; Optical fiber sensing technology

Introduction

Thermo-baric has the feature of high explosion temperature and great explosive energy.Therefore, it is difficult to test the explosion temperature.Traditional explosives mainly take metal fragments, thermal jet, etc.as the main killing and damaging means.Therefore, they are often used for damaging above-ground buildings, injuring or even killing above-ground personnel.However, thermo-baric can burn violently after detonation and release a lot of heat energy within short time of period, thereby utilizing radiant heat energy to generate killing and damaging force.Thermo-baric is mainly used to damage effective strength in caves, underground fortifications, bunkers and other enclosed spaces.Therefore, the temperature of thermo-baric is an important index to measure the explosive force and it is important in study energy release rule and thermal damage effect.Thermo-baric has become the hotspot in research and development of mixed explosives[1-2].Owe to short explosion time, violent change of temperature, safety and other factors in thermo-baric, it is difficult to measure the explosion flame temperature.In recent years, improvement of multi-spectral theory and development of detection technology have laid foundation for measuring the true temperature in an explosion flame temperature field and provided the possibility for the detection of true temperature in an explosion flame temperature field.Multi-spectral thermometer based on prismatic decomposition is applied widely thanks to its simple structure, low cost, flexible design, among others.Harbin Institute of Technology successfully measured the true temperature of solid rocket wake flame[3-4]with prism multi-spectral thermometer, which proved that through elaborate design and improvement, multi-spectral thermometer of prismatic decomposition type could be applied in a hostile environment.The paper solves the problem based on multi-spectral method, wireless transmission and other critical technologies, and successfully designs the true temperature measuring apparatus applicable to the explosion field of thermo-baric explosives.The test system is distributed into the explosion field.In this way, the researcher can monitor the operating mode of the system in long distance and complete collection and storage of temperature parameter in the field.Afterwards, the measured temperature information is processed and reproduced by a computer[5-7].

1 Measurement principle of multi-spectral temperature

It is assumed that the multi-spectral temperature measurement system has N spectral channels and it is brightness temperature information passing through these different channels, then the voltage valueViof the output signal from channelican be expressed as

(1)

(2)

Type (1) divided by type (2)

(3)

(4)

We select coefficient of emissivitya>0 and emissivity model of second temperature are as below

(5)

(6)

(7)

(8)

where

Theanalysisaboveshowsthatthereisarelationshipbetweenthemulti-spectralalgorithmsandemissivityandrealizecontinuouscalculationwithoutassumingtheiterativeinitialvalue.Byappropriatelyselectiterativecut-offconditionEr,itcanmeettherequirementofthemeasurementprecisionexcepttheiterationtimeisdifferent.

Fig.1 Schematic of measurement

2 Overall structure of multi-spectral thermometry system

Multi-spectral radiation thermometry system consists of multiple spectral channels in one instrument to simultaneously obtain the multi-spectral radiance measurement information of the target point to be measured, which is processed to obtain the true temperature and spectral emissivity of target.Having no special requirements on the target, the method is particularly applied to simultaneous measurement of true temperature and material emissivity of high temperature and very high temperature target.The measurement system comprises mainly optical system (optical sight, optical splitting system and photoelectric converter), data conditioning system, high speed data acquisition system, fiber remote transmission module, PC and other parts.The general structure diagram of the measurement system is shown in figure 1.

3 Calibration of measurement system

Calibration of measurement device is divided into wavelength function (PWF) calibration and brightness temperature calibration.By using wavelength calibration, we get the working wavelength of each channel of the instrument.The specific calibration results for operating wavelength of the instrument in various channels are shown in Table 1 and wavelength functions of some channels are shown in figure 2.

Table 1 Effective wavelengths of pyrometer (nm)

Fig.2 Part of PWF of Target 1

Calibration is carried out in Beijing Aerospace Hospital (professional thermal measurement calibration station specified by the department of space).The pyrometer and standard meter are respectively aligned with the window of the high temperature blackbody furnace.The output spectral region of the blackbody furnace contains the spectral range of the pyrometer.From 900 to 3 000 ℃, every hundredth temperature point is taken as a measuring point and each measurement point is sampled for 500 times.Afterwards, the average value is seen as the measurement value.The output temperature value of the standard meter is taken as the brightness temperature value of the temperature point and recorded in pair with the voltage measurement value.Owing to the wide measurement temperature range of instrument, the brightness temperature calibration contains medium low temperature zone (below 2 000 ℃) and high temperature zone (above 2 000 ℃).For medium low temperature zone, we adopt whole hundredth calibration method and for high temperature zone, we adopt one point calibration method[8-10].Some brightness temperature calibration results are shown in tables 2 and 3.

Table 2 Data of brightness temperature calibration of target 1 (Unit: V)

Table 3 Data of brightness temperature calibration of target 2 (Unit: V)

Fig.3 Variation curves of voltage channel 1 and channel 5 corresponds with the time

4 Experimental results

The explosion processes of thermo-baric explosive with different proportion are measured based on above multi-spectral thermometry system and a series of curves of voltage U changing with time t are obtained.Fig.3 is the changing curve between voltage and time of thermo-baric explosive in two channels therein.

From figure 3, we can see that thermo-baric explosive temperature has obvious transient and large damage area accompanied by a strong shock.In the time of 600 μs, thermo-baric explosive generates a large amount of toxic gas and smoke, which lead to local combustion hypoxia.Therefore, it is measured that the voltage of the output channel has certain fluctuation and repeated phenomenon at about 600 μs.

It can be observed from figure 4 that a temperature peak appears in dozens of microseconds after explosion of thermo-baric explosive.Afterwards, temperature has obvious descending trend.With the change of time, the 2nd temperature peak appears after explosion of the thermo-baric explosive mainly because of burning of fuel particles.After explosion, thermo-baric explosive absorbs a great deal of oxygen from the surrounding air, which leads to the secondary aerobic combustion.Finally, with the extension of time, temperature gradually declined; At this stage, due to the fireball volume expanding and large amounts of energy is released, the degree of damage to the surrounding environment is getting more and more serious.

Fig.4 Curves of temperature change with time

5 Conclusion

Through the study of multi-spectral theory, we have successfully developed the multi-spectral thermometer applicable to detecting true temperature of thermo-baric explosive.The instrument appraises destructive power and killing ability of thermo-baric explosive from temperature angle.Long distance wireless temperature test helps with the wiring difficulties and the great dangers in measurement of explosion temperature field are get rid of by means of the wireless sensing network technology.Therefore, the paper is a foundation for multi-spectral detection in the explosion temperature field of thermo-baric explosive in the future and thereby is of practical significance.

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*通讯联系人

TK311

A

温压炸药爆炸瞬态多光谱真温高温计的研究

张福才1，孙晓刚1*，邢 键2

1.哈尔滨工业大学，黑龙江 哈尔滨 150001 2.哈尔滨工程大学，黑龙江 哈尔滨 150001

温压炸药爆炸温度高且具有较强的破坏力，因而使其爆炸温度测试较为困难。为有效评估温压炸药的热温度毁伤效力，将多光谱温度测量系统应用到温压炸药瞬态高温测试中，利用二次测量法计算出爆炸火焰的发射率与真温。在数据采集系统中结合光纤线传感技术，在确保参试人员的安全前提下，可在500 m外测试仪器状态进行数据采集，实现了测量数据信息的远距离传递。测试结果表明，所设计的测量系统工作稳定、安全性高，具有良好的应用前景。

温压炸药； 多光谱； 真温； 光纤传感技术

2014-12-07，

2015-04-06)

Foundation item：Special Project for Development of Major National Scientific Instrument and Equipment (2013YQ470767), Natural Science Foundation of China (61405045), Project Funding of Science and Technology Department of Heilongjiang Province(12521487)

10.3964/j.issn.1000-0593(2016)05-1598-06

Received：2014-12-07; accepted：2015-04-06

Biography：ZHANG Fu-cai，(1978—)，doctoral student of Harbin Institute of Technology e-mail: qingtengzfc@yeah.net *Corresponding author e-mail: 510132156@qq.com