Real-time Laser Absorption Spectroscopy for Polyfuel Combustion Engines

Real-time Laser Absorption Spectroscopy for Polyfuel Combustion Engines
Author: Kevin Schwarm
Publisher:
Total Pages: 0
Release: 2023
Genre:
ISBN:
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This dissertation details the development and application of mid-infrared laser absorption spectroscopy sensing methods towards advancing low-carbon reciprocating engines for high-efficiency and low-emission power generation in a decarbonized energy sector. The scope of this work includes advancement in methods for fundamental spectroscopic studies, integration of advanced sensors into production reciprocating engines for characterization of combustion of low-carbon fuel blends, and computational methods advancement for high-speed real-time signal processing. A high-temperature, high-pressure optical gas cell is designed to enable controlled studies of molecular absorption spectra at high temperatures (>1200 K) and high pressures (>200 atm) to validate spectroscopic parameters at the elevated conditions in combustion engines. A novel optical approach provides access to the mid-wave infrared wherein lies the fundamental rovibrational absorption bands of combustion species critical to characterization of combustion process and emissions formation. Laser absorption sensors are developed and utilized for experimental measurements in the exhaust of a production Honda single-cylinder spark-ignition engine through design of an in-line exhaust sensor module to gain optical access to exhaust gases close-coupled to the exhaust valve. High-temperature opto-mechanical design and laser fiber-coupling assist in achieving robust measurements of cycle-resolved temperature and species (CO and NO) concentration at a rate of 10 kHz. The exhaust sensor is demonstrated by capturing cycle-to-cycle and intra-cycle emissions dynamics and characterizing emissions response to low-carbon fuel blends incorporating natural gas, hydrogen, and ammonia. To enable real-time measurement output at 10 kHz, computational time of the sensor data processing is reduced to sub-ms scales through the use of machine learning algorithms on an embedded processing platform. Compact neural network and ridge regression models are developed to calculate species concentration and temperature directly from transmitted laser signals, removing the need for computationally-intensive nonlinear fitting methods. The machine learning algorithms are deployed to a field-programmable gate array (FPGA) for further acceleration. Hardware-in-the-loop demonstration yields computational time and latency below 100 μs to expand use of the 10 kHz exhaust sensor for real-time sensing applications. Complementary to the sensor development work, a time-resolved chemical-kinetic model is constructed within Cantera to evaluate reciprocating engine performance and emissions during fueling with low- and non-carbon blends. The simulation model provides insights into strategies for optimization of low-carbon combustion and serves as a foundation for sensor interpretation and future work in engine optimization. Discussion of ongoing work includes the design and development of an electro-hydraulic camless valvetrain for future integration into a reciprocating engine architecture to enhance adaptability for fuel-flexible operation.

Mid-infrared Laser Absorption Spectroscopy and Ignition Delay Time Measurements of Advanced Renewable Fuels at High Pressure in a Shock Tube

Mid-infrared Laser Absorption Spectroscopy and Ignition Delay Time Measurements of Advanced Renewable Fuels at High Pressure in a Shock Tube
Author: Erik Ninnemann
Publisher:
Total Pages: 104
Release: 2021
Genre:
ISBN:
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The United States government has set 2050 as the target for net-zero greenhouse gas emissions due to their increasing levels and the subsequent rise in global temperatures. To meet this target, there has been renewed interest in the combustion of high-energy biofuels that could combat these issues. Thus, the Department of Energy started the Co-Optimization of Fuels and Engines program to find bioderived blendstocks that can harmonize with current and future generation engines to increase power and efficiency, all while reducing overall emissions. As part of this program, it is crucial to understand the combustion of these fuels at the temperatures and pressures internal combustion engines operate at. Therefore, the oxidation and pyrolysis of several advanced biofuels--cyclopentanone, prenol, 1-pentene and trans-2 pentene, and methyl propyl ether--have been studied in a shock tube reactor to quantify some of their fundamental combustion properties. Measurements include ignition delay times and time-resolved species concentrations, including that of fuel decomposition and formation of intermediate species such as carbon monoxide and ethylene. These measurements are useful for validating and updating chemical kinetic mechanisms that provide the chemistry input into computational fluid dynamic codes. This study's measured data are compared to the predictions of the most recent literature chemical kinetic mechanisms for each fuel. When appropriate, sensitivity analyses were conducted to highlight reactions sensitive to the conducted measurements, and some reaction rate modifications were made.

Laser-Induced Breakdown Spectroscopy

Laser-Induced Breakdown Spectroscopy
Author: Jagdish P. Singh
Publisher: Elsevier
Total Pages: 455
Release: 2007-10-03
Genre: Science
ISBN: 0080551017
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Laser induced breakdown spectroscopy (LIBS) is basically an emission spectroscopy technique where atoms and ions are primarily formed in their excited states as a result of interaction between a tightly focused laser beam and the material sample. The interaction between matter and high-density photons generates a plasma plume, which evolves with time and may eventually acquire thermodynamic equilibrium. One of the important features of this technique is that it does not require any sample preparation, unlike conventional spectroscopic analytical techniques. Samples in the form of solids, liquids, gels, gases, plasmas and biological materials (like teeth, leaf or blood) can be studied with almost equal ease. LIBS has rapidly developed into a major analytical technology with the capability of detecting all chemical elements in a sample, of real- time response, and of close-contact or stand-off analysis of targets. The present book has been written by active specialists in this field, it includes the basic principles, the latest developments in instrumentation and the applications of LIBS . It will be useful to analytical chemists and spectroscopists as an important source of information and also to graduate students and researchers engaged in the fields of combustion, environmental science, and planetary and space exploration. * Recent research work* Possible future applications* LIBS Principles

Shock Tube and Laser Absorption Studies of Small Alkene Spectroscopy and Real Fuel Kinetics

Shock Tube and Laser Absorption Studies of Small Alkene Spectroscopy and Real Fuel Kinetics
Author: Thomas Parise
Publisher:
Total Pages:
Release: 2018
Genre:
ISBN:
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Growing demand for energy coupled with increased awareness of various deleterious effects of current energy generation techniques drive a demand for more efficient utilization of current feedstocks and addition of new streams. Accomplishing both more efficient utilization of current fuels and interoperability of new streams requires detailed chemical kinetic understanding of both existing and novel fuels. Shock tube/laser absorption strategies are well-suited for these fuel kinetics studies. In this work, several new infrared laser sensor strategies have been developed that have enabled the quantitative time-history measurements of critical fuel decomposition products. Using these sensors, the decomposition products of several fuels were measured. These data have been used in the development of the HyChem model for jet fuel. An existing facility, the Kinetic Shock Tube, has been modified through heating to more readily handle distillate fuels with low vapor pressures at ambient conditions. Additionally, the fuel handling and mixing system was modified allow for the production of mixtures of distillate fuels and oxidizers or inert diluents. A novel laser-absorption-based propene diagnostic was developed using an external cavity quantum cascade laser to allow measurement of the second-smallest alkene in shock tube experiments. Existing room-temperature resolved spectra spanning the infrared absorption of propene from 1.5 to 15 microns was considered to select a target wavelength region. A series of experiments at high temperatures were done to ensure that a maximally-absorbing wavelength was selected at high temperatures. The temperaturedependence of this propene absorption feature was then measured. This diagnostic was combined with an existing CO2 gas laser ethylene diagnostic to study the decomposition of propene at elevated temperatures. Simultaneous laser-based measurements of propene and ethylene were recorded for the first time. Propene decomposition measurements were reported between 1360 and 1710 K and compared to models in the literature to provide recommendations for further model refinement. These diagnostics were then combined with other laser diagnostics, including a HeNe gas laser fuel-absorption diagnostic at 3.39 microns and an interband cavity laser diagnostic for measuring methane at 3.18 microns, to measure a variety of species during the pyrolysis of two gasolines, two jet fuels, and a synthetic jet fuel Ethylene and iso-butene were measured during the pyrolysis of two Shell gasolines between 1050 and 1390 K; propene was also measured during these experiments for one of the gasolines. These measurements were compared to predictions from a recent gasoline surrogate mechanism. Ethylene and propene were measured during the pyrolysis of two distillate jet fuels between 1070 and 1440 K; iso-butene was also measured during these experiments for one of the jet fuels. Ethylene, propene, iso-butene, and methane formation were measured during the pyrolysis of a synthetic jet fuel between 1071 and 1317 K. These measured mole fractions were then compared to an existing model for large, branched hydrocarbons. These measurements were also used to constrain in-development hybrid chemistry (HyChem) models for the respective fuels. These studies demonstrate the utility of laser absorption studies in shock tubes to investigate real fuel pyrolysis kinetics through the measurement of both product formation rates and product distributions. Subsequently, these measurements can be used to constrain new chemical kinetic models, evaluate the accuracy of existing chemical kinetic models, and select appropriate surrogate compositions for surrogate-based models.

Practical Applications of Laser Absorption Spectroscopy for Aeroengine Testing

Practical Applications of Laser Absorption Spectroscopy for Aeroengine Testing
Author: Ian Schultz
Publisher:
Total Pages:
Release: 2014
Genre:
ISBN:
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Reliable air-breathing hypersonic propulsion systems offer the potential to revolutionize aircraft performance in a variety of high-speed aerospace applications through substantial efficiency gains and hardware cost savings. Supersonic combustion ramjet (scramjet) engines are one such device that promise propulsion capabilities up to about Mach 10. However, before these devices are ever practically realized, considerable technical challenges must be overcome in combustor-inlet interaction, fuel-air mixing, and coupled turbulent flow/combustion modeling. The growing power of computational tools have accelerated the pace of solving these problems, but the accuracy of computational approaches can only be validated by rigorous experimental testing. Thus, there is a need for both facilities capable of creating conditions experienced during hypersonic flight, as well as diagnostics that can characterize the operation of those facilities and provide experimental data for the validation of computational models. Optical diagnostics such as laser absorption spectroscopy are capable of providing non-intrusive, in situ measurements of important flow-field parameters such as temperature, velocity, species concentrations, which makes them an invaluable resource to hypersonic aeroengine researchers. Absorption spectroscopy, in particular, has benefited from recent advances in laser and optics technology, allowing access to a variety of wavelengths corresponding to absorption transitions of important combustion species such as O2, H2O, and CO2. Moreover, these sensors only require compact, low-power laser sources and light can be delivered via fiber-optics, which enables the sensor to more easily integrate with test facility hardware. As a result, laser absorption spectroscopy has become a workhorse in experimental scramjet research, and has been applied in test facilities around the world. Building upon this prior work, here the design and results of several different spectroscopic sensors for facility characterization and distinct scramjet operation modes are presented. Both hydrogen-fueled and hydrocarbon-fueled scramjets are investigated in a variety of geometric configurations. These results comprise the largest data set of laser absorption spectroscopy measurements within scramjet combustors published to date, and are a valuable resource for computational researchers who wish to compare their models with experimental data. A primary drawback of laser absorption spectroscopy is that some techniques are sensitive to nonuniformity along the measurement line-of-sight. In highly three-dimensional flows such as within a scramjet combustor, this can prove to be a considerable hindrance. However, in the work here particular care has been taken to account for nonuniformity along the measurement path, and new techniques, including a new approach to wavelength-modulation spectroscopy data reduction, have been developed and applied to provide quantitatively accurate path-integrated measurements in the presence of nonuniformities. Additionally, novel applications of laser absorption spectroscopy are presented, including the use of absorption data to place an upper bound on the cavity residence time within a scramjet combustor, and a new sensor design for measuring air temperature in high-enthalpy facilities by tracking the formation of nitric oxide.