The first part of this two-part review focused on the fundamental and diagnostics aspects of laser-induced plasmas, only touching briefly upon concepts such as sensitivity and detection limits and largely omitting any discussion of the vast panorama of the practical applications of the technique. Clearly a true LIBS community has emerged, which promises to quicken the pace of LIBS developments, applications, and implementations. With this second part, a more applied flavor is taken, and its intended goal is summarizing the current state-of-the-art of analytical LIBS, providing a contemporary snapshot of LIBS applications, and highlighting new directions in laser-induced breakdown spectroscopy, such as novel approaches, instrumental developments, and advanced use of chemometric tools. More specifically, we discuss instrumental and analytical approaches (e.g., double- and multi-pulse LIBS to improve the sensitivity), calibration-free approaches, hyphenated approaches in which techniques such as Raman and fluorescence are coupled with LIBS to increase sensitivity and information power, resonantly enhanced LIBS approaches, signal processing and optimization (e.g., signal-to-noise analysis), and finally applications. An attempt is made to provide an updated view of the role played by LIBS in the various fields, with emphasis on applications considered to be unique. We finally try to assess where LIBS is going as an analytical field, where in our opinion it should go, and what should still be done for consolidating the technique as a mature method of chemical analysis.

https://journals.sagepub.com/doi/pdf/10.1366/11-06574

Laser-induced breakdown spectroscopy (LIBS), part II: review of instrumental and methodological approaches to material analysis and applications to different fields.

The editors have assembled a world-class group of contributors who address the questions the combustion diagnostic community faces. They are chemists who identify the species to be measured and the interfering substances that may be present; physicists, who push the limits of laser spectroscopy and laser devices and who conceive suitable measuremen

Applied Combustion Diagnostics

The detection and characterization of energetic materials at distances up to 45 m using stand-off laser induced breakdown spectroscopy (LIBS) has been demonstrated. A field-portable open-path LIB spectrometer working under a coaxial configuration was used. A preliminary study allowed choosing a single-pulse laser source over a double-pulse system as the most suitable source for the stand-off analysis of organic samples. The C2 Swan system, as well as the hydrogen, oxygen and nitrogen emission intensity ratios were the necessary parameters to identify the analyte as an organic explosive, organic non-explosive and non-organic samples. O/N intensity ratios of 2.9 and 2.16 with relative standard deviations of 4.03% and 8.36% were obtained for 2,4-dinitrotoluene and aluminium samples, respectively. A field test with known samples and a blind test were carried out at a distance of 30 m from the sample. Identification of energetic compounds in such conditions resulted in 19 correct results out of 21 samples.

http://www.biblioteca.uma.es/bbldoc/articulos/16604180.pdf

Test of a stand-off laser-induced breakdown spectroscopy sensor for the detection of explosive residues on solid surfaces

Measurements of hydrocarbons using laser-induced breakdown spectroscopy

Coal is one of the world's most abundant primary energy sources. Real-time coal analysis technology is imperative for coal blending, combustion optimization, pollution reduction, and pricing. Laser-induced breakdown spectroscopy (LIBS) has been a promising candidate for coal analysis because of its uniquely fast, in situ, and online capabilities. Coal is a sedimentary rock with a complex and heterogeneous composition, and therefore, laser–coal interaction exhibits multiple phenomena. A systematic study of the experimental conditions required for stable coal–plasma formation and evolution is a headway for enhancing LIBS results. In coal-fired power plants, LIBS offers three installation sets, namely, inline, at-line, and offline, with minimal space requirements and ease of retrofit. Moreover, LIBS is a safer technique with lower installation and maintenance costs and fits the concern of coal-fired power plants for multielemental detection in fast records. Coal analysis mainly includes calorific heat value determination, proximate analysis, ultimate analysis, and other related analyses. LIBS data is handled with continuously developing mathematical and statistical modeling techniques to provide the smart extraction of the required spectral information for coal analysis. In this tutorial review, we summarize the previous research contributions utilizing LIBS for coal analysis, including fundamentals and key factors, operation modes, data processing, and analytical results. Over and above, LIBS contribution in fly ash analysis and certain literature concerning combustion diagnostics might be included to present a simple guideline for researchers interested in LIBS applications for coal utilization.

Coal analysis by laser-induced breakdown spectroscopy: a tutorial review

Laser-induced breakdown spectroscopy (LIBS) has been used to measure the equivalence ratio of a spark-ignited engine in a laboratory setting. Spectral features of C (711.3 nm), O (776.6 nm), N (746.3 and 743.8 nm), and CN (broad emission 707–734 nm) were used to quantify the equivalence ratio over a range from P = 0.8 to P = 1.2. The C/N and C/O peak ratios were found to be successful measurement metrics, compared with a standard exhaust gas oxygen analyzer, for averaged measurements. Some variation in the measurements was observed as a function of engine load. Single-shot data based on a CN/air peak ratio were evaluated using a separate calibration from averaged measurements, and the average of the single-shot data was found to agree well with the exhaust gas oxygen analyzer. The scatter in the single-shot data was substantially higher at lower equivalence ratios. The measurements including the CN peak were slightly sensitive to load, possibly due to pressure changes in the sample as the load increases, or possibly due to changes in the particle size distribution in the gas stream.

Laser-induced breakdown spectroscopy for on-line engine equivalence ratio measurements.

This paper demonstrates the use of laser induced breakdown spectroscopy (LIBS) as a diagnostic technique to obtain optical measurements of equivalence ratio in a sparkignited engine. Point measurements were obtained in the exhaust manifold of an automotive engine close to the exhaust port of a cylinder. The experimental apparatus was synchronized with the engine in order to obtain measurements in a fixed position during the cycle. Eighty-shot averaged measurements of equivalence ratio P, obtained in under 10 s, were shown to have ΔP = ±0.05 (95 per cent confidence interval). Single-shot measurements were hindered by noise in the signal, but it is shown that the statistical technique of principal component analysis can significantly improve the precision of the data and allows discrimination between measurements obtained in lean, stoichiometric, and rich conditions. The data presented represent one of the first applications of LIBS to optical measurements of the equivalence ratio in an engine, and ...

Real-time measurement of equivalence ratio using laser-induced breakdown spectroscopy:

The instantaneous air-to-fuel ratio (A/F) has a large effect on spark-ignited engine performance. Specifically, fluctuations in A/F influence performance, efficiency, and engine-out emissions. Benefits of improved control of A/F include enhancement of the aforementioned metrics, as well as potential for extension of the lean limit. Current direct research measurement methods providing data for individual charge A/F are limited to in-cylinder Raman scattering measurements of nitrogen and fuel. Indirect methods that have been applied to transient engine control include mapping using neural network algorithms, applied to engine airflow, and feed-forward control based on engine models. Emission sensing has been primarily limited to flow sensors such as the UEGO (Universal Exhaust Gas Oxygen) sensors, which are too slow to resolve individual cylinder / charge A/F.

https://www.osapublishing.org/viewmedia.cfm?uri=LIBS-2002-ThE23&seq=0

LIBS for real-time equivalence ratio measurements in a spark-ignited engine

Practical combustion systems are characterized by rapid fluctuations due to turbulence and unsteady operation. Real-time diagnostic and analysis methods must be both highly sensitive and capable of capturing significant amounts of information instantly. This talk describes the use of Laser-Induced Breakdown Spectroscopy (LIBS) for combustion system analysis, including the measurement of complete mixture fraction, inorganic species concentrations, and/or associations of individual elements in aerosol particulate matter, in a single measurement. Equivalence ratio measurements in engines, parameterized by ratios of observed C, O, and N emission lines, have been used to determine fluctuations in operation and ascertain performance. In laboratory diffusion flames similar measurements have been used to determine PDFs of turbulent mixing between air and fuel. In addition, the composition of particulate matter may be monitored, both trace species and major species. These multiple measurement modalities make LIBS attractive as a general, broadband diagnostic for combustion systems. Future directions and new applications will be addressed.Practical combustion systems are characterized by rapid fluctuations due to turbulence and unsteady operation. Real-time diagnostic and analysis methods must be both highly sensitive and capable of capturing significant amounts of information instantly. This talk describes the use of Laser-Induced Breakdown Spectroscopy (LIBS) for combustion system analysis, including the measurement of complete mixture fraction, inorganic species concentrations, and/or associations of individual elements in aerosol particulate matter, in a single measurement. Equivalence ratio measurements in engines, parameterized by ratios of observed C, O, and N emission lines, have been used to determine fluctuations in operation and ascertain performance. In laboratory diffusion flames similar measurements have been used to determine PDFs of turbulent mixing between air and fuel. In addition, the composition of particulate matter may be monitored, both trace species and major species. These multiple measurement modalities make LIBS ...

Francesco Ferioli

Papers

Measurements of hydrocarbons using laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy for on-line engine equivalence ratio measurements.

Real-time measurement of equivalence ratio using laser-induced breakdown spectroscopy:

LIBS for real-time equivalence ratio measurements in a spark-ignited engine

Combustion system analysis using laser-induced breakdown spectroscopy