Hai Wang

Hai Wang
Stanford University | SU · Department of Mechanical Engineering

Ph.D.

About

256
Publications
39,109
Reads
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16,970
Citations
Citations since 2017
54 Research Items
7654 Citations
201720182019202020212022202302004006008001,0001,2001,400
201720182019202020212022202302004006008001,0001,2001,400
201720182019202020212022202302004006008001,0001,2001,400
201720182019202020212022202302004006008001,0001,2001,400

Publications

Publications (256)
Article
Three-dimensional (3D) detonation simulations solving the compressible Navier-Stokes equations with detailed chemistry are performed in both square channel and round tube geometries. The simulations are compared with each other and with two-dimensional (2D) channel simulations and round tube experiments of identical mixture and conditions (stoichio...
Article
The dependence of detonation cell regularity on mixture gasdynamic and chemical kinetic properties are investigated through hydrogen-oxygen detonations with different diluent and ozone addition. A total of seven mixtures are specifically designed such that the post-shock specific heat ratio γVN, representing the gasdynamic effect, and the effective...
Article
Flame-formed carbon nanoparticles exhibit apparent size-dependent optical and electronic band gaps, consistent with the quantum confinement effect found in semiconductor materials. Understanding the effect of chemical composition on the band gap variations in carbon nanoparticles requires the investigation of the HOMO-LUMO gap of large aromatics. G...
Article
Detonation properties of methane and natural gas were studied using ZND simulations and detonation limit experiments. The experiments were performed in two tube sizes, 32 mm and 6.4 mm in inner diameter over a range of initial pressures (between 3.4 kPa and 35 kPa) and with stoichiometric fuel-oxygen compositions. The fuels considered are high puri...
Preprint
Full-text available
Soot nucleation is one of the most complex and debated steps of the soot formation process in combustion. In this work, we used scanning tunneling microscopy (STM) and spectroscopy (STS) to probe morphological and electronic properties of incipient soot particles formed right behind the flame front of a lightly sooting laminar premixed flame of eth...
Article
Significance Beyond lithium-ion technologies, sodium-sulfur batteries stand out because of their multielectron redox reactions and high theoretical specific energy (1,274 Wh per kg of sulfur). They hold the potential of overcoming the capacity limitation of intercalation-based chemistry (<400 Wh kg ⁻¹ ). Major challenges in realizing this potential...
Conference Paper
The deflagration-to-detonation transition (DDT) process inside reactant-product mixing layers is studied using one-dimensional transient simulations of stoichiometric hydrogen-air mixtures. Such processes are seen to be responsible for the multi-front detonation propagation in rotating detonation engines (RDEs). For a given mixture, two modes of co...
Conference Paper
A diverse computational toolset is needed to understand and design devices which use detonation. State-of-the-art detonation simulations are highly resolved and are thus expensive and challenging to setup. We developed a model, detgem, which leverages the underlying physics of cellular structure to predict detonation propagation at a cost many orde...
Article
Flow reactors are commonly employed in investigations of the pyrolysis and oxidation chemistry of fuels. Typical flow reactors use either electrical heaters or vitiation heaters to provide the energy to preheat the reactants to the desired experimental conditions. The present study seeks to determine the impact of vitiation on flow reactor studies...
Article
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...
Article
Electronic and optical properties of flame-generated carbon nanoparticles were modeled based on quantum confinement and amorphous semiconductor theory of monodispersed particles. The ionization energies and optical band gaps of polydispersed particles 4–23 nm in volume median diameter (Liu et al., Proc. Natl. Acad. Sci. U.S.A. 116 (2019) 12692–1269...
Article
A geometric model with a low computational complexity capable of simulating detonation behavior in physical systems is proposed. In support of the geometric model development, a series of cylindrical 1D simulations with a variable size initiation kernel are performed in hydrogen-oxygen mixtures. From these 1D simulations a detonation cell stabiliza...
Article
The electronic band gap of flame-formed carbon nanoparticles (CNPs) is determined for the first time using scanning tunneling spectroscopy (STS). CNPs are sampled from a laminar, burner-stabilized stagnation ethylene-air flame through in-situ insertion of gold-coated mica substrates, on which CNPs are collected as thin films. Optical band gap measu...
Article
Ozone as an ignition promoter was used to study the detonation limit behavior in small, round tubes. Experimentally, detonation cellular structures and velocity deficits of fuel-oxygen mixtures with and without 3000 PPM of ozone were measured in tubes of 32 and 6 mm in inner diameter. Both hydrogen-oxygen and methane-oxygen mixtures were tested. Th...
Article
Real transportation fuels are complex mixtures of a variety of hydrocarbon components. Predicting NOx formation in practical combustors burning real fuels is usually made with the assumption that the NOx submodels developed and tested for small hydrocarbon combustion are applicable to mixtures of large hydrocarbons as found in real fuels. Additiona...
Article
A systematic computational study is conducted to understand the propagation of uncertain chemical kinetic parameters into turbulent premixed flame simulations. Two snapshots of the cross-section of a spherical flame kernel in homogeneous isotropic turbulence is extracted from a three dimensional direct numerical simulation (DNS) and serve as the in...
Article
Significance Flame-formed carbon nanoparticles are observed to exhibit quantum confinement behaviors. We demonstrate that the size dependence of photoemission ionization energy in air and optical band gap of flame-generated carbon particles can be well explained by available quantum confinement theory. Carbon nanoparticles comprising mainly polycyc...
Article
Momentum accommodation is a key factor governing the transport of particles in gases from electric mobility and Brownian diffusion to thermophoresis. This paper explores the relationship between momentum accommodation of nanoparticles in dilute gases and surface adsorption. We demonstrate that the momentum accommodation factor is fundamentally equa...
Conference Paper
An experimental study of detonation limit behavior and velocity deficit was performed for hydrogen detonations using ozone as an ignition promoter. Ozone, even in low concentrations, is known to significantly reduce ignition delay and detonation cell size. The purpose of the present study is to examine the relation between detonation cell structure...
Conference Paper
To study the effect of boundary conditions on detonation simulations, a physics-based multi-dimensional geometric model was developed to simulate and predict detonation cellular structure. The model is based on the point-blast theory, experimental measurements of apparent cell structure, and the measured detonation propagation velocity distribution...
Conference Paper
Full-text available
Polycyclic Aromatic Hydrocarbons (PAHs) are precursors to soot formation. The mass and thermal diffusion of gaseous PAHs can play an important role in their formation in flames. To date, the binary diffusion coefficients of gases are most commonly evaluated using the Chapman-Enskog (CE) theory with spherical Lennard-Jones potential parameters estim...
Article
The effect of ignition promoters on H2O2 detonation structure was evaluated with one-dimensional ZND calculations and experimental detonation cell measurements. Test conditions include a sweep of ozone concentration (up to 3000 PPM by mole), initial pressure (10 to 30 kPa), equivalence ratio (0.4–1.5), Ar and N2 dilution (up to 50%), and CF3I conce...
Article
Full-text available
High-resolution Transmission Electron Microscopy (HRTEM) imaging of nascent soot was carried out with an emphasis in demonstrating the annealing of soot samples under continuous irradiation of the high-energy electron beam. Images were taken for several soot samples over the duration of 16 min in 2 min time intervals to reveal the crystallization p...
Article
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...
Article
The method of uncertainty minimization by polynomial chaos expansions is extended to Arrhenius prefactor and activation energy co-optimization and uncertainty minimization. A covariance matrix is formulated to describe the joint probability distribution of the reaction rate parameters. The method is tested on a recently proposed foundational fuel c...
Article
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...
Article
Real jet fuels are complex mixtures of many organic components, some of which are aromatic compounds. Towards the high-temperature end of the distillation curve, some of the fuel components are multi-ring compounds. A small amount of these high molecular weight species in the fuel could impact soot nucleation in practical engines especially when th...
Article
The molecular structures of hydrocarbon fuels are known to have a substantial impact on their combustion properties. However, the relationship between the fuel structure and thermal decomposition intermediate products, which determine the global combustion behaviors, is not as well known. In this study, four octane isomers, n-octane, 2,5-dimethylhe...
Article
A typical Jet A fuel was pyrolyzed in a high-pressure shock tube at 25 and 90 atm under highly diluted conditions from 900 to 2200 K. The key species produced from the pyrolysis process were measured by gas chromatography as a function of the shock temperature. It was found that despite the compositional complexity of the fuel, the major pyrolysis...
Article
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...
Article
Real distillate fuels usually contain thousands of hydrocarbon components. Over a wide range of combustion conditions, large hydrocarbon molecules undergo thermal decomposition to form a small set of low molecular weight fragments. In the case of conventional petroleum-derived fuels, the composition variation of the decomposition products is washed...
Article
Full-text available
Large Eddy Simulation (LES) is progressively becoming a crucial design tool for the next generation of aeronautical combustion chambers. However, further improvements of the predictive capability of LES is required especially for predictions of pollutant formation. In general, the exact description of real fuel combustion requires to take into acco...
Article
In view of the critical role of the underlying uncertainties of the reaction model in future progress of combustion chemistry modeling, Foundational Fuel Chemistry Model 1.0 (FFCM-1) was developed with uncertainty minimization against available fundamental combustion data of H2, H2/CO, CH4, CH2O, and C2H6. As a critical feature, FFCM-1 not only rec...
Article
The Cover Feature depicts the role of oxygen desorption in the phase preference of titanium oxide (TiO2) nanoparticles synthesized in a flat flame. The rutile–anatase phase equilibrium is impacted by surface oxygen coverage. A more generalized thermodynamic approach is proposed to account for the effect of O2 desorption on surface energy and crysta...
Article
Full-text available
Nano-scale titanium oxide (TiO2) is a material useful for a wide range of applications. In a previous study, we showed that TiO2 nanoparticles of both rutile and anatase crystal phases could be synthesized over the size range of 5 to 20 nm in flame-assisted chemical vapor deposition. While rutile was unexpectedly dominant in oxygen-lean synthesis c...
Article
Full-text available
Twenty reaction models published in five consecutive issues of Combustion and Flame in 2015 and 2016 were screened for the occurrence of collision limit violations. It was found that among the 20 models tested, 15 of them contain either considerable numbers of rate coefficients that exceed their respective collision limits or reactions exceeding th...
Conference Paper
Full-text available
In the present study, reduced kinetic models, including fuel-specific reduced models and a universal reduced foundational fuel chemistry model for jet fuel combustion, are developed based on the recently developed HyChem models. The HyChem approach takes advantage of the de-coupling between fuel pyrolysis and oxidation of the pyrolysis products tha...
Conference Paper
Transportation fuels consist of a large number of hydrocarbon components and combust through an even larger number of intermediates. Detailed chemical kinetic models of these fuels typically consist of hundreds of species, and are computationally expensive to include directly in 3D CFD simulations. HyChem (Hybrid Chemistry) is a recently proposed m...
Conference Paper
Full-text available
Real jet fuels are complex mixtures of many organic components, some of which are aromatic compounds. Towards the high-temperature end of the distillation curve, some of the aromatics may contain multiple rings. A trace amount of these high molecular weight species in the fuel would directly allow for soot nucleation in practical engines especially...
Conference Paper
Full-text available
Real fuels may contain thousands of hydrocarbon components. This paper examines how nature simplifies the problem. We will discuss the internal structure of the fuel oxidation process at high temperatures. Over a wide range of conditions, large hydrocarbon molecules undergo thermal decomposition to form a small set of low-molecular weight fragments...
Conference Paper
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...
Conference Paper
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...
Conference Paper
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...
Conference Paper
The recently released Foundational Fuel Chemistry Model version 1 (Smith et. al., 2016) aims to access and minimize the uncertainties underlying the current state of kinetic knowledge and advance a reaction model for the combustion of hydrogen, carbon monoxide and small hydrocarbons with well-defined uncertainties. FFCM-1 comprises 291 elementary r...
Article
Full-text available
Towards the implementation of alternative jet fuels in aviation gas turbines, testing in combustor rigs and engines is required to evaluate the fuel performance on combustion stability, relight, and lean blow-out (LBO) characteristics. The objective of this work is to evaluate the effect of different fuel candidates on the operability of gas turbin...
Technical Report
Full-text available
Large Eddy Simulation (LES) of an aeronautical burner is performed with two combustion models and a reduced chemical scheme able to accurately describe the combustion of a real multi-component kerosene aviation fuel. The accuracy of the reduced scheme is first assessed on laminar flame cases through comparison with detailed chemistry mechanism. Sub...
Article
Full-text available
The cation-π interactions in complexes that could be formed from the association of flame-generated chemi-ions with neutral aromatic molecules, including benzene, naphthalene, phenanthrene and pyrene, were examined by electronic structure calculations using the MP2 and B3LYP methods with the 6-311++G(d,p) basis set. Single-point CCSD(T) calculation...
Article
Laminar flame speed measurements were carried for mixture of air with eight C 3-4 hydrocarbons (propene, propane, 1,3-butadiene, 1-butene, 2-butene, iso-butene, n-butane, and iso-butane) at the room temperature and ambient pressure. Along with C 1-2 hydrocarbon data reported in a recent study, the entire dataset was used to demonstrate how laminar...
Article
Full-text available
Analytical expressions are derived for aerodynamic drag force on small cylinders in the free molecule flow using the gas-kinetic theory. The derivation considers the effect of intermolecular interactions between the cylinder and gas media. Two limiting collision models, specular and diffuse scattering, are investigated in two limiting cylinder orie...
Article
Full-text available
Evolution of particle size distribution function (PSDF) was studied in premixed stretch-stabilized flat flames for the first time. The purpose is to demonstrate that stretch-stabilized flames can broaden the experimental flame condition space for studying soot formation in a pseudo-one dimensional flow configuration. PSDFs were measured in three se...
Article
Full-text available
The current study aims to resolve the experimental and modeling discrepancies previously observed for the extinction strain rates of counterflow, non-premixed n-decane and n-dodecane/nitrogen mixture versus oxygen. To achieve this goal, a recently developed transport theory of cylindrical molecular structure in dilute gases is used to model the bin...
Article
Full-text available
The evolution of mobility particle size distribution function (PSDF) for premixed propene flame soot was investigated in the burner stabilized stagnation (BSS) flame configuration. The measurements were car- ried out for two series of flames with the equivalence ratio equal to 1.8 and 2.07, as a function of the burner-to-stagnation surface separati...
Article
Probe sampling of soot particles in laminar premixed flames is a common method for characterizing nascent soot formation. Probe intrusiveness into the flame can introduce significant uncertainty in interpretation of experimental data and comparison with numerical results. The aim of the present work is to study the probe-induced effects on soot sam...
Article
Full-text available
The current study investigates n -dodecane ( n -C 12 H 26 ) pyrolysis and oxidation kinetics in the temperature regime of 10 0 0–130 0 K in the Stanford Variable Pressure Flow Reactor facility. The reactor environment is vitiated and the experiments were conducted at atmospheric pressure. Species time history data were col- lected for n -dodecane a...
Article
Full-text available
The evolution of the nascent soot particle size distribution function (PSDF) was determined by mobility sizing for two series of atmospheric pressure premixed ethylene flames in the burner stabilized stagnation flame configuration. The first series of flames has an equivalence ratio of 1.8, corresponding to conditions just above the sooting limit....
Article
Full-text available
Oxidation kinetics of soot is typically measured with well aged soot as substrates. Recent studies show that nascent soot can have structures and surface composition drastically different from mature, graphitized soot. In the present study, the kinetics of nascent soot oxidation by molecular oxygen was observed at temperatures of 950, 1000 and 1050...
Article
A systematic approach to developing compact reduced reaction models is proposed for liquid hydrocarbon fuels using n-dodecane and n-butane as the model fuels. The approach has three elements. Fast fuel cracking reactions are treated by the quasi-steady state approximation (QSSA) and lumped into semi-global reactions to yield key cracking products t...
Article
The burner stabilized stagnation flame technique coupled with micro-orifice probe sampling and mobility sizing has evolved into a useful tool for examining the evolution of the particle size distribution of nascent soot in laminar premixed flames. Several key aspects of this technique are examined through a multi-university collaborative study that...
Article
The current study investigates n-dodecane (n-C12H26) pyrolysis and oxidation kinetics in the temperature regime of 1000-1300 K in the Stanford Variable Pressure Flow Reactor facility. The reactor environment is vitiated and the experiments were conducted at atmospheric pressure. Species time history data were collected for n-dodecane and oxygen, as...
Article
Full-text available
It has previously been demonstrated that organopalladium precursors can break down under combustion conditions, forming nanoparticles that catalyze ignition. Here, we use in situ small-angle X-ray scattering (SAXS) to probe the formation and growth of palladium nanoparticles in an ethylene flame doped with 28 ppm (mol) of Pd(acetate)2. The particle...
Article
Full-text available
A detailed population balance model is used to perform a parametric sensitivity study on the computed particle size distributions (PSDs) for a laminar premixed ethylene burner-stabilised stagnation flame. The soot morphology in the post-flame region is studied using computed sintering level distributions, fringe length analysis of the polycyclic ar...
Article
A detailed model of soot formation is proposed, which consists of a gas-phase kinetic model for the pyrolysis and oxidation of selected hydrocarbon fuels and a kinetic mechanism of soot nucleation and mass/size growth through coagulation and surface reactions. The gas-phase model (Ranzi et al., 2012) was expanded to include the chemistry of Polycyc...
Conference Paper
Full-text available
The oxidation state and particle size are key properties that impact the electrochemical pseudocapacitance of manganese oxide nanoparticles. In this work, ultrafine manganese oxide nanoparticles were synthesized by the technique of flame stabilized on a rotating surface. Methylcyclopentadienyl manganese tricarbonyl (MMT) precursor was oxidized in a...
Conference Paper
An accurate and reliable foundational fuel chemistry model is critical to our ability to make quantitative predictions for combustion of all hydrocarbon fuels. The current work is a part of our effort centered on the development of a foundational fuel chemistry model with well-defined and minimized uncertainties. This paper discusses the model of H...
Article
Chemical dynamics simulations were performed to study the unimolecular dissociation of randomly excited Na +(Bz) and Na +(Bz)2 clusters; Bz = benzene. The simulations were performed at constant energy, and temperatures in the range of 1200–2200 K relevant to combustion, using an analytic potential energy surface (PES) derived in part from MP2/6-311...
Article
This article examines a seemingly trivial issue, namely, the apparently large scatter found for the laminar flame speeds of fuel-rich mixtures as compared to those of lean mixtures. Using the hydrogen/air flame speed at atmospheric pressure as an example, it is demonstrated that this perceptive notion is based on rather uninformed data presentation...
Article
A detailed model of soot formation is proposed, which consists of a gas-phase kinetic model for the pyrolysis and oxidation of selected hydrocarbon fuels and a kinetic mechanism of soot nucleation and mass/size growth through coagulation and surface reactions. The gas-phase model (Ranzi et al., 2012) was expanded to include the chemistry of Polycyc...
Article
The current interest in the combustion chemistry of hydrocarbon fuels, including the various alcohol and biodiesel compounds, motivates this review of the methods and applic