William L. Roberts

• PhD
• Managing Director at King Abdullah University of Science and Technology

Ultrasound driven cavitation is widely used to intensify lab and industrial-scale processes. Various studies and experiments demonstrate that the acoustic energy, dissipated through the bubbles collapse, leads to intense physicochemical effects in the processed liquid. A better understanding of these phenomena is crucial for the optimization of ult...

Traditionally, the cavitation threshold is defined by some combination of vapor pressure and surface tension. However, these formulations present a large discrepancy with experimental data for cases where cavitation is induced by acoustic waves. The present study aims to identify a more suitable cavitation threshold for such cases. The method adopt...

Ammonia combustion poses challenges due to low reactivity and high NO x emissions, requiring optimization of combustor designs and fueling strategies. This study examines NO emissions, flame stability, and structure in co-fired premixed NH 3 /CH 4 /air flames using a double-swirl burner. The inner swirl stream consists of NH 3 /CH 4 /air mixtures w...

This study explores the application of the density gradient theory to assess the validity of the two-phase spray atomization theory in multi-component ammonia sprays under conditions relevant to practical applications. The research focuses on analyzing the liquid–vapor interface structure at thermodynamic equilibrium. The most recent Helmholtz ener...

The utilization of water is the core of our lives at every moment, through direct and indirect use. Indeed, industries are a significant player in water consumption, for various functions such as processing, diluting, cooling and washing. These processes often leave contaminated water streams. ~15% of the water globally used ends up as industrial w...

Cracking NH3 into a mixture of NH3/H2/N2 effectively addresses its low reactivity when used as a fuel. In this study, large eddy simulation (LES) and experiments are conducted for non-premixed NH3/H2/N2-air jet flames with simulated cracking ratios of 14 % and 28 % at an elevated pressure of 5 bar. Detailed experimental data on the flow field are p...

Along with the transition to cleaner energy production methods, closing the processing loop on batteries is becoming one of the significant issues to tackle in this decade. The most promising recycling technique consists in the leaching of crushed cathode material, i.e. the dissolution of the solid battery material in an acid solution, to recover v...

Asphaltenes are the most complex and the least understood portions of heavy oils. In the current study, a powerful tool Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS) coupled with positive atmospheric pressure photoionization (APPI) and positive electrospray ionization (ESI) ionizers was used, respectively, to analyze and u...

This paper reports the first quantitative characterization of transient hydrogen (H2) jets issued from a single-hole injector into nitrogen (N2), using high-speed 1-D and 2-D Raman scattering techniques. By employing the pulse-burst laser as the light source together with the low-noise EMCCD cameras running in subframe burst gating mode for signal...

In the context of low-carbon transition, ammonia (NH3) is considered as a promising zero-carbon fuel owing to its high hydrogen density, well-established storage, and transportation systems. However, its low reactivity and high nitrogen content could induce flame instability and high NO emission problems during combustion, which hinders its large-s...

Ammonia is a carbon-free alternative fuel that can replace fossil fuels in most energy systems. It is also a hydrogen carrier that is more cost-effective than hydrogen for liquefying, storing, and transporting. The production cost of ammonia depends highly on the cost of hydrogen production. Its utilization as a fuel is challenging because of its l...

The present study is an extension of our earlier mixing field investigation in partially premixed flames. In the current work, the link between the mixing field and flame structure, and hence flame curvature and surface density are experimentally studied. The flame structure is captured using a high-speed OH-PLIF technique, whereas the crosswise mi...

The combustion of cracked ammonia is crucial for enhancing flame stability and reducing pollutant emissions in ammonia-based combustion systems. This study investigated the flame structure and pollutant formation in cracked ammonia jet flames (CAJFs) to improve our understanding of the turbulence-chemistry interactions in ammonia combustion. A simu...

Autothermal reforming (ATR), which uses the inverse diffusion flame (IDF) configuration, is a promising technology to economically mass-produce hydrogen, which is seen as a key energy source in the future decarbonized society, from methane. Flame length is an important characteristic of IDFs, as it is used to validate theoretical, numerical and phe...

Efforts to reduce NO x emissions by utilizing ammonia-fired combustors are made through various methods; this work investigates the possibility of combining the effects of pressure and stretch rate to reduce NO x emissions in laminar premixed flames. NO x emissions, including NO, NO 2 , N 2 O, NH 3 , and HCN, from NH 3 /CH 4 /air and NH 3 / H 2 /ai...

Quantitative 1-D measurement of H 2 mole fraction in transient jets is reported. By using the pulse-burst laser along with the EMCCD cameras operated in subframe burst gating mode, repetition rate of 50 kHz is achieved.

Wetted wires are a unique column internal with several advantages compared to spray and packed columns. These include near-perfect liquid distribution, extremely low pressure drops, and better heat or mass transfer due to droplet circulation. Currently, wetted-wire columns remain within the laboratory prototyping stage. The primary goal of this rev...

Polycyclic aromatic hydrocarbons are the main precursors to soot particles in combustion systems. A lack of direct experimental evidence has led to controversial theoretical explanations for the transition from gas-phase species to organic soot clusters. This work focuses on sampling infant soot particles from well-defined flames followed by analys...

Post-combustion capture of carbon dioxide usually requires other upstream pollutant capture systems such as selective catalytic reduction for NOx, flue gas desulfurization, electrostatic precipitators, etc (Dziejarski et al. (2023)). Traditional carbon capture technologies cannot be deployed at point emission sources that do not have these systems...

This work presents the design and assessment of an experimental rig intended to carry out material sustainability studies in ammonia (NH3) environments. The designed facility aims at furthering the understanding of the nitridation potential of NH3 under extreme conditions, particularly at both high pressure and high temperature, when interacting wi...

The global extinction limits of non-premixed nitrogen/ammonia-substituted methane− and ethylene−air coun-terflow flames were experimentally evaluated. In comparison to nitrogen substitution, ammonia substitution reduced the extinction strain rates more. Measurements of OH* chemiluminescence, of which the intensity correlates with extinction limits,...

Phenols are recalcitrant compounds that constitute the majority of organic contaminants in industrial wastewaters. Their removal at large scales require a combination of various processes to reach the desired discharge quality. An extensive body of work has already been published in the area of phenol removal from wastewater, however none of them h...

Thermally induced secondary atomization (TISA) is a complex phenomenon that accelerates phase change in the combustion chamber. It occurs if multi-component fuels, having a wide boiling range, are exposed to high temperatures. Several airlines are recently experimenting with bio- and fossil fuels blends. However, the characteristics of droplet TISA...

Pyrolysis is perceived as the missing link between the management of end-of-life tires (ELTs) and the tire industry because it strikes directly in the transition from a linear to a circular economy model and toward the defossilization of diverse economic sectors. Tire pyrolysis oil (TPO) is one of the most valuable and interesting fractions derived...

Despite the transition toward carbon-free energy carriers, liquid fossil fuels are expected to occupy an important market share in the future. Therefore, it is crucial to develop innovative technology for better combustion reducing the emissions of pollutants associated with their utilization. Water in oil (w/o) emulsions contribute to greener comb...

CO2-diluted methane fuel is relevant to biogas combustion applications. Despite its poor heating value and low reactivity, which limit its practical applicability, biogas gains popularity as a renewable fuel. However, implementing it in combustion systems requires either modifying or replacing the existing burners. This study investigates the stabi...

CO2-diluted methane fuel is relevant to biogas combustion applications. Despite its poor heating value and low reactivity, which limit its practical applicability, biogas gains popularity as a renewable fuel. However, implementing it in combustion systems requires either modifying or replacing the existing burners. This study investigates the stabi...

Enhancement of ammonia reactivity is crucial for potential applications of ammonia as an engine and gas turbine fuel. A common strategy for improving ammonia's poor reactivity is blending it with more reactive fuels like hydrogen and methane. However, fundamental studies of ammonia combustion with higher hydrocarbons and key intermediate oxidation...

CO 2 -diluted methane fuel is relevant to biogas combustion applications. Despite its poor heating value and low reactivity, which limit its practical applicability, biogas gains popularity as a renewable fuel. However, implementing it in combustion systems requires either modifying or replacing the existing burners. This study investigates the sta...

Carbon and metal-oxide nanoparticles (NP) are currently synthesized worldwide for various applications in the solar-energy, optical, pharmaceutical, and biomedical industries, among many others. Gas phase methods comprise flame synthesis and flame spray pyrolysis (FSP), which provide high efficiency, low cost, and the possibility of large-scale app...

Ammonia combustion is a meaningful method to retrieve stored amounts of excess variable renewable energy. The practical combustors like engines and gas turbines fired by the common hydrocarbon fuels need to be operated by the carbon-free like ammonia or ammonia/hydrogen blends shortly. Thus, in this study, the turbulent flame speed (S T) and NO emi...

This study investigated the turbulent flame speed (ST) of NH3/CH4/H2/air mixtures subjected to differential-diffusion effect characterized by sub-unity Lewis number (Le) at elevated pressures (1 and 5 atm), temperature (373 K), lean equivalence ratios (ϕ = 0.6–0.91) with and without 10% volumetric H2O dilution. The experiments were conducted in a f...

This study presents the characterization of the thermal decomposition (oxidation and pyrolysis) behavior of the oil (TPO) derived from the pyrolysis of End-of-Life Tires (ELT) in a twin-auger pyrolyzer, by means of ther-mogravimetric and calorimetric analyses, coupled with Fourier transform infrared spectroscopy (TG-FTIR). TPO oxidation and pyrolys...

This work presents an experimental study on the influence of the pilot flame characteristics on the flame morphology and exhaust emissions of a turbulent swirling flame. A reduced-scale burner, inspired by that fitted in the AE-T100 micro gas turbine, was employed as the experimental platform to evaluate methane (CH4) and an ammonia-methane fuel bl...

In this study, two series of pressurized turbulent jet sooting flames at 1 bar, 3 bar and 5 bar with either fixed jet velocity or fixed Reynolds number are simulated to study the pressure effects on soot formation and evolution. Via a Radiation Flamelet Progress Variable (RFPV) approach with a conditional soot sub-filter Probability Density Functio...

Resonant pulse combustors, one of the deflagration-based pressure gain combustion devices, can significantly increase thermal efficiency in gas turbine engines. This experimental study investigates the stability characteristics of a newly designed actively valved resonant pulse combustor, capable of sustained operation and meaningful stagnation pre...

Thermally-induced secondary atomization (TISA) enables enhanced atomization, better mixing and faster evaporation in multi-component sprays. Despite its importance in a number of applications, TISA is not yet well understood. In this work we study numerically the effects of key physical parameters on TISA dynamics, with particular emphasis on break...

Despite the extensive studies, accurate and reliable modeling of the soot inception process, especially at high pressure conditions, amenable to multi-dimensional flame simulations remains a challenge. In this study, the physical inception model was comprehensively evaluated in the fully-resolved simulations of laminar normal diffusion flame (NDF)...

Formic acid (FA) is a potential hydrogen energy carrier and low-carbon fuel by reversing the decomposition products, CO2 and H2, back to restore FA without additional carbon release. However, FA-air mixtures feature high ignition energy and low flame speed; hence stabilizing FA-air flames in combustion devices is challenging. This study experimenta...

This study reports on the performance of the Ansaldo AE-T100 commercial micro gas turbine (mGT) when fueled by ammonia-methane blends instead of its design fuel, natural gas. This micro gas turbine was used as the experimental platform to understand effects of ammonia addition, and its hardware was only marginally updated. Ammonia was added to the...

MILD (moderate or intense low-oxygen dilution) combustion is a promising technology for mitigating NOx emission from fuel combustion, but the combustion stability becomes an issue when using low-preheat air due to the slower reaction at the burner exit. In this study, an inverse-diffusion flame (IDF) burner configuration is proposed to enhance the...

Catalyst degradation due to soot formation is one of the main issues in the autothermal reforming (ATR) process, which is widely regarded as the future technology for hydrogen production from natural gas. In this work, soot formation under conditions similar to ATR was systematically investigated, focusing specifically on the effects of pressure on...

Ammonia is a very promising carbon-free fuel, but its combustion is prone to generate a large amount of harmful nitric oxide (NO). Designing NO reduction strategies for ammonia flames requires computational fluid dynamics and accurate kinetic mechanisms. However, there are currently no available experimental data that can be used to validate models...

Soot sensitivity to strain rate is mainly responsible for soot formation intermittence in practical combustion devices. This work provides a fundamental study on soot formation in Soot Formation Oxidation (SFO) counterflow flames at varying strain rates. While the problem has been extensively studied in Soot Formation (SF) configurations, where the...

This study reports on the lean stability limits and exhaust emissions of ammonia-methane-air swirl flames with varied ammonia fuel fractions. A reduced-scale burner was manufactured, inspired by Ansaldo’s micro gas turbine AE-T100 burner, and it was installed inside a high-pressure combustion duct to operate at 4.5 bar. This pressure corresponds to...

Aiming at the zero boil-off demand of liquid hydrogen storage tank, this paper uses SAGE software to design and simulate 300 W @ 20 K regenerative heat-driven cryocoolers, verifying the principle feasibility of duplex free-piston Stirling cryocooler and thermoacoustic heat-driven pulse tube cryocooler for the zero boil-off storage of liquid hydroge...

This work presents the first quantitative Raman measurements of temperature, mass fractions, and mixture fractions in two turbulent ammonia/hydrogen/nitrogen-air diffusion jet flames simulating 14% (CAJF14) and 28% (CAJF28) partial ammonia cracking ratio with Reynolds numbers of 11,200. The precision and accuracy of the system were validated in lam...

The incipient sooting tendencies of oxygenated fuels in counterflow diffusion flames were systematically assessed by doping selected oxygenate fuels into the baseline fuel of ethylene with various mixing ratios. Laser light scattering and planar laser-induced fluorescence (PLIF) techniques were adopted. The critical oxygen mole fractions at differe...

This work reports on the chemiluminescence signature of premixed ammonia-methane-air swirling flames. Wide ranges of equivalence ratios (0.6 ≤ Φ ≤ 1.3), ammonia fractions in the fuel blend (0 ≤ XNH3 ≤ 0.70), and Reynolds numbers (10,000 ≤ Re ≤ 40,000) were investigated to understand effects of these parameters on the light emitted by these flames....

Accurate measurements and modelling of soot formation in turbulent flames at elevated pressures form a crucial step towards design methods that can support the development of practical combustion devices. A mass and number density preserving sectional model is here combined with a transported joint-scalar probability density function (JDPF) method...