
Jiankun ShaoStanford University | SU · Department of Mechanical Engineering
Jiankun Shao
PhD candidate
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43
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Introduction
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August 2012 - May 2014
Publications
Publications (43)
Real fuels contain hundreds of components. The impact of differences in the composition of a fuel are more strongly manifested during its oxidation in the low-temperature combustion (LTC) and the negative temperature coefficient (NTC) regimes. These differences make kinetic modeling of real fuel oxidation in these regimes especially challenging. In...
NOx formation from ammonia impurities and its effects on fuel oxidation is not well understood for high-pressure supercritical CO2 oxy-combustion conditions. This effect is investigated computationally and experimentally in the present work. A chemical kinetic analysis revealed that the reaction between NH radical and CO2 plays an important role in...
We address the role of the linear mixing rule in the kinetics of the H2O2 decomposition system by reporting the rate constant for H2O2 + M = 2OH + M (M = Ar and CO2) in the temperature range of 1087–1234 K at low pressures in a mixture of 20% CO2 in Argon. The reaction rate constant was inferred from H2O concentrations monitored by using a laser-ab...
The complexity of modeling the oxidation kinetics of conventional transportation and aviation fuels stems from the immense number of unique components that constitute them. Unsurprisingly, these components give rise to a multitude of possible chemical pathways. Identifying and modeling each of these pathways accurately is a challenge that has attra...
The large theoretical thermal efficiency offered by supercritical CO2 (sCO2) based power cycles has attracted a multitude of research efforts in the recent years [1–3]. However, one of the major obstacles towards realizing sCO2 cycles is the lack of knowledge in oxy-fuel combustion under supercritical pressures. Similarly, the influence of sulphur...
Quantum-cascade-laser dual-comb spectroscopy (QCL-DCS) is a promising technology with ultra-fast time resolution capabilities for chemical kinetics, atmospheric gas sensing, and combustion applications. A pair of quantum-cascade frequency combs were used to measure absorbance from methane's ${\nu _4}$ band between 1270 and 1315 cm−1 at high-tempera...
Evidence of line mixing has been observed in the infrared spectra of many gaseous species at high densities or in the low absorbing windows between optical transitions. However, up to this point, no study exists of nitric oxide line mixing at pressures above atmosphere or temperatures several hundred degrees above room temperature. In this paper, t...
Time-histories of the concentration of major products of ethanol pyrolysis at 1 atm and 10 atm in the temperature range of 1200–1600 K were measured behind reflected shock waves using fixed-wavelength laser absorption spectroscopy. Measurement of absorbance at nine wavelengths enabled the determination of the evolution of CH4, C2H4, C2H5OH, CO, CH2...
The rate constants of two unimolecular decomposition channels of ethanol, C2H5OH(+Ar) = CH3 + CH2OH(+Ar), and C2H5OH(+Ar) = C2H4 + H2O(+Ar) were measured near 1 atm and 10 atm behind reflected shock waves between 1190 and 1550 K by tracking the evolution of CO and C2H4, respectively. Use of sensitive laser diagnostics in conjunction with carefully...
A high-pressure shock tube was used to study ignition delay times (IDT) of CH4/O2/Ar and natural gas/O2/Ar mixtures behind reflected shock waves. Reaction progress was monitored using sidewall pressure and direct laser absorption diagnostics of CH4 near 3.175 µm and ethylene near 10.532 µm. Stoichiometric, fuel-rich and fuel-lean mixtures of CH4/O2...
The HyChem (hybrid chemistry) approach is utilized for modeling the combustion behaviors of gasoline fuels. The approach combines an experimentally constrained, lumped-step model for fuel pyrolysis under the high-temperature combustion condition and a detailed foundation fuel chemistry model to describe the subsequent oxidation of the pyrolysis pro...
We report the first shock tube measurements of formaldehyde (CH 2 O) during the first stage ignition of n-heptane, 2-methylhexane and 3,3-dimethylpentane, in highly diluted fuel/oxygen mixtures in the pressure range of 7-10 atm and temperature range of 700-880 K. Combined time histories of all carbonyl (-C = O) species, CO and fuel were also measur...
Homogeneous and inhomogeneous ignition modes of n-heptane were studied using high-speed imaging in a high-pressure shock tube (HPST). n-Heptane, a fuel with strong negative temperature coefficient (NTC) behavior, was mixed with 4%-21% oxygen in argon or nitrogen and ignited over a wide temperature range (700–1250 K) and at elevated pressures (> 10...
Ethane pyrolysis chemistry plays a critical role in the combustion behavior of natural gas and gives insight into the decomposition patterns of larger alkanes. In this work, ethane pyrolysis was studied behind reflected shock waves with a convex optimization-based laser absorption speciation technique. Species time-histories of ethane, ethylene, me...
The development and demonstration of a high-bandwidth two-color temperature sensor for high-pressure environments using intensity-modulation spectroscopy (IMS) is presented. The sensor utilized rapid intensity modulation, beam coalignment, and frequency multiplexing to deal with common challenges for laser absorption spectroscopy systems at high pr...
The rate constant for the reaction CH3+C2H6→CH4+C2H5 was studied behind reflected shock waves at temperatures between 1369 and 1626 K and pressures from 8.6 to 47.4 atm in mixtures of methane, ethane and argon. Ethylene time-histories were measured using laser absorption of radiation from a carbon dioxide gas laser near 10.532 microns. The resultin...
Ignition delay times (IDT) of n-heptane, iso-octane, n-dodecane, and iso-octane/n-dodecane blends, in stoichiometric mixtures with air, were measured behind reflected shock waves in a heated, high-pressure shock tube. Measurements were taken at temperatures of 665–1250 K, pressures of 28–70 atm, and equivalence ratios near unity. Pressure time-hist...
The reaction rate of H + O2+M = HO2+M in the low-pressure limit was determined in the temperature range of 1450– 2000 K, with Argon, Nitrogen, and Carbon Dioxide as the third-body collision partners, by measuring the OH time-history after the induction time during lean oxidation of Hydrogen. Test conditions were optimized to suppress the sensitivit...
Pyrolysis of ethanol was studied behind reflected shock waves at 10 atm in the Stanford High-Pressure Shock Tube (HPST) facility, in the temperature range of 1200 K-1600 K. Laser absorption spectroscopy was used to measure the time history of CO, C2H4, and C2H5OH during these experiments. Significant disagreements were found between these measureme...
In engine applications, small concentrations of very reactive chemical species such as nitric oxide (NO) can have a very important impact on the onset of combustion. The small amount of NO can come from various sources including EGR, residual gas, and vitiated oxidizer streams. Combustion of distillate fuels and their surrogates with NO addition af...
As part of the effort to understand oxy-fuel combustion with large CO2 dilution, we have measured shock tube ignition delay times for methane/O2/CO2 mixtures and hydrogen/O2/CO2 mixtures. Ignition delay times (IDT) were measured using sidewall pressure and OH* emission near 306 nm. IDT measurements were performed near 80 atm for 3.91% methane/9.92%...
We experimentally demonstrate the non-absorbing interference rejection capabilities of wavelength modulation spectroscopy (WMS) speciation in shock tube experiments by directly comparing WMS measurements against direct-absorption spectroscopy (DA) measurements. The improved capability is demonstrated by probing the P(20) transition of the CO fundam...
The rate constant for the reaction C2H4+H⇒C2H3+H2 was studied behind reflected shock waves at temperatures between 1619 and 1948 K and pressures near 10 atm in a mixture of C2H4, CH4, H2, and argon. C2H4 time-histories were measured using laser absorption of a CO2 gas laser near 10.53 microns. Experimental mixtures were designed to optimize sensiti...
The Hybrid Chemistry (HyChem) approach has been proposed previously for combustion chemistry modeling of real, liquid fuels of a distillate origin. In this work, the applicability of the HyChem approach is tested for single-component fuels using JP10 as the model fuel. The method remains the same: an experimentally constrained, lumped single-fuel m...
The development of compact HyChem hybrid models for jet fuels requires datasets of pyrolysis product yields to constrain the model and of kinetic targets to evaluate the model. To this end, we have measured selected species time-histories during fuel pyrolysis using laser absorption, and ignition delay times using multiple methods behind reflected...
Ignition delay times (IDT) of small hydrocarbons at elevated pressures provide a valuable constraint for the refinement of the core small-hydrocarbon sub-mechanisms used in all combustion kinetics. Current knowledge of these core mechanisms is based largely on low-pressure data, with only limited high-pressure data available. To remedy this, the pr...
Kun Wang Rui Xu Tom Parise- [...]
Hai Wang
A Hybrid Chemistry (HyChem) approach has been recently developed for the modeling of real fuels; it incorporates a basic understanding about the combustion chemistry of multicomponent liquid fuels that overcomes some of the limitations of the conventional surrogate fuel approach. The present work extends this approach to modeling the combustion beh...
The need for more efficient power cycles has attracted interest in super-critical CO2 (sCO2) cycles. However, the effects of high CO2 dilution on auto-ignition at extremely high pressures has not been studied in depth. As part of the effort to understand oxy-fuel combustion with massive CO2 dilution, we have measured shock tube ignition delay times...
Ignition delay times (IDT) for high-octane-number gasolines and gasoline surrogates were measured at very high pressures behind reflected shock waves. Fuels tested include gasoline, gasoline with oxygenates, and two surrogate fuels, one dominated by iso-octane and one by toluene. RON/MON for the fuels varied from 101/94 to 106.5/91.5. Measurements...
The rate constants for the reaction H + O2 + M→HO2 + M were investigated at elevated pressures from 12 to 33 atm using ignition delay time (IDT) measurements behind reflected shock waves in H2/O2/M mixtures with different collision partners M = Ar, H2O, N2 and CO2. The temperature and pressure ranges where the rate constants of the reactions H + O2...
We propose and test an alternative approach to modeling high-temperature combustion chemistry of multicomponent real fuels. The hybrid chemistry (HyChem) approach decouples fuel pyrolysis from the oxidation of fuel pyrolysis products. The pyrolysis (or oxidative pyrolysis) process is modeled by seven lumped reaction steps in which the stoichiometri...
In this work we introduce an unconventional approach to modeling the high-temperature combustion chemistry of multicomponent real fuels. The hybrid chemistry (HyChem) approach decouples fuel pyrolysis from the oxidation of fuel decomposition intermediates. The thermal decomposition and oxidative thermal decomposition processes are modeled by seven...
The development of a compact HyChem reaction mechanisms for jet fuels requires datasets both for pyrolysis products yields to constrain the model and for kinetic targets to evaluate the model. To this end, we have measured selected species time-histories during fuel pyrolysis using laser absorption, and ignition delay times using multiple methods b...
With increasing use of alternative fuels, approaches that can efficiently model their combustion chemistry are essential to facilitate their utilization. The hybrid chemistry (HyChem) method incorporates a basic understanding about the combustion chemistry of multicomponent liquid fuels that overcomes some of the limitations of the surrogate fuel a...
The hybrid chemistry modeling approach, termed HyChem, was used to explore the combustion chemistry of blended petroleum and bio-derived jet fuels. The pyrolysis products of conventional petroleum derived-fuels, such as Jet A, are dominated by ethylene and propene, whereas in many bio-derived fuels, such as alcohol to jet (ATJ) fuels, the fuel comp...
Ignition delay times were measured behind reflected shock waves in a shock tube for a wide variety of distillate fuels over a range of temperatures, pressures and mixtures. The fuels studied include: jet fuels (JP-5, JP-8, and Jet A), rocket propellants (RP-2), diesel fuels (F-76 and DF-2) and gasoline. A simple correlation was found to describe th...
Knock is the main obstacle toward increasing the compression ratio and using lower octane number fuels. In this paper, a small two-valve aircraft spark ignition engine, Rotax-914, was used as an example to investigate different methods to suppress engine knock. It is generally known that if the octane number is increased and the combustion period i...
Knock in a Rotax-914 engine was modeled and investigated using an improved version of the KIVA-3V code with a G-equation combustion model, together with a reduced chemical kinetics model. The ERC-PRF mechanism with 47 species and 132 reactions [1] was adopted to model the end gas auto-ignition in front of the flame front. The model was validated by...