A comprehensive experimental and modeling study of the ignition delay time characteristics of ternary and quaternary blends of methane, ethane, ethylene, and propane over a wide range of temperature, pressure, equivalence ratio, and dilution

The ignition delay time (IDT) characteristics of new ternary and quaternary blended C 1 ¿C 3 gaseous hy- drocarbons, including methane/ethane/ethylene and methane/ethane/ethylene/propane, are studied over a wide range of mixture composition, temperature ( ~800 ¿ 2000 K), pressure ( ~1 ¿135 bar), equiva- lence ratio ( ~0.5 ¿2.0), and dilution ( ~75 ¿90%) using both experimental data and kinetic modeling tools. In this regard, all of the experimental tests were designed using the Taguchi approach (L 9 ) to fulfill the experimental matrix required to generate a comprehensive set necessary to validate a detailed chem- ical kinetic model. High- and low-temperature IDTs were recorded using low/high-pressure shock tubes (L/HPST) and rapid compression machines (RCM), respectively. The model predictions using NUIGMech1.2 are evaluated versus all of the newly recorded experimental data. Moreover, the individual effects on IDT predictions of the parameters studied, including mixture composition and pressure, are investigated over the temperature range. The results show that NUIGMech1.2 can reasonably reproduce the experimental IDTs over the wide range of the conditions studied. The constant-volume simulations using the chemical kinetic mechanism reveal the synergistic/antagonistic effect of blending on IDTs over the studied tem- perature range so that IDTs in certain temperature ranges are very sensitive to even small changes in mixture composition.The authors would like to express their gratitude to Shell Research Ltd. and Science Foundation Ireland (SFI) for funding via project numbers 15/IA/3177 and 16/SP/3829, and KAY-ICHEC via the project ngche079c. The authors from PCFC, RWTH Aachen University, would like to recognize the funding support from the German Research Foundation (Deutsche Forschungsgemeinschaft, DFG) through project number – 322460823 (HE7599/2-1).peer-reviewe

Understanding the antagonistic effect of methanol as a component in surrogate fuel models: A case study of methanol/n-heptane mixtures

Methanol is a widely used engine fuel, blend component, and additive. However, no systematic auto-ignition data or laminar flame speed measurements are available for kinetic studies of the effect of methanol as a blending or additive component. In this work, both ignition delay times and laminar flame speeds of pure methanol, n-heptane and their blends at various blending ratios were measured at engine-relevant conditions. Results show that increasing methanol in a blend promotes reactivity at high temperatures and inhibits it at low temperatures, with the crossover temperature occurring at approximately 970¿980 K with it being almost independent of pressure. The experimental data measured in this work, together with those in the literature are used to validate NUIGMech1.1, which predicts well the experimental ignition delay times and laminar flame speeds of the pure fuels and their blends over a wide range of conditions. Furthermore, kinetic analyses were conducted to reveal the effects of methanol addition on the oxidation pathways of n-heptane and the dominant reactions determining the fuel reactivities. It is found that competition for ¿H radicals between methanol and n-heptane plays an important role in the auto-ignition of the fuel blends at low temperatures. At high temperatures, methanol produces higher concentrations of H¿2 radicals which produce two ¿H radicals either through the production of H2O2 and its subsequent decomposition or through direct reaction with ¿ atoms. This promotes the high temperature reactivity of methanol/n-heptane mixtures for ignition delay times and laminar flame speeds, respectively.This work is supported by the National Natural Science Foundation of China (51722603). The work at NUI Galway is supported by Science Foundation Ireland (SFI) via grant awards 15/IA/3177 and 16/SP/3829. Yingtao Wu would like to thank the financial support from the China Scholarship Council (No. 201806280105). Jinhu Liang acknowledges the support from the International Scientific Cooperation Projects of Key R&D Programs (201803D421101).peer-reviewe

An experimental and kinetic modeling study of the ignition delay characteristics of binary blends of ethane/propane and ethylene/propane in multiple shock tubes and rapid compression machines over a wide range of temperature, pressure, equivalence ratio, and dilution

In this work, the ignition delay time characteristics of C2 – C3 binary blends of gaseous hydrocarbons including ethylene/propane and ethane/propane are studied over a wide range of temperatures (750 – 2000 K), pressures (1 – 135 bar), equivalence ratios (φ = 0.5 – 2.0) and dilutions (75 – 90%). A matrix of experimental conditions is generated using the Taguchi (L9) approach to cover the range of conditions for the validation of a chemical kinetic model. The experimental ignition delay time data are recorded using low- and high-pressure shock tubes and two rapid compression machines (RCM) to include all of the designed conditions. These novel experiments provide a direct validation of the chemical kinetic model, NUIGMech1.1, and its performance is characterized via statistical analysis, with the agreement between experiments and model being within ~ 26.4% over all of the conditions studied, which is comparable with a general absolute uncertainty of the applied facilities (~ 20%). Sensitivity and flux analyses allow for the key reactions controlling the ignition behavior of the blends to be identified. Subsequent analyses are performed to identify those reactions which are important for the pure fuel components and for the blended fuels, and synergistic/antagonistic blending effects are therefore identified over the wide range of conditions. The overall performance of NUIGMech1.1 and the correlations generated are in good agreement with the experimental data.The authors would like to express their gratitude to Science Foundation Ireland (SFI) via their Research Centre Program through project numbers 15/IA/3177 and 16/SP/3829, KAY-ICHEC via the project ngche079c, and to Shell Research Ltd. The authors from PCFC RWTH Aachen University would like to recognize the funding support from the German Research Foundation (Deutsche Forschungsgemeinschaft, DFG) through the project number –322460823 (HE7599/2–1).peer-reviewe

Direct observation of the dead-cone effect in quantum chromodynamics

The direct measurement of the QCD dead cone in charm quark fragmentation is reported, using iterative declustering of jets tagged with a fully reconstructed charmed hadron

Direct observation of the dead-cone effect in quantum chromodynamics

At particle collider experiments, elementary particle interactions with large momentum transfer produce quarks and gluons (known as partons) whose evolution is governed by the strong force, as described by the theory of quantum chromodynamics (QCD) [1]. The vacuum is not transparent to the partons and induces gluon radiation and quark pair production in a process that can be described as a parton shower [2]. Studying the pattern of the parton shower is one of the key experimental tools in understanding the properties of QCD. This pattern is expected to depend on the mass of the initiating parton, through a phenomenon known as the dead-cone effect, which predicts a suppression of the gluon spectrum emitted by a heavy quark of mass m and energy E, within a cone of angular size m/E around the emitter [3]. A direct observation of the dead-cone effect in QCD has not been possible until now, due to the challenge of reconstructing the cascading quarks and gluons from the experimentally accessible bound hadronic states. Here we show the first direct observation of the QCD dead-cone by using new iterative declustering techniques [4, 5] to reconstruct the parton shower of charm quarks. This result confirms a fundamental feature of QCD, which is derived more generally from its origin as a gauge quantum field theory. Furthermore, the measurement of a dead-cone angle constitutes the first direct experimental observation of the non-zero mass of the charm quark, which is a fundamental constant in the standard model of particle physics.The direct measurement of the QCD dead cone in charm quark fragmentation is reported, using iterative declustering of jets tagged with a fully reconstructed charmed hadron.In particle collider experiments, elementary particle interactions with large momentum transfer produce quarks and gluons (known as partons) whose evolution is governed by the strong force, as described by the theory of quantum chromodynamics (QCD). These partons subsequently emit further partons in a process that can be described as a parton shower which culminates in the formation of detectable hadrons. Studying the pattern of the parton shower is one of the key experimental tools for testing QCD. This pattern is expected to depend on the mass of the initiating parton, through a phenomenon known as the dead-cone effect, which predicts a suppression of the gluon spectrum emitted by a heavy quark of mass $m_{\rm{Q}}$ and energy $E$, within a cone of angular size $m_{\rm{Q}}$/$E$ around the emitter. Previously, a direct observation of the dead-cone effect in QCD had not been possible, owing to the challenge of reconstructing the cascading quarks and gluons from the experimentally accessible hadrons. We report the direct observation of the QCD dead cone by using new iterative declustering techniques to reconstruct the parton shower of charm quarks. This result confirms a fundamental feature of QCD. Furthermore, the measurement of a dead-cone angle constitutes a direct experimental observation of the non-zero mass of the charm quark, which is a fundamental constant in the standard model of particle physics

Investigation of K+K− interactions via femtoscopy in Pb-Pb collisions at √sNN = 2.76 TeV at the CERN Large Hadron Collider

Femtoscopic correlations of non-identical charged kaons (K+K−) are studied in Pb−Pb collisions at a center-of-mass energy per nucleon−nucleon collision sNN−−−√=2.76 TeV by ALICE at the LHC. One-dimensional K+K− correlation functions are analyzed in three centrality classes and eight intervals of particle-pair transverse momentum. The Lednický and Luboshitz interaction model used in the K+K− analysis includes the final-state Coulomb interactions between kaons and the final-state interaction through a0(980) and f0(980) resonances. The mass of f0(980) and coupling were extracted from the fit to K+K− correlation functions using the femtoscopic technique for the first time. The measured mass and width of the f0(980) resonance are consistent with other published measurements. The height of the ϕ(1020) meson peak present in the K+K− correlation function rapidly decreases with increasing source radius, qualitatively in agreement with an inverse volume dependence. A phenomenological fit to this trend suggests that the ϕ(1020) meson yield is dominated by particles produced directly from the hadronization of the system. The small fraction subsequently produced by FSI could not be precisely quantified with data presented in this paper and will be assessed in future work

Two-particle transverse momentum correlations in pp and p-Pb collisions at energies available at the CERN Large Hadron Collider

Two-particle transverse momentum differential correlators, recently measured in Pb-Pb collisions at LHC energies, provide an additional tool to gain insights into particle production mechanisms and infer transport properties, such as the ratio of shear viscosity to entropy density, of the medium created in Pb-Pb collisions. The longitudinal long-range correlations and the large azimuthal anisotropy measured at low transverse momenta in small collision systems, namely pp and p-Pb, at LHC energies resemble manifestations of collective behaviour. This suggests that locally equilibrated matter may be produced in these small collision systems, similar to what is observed in Pb-Pb collisions. In this work, the same two-particle transverse momentum differential correlators are exploited in pp and p-Pb collisions at s√=7 TeV and sNN−−−√=5.02 TeV, respectively, to seek evidence for viscous effects. Specifically, the strength and shape of the correlators are studied as a function of the produced particle multiplicity to identify evidence for longitudinal broadening that might reveal the presence of viscous effects in these smaller systems. The measured correlators and their evolution from pp and p-Pb to Pb-Pb collisions are additionally compared to predictions from Monte Carlo event generators, and the potential presence of viscous effects is discussed