This review covers the results obtained in the period 2006–2014 in the field of plasma-assisted combustion, and in particular the results on ignition and combustion triggered or sustained by pulsed nanosecond discharges in different geometries. Some benefits of pulsed high voltage discharges for kinetic study and for applications are demonstrated. The necessity of and the possibility of building a particular kinetic mechanism of plasma-assisted ignition and combustion are discussed. The most sensitive regions of parameters for plasma–combustion kinetic mechanisms are selected. A map of the pressure and temperature parameters (P–T diagram) is suggested, to unify the available data on ignition delay times, ignition lengths and densities of intermediate species reported by different authors.

https://iopscience.iop.org/article/10.1088/0022-3727/47/35/353001/pdf

Plasma-assisted ignition and combustion: nanosecond discharges and development of kinetic mechanisms

Direct numerical simulation (DNS) of the near field of a three-dimensional spatially developing turbulent lifted hydrogen jet flame in heated coflow is performed with a detailed mechanism to determine the stabilization mechanism and the flame structure. The DNS was performed at a jet Reynolds number of 11,000 with over 940 million grid points. The results show that auto-ignition in a fuel-lean mixture at the flame base is the main source of stabilization of the lifted jet flame. A chemical flux analysis shows the occurrence of near-isothermal chemical chain branching preceding thermal runaway upstream of the stabilization point, indicative of hydrogen auto-ignition in the second limit. The Damkoehler number and key intermediate-species behaviour near the leading edge of the lifted flame also verify that auto-ignition occurs at the flame base. At the lifted-flame base, it is found that heat release occurs predominantly through ignition in which the gradients of reactants are opposed. Downstream of the flame base, both rich-premixed and non-premixed flames develop and coexist with auto-ignition. In addition to auto-ignition, Lagrangian tracking of the flame base reveals the passage of large-scale flow structures and their correlation with the fluctuations of the flame base. In particular, the relative position of themore » flame base and the coherent flow structure induces a cyclic motion of the flame base in the transverse and axial directions about a mean lift-off height. This is confirmed by Lagrangian tracking of key scalars, heat release rate and velocity at the stabilization point.« less

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/F90F81BFEB5324713BC67D3B8A762579/S0022112009991388a.pdf/div-class-title-three-dimensional-direct-numerical-simulation-of-a-turbulent-lifted-hydrogen-jet-flame-in-heated-coflow-flame-stabilization-and-structure-div.pdf

Three-dimensional direct numerical simulation of a turbulent lifted hydrogen jet flame in heated coflow: flame stabilization and structure

Polymer production and utilization are currently widespread and have greatly improved people's standards of living. However, due to their stable and nonbiodegradable nature, postconsumer polymers pose challenging issues to the environment and ecosystems. Efforts are being made not only to contain the generation of polymer wastes and associated littering but, also, to find ways of utilizing them sustainably. Aside from mechanical recycling, which turns postconsumer polymers into new polymer products, and thermal recycling, which releases the thermal energy contained within waste plastics through combustion, chemical recycling converts waste polymers into feedstock for chemicals/materials/fuels production. This manuscript reviews prior work on a special application of the particular chemical recycling route that converts polymers into carbon-based nanomaterials. These materials feature extraordinary physical and chemical properties with tremendous applications potential. However, their production processes are both resource- and energy-intensive. Yet, by taking advantage of the high carbon content of waste polymers, as well as of their high energy content, a cost-effective, environmentally-friendly, and self-sustaining production of carbon nanomaterials can be achieved. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39931.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/app.39931

Upcycling waste plastics into carbon nanomaterials: A review

In this paper, we develop a first principles model that connects respiratory droplet physics with the evolution of a pandemic such as the ongoing Covid-19. The model has two parts. First, we model the growth rate of the infected population based on a reaction mechanism. The advantage of modeling the pandemic using the reaction mechanism is that the rate constants have sound physical interpretation. The infection rate constant is derived using collision rate theory and shown to be a function of the respiratory droplet lifetime. In the second part, we have emulated the respiratory droplets responsible for disease transmission as salt solution droplets and computed their evaporation time, accounting for droplet cooling, heat and mass transfer, and finally, crystallization of the dissolved salt. The model output favourably compares with the experimentally obtained evaporation characteristics of levitated droplets of pure water and salt solution, respectively, ensuring fidelity of the model. The droplet evaporation/desiccation time is, indeed, dependent on ambient temperature and is also a strong function of relative humidity. The multi-scale model thus developed and the firm theoretical underpinning that connects the two scales-macro-scale pandemic dynamics and micro-scale droplet physics-thus could emerge as a powerful tool in elucidating the role of environmental factors on infection spread through respiratory droplets.

/pdf/modeling-the-role-of-respiratory-droplets-in-covid-19-type-5060qb77yf.pdf

Modeling the role of respiratory droplets in Covid-19 type pandemics

An experimental and numerical study on laminar flame characteristics of methane oxy-fuel mixtures highly diluted with CO2 was conducted using a constant volume chamber and CHEMKIN package. The effects of high CO2 dilution on combustion chemical reaction, flame instability, and flame radiation of CH4/CO2/O2 mixtures were studied. The laminar burning velocities of CH4/CO2/O2 mixtures decrease with the increase of the CO2 fraction. CO2 directly participates in the chemical reaction through the elementary reaction OH + CO = H + CO2 and inhibits the combustion process by the competition of the H radical between the reverse reaction of OH + CO = H + CO2 and the reaction H + O2 = O + OH. This effect is more obvious for highly diluted CO2 in the case of CH4/CO2/O2 mixtures. CO2 suppresses the flame instability by the combined effect of hydrodynamic and thermal-diffusive instabilities. The radiation of CH4 oxy-fuel combustion is much stronger than that of CH4/air combustion mainly because of the existence of a lar...

Chung K. Law

Papers

Combustion Physics: Subject Index