School of Chemistry (Scholarly Articles)

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  • Publication
    Estimating Poly(N-isopropylacrylamide) size in solution below the LCST using fluorescence correlation spectroscopy with non-covalent bound fluorophores
    (Elsevier, 2024-06-25) van Zanten, Camila; Ryder, Alan G.
    Accurate size measurements of nanosized polymer chains in dilute solutions is important for understanding polymer behavior, however, these measurements can be challenging to implement accurately, and are technique dependent. Here we explore the use of Fluorescence Correlation Spectroscopy (FCS) to determine the size of single polymer chains in dilute solutions (<2 wt%). FCS, a technique with single molecule sensitivity, generally requires the use of covalently labelled polymers which can distort physicochemical behavior. Here, FCS based size measurements were based on the non-covalent interaction of fluorophores (Alexa 405, Atto 390, and Atto 425) with PNIPAm in water at 25 °C (below the Lower Critical Solution Temperature). FCS estimated size (hydrodynamic radius) of three different MW PNIPAm samples in water were: 5.0 ± 1.0 nm (28.5 kDa), 5.0 ± 1.0 nm (38 kDa), 3.3 ± 0.5 nm (55.5 kDa), in reasonable agreement with theoretical calculations. Accuracy was directly related to the fraction of PNIPAm-bound fluorophore, which were, for 1 wt% PNIPAm solutions in water: ∼11.5 % (Atto 390), ∼8.1 % (Atto 425), and 4 % (Alexa 405). This method has several advantages in that it does not require a covalent labelling of PNIPAm, it can be implemented on very small sample volumes, and allows for in-situ measurements.
  • Publication
    Effects of viscosity and refractive index on the emission and diffusion properties of Alexa Fluor 405 using fluorescence correlation and lifetime spectroscopies
    (Springer, 2021-03-19) van Zanten, Camila; Melnikau, Dzmitry; Ryder, Alan G.; Science Foundation Ireland; European Regional Development Fund; Health Research Board
    Fluorescence Correlation Spectroscopy (FCS) studies of the interaction of polymers or proteins in solution are strongly affected by the viscosity and refractive index of the medium, and the effects are likely to be more significant with the use of short wavelength excitation (e.g., 405 nm diode lasers). Failing to account for these issues can lead to incorrect measurement of average size, conformational changes, and dynamic behaviour of polymers and proteins. Steady-state, time-resolved, and FCS measurements of Alexa 405 in glycerol:water mixtures were performed to determine its suitability for FCS measurements with 405 nm excitation. The effects of the refractive index and viscosity on the diffusion coefficient and photophysical parameters (lifetime and relative quantum yield) of the fluorophore were determined. Alexa 405 lifetime decreased from 3.55 ns in water to 3.25 ns in a 50:50 glycerol:water mixture, while its diffusion coefficient dropped from 333 ± 16 to 44 ± 1 µm2s− 1. Lifetime data collected from micromolar solutions of Alexa 405 did however also suggest that as solvent polarity decreased, aggregates (excimers) were formed as evidenced by the appearance of a rising edge in the decay plots. The interdependence between lifetime, refractive index, and diffusion coefficient could be accurately fitted by a simple polynomial function indicating that the probe is well behaved and predictable in the glycerol:water model system. Overall, Alexa 405 is a most promising and reliable probe for FCS measurement using violet laser diode excitation sources.
  • Publication
    Implementation of an ISO 50001 energy management system using Lean Six Sigma in an Irish dairy: a case study
    (Emerald, 2023-12-18) Trubetskaya, Anna; McDermott, Olivia; McGovern, Seamus
    Purpose This article aims to optimise energy use and consumption by integrating Lean Six Sigma methodology with the ISO 50001 energy management system standard in an Irish dairy plant operation. Design/methodology/approach This work utilised Lean Six Sigma methodology to identify methods to measure and optimise energy consumption. The authors use a single descriptive case study in an Irish dairy as the methodology to explain how DMAIC was applied to reduce energy consumption. Findings The replacement of heavy oil with liquid natural gas in combination with the new design of steam boilers led to a CO2 footprint reduction of almost 50%. Practical implications A further longitudinal study would be useful to measure and monitor the energy management system progress and carry out more case studies on LSS integration with energy management systems across the dairy industry. Originality/value The novelty of this study is the application of LSS in the dairy sector as an enabler of a greater energy-efficient facility, as well as the testing of the DMAIC approach to meet a key objective for ISO 50001 accreditation.
  • Publication
    Industry 4.0 readiness in west of Ireland small and medium and micro enterprises – an exploratory study
    (Taylor & Francis, 2023-03-21) McDermott, Olivia; Nelson, Stuart; Antony, Jiju; Sony, Michael
    Quality 4.0 is the new paradigm in the field of quality management, due to the advent of technological advancement and digital transformation of many organizations. The field of Quality 4.0 is still in its nascent stage, and there is no self-assessment tool to assess whether an organization is ready or not in implementing Quality 4.0. This study uses a five-phase approach to develop a Quality 4.0 readiness self-assessment tool. Phase 1 of the study was devoted to a literature review to identify the readiness factors and sub-factors. In Phase 2 experts¿ opinions sought sure that none of the readiness factors are missed out in our research. Phase 3 was devoted to questionnaire development. Phase 4 was devoted to data collection. In this phase, we identified 6 packaging companies that were willing to participate in the research. Phase 5 was devoted to data analysis and readiness assessment for each of the factors and sub-factors across the participating organizations. The readiness factors identified in the study were: top management commitment and support, leadership, organizational culture, employee competency, and ISO QMS Standard in place. Further, a methodology was developed to classify the participating organizations into five different quality readiness assessment levels.
  • Publication
    The misplacement of ISO 18404:2015 in organisational improvement: a point-counterpoint article
    (Emerald, 2023-09-05) McDermott, Olivia; Antony, Jiju; Sony, Michael; Swarnakar, Vikas
    This paper gives the background to the ISO 18404:2015 standard and explains its rationale. It aims to rebut the Oudrhiri et al. (2022) paper. Furthermore, this paper adds further evidence of the misplacement and unfitness for use of the standard, as evidenced in the previous work by Antony et al. (2021, 2022). A point-counterpoint methods approach with a literature review of studies available on ISO 18404:2015 to respond to the Oudrhiri et al. (2022) study. The findings indicate that Oudrhiri et al.'s (2022) work is not open minded in relation to ISO18404. Each point raised in the Oudrhiri et al. (2020) study has been answered and counter-argued. Other than Antony et al.'s three studies (2021 and 2022) and Oudrhiri et al.¿s (2022) study empirical studies looking into the impact of the ISO 18404 standard in the literature were limited. As the literature has shown, many companies are not utilising the standard given its current format; hence, a lack of information relating to the practical implementation is sparse. The findings indicate that Oudrhiri et al.'s (2022) work can be answered and counter-argued. This study consolidates and strengthens the findings from the three studies by Antony et al. (2021 and 2022) and acts as a rebuttal to the Oudrhiri et al. (2022) study.
  • Publication
    Mapping the terrain for the Lean Supply Chain 4.0
    (Emerald, 2023-10-03) McDermott, Olivia; Antony, Jiju; Sony, Michael; Swarnakar, Vikas
    This study aims to carry out a systematic literature review (SLR) on the integration of Lean, Industry 4.0 and the supply chain or the Lean Supply Chain (LSC) 4.0. The research analyses the current research on the LSC 4.0 concept in an increasingly digitalised world. The authors present the benefits, motivations, critical success factors and challenges of integrating the LSC with Industry 4.0 technologies within this emerging area of research. Design/methodology/approach An SLR is carried out on how Lean can be integrated with Supply Chain 4.0. Using the search strings of ¿Lean Supply Chain 4.0,¿ ¿Lean Supply Chain Management 4.0¿ and ¿Lean Supply Chain Digitalisation,¿ a review of published literature was carried out via searches on academic databases. Findings Industry 4.0 has a synergistic effect on the LSC and, depending on the technology and sector applied in, can complement and enhance the LSC. Similarly, the LSC is a precursor for digitalisation. There are considerable implications in the LSC 4.0 for green and sustainable processes. Practical implications Organisations can use this study to understand what the LSC 4.0 means to industry, the benefits and motivating factors for implementation, the critical success factors (CSFs) to implementation and the challenges for implementation. Originality/value This study adds to state of the art around the LSC 4.0 and future directions in this nascent research area. This study will aid organisations in understanding how Lean, supply chain management and Industry 4.0 can be integrated.
  • Publication
    Employee's performance and Kaizen events' success: does supervisor behaviour play a moderating role?
    (Emerald, 2023-12-05) Kharub, Manjeet; Gupta, Himanshu; Rana, Sudhir; McDermott, Olivia
    The study's goal was to identify the factors contributing to the practical completion of Kaizen events (KEs). The effect of the work-study man's characteristics, the supervisor's conduct and the autonomy of the Kaizen team are analysed in this study. Data were collected from 249 respondents working in the manufacturing sector in India, mainly those who had been involved in Kaizen projects. Three-step procedures, namely, exploratory factor analysis, confirmatory factor analysis and partial least squares, have been applied to test the research hypotheses through structural equational modelling. The exploratory factor analysis extracted in-role performance, creative performance and human aspect as latent variables explaining work-study man's performance (eigenvalue = 1). The study's findings indicate that the performance of work-study man (in-role, creative and human) and supervisors' conduct is directly related to the success of KEs. It was shown that supervisors might influence the outcomes of KEs only by moderating the human aspects. Additionally, the degree of autonomy of the Kaizen team was found having a significant positive relationship with the success of KEs.
  • Publication
    Size exclusion chromatography for screening yeastolate used in cell culture media
    (Elsevier, 2023-09-18) Kyne, Michelle; de Faria e Silva, Ana Luiza; Vickroy, Bruce; Ryder, Alan G.; Science Foundation Ireland; European Regional Development Fund
    Yeastolate is often used as a media supplement in industrial mammalian cell culture or as a major media component for microbial fermentations. Yeastolate variability can significantly affect process performance, but analysis is technically challenging because of compositional complexity. However, what may be adequate for manufacturing purposes is a fast, inexpensive screening method to identify molecular variance and provide sufficient information for quality control purposes, without characterizing all the molecular components. Here we used Size Exclusion Chromatography (SEC) and chemometrics as a relatively fast screening method for identifying lot-to-lot variance (with Principal Component Analysis, PCA) and investigated if Partial Least Squares, PLS, predictive models which correlated SEC data with process titer could be obtained. SEC provided a relatively fast measure of gross molecular size hydrolysate variability with minimal sample preparation and relatively simple data analysis. The sample set comprised of 18 samples from 12 unique source lots of an ultra-filtered yeastolate (10 kDa molecular weight cut-off) used in a mammalian cell culture process. SEC showed significant lot-to-lot variation, at 214 and 280 nm detection, with the most significant variation, that correlated with process performance, occurring at a retention time of ~6 minutes. PCA and PLS regression correlation models provided fast identification of yeastolate variance and its process impact. The primary drawback is the limited column lifetime (
  • Publication
    A route to 1-Deoxynojirimycin and 1-Deoxymannojirimycin derivatives with quaternary centers adjacent to the ring nitrogen from Methyl α-d-Mannopyranoside
    (Wiley, 2020-02-03) Chadda, Rekha; Murphy, Paul V.; Science Foundation Ireland; European Regional Development Fund
    6-Alkylated-8-azido-1,6-octadiene derivatives were prepared from methyl α-D-mannopyranoside. The sequence to allylic azide precursors included a Horner-Wadsworth-Emmons reaction with a concomitant epimerization that ultimately enabled synthesis of 1-deoxynojirimycin as well as 1-deoxymannojirimy- cin derivatives. Thermally promoted allylic acid rearrangement followed by triazoline formation, then decomposition to aziridine and finally reaction with acetic acid was used to generate products that have quaternary anomeric centers adjacent to the piperidine ring nitrogen atom (cyclic α-tertiary amines). The stereoselectivity is accounted for based on minimization of steric interactions in the transition state structure, favouring the product where the larger methyl substituent is equatorial and the vinyl group prefers to be axial.
  • Publication
    Advanced spectroscopy and APBS modeling for determination of the role of His190 and Trp103 in mouse thymidylate synthase interaction with selected dUMP analogues
    (MDPI, 2021-03-06) Prokopowicz, Małgorzata; Jarmuła, Adam; Casamayou-Boucau, Yannick; Gordon, Fiona; Ryder, Alan; Sobich, Justyna; Maj, Piotr; Cieśla, Joanna; Zieliński, Zbigniew; Fita, Piotr; Rode, Wojciech
    A homo-dimeric enzyme, thymidylate synthase (TS), has been a long-standing molecular target in chemotherapy. To further elucidate properties and interactions with ligands of wild-type mouse thymidylate synthase (mTS) and its two single mutants, H190A and W103G, spectroscopic and theoretical investigations have been employed. In these mutants, histidine at position 190 and tryptophan at position 103 are substituted with alanine and glycine, respectively. Several emission-based spectroscopy methods used in the paper demonstrate an especially important role for Trp 103 in TS ligands binding. In addition, the Advanced Poisson Boltzmann Solver (APBS) results show considerable differences in the distribution of electrostatic potential around Trp 103, as compared to distributions observed for all remaining Trp residues in the mTS family of structures. Together, spectroscopic and APBS results reveal a possible interplay between Trp 103 and His190, which contributes to a reduction in enzymatic activity in the case of H190A mutation. Comparison of electrostatic potential for mTS complexes, and their mutants, with the substrate, dUMP, and inhibitors, FdUMP and N4-OH-dCMP, suggests its weaker influence on the enzyme ligand interactions in N4OH-dCMP-mTS compared to dUMP-mTS and FdUMP-mTS complexes. This difference may be crucial for the explanation of the abortive reaction inhibitory mechanism of N4OH-dCMP towards TS. In addition, based on structural analyses and the H190A mutant capacity to form a denaturation-resistant complex with N4-OH-dCMP in the mTHF-dependent reaction, His190 is apparently responsible for a strong preference of the enzyme active center for the anti rotamer of the imino inhibitor form.
  • Publication
    Modelling Förster resonance energy transfer (FRET) using anisotropy resolved multi-dimensional emission spectroscopy (ARMES)
    (Elsevier, 2020-11-16) Gordon, Fiona; Elcoroaristizabal, Saioa; Ryder, Alan G.; Science Foundation Ireland; European Regional Development Fund
    Background Förster Resonance Energy Transfer (FRET) is widely used to study the structure and dynamics of biomolecular systems and also causes the non-linear fluorescence response observed in multi-fluorophore proteins. Accurate FRET analysis, in terms of measuring changes in donor and acceptor spectra and energy transfer efficiency is therefore critical. Methods We demonstrate a novel quantitative FRET analysis using anisotropy resolved multidimensional emission spectroscopy (ARMES) in a Human Serum Albumin (HSA) and 1,8-anilinonaphathalene sulfonate (ANS) model. ARMES combines 4D measurement of polarized excitation emission matrices (pEEM) with multivariate data analysis to spectrally resolve contributing fluorophores. Multivariate analysis (Parallel Factor, PARAFAC and restricted Tucker3) was used to resolve fluorophore contributions and for modelling the quenching of HSA emission and the HSA-ANS interactions. Results pEEM spectra were modelled using Tucker3 which accommodates non-linearities introduced by FRET and a priori chemical knowledge was used to optimise the solution, thus resolving three components: HSA emission, ANS emission from indirect FRET excitation, and ANS emission from direct excitation. Perpendicular emission measurements were more sensitive to indirectly excited acceptor emission. PARAFAC modelling of HSA, donor emission, separated ANS FRET interacting (Tryptophan) and non-interacting (Tyrosine) components. This enabled a new way of calculating quenching constants using the multi-dimensional emission of individual donor fluorophores. Conclusions FRET efficiency could be calculated using the multi-dimensional, resolved emission of the interacting donor fluorophores only which yielded higher ET efficiencies compared to conventional methods. General significance Shows the potential of multidimensional fluorescence measurements and data analysis for more accurate FRET modelling in proteins.
  • Publication
    Analyzing protein conjugation reactions for antibody-drug conjugate synthesis using polarized excitation emission matrix spectroscopy
    (Wiley, 2022-09-07) de Faria e Silva, Ana L.; Ryder, Alan G.; Science Foundation Ireland; European Regional Development Fund
    Antibody-drug conjugates (ADCs) are promising anticancer therapeutics, which offer important advantages compared to more classical therapies. There are a variety of ADC critical quality attributes (CQAs) such as the protein structure, aggregation, and drug-to-antibody ratio (DAR), which all impact on potency, stability, and toxicity. Production processes can destabilize antibodies via a variety of physical and chemical stresses, and or by increased aggregation after conjugation of hydrophobic drugs. Thus, a proper control strategy for handling, production, and storage is necessary to maintain CQA levels, which requires the use of in-process quality measurements to first identify, then understand, and control the variables which adversely affect ADC CQAs during manufacturing. Here, we show how polarized excitation emission matrix (pEEM) spectroscopy, a sensitive, nondestructive, and potentially fast technique, can be used for rapidly assessing aggregation and DAR in a single measurement. pEEM provides several sources of information for protein analysis: Rayleigh scatter for identifying aggregate/particle formation and fluorescence emission to assess chemical and structural changes induced by attachment of a linker and/or a small molecule drug payload. Here, we used a nontoxic ADC mimic (monoclonal antibody with linker molecule) to demonstrate efficacy of the measurement method. Emission changes caused via light absorption by the attached linker, allowed us to predict DAR with good accuracy using fluorescence signal from the final purified products (6% relative error of prediction [REP]) and also from unpurified alkylation intermediates (11% REP). pEEM changes could also be correlated with size (hydrodynamic radius, Rh) and aggregate content parameters obtained from dynamic light scattering and size exclusion chromatography (SEC). For the starting material and purified product samples, pEEM correlated better with Rh (R2¿=¿0.99, 6% REP) than SEC determined aggregate content (18% REP). Combining both fluorescence and light scatter signals also enabled in-process size quantification (6% REP). Overall, combining polarized measurements with EEM and Rayleigh scatter provides a single measurement, multi-attribute test method for ADC manufacturing.
  • Publication
    Development of a rapid Polarized Total Synchronous Fluorescence Spectroscopy (pTSFS) method for protein quantification in a model bioreactor broth
    (Wiley, 2021-01-27) Boateng, Bernard O.; Elcoroaristizabal, Saioa; Ryder, Alan G.; Science Foundation Ireland; European Regional Development Fund
    Protein quantification during bioprocess monitoring is essential for biopharmaceutical manufacturing and is complicated by the complex chemical composition of the bioreactor broth. Here we present the early-stage development and optimization of a polarised Total Synchronous Fluorescence Spectroscopy (pTSFS) method for protein quantification in a hydrolysate-protein model (mimics clarified bioreactor broth samples) using a standard benchtop laboratory fluorometer. We used UV transmitting polarizers to provide wider range pTSFS spectra for screening of the four different TSFS spectra generated by the measurement: parallel (||), perpendicular (¿), unpolarized (T) intensity spectra and anisotropy maps. TSFS|| (parallel polarised) measurements were the best for protein quantification compared to standard unpolarized measurements and the Bradford assay. This was because TSFS|| spectra had a better analyte signal to noise ratio (SNR), due to the anisotropy of protein emission. This meant that protein signals were better resolved from the background emission of small molecule fluorophores in the cell culture media. SNR of > 5000 was achieved for concentrations of BSA/YST 1.2/10 g L-1 with TSFS|| . Optimisation using genetic algorithm and interval Partial Least Squares based variable selection enabled reduction of spectral resolution and number of excitation wavelengths required without degrading performance. This enables fast (
  • Publication
    Evaluating the interaction of human serum albumin (HSA) and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) liposomes in different aqueous environments using anisotropy resolved multi-dimensional emission spectroscopy (ARMES)
    (Elsevier, 2022-01-07) Gordon, Fiona; Casamayou-Boucau, Yannick; Ryder, Alan G.; Science Foundation Ireland; European Regional Development Fund
    Studying the interaction between plasma proteins and liposomes is critical, particularly for their use as drug delivery systems. Here, the efficacy of anisotropy resolved multidimensional emission spectroscopy (ARMES) for investigating the interaction of human serum albumin (HSA) with liposomes was explored and compared to conventional spectroscopic techniques. Dynamic Light Scattering (DLS) and absorbance spectroscopy (with Multivariate Curve Resolution (MCR) modeling) indicated that the highest degree of liposome rupturing, and aggregation occurred in water, with less in ammonium bicarbonate buffer (ABC) and phosphate buffered saline (PBS). Fluorescence emission spectra of HSA-liposome mixtures revealed significant hypsochromic shifts for water and ABC, but much less in PBS, where the data suggests a non-penetrating protein layer was formed. Average fluorescence lifetimes decreased upon liposome interaction in water (6.2¿5.2 ns) and ABC buffer (6.3¿5.6 ns) but increased slightly for PBS (5.6¿5.8 ns). ARMES using polarized Total Synchronous Fluorescence Scan measurements with parallel factor (PARAFAC) analysis resolved intrinsic HSA fluorescence into two components for interactions in water and ABC buffer, but only one component for PBS. These components, in water and ABC buffer, corresponded to two different HSA populations, one blue-shifted and penetrating the liposomes (¿ex/em = ~ 280/320 nm) and a second, similar to free HSA in solution (¿ex/em = ~ 282/356 nm). PARAFAC scores for water and ABC buffer suggested that a large proportion of HSA interacted in an end on configuration. ARMES provides a new way for investigating protein-liposome interactions that exploits the full intrinsic emission space of the protein and thus avoids the use of extrinsic labels. The use of multivariate data analysis provided a comprehensive and structured framework to extract a variety of useful information (resolving different fluorescent species, quantifying their signal contribution, and extracting light scatter signals) all of which can be used to discriminate between interaction mechanisms.
  • Publication
    Experimental and kinetic modeling study of 3-Methyl-2-butenol (Prenol) oxidation
    (American Chemical Society, 2021-08-19) Lokachari, Nitin; Wagnon, Scott W.; Kukkadapu, Goutham; Pitz, William J.; Curran, Henry J.; Science Foundation Ireland
    Longer chain alcohols with 4–5 carbon atoms are attractive alternative fuels as they can be derived from biological sources and since their combustion leads to lower exhaust gas levels of NOx and soot compared to commercial fossil fuels. The auto-ignition behavior of fuels that contain both a hydroxyl group and a C═C double bond in their molecular structure is not well established in the literature. Understanding the influence of these functional groups on the ignition behavior of fuels is critical in the development of tailor-made fuels for advanced combustion engines. In this study, ignition delay times of an unsaturated alcohol, 3-methyl-2-butenol (prenol), are measured using a high-pressure shock tube and a rapid compression machine at pressures of 15 and 30 bar at equivalence ratios of 0.5, 1.0, and 2.0 in “air” in the temperature range 600–1400 K. A detailed kinetic model is developed and validated using the new experimental data in this study. In addition, speciation data in a jet-stirred reactor, ignition delay times, and laminar burning velocities available in the literature were also used to validate the new kinetic model. Fuel flux and sensitivity analyses are performed using this new model to determine the important fuel consumption pathways and critical reactions that affect the reactivity of prenol.
  • Publication
    Hierarchical study of the reactions of hydrogen atoms with alkenes: A theoretical study of the reactions of hydrogen atoms with C2–C4 alkenes
    (American Chemical Society, 2021-06-08) Power, Jennifer; Somers, Kieran P.; Nagaraja, Shashank S.; Curran, Henry J.; Science Foundation Ireland; Irish Centre for High-End Computing
    The present study complements our previous studies of the reactions of hydrogen atoms with C5 alkene species including 1- and 2-pentene and the branched isomers (2-methyl-1-butene, 2-methyl-2-butene, and 3-methyl-1-butene), by studying the reactions of hydrogen atoms with C2¿C4 alkenes (ethylene, propene, 1- and 2-butene, and isobutene). The aim of the current work is to develop a hierarchical set of rate constants for ¿ atom addition reactions to C2¿C5 alkenes, both linear and branched, which can be used in the development of chemical kinetic models. High-pressure limiting and pressure-dependent rate constants are calculated using the Rice¿Ramsperger¿Kassel¿Marcus (RRKM) theory and a one-dimensional master equation (ME). Rate constant recommendations for ¿ atom addition and abstraction reactions in addition to alkyl radical decomposition reactions are also proposed and provide a useful tool for use in mechanisms of larger alkenes for which calculations do not exist. Additionally, validation of our theoretical results with single-pulse shock-tube pyrolysis experiments is carried out. An improvement in species mole fraction predictions for alkene pyrolysis is observed, showing the relevance of the present study.
  • Publication
    Development of multipurpose skeletal core combustion chemical kinetic mechanisms
    (American Chemical Society, 2021-03-25) Wang, Quan-De; Panigrahy, Snehasish; Yang, Shiyou; Martinez, Sergio; Liang, Jinhu; Curran, Henry J.; Fundamental Research Funds for the Central Universities; Science Foundation Ireland; International Scientific Cooperation Projects of Key R&D Programs in Shanxi Province
    Core combustion kinetic mechanisms for small C0¿C4 fuel molecules are not only of the utmost importance in understanding their individual combustion properties but are also the foundation for the development of kinetic models of real fuels. This brief communication intends to develop efficient skeletal core combustion mechanisms for the oxidation of C0¿C3/C4 fuels using the recently developed NUIGMech1.1 as the detailed mechanism. A combination of different skeletal mechanism reduction methods is employed to produce two skeletal mechanisms for C0¿C3 and C0¿C4 fuels, separately. The skeletal mechanisms have been validated by comparing against a wide range of combustion targets, and the maximum error in ignition delay time predictions is less than 10% for all of the targeted fuels. The C0¿C3 skeletal mechanism is also employed as the core mechanism in the development of a five-component skeletal mechanism for real gasoline. The developed skeletal mechanisms should represent a valuable resource for mechanism development and kinetic modeling within the combustion community.
  • Publication
    The impact of the third O2 addition reaction network on ignition delay times of neo-pentane
    (Elsevier, 2020-08-27) Hansen, N.; Kukkadapu, G.; Chen, B.; Dong, S.; Curran, Henry J.; Taatjes, C. A.; Eskola, A. J.; Osborn, D. L.; Sheps, L.; Pitz, W. J.; Moshammer, K.; Jasper, A. W.; Chen, W.; Yang, J.; Wang, Z.; Science Foundation Ireland
    We studied the oxidation of neo-pentane by combining experiments, theoretical calculations, and mechanistic developments to elucidate the impact of the 3rd O2 addition reaction network on ignition delay time predictions. The experiments are based on photoionization mass spectrometry in jet-stirred and time-resolved flow reactors allowing for sensitive detection of the keto-hydroperoxide (KHP) and keto-dihydroperoxide (KDHP) intermediates. With neo-pentane exhibiting a unique symmetric molecular structure, which consequently results only in single KHP and KDHP isomers, theoretical calculations of ionization and fragment appearance energies and of absolute photoionization cross sections enabled the unambiguous identification and quantification of the KHP intermediate. Its temperature and time-resolved profiles together with calculated and experimentally observed KHP-to-KDHP signal ratios were compared to simulation results based on a newly developed mechanism that describes the 3rd O2 addition reaction network. A satisfactory agreement has been observed between the experimental data points and the simulation results, thus adding confidence to the model's overall performance. Finally, this mechanism was used to predict ignition delay times reported previously in shock tube and rapid compression machine experiments (J. Bugler et al., Combust. Flame 163 (2016) 138¿156). While the model accurately reproduces the experimental data, simulations with and without the 3rd O2 addition reaction network included reveal only a negligible effect on the predicted ignition delay times at 10 and 20 atm. According to model calculations, low temperatures and high pressures promote the importance of the 3rd O2 addition reactions.
  • Publication
    A kinetics and dynamics study on the auto-ignition of dimethyl ether at low temperatures and low pressures
    (Elsevier, 2020-09-14) Huan, Wenlin; Zhao, Qian; Huang, Zuohua; Curran, Henry J.; Zhang, Yingjia; National Natural Science Foundation of China; Shanxi National Science Foundation
    Though the combustion chemistry of dimethyl ether (DME) has been widely investigated over the past decades, there remains a dearth of ignition data that examines the low-temperature, low-pressure chemistry of DME. In this study, DME/`air¿ mixtures at various equivalence ratios from lean (0.5) to extremely rich (5.0) were ignited behind reflected shock waves at a fixed pressure (3.0 atm) over the temperature range 625¿1200¿K. The ignition behavior is different from that at high-pressures, with a repeatable ignition delay time fall-off feature observed experimentally in the temperature transition zone from the negative temperature coefficient (NTC) regime to the high-temperature regime. This could not be reproduced using available kinetic mechanisms as conventionally homogeneous ignition simulations. The fall-off behavior shows strong equivalence ratio dependence and disappears completely at an equivalence ratio of 5.0. A local ignition kernel postulate was implemented numerically to quantifiably examine the inhomogeneous premature ignition. At low temperature, no pre-ignition occurs in the mixture. A conspicuous discrepancy was observed between the measurements and constrained UV simulations at temperatures beyond the NTC regime. A third O2 addition reaction sub-set was incorporated into AramcoMech 3.0, together with related species thermochemistry calculated using the G3/G4/CBS-APNO compound method, to explore the low-temperature deviation. The new reaction class does not influence the model predictions in IDTs, but the updated thermochemistry does. Sensitivity analyses indicate that the decomposition of hydroperoxy-methylformate plays a critical role in improving the low-temperature oxidation mechanism of DME but unfortunately, the thermal rate coefficient has never been previously investigated. Further experimental and theoretical endeavors are required to attain holistic quantitative chemical kinetics based on our understanding of the low-temperature chemistry of DME.
  • Publication
    An experimental and kinetic modeling study of the auto-ignition of natural gas blends containing C1–C7 alkanes
    (Elsevier, 2020-07-16) Mohamed, Ahmed Abd El-Sabor; Panigrahy, Snehasish; Sahu, Amrit Bikram; Bourque, Gilles; Curran, Henry J.; Science Foundation Ireland; Siemens Canada
    Ignition delay time measurements for multi-component natural gas mixtures were carried out using a rapid compression machine at conditions relevant to gas turbine operation, at equivalence ratios of 0.5–2.0 in ‘air’ in the temperature range 650–1050 K, at pressures of 10–30 bar. Natural gas mixtures comprising C1–C7 n-alkanes with methane as the major component (volume fraction: 0.35–0.98) were considered. A design of experiments was employed to minimize the number of experiments needed to cover the wide range of pressures, temperatures and equivalence ratios. The new experimental data, together with available literature data, were used to develop and assess a comprehensive chemical kinetic model. Replacing 1.875% methane with 1.25% n-hexane and 0.625% n-heptane in a mixture containing C1–C5 components leads to a significant increase in a mixture's reactivity. The mixtures containing heavier hydrocarbons also tend to show a strong negative temperature coefficient and two-stage ignition behavior. Sensitivity analyses of the C1–C7 blends have been performed to highlight the key reactions controlling their ignition behavior.