Doctor of Philosophy, Stanford University, EE-PMN (2017)
Doctor of Philosophy, Stanford University, ME-PHD (2017)
Master of Science, Stanford University, ME-MS (2012)
Bachelor of Science, Peking University, Theoretical& Applied Mechanics (2010)
Kinetics of Excited Oxygen Formation in Shock-Heated O2-Ar Mixtures.
journal of physical chemistry. A
The formation of electronically excited atomic oxygen was studied behind reflected shock waves using cavity-enhanced absorption spectroscopy. Mixtures of 1% O2-Ar were shock-heated to 5400-7500 K, and two distributed-feedback diode lasers near 777.2 and 844.6 nm were used to measure time-resolved populations of atomic oxygen's (5)S° and (3)S° electronic states, respectively. Measurements were compared with simulated population time histories obtained using two different kinetic models that accounted for thermal nonequilibrium effects: (1) a multitemperature model and (2) a reduced collisional-radiative model. The former assumed a Boltzmann distribution of electronic energy, whereas the latter allowed for non-Boltzmann populations by treating the probed electronic states as pseudospecies and accounting for dominant electronic excitation/de-excitation processes. The effects of heavy-particle collisions were investigated and found to play a major role in the kinetics of O atom electronic excitation at the conditions studied. For the first time, rate constants (kM) for O atom electronic excitation from the ground state ((3)P) due to collisions with argon atoms were directly inferred using the reduced collisional-radiative model, kM((3)P → (5)S°) = 7.8 × 10(-17)T(0.5) exp(-1.061 × 10(5)K/T) ± 25% cm(3) s(-1) and kM((3)P → (3)S°) = 2.5 × 10(-17)T(0.5) exp(-1.105 × 10(5)K/T) ± 25% cm(3) s(-1).
View details for PubMedID 27689820
Shock Tube Measurement for the Dissociation Rate Constant of Acetaldehyde Using Sensitive CO Diagnostics.
journal of physical chemistry. A
2016; 120 (35): 6895-6901
The rate constant of acetaldehyde thermal dissociation, CH3CHO = CH3 + HCO, was measured behind reflected shock waves at temperatures of 1273-1618 K and pressures near 1.6 and 0.34 atm. The current measurement utilized sensitive CO diagnostics to track the dissociation of CH3CHO via oxygen atom balance and inferred the title rate constant (k1) from CO time histories obtained in pyrolysis experiments of 1000 and 50 ppm of CH3CHO/Ar mixtures. By using dilute test mixtures, the current study successfully suppressed the interferences from secondary reactions and directly determined the title rate constant as k1(1.6 atm) = 1.1 × 10(14) exp(-36 700 K/T) s(-1) over 1273-1618 K and k1(0.34 atm) = 5.5 × 10(12) exp(-32 900 K/T) s(-1) over 1377-1571 K, with 2σ uncertainties of approximately ±30% for both expressions. Example simulations of existing reaction mechanisms updated with the current values of k1 demonstrated substantial improvements with regards to the acetaldehyde pyrolysis chemistry.
View details for DOI 10.1021/acs.jpca.6b03647
View details for PubMedID 27523494
Improved Shock Tube Measurement of the CH4 + Ar = CH3 + H + Ar Rate Constant using UV Cavity-Enhanced Absorption Spectroscopy of CH3.
journal of physical chemistry. A
2016; 120 (28): 5427-5434
We report an improved measurement for the rate constant of methane dissociation in argon (CH4 + Ar = CH3 + H + Ar) behind reflected shock waves. The experiment was conducted using a sub-parts per million sensitivity CH3 diagnostic recently developed in our laboratory based on ultraviolet cavity-enhanced absorption spectroscopy. The high sensitivity of this diagnostic allowed for measurements of quantitatively resolved CH3 time histories during the initial stage of CH4 pyrolysis, where the reaction system is clean and free from influences of secondary reactions and temperature change. This high sensitivity also allowed extension of our measurement range to much lower temperatures (<1500 K). The current-reflected shock measurements were performed at temperatures between 1487 and 1866 K and pressures near 1.7 atm, resulting in the following Arrhenius rate constant expression for the title reaction: k(1.7 atm) = 3.7 × 10(16) exp(-42 200 K/T) cm(3)/mol·s, with a 2σ uncertainty factor of 1.25. The current data are in good consensus with various theoretical and review studies, but at the low temperature end they suggest a slightly higher (up to 35%) rate constant compared to these previous results. A re-evaluation of previous and current experimental data in the falloff region was also performed, yielding updated expressions for both the low-pressure limit and the high-pressure limit rate constants and improved agreement with all existing data.
View details for DOI 10.1021/acs.jpca.6b02572
View details for PubMedID 27380878
- Cavity-enhanced absorption spectroscopy with a ps-pulsed UV laser for sensitive, high-speed measurements in a shock tube OPTICS EXPRESS 2016; 24 (1): 308-318
Shock-tube measurements of excited oxygen atoms using cavity-enhanced absorption spectroscopy
2015; 54 (29): 8766-8775
We report the use of cavity-enhanced absorption spectroscopy (CEAS) using two distributed feedback diode lasers near 777.2 and 844.6 nm for sensitive, time-resolved, in situ measurements of excited-state populations of atomic oxygen in a shock tube. Here, a 1% O2/Ar mixture was shock-heated to 5400-8000 K behind reflected shock waves. The combined use of a low-finesse cavity, fast wavelength scanning of the lasers, and an off-axis alignment enabled measurements with 10 μs time response and low cavity noise. The CEAS absorption gain factors of 104 and 142 for the P35←S520 (777.2 nm) and P0,1,23←S310 (844.6 nm) atomic oxygen transitions, respectively, significantly improved the detection sensitivity over conventional single-pass measurements. This work demonstrates the potential of using CEAS to improve shock-tube studies of nonequilibrium electronic-excitation processes at high temperatures.
View details for DOI 10.1364/AO.54.008766
View details for Web of Science ID 000362667200028
View details for PubMedID 26479817
- Shock Tube Measurement of the High-Temperature Rate Constant for OH + CH3 -> Products JOURNAL OF PHYSICAL CHEMISTRY A 2015; 119 (33): 8799-8805
Shock-Tube Measurement of Acetone Dissociation Using Cavity-Enhanced Absorption Spectroscopy of CO
JOURNAL OF PHYSICAL CHEMISTRY A
2015; 119 (28): 7257-7262
A direct measurement for the rate constant of the acetone dissociation reaction (CH3COCH3 = CH3CO + CH3) was conducted behind reflected shock wave, utilizing a sub-ppm sensitivity CO diagnostic achieved by cavity-enhanced absorption spectroscopy (CEAS). The current experiment eliminated the influence from secondary reactions and temperature change by investigating the clean pyrolysis of <20 ppm acetone in argon. For the first time, the acetone dissociation rate constant (k1) was directly measured over 5.5 orders of magnitude with a high degree of accuracy: k1 (1004-1494 K, 1.6 atm) = 4.39 × 10(55) T(-11.394) exp(-52 140K/T) ± 24% s(-1). This result was seen to agree with most previous studies and has bridged the gap between their temperature and pressure conditions. The current work also served as an example demonstration of the potential of using the CEAS technique in shock-tube kinetics studies.
View details for DOI 10.1021/jp511642a
View details for Web of Science ID 000358337600019
- High-sensitivity interference-free diagnostic for measurement of methane in shock tubes JOURNAL OF QUANTITATIVE SPECTROSCOPY & RADIATIVE TRANSFER 2015; 156: 80-87
- High temperature measurements for the rate constants of C-1-C-4 aldehydes with OH in a shock tube PROCEEDINGS OF THE COMBUSTION INSTITUTE 2015; 35: 473-480
- Constrained reaction volume shock tube study of n-heptane oxidation: Ignition delay times and time-histories of multiple species and temperature PROCEEDINGS OF THE COMBUSTION INSTITUTE 2015; 35: 231-239
- Reaction Rate Constant of CH2O + H = HCO + H-2 Revisited: A Combined Study of Direct Shock Tube Measurement and Transition State Theory Calculation JOURNAL OF PHYSICAL CHEMISTRY A 2014; 118 (44): 10201-10209
- Effects of size polydispersity on electron mobility in a two-dimensional quantum-dot superlattice PHYSICAL REVIEW B 2014; 90 (14)
- Time-resolved in situ detection of CO in a shock tube using cavity-enhanced absorption spectroscopy with a quantum-cascade laser near 4.6 mu m OPTICS EXPRESS 2014; 22 (20): 24559-24565
Sensitive and rapid laser diagnostic for shock tube kinetics studies using cavity-enhanced absorption spectroscopy
2014; 22 (8): 9291-9300
We report the first application of cavity-enhanced absorption spectroscopy (CEAS) using a coherent light source for sensitive and rapid gaseous species time-history measurements in a shock tube. Off-axis alignment and fast scanning of the laser wavelength were used to minimize coupling noise in a low-finesse cavity. An absorption gain factor of 83 with a measurement time resolution of 20 µs was demonstrated for C2H2 detection using a near-infrared transition near 1537 nm, corresponding to a noise-equivalent detection limit of 20 ppm at 296 K and 76 ppm at 906 K at 50 kHz. This substantial gain in signal, relative to conventional single-pass absorption, will enable ultra-sensitive species detection in shock tube kinetics studies, particularly useful for measurements of minor species and for studies of dilute reactive systems.
View details for DOI 10.1364/OE.22.009291
View details for Web of Science ID 000335902200046
View details for PubMedID 24787817
- High-temperature laser absorption diagnostics for CH2O and CH3CHO and their application to shock tube kinetic studies COMBUSTION AND FLAME 2013; 160 (10): 1930-1938
- Constrained reaction volume approach for studying chemical kinetics behind reflected shock waves COMBUSTION AND FLAME 2013; 160 (9): 1550-1558
- On the rate constants of OH + HO2 and HO2 + HO2: A comprehensive study of H2O2 thermal decomposition using multi-species laser absorption PROCEEDINGS OF THE COMBUSTION INSTITUTE 2013; 34: 565-571