New Diagnostics Enabling Bio-Fuels in Transportation with Reduced Air Pollutant Emissions and Improved Efficiency
2011 New Investigator Award
This project focuses on the development of in-situ sensing technology to measure important radical species, like HO2, during the combustion of biofuels and to provide insights into the low temperature oxidation kinetics of the combustion process. This is critical to the development of advanced engine technologies that aim at providing reduction in emissions and increase in fuel efficiency through implementation of the low temperature and high pressure oxidation chemistry (< 1000 K) of biofuels.
Existing diagnostic methods are not able to easily measure such key chemical species as HO2, H2O2, CH2O, and NOx due to lack of sensitivity or interference from other molecules. Through the interdisciplinary collaboration supported by the Grand Challenges award, it was possible to develop a sensitive in situ laser diagnostic based on Faraday Rotation Spectroscopy (FRS) for measurement of HO2. Since the low temperature chemistry of biofuel combustion is dominated by the formation of HO2, this project results in better understanding of this critical combustion regime, which in turn is expected to help with reduction of formaldehyde and NOx emissions that are of serious environmental concerns.
Before this work, there was no interference-free diagnostic method for in situ measurement of radical species in the combustion process at elevated pressure available to the combustion scientists. The new HO2 laser diagnostic was implemented in conjunction with already existing instrumentation for measurement of stable non-radical species (i.e. CO,CO2,H2O,CH2O, H2O2) to study the oxidation chemistry of a biofuel from an atmospheric flow reactor. The following list summarizes the key accomplishments during the project funding period:
- A new mid-IR FRS system to measure HO2 at sub-ppmv levels generated by oxidation of a biofuel in a flow reactor has been developed and tested.
- A theoretical FRS spectral model has been developed to extract HO2 concentration via non-linear least-squares fitting of the experimental data.
- The first direct in situ measurement of HO2 from an atmospheric flow reactor has been demonstrated.
- Implementation of a novel dual-modulation (DM)-FRS sensing technology (see Fig. 1) has been performed to increase the sensitivity of the FRS HO2 measurement.
- The HO2 laser FRS diagnostic was combined with conventional measurement techniques (gas chromatography and mass spectroscopy) to enable real time measurements of stable non-radical products during biofuel oxidation.
- The first combined direct measurements of HO2 and H2O2 were successfully carried out under identical experimental conditions using DM-FRS and molecular beam mass spectroscopy (MBMS) respectively (see Fig. 2).
- Experiments that focused on validation of chemical kinetic models used to describe biofuel oxidation with experimental observations of HO2 and H2O2 have been performed and analyzed.
The successful development of an FRS system for HO2 measurement paves the way for development of FRS diagnostics for OH and NOx chemical species (also radicals) with sub-ppmv detection sensitivities. The experimental set-up used for DM-FRS measurement of HO2 at the exit of a flow reactor is shown in Fig. 3. DM-FRS is implemented using high frequency laser wavelength modulation and two-stage lock-in detection used to demodulate the DM-FRS signal. This DM-FRS system provided near fundamental shot-noise limited performance in quantification of HO2 at the exit of an atmospheric flow reactor. Additionally to improvements in system sensitivity the DM-FRS eliminates the uncontrollable effects of parasitic electromagnetic interference present in conventional FRS systems. This sensitive radical-selective diagnostics, when combined with the future planned development of sensitive mid-IR absorption spectroscopy of CH2O and H2O2, will provide an unparalleled set of measurement capabilities for combustion chemistry research. As discussed in the “Other Outcomes” and “Future Directions” sections below the future development of additional diagnostics will be supported, and will lead to, additional external funding for studying the fundamental chemical reactions that play a crucial role in understanding the low-temperature oxidation of biofuels.
In the year one of the project, PIs Wysocki and Ju have jointly developed a new course entitled “Cleaner transport fuels, combustion sensing and emission control” (ELE/MAE/CEE 428) that has been offered in the Spring semester of 2011. The course was closely linked to the conducted research and it covered fundamental aspects related to the physics of fuel combustion, light-matter interactions in combustion diagnostics, and provided a broad overview of research and development in the areas of green fuels, global environmental impacts, and emission regulations.
In the spring of 2013 Wysocki taught a course ELE555 “Laser Spectroscopy: New Technologies and Applications” which covers broad aspects of spectroscopic sensing that has a significant impact on a wide range of disciplines including environmental and atmospheric science, medicine, energy research and fundamental science. This graduate level course has been enhanced with materials originating from the research conducted within this project and exposed the students to the latest development in laser spectroscopy as reported in the recent literature. The research also helps the teaching of MAE 228 (Energy solutions for the 21st Century) in quantification of emissions and species from combustion.
Peer Reviewed Papers:
- B. Brumfield, W. T. Sun, Y. G. Ju, and G. Wysocki, “Direct In Situ Quantification of HO2 from a Flow Reactor”, J. Phys. Chem. Lett. 4, 872 (2013)
- N. Kurimoto, B. Brumfield, X. Yang, T. Wada, P. Dievart, and G. J. Wysocki, Yiguang, "Quantitative Measurements of HO2/H2O2 and Intermediate Species in Low and Intermediate Temperature Oxidation of Dimethyl Ether",(2013): submitted contribution to 35th International Symposium on Combustion, accepted papers will be published in: Proc. Combst. Inst. 35, (2015)
- B. Brumfield, W. Sun, Y. Ju, and G. Wysocki, "Dual Modulation Faraday Rotation Spectroscopy of HO2 from an Atmospheric Flow Reactor",(2013): Pre-submission manuscript available at: arXiv:1310.2766
- B. Brumfield, W. Sun, Y. Ju, and G. Wysocki, "Faraday Rotation Spectroscopy of Radicals Relevant to Combustion," presented at the Optical Instrumentation for Energy and the Environmental Applications, Eindhoven, Netherlands, 2012, EM4C.5
- B. Brumfield, W. Sun, G. Wysocki, and Y. Ju, "Quantification of HO2 from an Atmospheric Flow Reactor Using Faraday Rotation Spectroscopy," in 8th U.S. National Combustion Meeting (Park City, UT, 2013)
- B. Brumfield, W. Sun, G. Wysocki, and Y. Ju, "Faraday Rotation Spectroscopy of HO2 from an Atmospheric Flow Reactor," presented at the Sixty-Eighth International Symposium on Molecular Spectroscopy, The Ohio State University, Columbus, OH 2013
- B. Brumfield, W. Sun, G. Wysocki, and Y. Ju, "Application of Faraday Rotation Spectroscopy for Quantifying HO2 Radicals in Combustion Processes," presented at the CLEO: 2013, San Jose, California 2013
- B. Brumfield, W. Sun, Y. Ju, and G. Wysocki, "Dual Modulation Faraday Rotation Spectroscopy of HO for Combustion Diagnostics," presented at the Optical Instrumentation for Energy and Environmental Applications, Tucson, Arizona 2013
New funding obtained as a result of scientific accomplishments from Grand Challenges support:
- Andlinger Innovation Project Fund Award, Funding Period 03/2013-06/2014,
Project Title: New multi-species diagnostics and elementary rate constant measurements in biofuel combustion
The PIs look forward to continuing their interdisciplinary collaborative work on further development of the FRS diagnostics for HO2 and ON radicals as well as NOx. Moving forward, sensitive mid-IR absorption diagnostics for important non-radical species in low-temperature oxidation of biofuels (i.e. H2O2 and CH2O) will be pursued. They are currently developing a new flow reactor that will enable fundamental kinetic studies of chemical reactions that are important in combustion and atmospheric chemistry and involve OH and HO2 radicals. The successful outcomes of this research project provided the necessary instrumentation and diagnostics to pursue external funding for future projects through the following programs:
- The Combustion, Flame, and Plasma Systems program of the National Science Foundation
- The Petroleum Research Fund of the American Chemical Society