W.M. Yang

• Professor (Assistant) at National University of Singapore

This paper presents a numerical investigation of premixed methane/oxygen heterogeneous reaction characteristics in a micro-catalytic combustion chamber under various boundary and wall thermophysical conditions. A 3-D model was simulated using ANSYS Fluent and validated against experimental data, with a maximum difference of only 1.92% using a pure...

The in-depth study of the mutual coupling between the flame and the wall can significantly enhance the efficiency of actual combustion devices. A two-dimensional numerical model of the heat transfer characteristics of methane-air premixed jet flames with flat/hemispherical walls has been developed. An examination of the effects of wall shape on the...

Chemical kinetic mechanisms are crucial for modeling the combustion processes of solid propellants, but the specific impacts of these mechanism's parameters on combustion have not been fully assessed. This study conducted a comprehensive sensitivity analysis on kinetics, thermodynamics, and transport parameters affecting solid propellant mechanisms...

Ammonia is considered one of the most promising fuels, and mixing ammonia with hydrogen as fuel can achieve zero carbon emissions for engines. In this study, an experimental platform for an ammonia/hydrogen rotary engine was constructed, and successful ignition combustion was performed, demonstrating the possibility of the ammonia/hydrogen rotary e...

Numerical simulations of flows with dilute disperse phase play an important role in a wide range of industrial applications. The most commonly used technique for solving such problems is the Eulerian-Lagrangian approach, in which individual particles are tracked inside the domain. However, the use of sliding and moving mesh in complex engineering a...

Dimethyl carbonate (DMC), ethanol (EtOH), polyoxymethylene dimethyl ether 1 (PODE1) and polyoxymethylene dimethyl ether 4 (PODE4) were blended with Jet A1 into fuel blends with 5 % oxygen content to investigate the effect of the oxygenated fuels on the soot produced by a compression ignition engine. Particle size distribution (PSD) was measured usi...

A micro fluidized bed reactor was used to study the self-sustaining catalytic combustion of carbon monoxide (CO). The Cu1−xCexOy catalyst, as well as the pure CuO and CeO2, are used to investigate the contributing mechanism of different active sites including dispersed CuO and Cu—Ce solid solutions. The ignition temperature (Ti) of CO over these ca...

Polyoxymethylene Dimethyl Ether (PODEn) is a promising diesel additive that can reduce particulate matter (PM) emission effectively, yet the changes in chemical and physical characteristics of PM emissions due to the application of PODEn-diesel blended fuel remain largely unexplored. This laboratory study investigates the effects of PODE3–diesel bl...

In this study, we perform experiments on a common-rail diesel engine to investigate the effect of diesel/n-butanol blends on particulate matter (PM) emission under pilot-main injection strategy. Three different blends (diesel, D80B20, D50B50) are compared under two distinct loads (∼30 %, ∼60 %) and two injection pressures (40 MPa, 60 MPa). Under id...

Two C8 biofuels, n-octanol (OCT) and di-n-butylether (DnBE), have attracted much attention due to their potential to replace diesel. In this work, compression ignition (CI) engines fueled by OCT and DnBE were numerically compared in terms of combustion characteristics and emissions formation. The KIVA4-CHEMKIN code package was used to model the com...

The dual-fuel combustion mode has drawn much attention due to its high thermal efficiency and low emissions. In this study, to realize the dual-fuel combustion, n-butanol was selected as the port-injected fuel (PIF); whereas two C8-biofuels, i.e., n-octanol and di-n-butyl ether (DNBE), were used as the direct-injected fuels, respectively. A compara...

This paper investigates the pyrolysis of PODEn (n = 3, 4, 5) using ReaxFF molecular dynamics simulation. A large-scale model, which contains 2000 PODEn molecules, is simulated at 3000 K. The higher frequencies of the initial PODEn decomposition reaction at α or β C-O bond show that the α or β C-O bond in PODEn is not easy to break, which is approxi...

Micro combustion is challenged by small size, high area-volume ratio and heat loss ratio, affecting the flame stability and energy efficiency. Premixed H2/air combustion with C3H8 blending and porous media (PM) setting are experimentally and numerically investigated in two size burners. Results indicate that partially inserted PM and enlarged combu...

Ammonia (NH3) as a carbon-free fuel is gaining much attention in the shipping industry for its enormous potential of global decarbonization, which is expected to achieve large-scale applications in marine engines by dual-fuel (DF) combustion technology. As such, this study was conducted to explore the emission reduction potential of NH3/diesel DF c...

Handling of non-conformal interfaces communication is one of the challenges from which the parallelization of multi-zone unstructured grids technology suffers. Especially for dynamic mesh simulation, changing dynamic communication patterns induced by the grids relative motion requires data to be correctly transferred across discrete non-conformal i...

Combustion characteristics and thermal performance of premixed H2/C3H8/air in a micro planar combustor with block insert are experimentally and numerically tested. Effects of hydrogen blended fraction, equivalence ratio, flow rate and block width on the flame stability and heat transfer are discussed and analyzed. The results indicate that hydrogen...

Some ash deposits were sampled from a 11.2 MW moving grate boiler to study the mineral transformation, ash deposition and mineral texture evolution behavior, which were determined by different analytical methods. Rietveld refinement was applied to determine the mineralogy, refine the crystallographic structures of minerals, and characterize texture...

This research is aimed at studying the different effects and mechanisms of CO2 and N2 on inhibiting coal spontaneous combustion (CSC) and providing theoretical guidance for the prevention and control of CSC in the goaf. The variations of free radicals and functional groups and the generation of indicator gas CO during low-temperature oxidation of c...

The release and transformation of inorganic species during combustion will cause severe ash-related issues, often leading to serious operational problems. To better understand these issues, several ash deposit samples collected from a biomass-fired moving grate boiler were characterized by inductively coupled plasma atomic emission spectroscopy, X-...

A new and efficient sectional method is developed and presented in this work. This new method, namely hybrid sectional moment projection method, seeks to combine the techniques of moment projection method and sectional method in a flexible and accurate way. It adopts the concept of weighted particles from moment projection method to handle the part...

In order to improve the performance of the rotary engine, this paper has designed a new type of dual-pit rotary engine combustion chamber structure, and compares the combustion and emission characteristics with the rotary engine with a traditional combustion chamber. The existence of the dual-pit combustion chamber strengthens the overall vortex in...

Jet fuel has been recognized as a potential alternative for traditional diesel engines because of its ability to reduce particulate matter (PM) emissions while retaining engine power output. In this study, the particulate formation process has been studied in detail using diesel/Jet A-1 blends with evenly staggered ratios. The number concentration...

Polyoxymethylene Dimethyl Ether (PODE) is known as a promising additive in the traditional diesel engine because it can reduce particulate matter emission in the exhaust gas. The reduction of the particulate matter emission when PODE is used as fuel additives is often attributed to the absence of C-C bond and the high oxygen content of the PODE mol...

With high oxygen content and cetane number, PODE3 is a favorable renewable fuel for engines. PODE3/diesel/gasoline blends in a HCCI engine are numerically studied for the first time. The effects of fuel blend ratio and equivalence ratio (ER) on auto-ignition are investigated. A highly compact and robust chemical mechanism has been implemented. Cran...

Numerical investigation on the premixed H2/air combustion in a micro heat-recirculation combustor inserted with/without block is conducted. Effects of block setting, heat-recirculation, and flow rate on combustion characteristics and thermal performance are depicted and analyzed. The results demonstrate that the block enhances the flame stability a...

The premixed H2/air combustion with varied porosity of porous medium (PM) is experimentally and numerically studied. The influences of porosity and arrangement of PM as well as the effects of multi-PM-layers on combustion characteristics and energy conversion are comprehensively investigated. The results indicate that a small porosity of porous med...

A compact kinetic reaction mechanism for simulating the oxidation of the unsaturated furanic fuels including furan, 2-methylfuran (MF2) and 2,5-dimethylfuran (DMF) is proposed in this work. The mechanism is developed by integrating the major reaction pathways for the three furanic fuel components into a toluene reference fuel reaction mechanism. Th...

An innovative kinetic mechanism reduction method, Species’ Participation in Element Fluxes (SPEF), is developed in this study. It utilises species’ participation in element fluxes to evaluate the importance of the species during the combustion process. The SPEF method has two main benefits: (1) it targets at C, H and O elements instead of pre-selec...

This paper numerically investigated the coal ignition, burnout, char consumption, and NO x conversion behaviors under moderate and intensive low-oxygen dilution (MILD) combustion with the implementation of fuel-rich/lean technology in a semi-industrial scale furnace. For the ignition behavior, the results show that the fuel-rich/lean technology can...

Porous medium with a high heat capacity, conductivity and emissivity effectively enhances the heat transfer in the combustor chamber. In order to improve the thermal performance and efficiency of the micro-TPV (thermophotovoltaic) system, premixed hydrogen-air combustion in the combustor inserted with porous medium is numerically simulated and anal...

In order to reduce the blindness in developing a new skeletal mechanism, a chaos genetic algorithm (CGA) is proposed for optimizing the progress of reaction rates adjustment against traditional manual operator. By this way, an optimized mechanism has been generated from a skeletal mechanism including 112 species and 498 reactions, which was reduced...

PODE 3 reaction mechanism developments are still in the early stages with very limited research. In particular, reaction mechanisms to characterize PODE 3 combustion are neither sufficiently compact nor robust for 3D numerical simulations. Hence, the current work seeks to develop a compact yet reliable PODE 3 reaction mechanism, embedded with appro...

To analyze the secondary oxidation of the active structures of pulverized coal and reduce risks of coal spontaneous combustion, free radical theory and functional group analysis were combined to study the effects of particle size and oxidation temperature on the active structure of coal molecules. This process was based on electron paramagnetic res...

It is important to improve the combustion performance of the diesel Wankel engine for its further engineering applications. Therefore, the main objective of this study was to study the dual-fuel mixture formation and stratified combustion process in the novel natural gas blended diesel Wankel engine. Meanwhile, the effects of assisted-ignition timi...

Extensive research has been devoted to engineering analysis in the presence of parameter uncertainties. Meanwhile, parameter estimations with uncertainty quantifications facilitate the reduction of bias and physical unrealistic estimates on interpreting model predictions. In this study, the sooting propensity from wick-fed diffusion flames tested b...

The secondary oxidation of active groups was studied for crushed coals with various particle sizes. Then, free radicals of these crushed coals were comparatively analyzed after primary and secondary oxidation. The secondary oxidation of active structures on the coal surface was studied by combining the theories of free radicals and functional group...

In order to investigate the micro combustion characteristic, thermal performance, as well as boost the energy efficiency and extend its application, the effects of burner size and fuel properties on combustion and working performance are studied. The results indicate that 5% propane added to premixed H2/air combustion contributes to the flame reloc...

The purpose of the present paper is to investigate the hydrogen injection strategy on the combustion performance of a natural gas/hydrogen rotary engine. Considering that apex seal leakage (ASL) is an inevitable problem in the actual working process of a rotary engine, the action of ASL cannot be ignored for an in-depth study of its combustion perf...

Considering climate change and energy crisis, the high-carbon alcohol has become a popular substitute fuel for diesel engines. In this study, diesel (D100), n-octanol/diesel (D50O50), and n-butanol/diesel (D50B50) blends were tested in a single-cylinder CI engine to evaluate the effects of n-octanol and n-butanol on the engine combustion characteri...

The premixed H2/air combustion with various propane blended ratios in two size stepped combustors with porous medium is experimentally and numerically studied. In order to improve the energy efficiency and power output of the micro thermophotovoltaic (TPV) system with InGaAsSb PV cells, the effects of step length and porous medium length in the cha...

Polyoxymethylene dimethyl ether 3 (PODE3) is an up-and-coming renewable fuel. In this study, the effects of PODE3 addition and injection pressure on combustion performance in a diesel engine have been investigated for the first time, with an emphasis on PM emissions in terms of both volume and number concentrations to account for ultrafine particle...

Currently fouling is still a major issue for the woodchip-fired boilers, which limits the utilization of the woody type fuel. In this work, a mechanistic fouling model considering both ash deposition and removal mechanisms was developed to model ash deposition. New criterions for the sliding and rolling particle detachment were proposed, and the ef...

Successful simulation of the 3D biodiesel engine relies on the accurate input-parameter tuning of the 3D platform named KIVA4-CHEMKIN, which was time- and resource-consuming through traditional uncertainty analyses or experimental design methods. In this study, the input-parameter tuning was treated as an optimization procedure to minimize the root...

In order to provide the key parameters of initial coal concentration to low-NOx bias combustion technology and enrich the pulverized-coal bias combustion theory, pilot-scale ignition experiments of bias coal streams were carried out using a 250-kW fuel input bias combustion facility. The experimental results including combustion temperature, unburn...

Polyoxymethylene dimethyl ether 3 (PODE3) is a highly promising renewable fuel. Not only does it have physical characteristics which are suitable for practical engine applications, but it is also expected to facilitate prominent soot reduction. In this work, neat PODE3 is added to diesel in an engine to evaluate its practicality in terms of curbing...

The purpose of this study is to develop a multi-component skeletal mechanism including renewable fuels of n-butanol, n-octanol, and DnBE (di-n-buthylether) for engine combustion. Mechanism reductions using the directed relation graph, directed relation graph with error propagation and sensitivity analysis, peak concentration analysis, and isomer lu...

This work presents a compact and robust chemical reaction mechanism for modeling the combustion of saturated furans including tetrahydrofuran, 2-methyltetrahydrofuran and 2-buthyltetrahydrofuran under engine relevant conditions. A decoupling method is adopted to construct the mechanism. The oxidation reaction for the small species is described by a...

To explore the effect of coalbed methane (CBM) airflow on coal oxidation under low temperatures, an experimental apparatus was developed and applied to simulate coal oxidation under different oxidizing atmospheres. The formation of carbon monoxide CO, the index gas, in CBM airflow was analyzed to obtain the optimum concentration of CH4 that exerted...

A swirl micro-combustor for premixed hydrogen/air flames is proposed to improve flame stability. The swirl micro-combustor consists of a cylindrical combustion chamber and an inlet section where a swirler with 6 straight vanes at an angle of 45° is placed in an annular inlet duct. The flame stabilization mechanism and combustion characteristics at...

This paper presents a model developed to numerically simulate the combustion of blended solid fuel in the grate boiler. The model can efficiently reproduce the thermal conversion process through a separate definition of the participating fuel by their unique physical and chemical properties. The advantage of this consideration is its flexibility an...

The impact of Jet A-1 fuel on diesel engine performance and particulate matter emission was experimentally and analytically investigated in this study. Differential mobility spectrometer 500 and soot particle aerosol mass spectrometer were employed to analyze the size distributions and chemical compositions of soot particles from engine. Since the...

Ignition experiments regarding the combustion of Indonesian coal were performed in a reducing atmosphere using a bias combustion simulator with a thermal power of 250-kW. Flame spectra, gas temperatures and gas species were recorded, and coal combustion residues were sampled. The influences of exit velocity on the ignition mechanism, ignition delay...

To explore the microstructure and oxidation reactivity of crushed coal, the free radicals and functional groups of coals with different ranks in the crushing process were analyzed based on electron paramagnetic resonance (EPR) and Fourier transform infrared (FTIR) spectrometry. The low-temperature oxidation of different-sized crushed coals was also...

Great efforts have been made over the last few decades in understanding of the mechanisms and phenomenology of soot formation and burnout in combustion systems. In this paper, theoretical advances in modelling soot formation and oxidation under engine circumstance are surveyed based on the published works, particularly focus on the practical soot m...

Parameters describing soot particle processes are generally derived from a limited number of experimental studies. These parameters then have to be carefully calibrated for different operating conditions in internal combustion engine applications. This paper presents an innovative calibration procedure for soot simulation in Diesel engines. A Diese...

Three dual-fuel strategies, i.e. Strategy S (syngas-biodiesel), Strategy U (upgraded syngas-biodiesel), and Strategy D (DME-biodiesel), for utilization of syngas and biodiesel from biomass wastes in internal combustion engines have been proposed in this study. To compare both the combustion and emission performance of the three strategies, an integ...

This work optimized the operation of a syngas-fueled spark ignition (SI) engine in the gasifier-generator (GG) system to achieve improved combustion performance and reduced emission adapting to the electrical power output. The combustion performance and emissions of the SI engine were modeled by an experimentally validated 3D KIVA4-CHEMKIN model wi...

This paper investigates the effect of operating pressure (up to 8 atm) on the moderate or intense low-oxygen dilution (MILD) combustion of methane. Computational fluid dynamics (CFD) modeling was firstly conducted for a laboratory-scale combustor to obtain the distributions of temperature and minor species (CH2O and OH), and pollutants (CO and NO)...

The study of premixed H2/C3H8/air combustion in the combustor inserted with porous medium (PM), which involved ten kinds of PM and varied with porosity, wire diameter and pores per inch (PPI), is experimentally and numerically conducted. Moreover, in order to boost the electrical power output and efficiency of the micro thermophotovoltaic (TPV) sys...

Ash deposition on heat transfer surfaces is still a significant problem in existing conventional utility boilers. Understanding the formation of ash deposit is thereby very important, which is helpful to optimize the design and operation procedure of boilers. In this study, a dynamic numerical method based on the commercial software ANSYS FLUENT wa...

In this work, a reduced toluene-decalin reaction mechanism containing 108 species and 566 reactions was proposed for computational fluid dynamics (CFD) simulations and polycyclic aromatic hydrocarbon (PAH) formation predictions in combustion engines. The present mechanism was validated with the available literature data including ignition delay tim...

This work focuses on the development of a highly compact and robust chemical reaction mechanism for unsaturated furans oxidation in internal combustion engines. Recently, furans have gathered much attention in the research community as they are second generation biofuels which do not compete with food supplies unlike the first generation biofuels....

Integrating the gasification process with the chemical looping technology presents a promising route for biomass conversion with the objective to obtain high quality syngas without air separation. In this study, the biomass gasification with iron-based oxygen carrier and continuous feedstock in the bubbling fluidized bed (BFB) fuel reactor has been...

In this study, a comprehensive investigation of combustion and emission characteristics of Jet A-1 applied in diesel engine was experimentally conducted. Analysis is emphasized on engine performance and soot particle emission both in size and number concentrations when fueled with Jet A-1, compared with traditional diesel fuel. It is concluded that...

This paper aims at exploring a cleaner way of waste wood biomass grate-firing with a focus on NOX emission. The objective is to evaluate the potential of biomass co-combustion with methane for NOX abatement. NOX model involving three major gaseous N-species: NO, NH3 and HCN is incorporated into the dynamic fuel bed model, in which the dependency of...

Micro combustion stabilization is challenged by the large heat loss ratio, and the operating conditions are narrow because of the small combustor size. In this work, experimental tests combined with numerical simulations are carried out to investigate the premixed H2-air combustion with and without porous medium. The results indicate that the flame...

In this work, a new pseudo bi-variate soot model is proposed for description of soot aggregate formation and oxidation in compression ignition engines. This soot model is a combination and modification of existing sub-models for soot nucleation, aggregation, surface growth and oxidation. The main advantage of this model over other bi-variate models...

In this work, an efficient numerical approach for detailed soot particle dynamics modeling in three-dimensional engine simulation is proposed. The recently developed moment projection method is incorporated into engine computational fluid dynamics codes to handle the detailed soot particle dynamics. The main advantage of moment projection method ov...

A joint moment projection method and maximum entropy approach for treating the soot population balance equations is developed and presented in this work. The moment projection method is used to solve the population balance equations and generate moments that are supplied to the maximum entropy approach as a post-processing technique to reconstruct...