Temperature-dependent ion chemistry in nanosecond discharge plasma-assisted CH4 oxidation

Ion chemistry with temperature evolution in weakly ionized plasma is important in plasma-assisted combustion and plasma-assisted catalysis, fuel reforming, and material synthesis due to its contribution to plasma generation and state transition. In this study, the kinetic roles of ionic reactions in nanosecond discharge (NSD) plasma-assisted temperature-dependent decomposition and oxidation of methane are investigated by integrated studies of experimental measurements and mathematical simulations. A detailed plasma chemistry mechanism governing the decomposition and oxidation processes in a He/CH4/O2 combustible mixture is proposed and studied by including a set of electron impact reactions, reactions involving excited species, and ionic reactions. A zero-dimensional model incorporating the plasma kinetics solver ZDPlasKin and the combustion chemical kinetics solver CHEMKIN is used to calculate the time evolution of the ion density. Uncertainty analysis of ionic reactions on key species generation is conducted by using different referenced data, and insignificant sensitivity is found. The numerical model is consistent with experimental data for methane consumption and generation of major species including CO, CO2, and H2. By modeling the temporal evolution of key ions, it is observed that O2+ presents the largest concentration in the discharge stage, followed by CH4+, CH3+, and CH2+, which is in accordance with the traditional ion chemistry in hydrocarbon flames and agrees well with molecular-beam mass spectrometer investigations. The path flux shows that the concentrations of key species, including electrons, O, OH, H, O(1D), O2(a1Δg), O2+, CH3+, and CH4+, change within 1–2 orders of magnitude and that the transition from a homogeneous state to a contracted/constricted state does not occur. The path flux and sensitivity analysis reveal the significant roles of cations in the stimulation of active radical generation, including CH, O, OH, and O(1D), thus accelerating methane oxidation. This work provides a deep insight into the ion chemistry of temperature-dependent plasma-assisted CH4 oxidation.

SPECTRAL DIAGNOSTICS OF THE HYDROCARBON FUEL COMBUSTION PROCESS

It is proposed to use the methods of applied optical spectroscopy to solve the problem of control and diagnostics of gaseous hydrocarbon fuel combustion in this work. The results of an experimental study of spectroscopic informative parameters characterizing the propane combustion process are presented for three modes: combustion of pure propane without air supply, stoichiometric combustion and combustion with a change in the amount of supplied air relative to stoichiometric combustion. As a result of the experiment, it was found that the most intense bands in the emission spectrum of the flame arising from the combustion of propane correspond to the spectral bands of radicals of combustion products: OH, CH, and C2. While the intensities of various systems of bands in the flame spectrum depend significantly on the composition of the combustible mixture.

Experimental investigation of biodiesel-n-butanol fuels blends on performance and emissions in a diesel engine

The paper presents the experimental test results reflecting the comparative changes in the performance efficiency and emissions of the exhaust of a naturally aspirated, four-stroke, single-cylinder, air-cooled diesel engine due to its transition from neat rapeseed oil biodiesel to fuel blends prepared by mixing in various proportion (by volume) rapeseed methyl ester (B) and butanol (Bu). The lubricity properties of biodiesel-n-butanol fuel blends were studied using HFRR method. In contrast to previous works, the undertaken investigation is performed with a totally renewable, binary liquid biofuel blends. The purpose of the research is to reduce simultaneously the production of NOx emissions and the exhaust smoke with respect to neat biodiesel due to potentially improved homogeneity of combustible mixture and particulate matter emissions benefits suggested by the higher oxygen content (21.62wt%) and the relatively lower carbon-to-hydrogen ratio (4.8) of the normal n-butanol. The tests revealed that the brake specific fuel consumption for the binary biodiesel-n-butanol fuel blends is always higher than that neat biodiesel produces under the same loading conditions. Maximum nitrogen oxide (NOx) emissions were obtained with the engine running on neat biodiesel (2290 ppm). At full (100%) load conditions, the lowest NOx emission was obtained with the engine running on a biofuel BBu20 blend. The lowest level of carbon monoxide emissions (CO) was observed, when engine running with the most butanol-oxygenated biofuel blend BBu20.The highest smoke opacity of the exhaust was obtained when the engine was fuelled with neat biodiesel and at full load.

Research results on the use of combined fuels

At present, much attention is paid to reducing the emission of harmful impurities into the atmosphere in exhaust gases. This is achieved by using alternative sources of thermal energy necessary for the operation of the internal combustion engine operating by using electrical energy and transferring existing internal combustion engines operating on liquid fuel (diesel or carburetor) to gas. At the same time, the issue of transferring energy resources used in agricultural production to the above-mentioned sources of thermal energy is very acute. This is since the transfer to alternative fuels requires a certain amount of money. This issue is especially acute in small farms that do not have sufficient funds to buy a new one or transfer existing energy resources to more environmentally friendly fuels. The presented article presents the results of studies on increasing the efficiency of using available energy resources and improving the quality of fuel combustion using a combined composition of the combustible mixture. Keywords: TRACTOR, FUEL, FUEL MIXTURE, TORQUE, EFFICIENT ENGINE POWER

PROSPECTS FOR OBTAINING A COMBUSTIBLE MIXTURE OF GASES FROM VEGETABLE AGRICULTURAL WASTE USING SOLAR ENERGY

This paper discusses the possibility of obtaining a combustible gas mixture (GHA) from a number of agricultural waste, such as stalks of cotton, grapes and tobacco, walnut and hazelnut shells, etc., by pyrolysis and gasification, using solar energy, in in particular, a solar high-temperature installation (SVTU), in which a parabolic concentrator (PC) is used to convert the sun's radiant energy into thermal energy. Provides data on solar energy resources, as well as plant waste available in various regions of Azerbaijan.

Improvement of mixing processes in diesel engines

The object of research is gas-dynamic vortex processes in heterogeneous polydisperse flows. One of the most problematic issues in engine building is the completeness of combustion and the rate of fuel burnout in the given coordinates on the allotted hourly interval in the combustion chamber. These indicators, in turn, determine stringent requirements for used fuels in terms of thermophysical parameters that affect sawing, evaporation and mixing with an oxidizer. In the course of the study, methods of mathematical modeling were used based on the theory of similarity. Methods have been developed for preparing a combustible mixture for detonation-free combustion of a cheap alternative fuel. A method for assessing the quality of spraying low cetane fuel is proposed. A mathematical model is obtained for calculating the change in the parameters of the quality of atomization and the differential characteristics of fuel injection. This is necessary for theoretical studies of gas-dynamic processes in additional power systems for diesel engines in an unsteady three-dimensional flow with variable parameters of a polydisperse flow of a combustible mixture. It has been proven that with a decrease in the camshaft rotational speed, the injection speed will be insufficient to achieve the required spray quality due to a decrease in the speed. This made it possible to redesign the additional system using a separate dual fuel supply. Research samples of an additional power supply system for the ЯМЗ–24 ОН diesel engine (Yaroslavl Motor Plant, Russia) have been developed. Comparative tests of the engine operation on stable gas condensate with the main fuel equipment and an additional system have been carried out. Oscillograms of the tests were obtained and analyzed. The research results provided the basis for the use of low cetane cheap gas condensate in diesel engines. This will improve the economic, power and environmental performance of the engines. Compared to standard cetane fuels, the price of fuel will decrease by 40 %, engine power will increase by 20 %, and the environmental performance of exhaust gases will decrease by 10–30 %.

Investigation on Flowfield and Fuel/Air Premixing Uniformities of Low Swirl Injector for Lean Premixed Gas Turbines

Based on the development trend of incorporating fuel holes into swirler-vanes and the advantages of wide operating conditions as well as low NOx emissions of LSI, this paper proposes an original lean premixed LSI with a convergent outlet. The influence of key structures on flowfields and fuel/air premixing uniformities of LSI is investigated by the combination of laser diagnostic experiments and numerical simulations. The flowfields of LSI shows that the main recirculation zone is detached from the convergent outlet and its axial dimensions are smaller than that of HSI, which can decrease the residence time of high-temperature gas to reduce NOx emissions. The fuel/air premixing characteristics show that the positions and diameters of fuel holes affect fuel/air premixing by changing the penetration depth of fuel. And when the penetration depth is moderate, it can give full play to the role of swirling air in enhancing premixing of fuel and air. In addition, the increase of the length of the premixing section can improve the uniformity of fuel/ar premixing, but it can also weaken the swirl intensity and increase the residence time of the combustible mixture within the LSI, which can affect flame stability and increase the risk of auto-ignition. Therefore, the design and selection of LSI structural parameters should comprehensively consider the requirements of fuel/air mixing uniformity, flame stability and avoiding the risk of auto-ignition. The results can provide the technical basis for LSI design and application in aero-derivative and land-based gas turbine combustors.

Dynamics of Explosions in Cylindrical Vented Enclosures: Validation of a Computational Model by Experiments

Recent explosions with devastating consequences have re-emphasized the relevance of fire safety and explosion research. From earlier works, the severity of the explosion has been said to depend on various factors such as the ignition location, type of a combustible mixture, enclosure configuration, and equivalence ratio. Explosion venting has been proposed as a safety measure in curbing explosion impact, and the design of safety vent requires a deep understanding of the explosion phenomenon. To address this, the Explosion Venting Analyzer (EVA)—a mathematical model predicting the maximum overpressure and characterizing the explosion in an enclosure—has been recently developed and coded (Process Saf. Environ. Prot. 99 (2016) 167). The present work is devoted to methane explosions because the natural gas—a common fossil fuel used for various domestic, commercial, and industrial purposes—has methane as its major constituent. Specifically, the dynamics of methane-air explosion in vented cylindrical enclosures is scrutinized, computationally and experimentally, such that the accuracy of the EVA predictions is validated by the experiments, with the Cantera package integrated into the EVA to identify the flame speeds. The EVA results for the rear-ignited vented methane-air explosion show good agreement with the experimental results.

Воспламенение топливной смеси с помощью многоточечного импульсного искрового разряда при различных начальных условиях

The development of efficient and reliable systems for the ignition of air/fuel mixtures is of interest for many practical applications associated with the use of combustion devices. To increase the total surface of the flame, ensure the reliability of ignition, increase the rate of combustion in the volume of the chamber and the completeness of combustion of the combustible mixture, multi-point ignition of the air/fuel mixture using several pulsed spark discharges is used. A comparison of the characteristics of combustion products in the working chamber when using different numbers of igniting spark discharges is made based on the data of a physical experiment. Measurements are carried out at various ignition points of the mixture, initial mixture pressures, and air/fuel ratios. The values of the air/fuel ratio used in the experiment are in the range, the boundaries of which are the lower and upper concentration limits of the ignition of the propane-air mixture.

Experimental study and 3D modeling of the working process of a hydrogen engine running on a lean mixture

A 3D mathematical model for a hydrogen engine based on the Navier—Stokes transport equations in the Reynolds form is developed and verified. The influence of the crankshaft rotating frequency, excess air ratio and ignition timing on the engine performance is established. The expediency of operation of a hydrogen engine with external mixture formation and forced ignition on a lean combustible mixture is proved. Keywords: hydrogen engine, mathematical modeling, local heat exchange, combustion chamber, lean fuel mixture [email protected] ,