Spectroscopic device and method for detecting alkali content and multi-fuel reaction characteristics

Abstract

The application belongs to the technical field of fuel analysis, and specifically discloses a spectral detection device and method for the reaction activity and alkali metal content of multi-element fuel, which comprises a sample unit, a LIBS detection unit and a NIRS detection unit, wherein: the sample unit is used for placing the multi-element fuel to be measured; the LIBS detection unit is used for LIBS detection on the multi-element fuel to be measured, so as to measure the element content of the multi-element fuel to be measured; and the NIRS detection unit is used for NIRS detection on the multi-element fuel to be measured at the pulse interval of the LIBS detection, so as to measure the functional group content of the multi-element fuel to be measured, and then obtain the reaction activity and alkali metal content of the multi-element fuel to be measured. By combining LIBS and NIRS, the application can reduce the unstable factors of NIRS measurement, and correct the functional group type by using the element content, so as to realize the rapid and synchronous detection of the dual-mode spectral information.

Description

Technical Field

[0001] This application belongs to the field of fuel analysis technology, and more specifically, relates to a spectroscopic detection device and method for the reactivity and alkali metal content of multi-component fuels. Background Technology

[0002] Driven by both the "dual carbon" goals and energy transition, organic solid wastes such as biomass (e.g., straw, forestry waste) and sludge (byproducts of wastewater treatment plants) are rapidly emerging as alternative fuels to coal. Various forms of co-firing alternative fuels (e.g., biomass and coal co-gasification to produce products, and coal co-firing with sludge for power generation) have made significant progress in practical applications. The utilization process of these multi-fuel systems differs from that of single fuels, exhibiting greater variation in fuel characteristics and higher complexity. The utilization process directly impacts the operating efficiency, service life, and fuel costs of generating units. With continuous advancements in energy technology and increasingly stringent environmental standards, in-depth research into the relationship between the utilization process and fuel reactivity and safety is particularly important.

[0003] Reactivity determines fuel combustion / gasification efficiency, and highly reactive fuels can improve unit thermal efficiency. Furthermore, alkali metals (such as sodium and potassium) in biomass and sludge are easily volatilized at high temperatures, leading to fouling, slagging, and corrosion of boiler heating surfaces, affecting operational safety. Therefore, the alkali metal content of raw materials is a key concern for operational safety. Real-time monitoring of fuel reactivity and alkali metal content provides a basis for optimizing feedstock compatibility and adjusting combustion / gasification conditions, becoming a core technological requirement for improving combustion / gasification efficiency and ensuring safety.

[0004] Currently, numerous scholars have conducted extensive research on fuel properties, including alkali metal content (CN219657480U), calorific value (CN108627500A), and elemental concentration (CN119223939A). However, these studies are limited to exploring single fuel properties, failing to consider the influence of multiple factors simultaneously, neglecting the detection of fuel reactivity, and not improving feedstock compatibility. CN118272131A discloses a coal blending method based on anthracite gasification in a fluidized bed. This method only studies anthracite and employs a traditional offline analysis mode, which suffers from drawbacks such as complex operation, long detection cycle, cumbersome process, and inability to perform simultaneous measurements. Static test data often cannot reflect the dynamic changes of fuel during actual utilization. Therefore, online detection technologies have emerged and have been successfully applied in industrial production, such as microwave technology, dual-energy gamma-ray attenuation technology, and rapid gamma-neutron activation analysis technology. However, these technologies have many problems in use, such as the inability to detect multiple indicators, the susceptibility of test accuracy to environmental influences, and the generation of radiation pollution during use. In recent years, laser-induced breakdown spectroscopy (LIBS) and near-infrared spectroscopy (NIRS) have gradually become research hotspots in the field of solid fuel detection due to their advantages such as speed, non-destructiveness, and simultaneous detection of multiple elements.

[0005] LIBS utilizes high-energy pulsed lasers to ablate fuel surfaces and induce plasma generation. The plasma emission spectrum is acquired and analyzed by a spectrometer to obtain information on the types and contents of elements in the sample. However, the presence of cold-absorbing atoms around the plasma leads to self-absorption in the laser-induced non-uniform plasma, thus requiring optimization of the stability and accuracy of LIBS quantitative analysis results. NIRS uses near-infrared light to irradiate fuel, generating infrared absorption spectra to obtain information on functional groups and molecular structures in solid samples. Variations in raw material particle size cause changes in the optical path of diffuse reflection between particles, thus affecting the spectral absorbance. Excessively large sample particle sizes increase spectral instability. Furthermore, fuel utilization involves multi-scale physicochemical processes, making it difficult for single spectroscopic techniques to comprehensively obtain key information such as the reactivity of alkali metals and the carbon skeleton. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this application provides a spectroscopic detection device and method for the reactivity and alkali metal content of multi-fuels, aiming to solve the problem that existing detection devices are limited to exploring a single property of fuels and cannot achieve simultaneous detection of multiple parameters.

[0007] According to one aspect of this application, a spectroscopic detection device for the reactivity and alkali metal content of a multi-component fuel is provided, specifically including a sample unit, a LIBS detection unit, and an NIRS detection unit, wherein: the sample unit is used to hold the multi-component fuel to be tested; the LIBS detection unit is used to perform LIBS detection on the multi-component fuel to be tested to determine the elemental content of the multi-component fuel; the NIRS detection unit is used to perform NIRS detection on the multi-component fuel to be tested during the pulse interval of the LIBS detection, thereby breaking up fuel particles through the laser ablation effect of the LIBS detection unit, reducing the instability factors of the NIRS measurement, so as to determine the functional group content of the multi-component fuel to be tested, and thus obtaining the reactivity and alkali metal content of the multi-component fuel to be tested.

[0008] Compared with the prior art, the above-described technical solution conceived in this application combines LIBS and NIRS. On the one hand, it can break up fuel particles through laser ablation, reducing the instability factors in NIRS measurement. On the other hand, it can obtain the element content and functional group content of the multi-element fuel to be tested, and use the element content to correct the functional group type, thereby realizing the rapid and synchronous detection of dual-mode spectral information.

[0009] As a further preferred embodiment, the spectral detection device further includes a microwave generator, which is used to emit microwaves to the multi-element fuel to be tested to assist in LIBS detection and suppress plasma self-absorption effect.

[0010] As a further preferred embodiment, the LIBS unit includes a laser, a digital delay unit, an ICCD, a spectrometer, and a light-receiving probe. The laser is used to emit laser light towards the multi-component fuel to be tested. The digital delay unit is connected to the laser and the ICCD and is used to control the laser and the ICCD. The light-receiving probe is connected to the spectrometer and is used to collect the light signal emitted by the plasma of the multi-component fuel to be tested and transmit it to the spectrometer. The spectrometer is connected to the ICCD and is used to disperse the light and output the spectral signal. The ICCD is used to convert the light signal into an electrical signal, thereby measuring the elemental content of the multi-component fuel to be tested.

[0011] As a further preferred embodiment, the NIRS detection unit includes an infrared light source, an interferometer, and an NIRS detector. The infrared light source is used to emit infrared light at the pulse interval of LIBS detection, and after interference by the interferometer, it illuminates the multi-component fuel to be tested. The NIRS detector is used to detect the light intensity signal of the multi-component fuel to be tested, and then measure the functional group content of the multi-component fuel to be tested.

[0012] As a further preferred embodiment, the spectral detection device also includes a control unit, which is connected to the sample unit, the LIBS detection unit, and the NIRS detection unit. The control unit is used to control the sample unit and collect data from the LIBS detection unit and the NIRS detection unit to calculate the reactivity and alkali metal content of the multi-component fuel to be tested.

[0013] According to another aspect of this application, a spectroscopic detection method for the reactivity and alkali metal content of a multi-component fuel is provided, specifically: performing LIBS detection on the multi-component fuel to determine its elemental content; performing NIRS detection on the multi-component fuel during the pulse interval of the LIBS detection, thereby breaking up fuel particles through the laser ablation effect of the LIBS detection, reducing the instability factors in the NIRS measurement, to determine the functional group content of the multi-component fuel, and thus obtaining the reactivity and alkali metal content of the multi-component fuel.

[0014] As a further preferred option, microwaves are emitted to the multi-element fuel to be tested during LIBS detection as an auxiliary process.

[0015] As a further preferred embodiment, the laser energy detected by the LIBS is 40 mJ / pulse to 100 mJ / pulse, and the pulse frequency is 2 Hz to 10 Hz.

[0016] As a further preferred option, the microwave power is 160W to 2000W.

[0017] As a further preferred embodiment, the spectral scanning range of the NIRS detection is 750 nm to 2500 nm.

[0018] In summary, compared with the prior art, the technical solutions conceived in this application have the following main technical advantages:

[0019] 1. This application combines LIBS and NIRS, which on the one hand can break up fuel particles through laser ablation and reduce the instability factors of NIRS measurement, and on the other hand can obtain the element content and functional group content of the multi-element fuel to be tested, and use the element content to correct the functional group type, thereby realizing the rapid and synchronous detection of dual-mode spectral information.

[0020] 2. At the same time, this application provides a microwave generator to emit microwaves to the multi-element fuel under test to assist in LIBS detection, which can suppress the plasma self-absorption effect and thus effectively improve the accuracy of LIBS detection. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the spectroscopic detection device for the reactivity of multi-fuels and the content of alkali metals provided in the embodiments of this application;

[0022] Figure 2 This is a flowchart of a spectroscopic detection method for the reactivity of multi-fuels and the content of alkali metals provided in the embodiments of this application.

[0023] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0024] 1-Laser, 2-Digital delay unit, 3-ICCD, 4-Spectrometer, 5-Light receiving probe, 6-Electric translation stage, 7-Data processing unit, 8-Microwave generator, 9-NIRS detector, 10-Infrared light source, 11-Interferometer, 12-Sample holder. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0026] like Figure 1 As shown, according to one aspect of this application, a spectroscopic detection device for the reactivity and alkali metal content of multi-component fuels is provided, specifically including a sample unit, a LIBS detection unit, and an NIRS detection unit. The sample unit is used to place the multi-component fuel to be tested. The sample unit includes an electric translation stage 6 and a sample holder 12 disposed on the electric translation stage. During operation, the electric translation stage 6 drives the sample holder 12 to move up and down to adjust the position of the multi-component fuel to be tested in the vertical direction. The sample holder 12 is used to drive the multi-component fuel to be tested to move in the horizontal direction to ensure that the laser irradiation position of the LIBS detection unit overlaps with the infrared irradiation position of the NIRS.

[0027] The LIBS detection unit is used to perform LIBS detection on the multi-element fuel to determine the elemental content of the multi-element fuel, including the precise content of basic elements such as C, O, H, and N, as well as the precise content of alkali metal elements such as Na and K.

[0028] The NIRS detection unit is used to perform NIRS detection on the multi-component fuel under test during the pulse interval of LIBS detection. The laser ablation effect of the LIBS detection unit breaks up the fuel particles, reducing the instability factors in NIRS measurement, so as to determine the functional group content of the multi-component fuel under test. The accurate content of elements (such as C, H, O, etc.) obtained by the LIBS testing unit can be used to correct the NIRS functional group detection (determine the functional group type). NIRS accurately inverts the sample moisture content through the absorption characteristics of hydrogen-containing groups (such as OH) in molecules, correcting the influence of moisture on plasma radiative transfer efficiency.

[0029] By analyzing the elemental and functional group content of the tested multi-element fuel, we can obtain information such as carbon-nitrogen ratio, oxygen content, average equivalent double bond number, ash content, volatile matter, fixed carbon, calorific value, and alkali metal content. This information can then be used to determine the reactivity of the tested multi-element fuel, including activation energy, combustibility index, and comprehensive combustion characteristic index, which can be used to output blending schemes.

[0030] Compared with the prior art, the above-described technical solution conceived in this application combines LIBS and NIRS. On the one hand, it can break up fuel particles through laser ablation, reducing the instability factors in NIRS measurement. On the other hand, it can obtain the element content and functional group content of the multi-element fuel to be tested, and use the element content to correct the functional group type, thereby realizing the rapid and synchronous detection of dual-mode spectral information.

[0031] Furthermore, the spectral detection device also includes a microwave generator 8, which is used to emit microwaves to the multi-element fuel to be tested to assist in LIBS detection and suppress plasma self-absorption effect.

[0032] Furthermore, the LIBS unit includes a laser 1, a digital delay unit 2, an ICCD 3, a light-receiving probe 5, and a spectrometer 4, wherein:

[0033] Laser 1 is used to emit laser light onto the multi-component fuel to be tested. By generating high-energy, highly directional laser beams and precisely emitting these laser beams onto the multi-component fuel to be tested, when the laser beam irradiates the surface of the multi-component fuel to be tested, due to its extremely high energy, it will instantly generate high temperature and high pressure in a local area of ​​the multi-component fuel to be tested, thereby triggering the ionization and excitation of the fuel and forming plasma. This process is the key step in generating optical signals, because the plasma will emit characteristic spectra during the cooling process, and these spectra contain rich information about the fuel composition.

[0034] Digital delay unit 2 is connected to laser 1 and ICCD 3 for precise control and synchronization of laser 1 and ICCD 3. Since precise timing is required between laser emission and optical signal acquisition, digital delay unit 2 can precisely control the emission time of laser 1 and the exposure time of ICCD 3 according to preset parameters.

[0035] The light-collecting probe 5 is connected to the spectrometer 4 to collect the light signal emitted by the multi-element fuel plasma to be tested and transmit it to the spectrometer 4;

[0036] The spectrometer 4 is connected to the ICCD3 to work together. The ICCD3 receives the optical signal after the spectrometer 4 has dispersed the light, converts it into an electrical signal, amplifies it, and records it. By acquiring the spectral signal after different time delays, the ICCD3 can obtain information on the evolution of the plasma spectrum over time, providing rich data support for elemental content analysis. The spectrometer 4 disperses the optical signal transmitted from the light receiving probe 5, and the dispersed light signal is used to convert the optical signal into an electrical signal, thereby measuring the elemental content of the multi-element fuel to be tested.

[0037] Furthermore, the NIRS detection unit includes an infrared light source 10, an interferometer 11, and an NIRS detector 9. The infrared light source 10 is used to emit infrared light at the pulse interval of LIBS detection, and after interference by the interferometer 11, it illuminates the multi-component fuel to be tested. The NIRS detector 9 is aligned with the multi-component fuel to be tested and is used to detect the light intensity signal of the multi-component fuel to be tested, thereby measuring the functional group content of the multi-component fuel to be tested.

[0038] Furthermore, the spectral detection device also includes a control unit 7, which is connected to the sample unit, LIBS detection unit, and NIRS detection unit. This control unit controls the sample unit and collects data from the LIBS and NIRS detection units to calculate the reactivity and alkali metal content of the tested multi-component fuel. The control unit 7 integrates modeling and adaptive calibration techniques: it employs various isospectral preprocessing methods (effective spectrum screening, normalization, standard normal transformation, etc.) to reduce noise and invalid spectra interference with fuel analysis; it extracts key features through principal component regression (PCR) and partial least squares regression (PLSR), and uses a random forest-partial least squares hybrid model (RF-PLSR) to achieve simultaneous and accurate prediction of fuel reactivity and alkali metal content; it integrates an adaptive calibration model to dynamically adjust model parameters, ensuring the accuracy of long-term analysis. In addition, the control unit 7 can output compatibility schemes for multi-component fuels: based on the fuel's combustion / gasification application scenario and the reactivity and alkali metal content of the multi-component fuel, it outputs corresponding compatibility schemes to promote efficient energy utilization.

[0039] According to another aspect of this application, such as Figure 2As shown, a spectroscopic detection method for the reactivity and alkali metal content of multi-component fuels is provided. Specifically, the method involves: performing LIBS detection on the multi-component fuel to determine its elemental content; then performing NIRS detection on the multi-component fuel during the pulse intervals of the LIBS detection. The laser ablation effect of LIBS detection breaks up fuel particles, reducing instability factors in NIRS measurement, thereby determining the functional group content of the multi-component fuel. Finally, a quantitative prediction model based on multispectral fusion data is used: fusing LIBS elemental intensity matrices (C, H, O, K, Na, etc.) and NIRS functional group absorbance (hydrocarbons 6050 cm⁻¹, etc.) data, and using a random forest-partial least squares hybrid model (RF-PLSR) to achieve simultaneous and rapid detection of the reactivity and alkali metal content of the multi-component fuel; more specifically:

[0040] Multiple isospectral preprocessing techniques (effective spectrum screening, normalization, standard normal transformation, etc.) are employed to reduce the interference of noise and invalid spectra on fuel analysis. Key features are extracted through principal component regression (PCR) and partial least squares regression (PLSR), and a random forest-partial least squares hybrid model (RF-PLSR) is used to achieve simultaneous and accurate prediction of fuel reactivity and alkali metal content. An adaptive calibration model is integrated to dynamically adjust model parameters and ensure the accuracy of long-term analysis.

[0041] Furthermore, microwaves are emitted toward the multi-element fuel to be tested to assist LIBS detection, thereby suppressing the plasma self-absorption effect.

[0042] Furthermore, the LIBS detection wavelength was 1064 nm, and the laser energy was 40 mJ / pulse to 100 mJ / pulse. Excessive laser energy could cause over-ablation of the sample and affect the accuracy of NIRS detection; insufficient energy would fail to effectively penetrate the sample surface, affecting plasma formation. The laser pulse frequency was 2 Hz to 10 Hz, and the microwave power was 160 W to 2000 W. If the microwave power was too low, it might not effectively excite electron transitions in the plasma, resulting in insignificant suppression of the self-absorption effect; if the microwave power was too high, it might lead to excessively high plasma temperature, thereby triggering plasma shielding effects or other nonlinear effects. NIRS detection was performed during the LIBS pulse interval of 1 ns to 5 ns, with a spectral scanning range of 750 nm to 2500 nm and a resolution of 2 cm⁻¹. -1 Set the diffuse reflection measurement mode.

[0043] The technical solutions provided in this application will be further described below with reference to specific embodiments.

[0044] Example 1

[0045] Taking the detection of coal, straw, and rice husks as examples, representative coal and biomass samples are first selected and subjected to appropriate crushing and homogenization to ensure sample representativeness and test accuracy. The processed samples are then placed on the sample stage of the LIBS-NIRS instrument. Next, the laser-induced breakdown spectroscopy (LIBS) and near-infrared spectroscopy are adjusted to their optimal operating conditions. The LIBS laser energy is set to 70 mJ / pulse, the frequency to 2 Hz, the delay time to 1 µs, and the microwave power to 200 W. Furthermore, the NIRS spectral scanning range is set to 12500–4000 cm⁻¹. -1 4 cm resolution -1 A diffuse reflectance measurement mode was set up, and NIRS spectral measurements were performed at 3 ns intervals between LIBS pulses. Raw spectral data were collected and preprocessed; baseline correction (wavelet denoising) and peak area normalization (CI 247.8 nm, KI 766.5 nm characteristic lines) were performed on the LIBS spectra; multivariate scattering correction (MSC) and Savitzky-Golay smoothing were applied to the NIRS spectra. A random forest-partial least squares mixture model (RF-PLSR) was used, with the LIBS elemental intensity matrix (C, H, O, etc.) and NIRS functional group absorbance (hydroxyl group 3400 cm⁻¹) as input. -1 Fatty acid chain 2920 cm -1 The system detects fuel carbon-hydrogen ratio, oxygen content, average equivalent double bond number, ash content, volatile matter, fixed carbon, calorific value, and alkali metal content. Based on this information, it calculates and outputs fuel reactivity (including activation energy, combustibility index, and overall combustion characteristic index), and also outputs alkali metal content. Multiple sets of standard samples are used for model training, a database is established, and R is cross-validated. 2 >0.95. The measured alkali metal content was 0.67 wt.% (K - 0.45 wt.%, Na - 0.12 wt.%); the activation energy, flammability index, and comprehensive combustion characteristic index were 114.61 kJ / mol, 8.2 × 10⁻⁶, and 8.2 × 10⁻⁶, respectively. -5 % / (min·℃ 2 ), 4.6×10 -7 % 2 / (min·℃ 3 According to the requirements of the fixed-bed gasification process, the output ratio is coal: straw: rice husk = 7:2:1.

[0046] Example 2

[0047] Taking the detection of coal, potassium-containing sludge, and rubber as examples, representative coal, sludge, and rubber samples were collected, preliminarily crushed, and screened to remove large impurities and non-target substances. The samples were then mixed thoroughly and compressed into tablets. The processed samples were placed on the sample stage of the LIBS-NIRS instrument, and the laser-induced breakdown spectroscopy and near-infrared spectroscopy were adjusted to their optimal operating conditions. When determining the content, the LIBS laser energy was set to 80 mJ / pulse, frequency 5 Hz, delay time 1.5 µs, and microwave power 300 W; the NIRS spectral scanning range was set to 800–2500 nm, and the resolution to 2 cm⁻¹. -1 The diffuse reflectance measurement mode was set, and NIRS spectral measurements were performed at 2.7 ns intervals between LIBS pulses. Raw spectral data and preprocessed spectra were collected and input into the trained model for calculation (as shown in Case 1). LIBS-NIRS detection output alkali metal content, activation energy, flammability index, and comprehensive combustion index as follows: 0.89 wt.% (K - 0.68 wt.%, Na - 0.21 wt.%), 99.71 kJ / mol, and 6.5 × 10⁻⁶ kJ / mol. -5 % / (min·℃ 2 ), 3.2×10 -7 % 2 / (min·℃ 3 According to the fluidized bed combustion process requirements, the output mixture is coal: potassium-containing sludge: rubber = 8:1:1.

[0048] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A spectroscopic detection device for the reactivity and alkali metal content of multi-fuel compounds, characterized in that, The device includes a sample unit, a LIBS detection unit, and an NIRS detection unit. The sample unit holds the multi-component fuel to be tested. The LIBS detection unit performs LIBS detection on the multi-component fuel to determine its elemental content. The NIRS detection unit performs NIRS detection on the multi-component fuel during the pulse intervals of the LIBS detection. The LIBS detection unit's laser ablation action breaks up fuel particles, reducing instability factors in NIRS measurement, thereby determining the functional group content of the multi-component fuel and ultimately obtaining its reactivity and alkali metal content. The LIBS unit includes a laser (1), a digital delay unit (2), an ICCD (3), a spectrometer (4), and a light-receiving probe (5). The laser (1) is used to emit laser light to the multi-element fuel to be tested. The digital delay unit (2) is connected to the laser (1) and the ICCD (3) and is used to control the laser (1) and the ICCD (3). The light-receiving probe (5) is connected to the spectrometer (4) and is used to collect the light signal emitted by the plasma of the multi-element fuel to be tested and transmit it to the spectrometer (4). The spectrometer (4) is connected to the ICCD (3) and is used to split the light and output the spectral signal. The ICCD (3) is used to convert the light signal into an electrical signal, thereby measuring the elemental content of the multi-element fuel to be tested. The NIRS detection unit includes an infrared light source (10), an interferometer (11), and an NIRS detector (9). The infrared light source (10) is used to emit infrared light at the pulse interval of LIBS detection, and after interference by the interferometer (11), it illuminates the multi-component fuel to be tested. The NIRS detector (9) is used to detect the light intensity signal of the multi-component fuel to be tested, and then measure the functional group content of the multi-component fuel to be tested.

2. The spectral detection device as described in claim 1, characterized in that, The spectral detection device also includes a microwave generator (8), which is used to emit microwaves to the multi-element fuel to be tested to assist in LIBS detection and suppress plasma self-absorption effect.

3. The spectral detection device as described in claim 1, characterized in that, The spectral detection device also includes a control unit (7), which is connected to the sample unit, the LIBS detection unit and the NIRS detection unit, and is used to control them and collect data from the LIBS detection unit and the NIRS detection unit to calculate the reactivity and alkali metal content of the multi-element fuel to be tested.

4. A spectroscopic method for detecting the reactivity and alkali metal content of multi-fuel compounds, characterized in that, Using the spectral detection device as described in any one of claims 1 to 3, specifically: performing LIBS detection on the multi-component fuel to determine the elemental content of the multi-component fuel; performing NIRS detection on the multi-component fuel during the pulse interval of LIBS detection, breaking up fuel particles through the laser ablation effect of LIBS detection, reducing the instability factors of NIRS measurement, so as to determine the functional group content of the multi-component fuel, and thus obtaining the reactivity and alkali metal content of the multi-component fuel.

5. The spectral detection method as described in claim 4, characterized in that, Microwaves are emitted to the multi-element fuel being tested during LIBS detection as an aid.

6. The spectral detection method as described in claim 4, characterized in that, The laser energy detected by the LIBS is 40 mJ / pulse to 100 mJ / pulse, and the pulse frequency is 2 Hz to 10 Hz.

7. The spectral detection method as described in claim 5, characterized in that, The power of microwaves ranges from 160W to 2000W.

8. The spectral detection method according to any one of claims 4 to 7, characterized in that, The spectral scanning range of the NIRS detection is 750 nm to 2500 nm.

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