Selecting a k-ε turbulence model for investigating n-decane combustion in a diesel engine combustion chamber

The results of a comparative numerical simulation of combustion and formation of toxic substances in a diesel engine combustion chamber are given. Experimental findings were used to identify the mathematical models. The impact of the standard, RNG and realizable k-ε turbulence models on the accuracy of numerical simulation of combustion and the formation of toxic substances was studied. The realizable k-ε turbulence model was shown to provide a closer agreement of computational and experimental data during simulation of the diesel engine process when turbulent flows are described

The impact of oxidiser humidity on methane combustion in a gas burner

The improvement of thermodynamic and environmental indicators of energy facilities is a vital and topical problem. Numerical simulation methods are used to investigate the processes of combustion and formation of hazardous substances by computation, and to work out recommendations on increasing the effectiveness of fuel combustion. The paper examines the impact of atmospheric air humidity on the process of combustion of a stoichiometric methane-air mixture in a burner. The combustion process is simulated in the 3D unsteady statement in Cartesian coordinates. In the investigation, the combustion of the methane-air mixture is considered in one stage. Air humidity is considered in the 0 to 100% range. The monoxide nitrogen formation process is described using the extended Zeldovich-Fenimore mechanism. A comparative study has found that increasing air humidity up to 100% reduces the mass emission of monoxide nitrogen by a factor of 1.27, as compared to dry air. The study results can be used for designing equipment that uses methane as fuel

Numerical Simulation of the Process of Combustion of a Stoichiometric Hydrogen-Oxygen Mixture in a Steam Generator

Numerical methods are used to study the process of combustion of a stoichiometric hydrogen-oxygen mixture. The mathematical models were validated using experimental data. The combustion process is modelled in the three-dimensional unsteady formulation. With account of the recommendations of other authors, the turbulent flows are described in the paper using the standard k-ε turbulence model. The Eddy Dissipation Model (EDM) is used to describe the process of combustion of the hydrogen-oxygen mixture. The description of the complex heat transfer between the gas, flame and walls in the paper accounts for radiant heat transfer by using the P1 model. The paper deals with combustion processes in a burner and a model steam generator. Numerical methods were used to evaluate the effect of inlet flow turbulisation, and the flow rate and the method of feeding extra water to the combustion chamber on the process of combustion of the stoichiometric hydrogen-oxygen mixture. The influence of the design and operating mode factors on the alteration of the flame-steam interface and on the flame extinguishing conditions were studied. The results obtained can be used in future in designing equipment that uses hydrogen as a fuel to increase nuclear power plant (NPP) manoeuvrability

Виявлення впливу плазмохімічної обробки пропан-бутанового палива на екологічні характеристики двигуна внутрішнього згоряння

One of the key problems of modern engine construction is the improvement of environmental performance while ensuring a competitive price of produced engines. This is achieved using state-of-the-art control systems, expensive fuel equipment, and complex exhaust gas neutralization systems. The search for ways to improve the environmental performance of transport engines without significant complication of their structure is a priority area of modern research. Plasma chemical treatment of gas makes it possible to reduce the level of harmful substances in exhaust gases by 1.5‒4 times relative to operation on propane-butane without processing. This paper considers the possibility of using a plasma dynamic stabilization technique and conducting an electric discharge without contact with metal electrodes for the implementation of endothermic reactions whose implementation requires energy from an external source. During test experiments, volt-ampere characteristics of the system with needle electrodes were established, the distance between which was 2‒5 mm at different feed pressures of propane-butane gas mixture (75 % propane and 25 % butane). At the outlet of the plasma-chemical reactor, a hydrogen-containing gas mixture is obtained, which is subsequently supplied to the combustion chamber through the regular gas fuel system of the engine. Next, when such a gas mixture burns in the combustion chamber, hydrogen acts as a catalyst for chemical reactions, which reduces the thickness of the flame extinguishing front, increases the speed and completeness of combustion of the gas mixture. Based on the results of comparative motor studies, it was found that plasma-chemical treatment of propane-butane has almost no influence on the effective efficiency of the engine and specific fuel consumption. It should also be noted that the use of plasma-chemical reactors on board a vehicle allows them to be integrated into regular gas fuel engine systems with minimal changes in their structure, which has almost no effect on the mass-size indicators and maintenance conditions of the gas fuel systemОднією з ключових проблем сучасного двигунобудування є поліпшення екологічних показників при забезпеченні конкурентоспроможної ціни виробляємих двигунів. Це досягається використанням надсучасних систем керування, коштовною паливною апаратурою та складними системами нейтралізації відпрацьованих газів. Пошук шляхів поліпшення екологічних показників транспортних двигунів без суттєвого ускладнення їх конструкції – є пріоритетним напрямом сучасних досліджень. Плазмохімічна обробка газу дозволяє в 1,5–4 рази знизити рівень шкідливих речовин у відпрацьованих газах відносно роботи на пропан-бутані без обробки. Розглянуто можливість застосування способу динамічної стабілізації плазми і проведення електричного розряду без контакту з металевими електродами для здійснення ендотермічних реакцій, на реалізацію яких необхідні витрати енергії від зовнішнього джерела. У процесі тестових експериментів було отримано вольт-амперні характеристики системи з голчастими електродами, відстань між якими становила 2–5 мм при різних тисках подачі пропан-бутанової газової суміші (75 % пропан і 25 % бутан). На виході з плазмохімічного реактора отримується водневовмісна газова суміш, яка в подальшому, через штатну газову паливну систему двигуна подається в камеру згоряння. В подальшому, при згорянні такої газової суміші у камері згоряння водень виступає у якості каталізатора хімічних реакцій, що дозволяє зменшити товщину фронту гасіння полум’я, підвищити швидкість та повноту згоряння газової суміші. За результатами порівняльних моторних досліджень встановлено, що плазмохімічна обробка пропан-бутану майже не впливає на ефективний ККД двигуна та питому витрату палива. Також слід зазначити, що використання плазмохімічних реакторів на борту транспортного засобу дозволяє їх інтегрувати у штатні газові паливні системи двигуна з мінімальними змінами їх конструкції, що майже не впливає на масогабаритні показники та умови обслуговування газової паливної систем

Методи та математичні моделі сучасних інформаційно-комунікаційних технологій

Мета роботи – розроблення методів, моделей та інформаційних технологій підвищення функціональної ефективності систем підтримки прийняття рішень в освіті та промисловості. Предмет дослідження – методи, моделі та інформаційні технології прийняття рішень в освіті та промисловості, оцінка функціональної ефективності інтелектуальних систем аналізу даних, методи захисту інформації в інфокомунікаційних системах, інформаційно-аналітичні системи в освіті

Convective Instability in Slip Flow in a Vertical Circular Porous Microchannel

Abstract The paper represents an analysis of convective instability in a vertical cylindrical porous microchannel performed using the Galerkin method. The dependence of the critical Rayleigh number on the Darcy, Knudsen, and Prandtl numbers, as well as on the ratio of the thermal conductivities of the fluid and the wall, was obtained. It was shown that a decrease in permeability of the porous medium (in other words, increase in its porosity) causes an increase in flow stability. This effect is substantially nonlinear. Under the condition Da > 0.1, the effect of the porosity on the critical Rayleigh number practically vanishes. Strengthening of the slippage effects leads to an increase in the instability of the entire system. The slippage effect on the critical Rayleigh number is nonlinear. The level of nonlinearity depends on the Prandtl number. With an increase in the Prandtl number, the effect of slippage on the onset of convection weakens. With an increase in the ratio of the thermal conductivities of the fluid and the wall, the influence of the Prandtl number decreases. At high values of the Prandtl numbers (Pr > 10), its influence practically vanishes

Comparison Analysis of Analytical and Lattice Boltzmann Methods for Simulation of Turbulence Decay in Flows in Converging and Diverging Channels

The paper focuses on a study of turbulence decay in flow with streamwise gradient. For the first time, an analytical solution of this problem was obtained based on the k‐ε model of turbulence in one‐dimensional (1D) approximation, as well as on the symmetry properties of the system of differential equations. Lie group technique enabled reducing the problem to a linear differential equation. The analytical solution enabled parametric studies, which are computationally cheap in comparison to CFD based simulations. The lattice Boltzmann method (LBM) in two‐dimensional approximation (2D) was used to validate the analytical results. Large eddy simulation (LES) Smagorinsky approach was used to close the LBM model. Computations revealed that the rate of turbulence decay is significantly different for the cases of positive and negative streamwise pressure gradient. The further comparisons showed that the analytical solution underpredicts the predictions by the numerical methodology, which can be attributed to the simplified problem statement used to derive the closed‐form analytical solution. Comparisons of calculations with experiments revealed that the theoretical models used in the study underpredict the measurements for flows with a positive pressure gradient. Hence it can be concluded that the LBM technique combined with the LES Smagorinsky model requires the further modification