Instantaneous Combustion Research Articles

NO Formation in Combustion Engines Fuelled by Mixtures of Hydrogen and Methane

The present work addresses the production of nitrogen oxides in ICEs burning hydrogen mixed with methane. A mathematical model that allows the calculation of nitrogen oxide emissions from such combustion was built; this model uses the extended chemical kinetic mechanism of Zeldovich. Numerical simulations were carried out on the production of NO, varying the following variables: proportion of H2 to CH4, the equivalence ratio of the reactant mixture, the compression ratio, and the engine speed. The essential purpose was to assess how NO production is affected by the mentioned variables. The main assumptions were (i) Otto cycle; (ii) instantaneous combustion; (iii) chemical equilibrium reached just at the end of combustion; (iv) the formation of NO only during the expansion stroke of pistons. Results were obtained for various proportions of hydrogen and methane, various equivalence ratios, speeds of rotation, and compression ratios of an engine. In short, the results obtained in the current work show that the lowering of the equivalence ratio leads to a lower concentration of NO; that increasing the compression ratio also lowers the concentration of NO; that NO production occurs until shortly after the beginning of the expansion stroke; and finally, that the NO concentration in the engine exhaust is not very sensitive to the H2/CH4 ratio in the fuel mixture.

PORT INJECTION OF DIESEL, BIODIESEL, AND PETROL IN A COMPRESSION IGNITION DIRECT INJECTION DIESEL ENGINE TO MITIGATE NITROGEN OXIDES AND SOOT EMISSIONS

The internal combustion engine is critical to modern society’s development. Spark ignition engine (SI) and compression ignition engine (CI) now use gasoline and diesel as their primary fuels. As a result of burning these fuels, significant amounts of pollutants are released into the atmosphere, resulting in environmental issues. Internal combustion (IC) engines are widely acknowledged as a significant source of environmental air pollution. The engine’s fuel oxidation process not only produces useful power, but also produces significant amounts of pollutant emissions such as carbon monoxide (CO), unburned hydrocarbons (HC), nitrogen oxide (NOx ), and particulate matter (PM). When developing a new combustion process, consideration must be given to: lean homogeneous air-fuel mixture, increased compression ratio, and total and instantaneous combustion, all of which result in Port Injection Compression Ignition (PICI), that is a highly efficient and clean method of combustion. The goal of this research is to conduct an experimental investigation of PICI process of compression in a Premixed Charge Compression Ignition (PCCI) mode with Pilot Injection (PI) as the combustion activator. It was found that when compared to the conventional mode, the PICI mode produces cooler exhaust gas temperatures. Temperatures were lower in the PICI mode with biodiesel and petrol as secondary and primary fuels than in the PICI mode with other fuel combinations. In the PICI mode, the HC emission decreases at higher load with all fuels. In the biodiesel conventional mode, HC emission is minimum than in other modes. For all modes of operation, the specific fuel consumption has reduced with load. Diesel and gasoline have the lowest specific fuel consumption as primary and secondary fuels, respectively. Fuel usage in the PICI mode is lower than in the normal mode.

Study on combustion characteristics of sinusoidal hydrogen pulsed jet with different frequencies in supersonic flows

Pulsed jets can effectively improve mixing and combustion efficiencies, while sinusoidal pulsed jets have the advantages of good performance and simple setup. Therefore, the three-dimensional Reynolds-Averaged Navier-Stokes (RANS) equations and Shear Stress Transfer k-omega model (SST) are utilized to study the combustion characteristics of sinusoidal pulsed jets with three different frequencies and steady jet in order to obtain an approach to improve the combustion performance in the supersonic flow. In the current study, the combustion performances of the steady jet and the pulsed jets with an equal average momentum flux ratio to the steady jet are compared and analyzed, and the instantaneous combustion characteristics of four different time points in one cycle of the pulsed jets are analyzed in detail. The obtained results show that the pulsed jet can obviously improve the combustion efficiency, although the total pressure loss is slightly larger than that of the steady jet. On the whole, the pulsed jets have a good impact on the combustion performance of the combustor, and the combustion performance of the f = 20 kHz pulsed jet case is the best in this study.

Combustion and micro-explosion characteristics of biodiesel–ethanol–aluminum powder particles droplet under simulated air nitrogen–oxygen

Compared with aviation fuel, biodiesel has a smaller energy density, so the flight range of aircraft using biodiesel as aviation fuel is relatively short. Adding aluminum powder particles can significantly improve the energy density of fuel and then improve the flight range of aircraft, but the combustion characteristics of fuel will change after adding aluminum powder particles to fuel. In this experiment, a tubular furnace was used to simulate the ratio of nitrogen to oxygen in air, and the micro-explosion and combustion characteristics of BD60E40 droplet and BD60E40 droplet 10%AP (8 μm) under 700 and 750 °C were compared and studied by using moving droplet tracking technology. It is found that the greater the steam pressure inside the droplet, the greater the intensity of micro-explosion, and the greater the initial velocity of the secondary droplet after micro-explosion. In addition, it is found that the proportion of aluminum powder in droplets increases gradually during the combustion cycle, and the frequency and intensity of micro-explosion of droplets increase gradually. The instantaneous combustion micro-explosion intensity model and the average combustion intensity model were established. It was found that the average combustion micro-explosion intensity of droplets increased gradually with the increase in temperature through calculation.

Quality of moxa from Artemisia argyi and A. stolonifera in different storage years based on simultaneous thermal analysis

The quality of moxa is an important factor affecting moxibustion therapy, and traditionally, 3-year moxa is considered optimal, although scientific data are lacking. This study focused on 1-year and 3-year moxa from Artemisia stolonifera and A. argyi(leaf-to-moxa ratio of 10∶1) as research objects. Scanning electron microscopy(SEM), Van Soest method, and simultaneous thermal analysis were used to investigate the differences in the combustion heat quality of 1-year and 3-year moxa and their influencing factors. The results showed that the combustion of A. stolonifera moxa exhibited a balanced heat release pattern. The 3-year moxa released a concentrated heat of 9 998.84 mJ·mg~(-1)(accounting for 54% of the total heat release) in the temperature range of 140-302 ℃, with a heat production efficiency of 122 mW·mg~(-1). It further released 7 512.51 mJ·mg~(-1)(accounting for 41% of the total heat release) in the temperature range of 302-519 ℃. The combustion of A. argyi moxa showed a rapid heat release pattern. The 3-year moxa released a heat of 16 695.28 mJ·mg~(-1)(accounting for 70% of the total heat release) in the temperature range of 140-311 ℃, with an instantaneous power output of 218 mW·mg~(-1). It further released 5 996.95 mJ·mg~(-1)(accounting for 25% of the total heat release) in the temperature range of 311-483 ℃. Combustion parameters such as-R_p,-R_v, D_i, C, and D_b indicated that the combustion heat quality of 3-year moxa was superior to that of 1-year moxa. It exhibited greater combustion heat, heat production efficiency, flammability, mild and sustained burning, and higher instantaneous combustion efficiency. This study utilized scientific data to demonstrate that A. stolonifera could be used as excellent moxa, and the quality of 3-year moxa surpassed that of 1-year moxa. The research results provide a scientific basis for the in-depth development of A. stolonifera moxa and the improvement of moxa quality standards.

Методика проведення чисельного дослідження камери імпульсного детонаційного двигуна

The subject of research in this article is the process of detonation propagation in the chamber of a pulse detonation engine. Experimental research on detonation engines is a complex and expensive process that requires high-speed, high-precision equipment to obtain high-quality reliable results. Therefore, to conduct preliminary research, numerical experiment methods using mathematical simulation tools should be used. This work analyzes the possibility of applying known calculation models to study the detonation propagation process in the chamber of a pulse detonation engine. The task: to study the influence of the application of existing calculation models on the accuracy of numerical simulation of the detonation process; analyze the use of existing calculation models for the study of the detonation propagation process. The main method used in this work is the method of mathematical simulation using CFD technologies. The following results were obtained. The work considered the application of various turbulence models, chemical transition models, solvers and mesh sizes in modeling processes in the chamber of a pulse detonation engine. The application k-ε and k-ω turbulence models and their modifications are considered. The closest to the real result is obtained when applying k-ω model turbulence with SST modification. Generalized modification of this model averages the parameters on the front of the detonation wave, which leads to the destruction of the structure of the front. Taking into account the peculiarities of the processes occurring at the front of the detonation wave, the eddy-dissipation concept method will be better for modeling chemical transition, compared to the finite-rate method. Using the finite-rate method shows instantaneous combustion at the front of the detonation wave. This leads to a sharp increase in the parameters at the detonation front with its further separation from the main flow. To obtain a qualitatively reliable result of the parameters at the front of the detonation wave, cell dimensions of no more than 1/16 mm should be used. The application of the eddy-dissipation concept method with k-ω SST turbulence model allows obtaining the closest results to the experimental data. The deviation of pressure and velocity values obtained during modeling does not exceed 5% from their actual values. The temperature deviation does not exceed 10%. This is determined by the selected kinetic scheme of chemical transitions. All considered models and methods affect only the structure and development of the detonation wave front. There are no significant differences in the values of the parameters along the front (in the Taylor zone). Conclusion. The obtained results are of practical importance for the design and research of detonation engines. The use of the proposed calculation models will allow conducting numerical experiments for the pulse detonation engine chamber with sufficient accuracy, in comparison with experimental data.

An Artificial Intelligence Regression Model for Prediction of NOx Emission from Flame Image

In this study, NOx emission has been estimated by processing the flame image of visible wavelength and its experimental verification has been presented. The experimental study has been performed by using a domestic coal boiler with a capacity of 85000 Kcal / h. The real NOx value has been measured from a flue gas analyzer device. The flame image has been taken by CCD camera from the observation hole on the side of the burner. The data set which is related to instantaneous combustion performance and flame images was recorded simultaneously on the same computer with time stamps once a second. The color flame image has been transformed into a gray scale. Features have been extracted from the gray image of flame. The features are extracted by using the cumulative projection vectors of row and column matrices. ANN regression model has been used as the learning model. The relationship between flame image and NOx emission has been obtained with the accuracy of R = 0.9522. Highly accurate measurement results show that the proposed NOx prediction model can be used in combustion monitor and control systems.

Investigation of heat and mass transfer characteristics during the flame propagation of biomass straw from an initial linear fire source

Biomass straw has gradually received attention as a new energy that is easily accessible. The deep understanding of burning characteristics is critical to the efficient and safe utilization of biomass straw as a new energy, and further benefit to estimate the hazard of straw fire disasters. In the present study, the straw stacked into a rectangle with a length of 1 m, and widths from 0.1 m to 0.6 m was ignited from in a width with a linear-source fire. The heat and mass transfer characteristics during the flame propagation were investigated. The results showed that the flame front shape evolved from concave to convex as the straw width widened. Specifically, the critical transition range of straw width was from 0.3 m to 0.4 m due to the change of the dominant heat transfer factors. The residual mass of straw decreased linearly because of the uniform flame spreading process, indicating a constant MLR. The MLR was determined by the function of the aspect ratio of the instantaneous combustion area, which is shown as n+1/n. The flame temperature above the center position of the rectangular straw increased first and then dropped gradually. The peak dimensionless temperature presented a piecewise function with (z−z0)m˙−2/5.

Time-frequency analysis application to the evaluation of instantaneous combustion noise

A novel approach to combustion noise has been proposed in the present paper with the time-frequency analysis technique. By evaluating the energy content of the combustion pressure signal, which has been measured as a function of time on Euro 5 and Euro 6 diesel engines, different combustion phases have been identified and the combustion noise due to the difference between in-cylinder pressure and motored trace has been evaluated for each phase. The algorithm for the calculus of this instantaneous combustion noise contribution versus time has been realized through a home-made tool and has been applied to single and double injection schedules.The time-frequency analysis allows more detailed information to be obtained on the contribution of the different combustion phases to the combustion noise and the cause-and-effect relationships between injection schedule and combustion noise to be better highlighted. The research investigation provides a hint for onboard diagnostics and real-time control of combustion noise, but the developed tool also can be provided as a practical validation tool for the refinement of combustion models.

Optical diagnostics and multi-point pressure sensing on the knocking combustion with multiple spark ignition

Engine knock is an abnormal combustion phenomenon that limits the thermal efficiency and service life of spark-ignition engines. A better understanding of the knock mechanisms and characteristics is beneficial to knock alleviation and engine efficiency improvement. In this study, a metal liner with four evenly-spaced spark plugs in the periphery of the combustion chamber is designed to initiate knock from different positions. Four spark strategies are applied to the single-cylinder optical research engine and six pressure sensors are utilized to analyze the local pressure oscillations in the cylinder. The knocking combustion is investigated by simultaneous 72 kHz high-speed imaging and 6-point pressure sensing. The experimental results indicate that using multiple spark-ignition could promote knock intensity, advance the start of auto-ignition and introduce more acoustic resonance modes. The center pressure sensor is more sensitive to the first radial resonant mode (0, 1) of the knock pressure oscillation, while the side sensors are more sensitive to the first and second circumferential resonant modes (1, 0) and (2, 0). The knock onset judged by natural flame photography is earlier than that by pressure analysis because the auto-ignition event happens first and induces the subsequent pressure fluctuation. Natural flame luminosity analysis demonstrates that the initial auto-ignition sites only cause weak pressure oscillations, and the instantaneous combustion of the remaining end-gas increases the heat release rate significantly and gives rise to more violent pressure oscillations. Statistically, the maximum amplitude of pressure oscillation follows an exponential relationship with the peak mean flame luminosity. The end-gas resides in the gaps among the flame fronts generated by different spark strategies while the first auto-ignition sites are not evenly distributed in the end-gas zone. This fact gives insights into the local temperature non-uniformity of the end gas zone that affects the spatial distributions of the initial auto-ignition sites in the cylinder.

Study on the combustion behavior and soot formation of single coal particle using hyperspectral imaging technique

This paper proposes a hyperspectral imaging technique for capturing radiative images at a high temporal–spatial resolution, for the purpose of spectrally visualizing the instantaneous combustion behaviors of single coal particles. We initially use a hyperspectral imaging device to record the combustion processes of two types of single pulverized coal particles on a McKenna flat-flame burner. From the snapshot images captured by the device, we observe the combustion processes, ignition characteristics, flame morphologies, and sizes of the two single coal particles. The observations indicate that the two single coal particles undergo volatile release/combustion and char ignition/oxidation during the luminous combustion process; moreover, both particles exhibit homogeneous ignition characteristics under the experimental conditions. Furthermore, based on the spectral radiative intensity images obtained via the device, the soot temperature and volume fraction images of the two single coal particles in the envelope flame are obtained at different burning times. Thereafter, the influences of the combustion behaviors and soot formation mechanisms on the distribution rules of the soot temperature and concentration at different combustion periods are discussed. Finally, the temperature and apparent spectral emissivity values of the two single char particles during the char oxidation process are also calculated to analyze their combustion behaviors. The results show that the temperature changes within a relatively narrow range with respect to the burning time during the oxidation stage, whereas the spectral emissivity continues to increase with the oxidation of chars and subsequently decreases.

Thermal evolution of gas-liquid-solid products and migration regulation of C/H/O elements during biomass pyrolysis

Pyrolysis is a fundamental part of the biomass thermal conversion and utilization. A one-stage fluidized bed reactor was used to study the characteristics of gas-liquid-solid products and the migration regulation of C/H/O elements during biomass pyrolysis. The specific conclusions are as follows: the char yield decreases from 24.3 %–14.9 % during pyrolysis from 500 °C to 800 °C. The tar yield decreases from 16.9 % to less than 5 %, while the gas yield increases from 24 % to 71.3 %. The graphitization of biochar decreases and its aromaticity increases during pyrolysis. The form of hydrogen existing in biochar is converted from aliphatic hydrogen to aromatic hydrogen during pyrolysis. The content of weaken-bound oxygen such as carboxyl and aldehyde decreases significantly while the content of strong-bound oxygen such as CO and COC is essentially unchanged. The peak emission of CO during the instantaneous combustion of biochar increases from 0.0013 L/(g min to 0.0032 L/(g min at 500 °C to 800 °C. The tar starts its aromatization at 700 °C. The aliphatic component disappears from 33 % at 500 °C–600 °C. The double bond equivalent parameter of tar increases significantly, while its H/C ratio and O/C ratio both decrease. The yields of CO/CO2/CH4 increase significantly from 500 °C to 700 °C. H2 starts to appear at 700 °C. A noticeable CH4 steam reforming reaction starts when raising to 800 °C, leading to a decrease in CH4 yield and an increase in CO yield and H2 yield. C/H/O elements in biochar and tar are gradually lost during pyrolysis. The gas phase becomes the main existing form of C/H/O elements after raising to 700 °C.

Conceptual Limitations of the Probability Density Function Method for Modeling Turbulent Premixed Combustion and Closed-Form Description of Chemical Reactions’ Effects

In this paper, we critically analyzed possibilities of probability density function (PDF) methods for the closed-form description of combustion chemical effects in turbulent premixed flames. We came to the conclusion that the concept of a closed-form description of chemical effects in the classical modeling strategy in the PDF method based on the use of reaction-independent mixing models is not applicable to turbulent flames. The reason for this is the strong dependence of mixing on the combustion reactions due to the thin-reaction-zone nature of turbulent combustion confirmed in recent optical studies and direct numerical simulations. In this case, the chemical effect is caused by coupled reaction–diffusion processes that take place in thin zones of instantaneous combustion. We considered possible alternative modeling strategies in the PDF method that would allow the chemical effects to be described in a closed form and came to the conclusion that this is possible only in a hypothetical case where instantaneous combustion occurs in reaction zones identical to the reaction zone of the undisturbed laminar flame. For turbulent combustion in the laminar flamelet regime, we use an inverse modeling strategy where the model PDF directly contains the characteristics of the laminar flame. For turbulent combustion in the distributed preheat zone regime, we offer an original joint direct/inverse modeling strategy. For turbulent combustion in the thickened flamelet regime, we combine the joint direct/inverse and inverse modeling strategies correspondingly for simulation of the thickened flamelet structure and for the determination of the global characteristics of the turbulent flame.

A theoretical study of stability of solid fuel burning with a two­phase gasification area

Theoretically, the combustion stability of solid fuel, which during the combustion process is decomposed according to the “solid phase – liquid phase – gas” scheme, is investigated. The physical and mathematical models for the propagation of small perturbations of combustion are constructed. The medium in all areas of combustion and in combustion products is assumed to be incompressible, and the viscosity of the fuel in the liquid phase is taken into account. Thus, perturbations of hydrodynamic parameters are considered not only in the two-phase gasification zone, but also in the combustion products area and the geometric perturbation of the instantaneous combustion front (flame), distorting the shape of its surface, is also specified. That is the characteristic feature of the presented physical model. The mathematical eigenvalue problem is set and solved. This problem is reduced to an algebraic characteristic equation for a dimensionless complex eigenvalue, which positivity determines the instability. It is proved that in the limiting case of the absence of a liquid phase, absolute instability takes place. At the other limiting case – for perturbations with infinite wavelength – a transition to stability takes place. The latter fact indicates that the presence of a viscous liquid film and changes in the length of the gasification zone under the influence of perturbations have a significant stabilizing effect on solid fuel combustion. In the general case, a sufficient condition for the instability of the roots of the characteristic equation is analytically determined. The physical interpretation of the mathematical results explains the processes of autoturbulization of solid fuel combustion and the possible transition of combustion to deflagration explosion or detonation. The results of the study are in qualitative agreement with experimental data and can additionally be used for theoretical analysis of the stability of the liquid fuel combustion process in the combustion chamber

Predicting the combustion behaviour of compression ignition engine fuelled with biodiesel from Stoechospermum marginatum, a macro algae.

Biodiesel is one among the recent developments in the field of renewable energy research. To enhance the combustion characteristics of compression ignition engine, industry and academicians were working towards clean and renewable energy resource. Algal biodiesel was one of the major research arenas in the recent decade of renewable energy. Bio-oil from marine brown macro algae, Stoechospermum marginatum was used as the test fuel in this study. The purpose of this numerical study was to analyse the combustion behaviour of compression ignition engine when fuelled with Stoechospermum marginatum biodiesel as a fuel. The numerical study was performed using the zero-dimensional combustion model by incorporating the dynamic combustion duration during the heat transfer using the MATLAB Simulink software. The developed model which incorporated the instantaneous combustion duration was a novel approach. Validations of the numerical results on combustion features like in-cylinder pressure, rate of pressure rise, rate of heat release, and cumulative heat release were done by comparing it with the experimental data. The deviation between the numerical and experimental values was found to be within 5 to 6%.

Experimental investigation on ignition, combustion and micro-explosion of RP-3, biodiesel and ethanol blended droplets

Based on an infusion set, measuring cylinder and different types of micro needles, a method for measuring the volume of micro-droplet was established. The same volume of aviation fuel (RP-3), biodiesel and ethanol mixed droplets were sent to a heatable experimental device to study the combustion characteristics. Through a movable slide rail with adjustable speed, the mixed droplets suspended on the high-temperature resistant wire were transported to a distance of about 2 mm from the preheating plug for heating. The ingle-lens-reflex (SLR) camera and a high-speed camera were used to capture the ignition characteristics and instantaneous combustion characteristics of mixed droplets during heating, respectively. The burning mixed droplets video captured by the SLR camera was processed into color pictures by Adobe Premiere Pro CC software. Through the processing and analysis of these images, the ignition, combustion and micro-explosion characteristics of mixed droplets during combustion were studied. The equation for calculating the micro-explosion intensity was established, the micro-explosion intensity of binary mixed droplets and ternary mixed droplets was calculated and analyzed.

Gasoline-diesel dual fuel intelligent charge compression ignition (ICCI) combustion: Conceptual model and comparison with other advanced combustion modes

The internal combustion engines can remain the advantage over competitor technologies for automotive driven, especially the engine efficiency, exceeded 50% while maintaining ultra-low emissions. In this paper, a novel combustion mode characterized by dual high-pressure common-rail direct injection systems, denoted as intelligent charge compression ignition (ICCI) combustion, is proposed to realize high efficiency and clean combustion in wide engine operating ranges. Specifically, commercial gasoline and diesel, which are considered to be complementary in physical and chemical properties, are directly injected into the cylinder by the two independent injection systems, respectively. Through this unique design, the in-cylinder air-fuel mixtures can be flexibly adjusted by regulating injection timing and duration of different fuels, consequently obtaining suitable combustion phase and heat release rate. The ICCI mode can widely run from indicated mean effective pressure 2 bar to 16 bar with an utterly controllable cylinder pressure rising rate, around 50% indicated thermal efficiency and low NOx emissions. A series of experiments were carried out to compare the combustion and emissions of ICCI with other combustion modes (including conventional diesel combustion, reactivity-controlled compression ignition, partially premixed combustion, and gasoline compression ignition). The results show that at the medium engine loads, ICCI mode can reach much high indicated thermal efficiency, especially up to 52% along with extremely low NOx emissions. Prospectively, ICCI mode can realize real-time adjustments of in-cylinder mixture stratification and instantaneous combustion mode switch in one cycle at any operating conditions, and has an excellent commercial application prospect for energy conservation and environmental improvement.

A dual timescale model for micro-mixing and its application in LES-TPDF simulations of turbulent nonpremixed flames

The numerical simulation of modern aero-engine combustion chamber needs accurate description of the interaction between turbulence and chemical reaction mechanism. The Large Eddy Simulation (LES) method with the Transported Probability Density Function (TPDF) turbulence combustion model is promising in engineering applications. In flame region, the impact of chemical reaction should be considered in TPDF molecular mixing model. Based on pioneer research, three new TPDF turbulence-chemistry dual time scale molecular mixing models were proposed tentatively by adding the chemistry time scale in molecular mixing model for nonpremixed flame. The Aero-Engine Combustor Simulation Code (AECSC) which is based on LES-TPDF method was combined with the three new models. Then the Sandia laboratory’s methane-air jet flames: Flame D and Flame E were simulated. Transient simulation results show that all the three new models can predict the instantaneous combustion flow pattern of the jet flames. Furthermore, the average scalar statistical results were compared with the experimental data. The simulation result of the new TPDF arithmetic mean modification model is the closest to the experimental data: the average error in Flame D is 7.6% and 6.6% in Flame E. The extinction and re-ignition phenomena of the jet flames especially Flame E were captured. The turbulence time scale and the chemistry time scale are in different order in the whole flow field. The dual time scale TPDF combustion model has ability to deal with both the turbulence effect and the chemistry reaction effect, as well as their interaction more accurately for nonpremixed flames.

Role of Tween 80 as surfactant in the solution combustion synthesis of TiO2 nanoparticles

TiO2 nanoparticles in the size range of 68–72 nm were prepared by the solution combustion synthesis method. The process was assisted by the use of a biocompatible surfactant, polysorbate (Tween 80). The synthesis was conducted in two steps with the precursors first being incubated with the surfactant and fuel (Dextrose) for 30 min before being subjected to instantaneous combustion at 250 °C. The structural and morphological properties of the resultant nanoparticles were studied and an antimicrobial evaluation was conducted. The irregular shaped nanoparticles elicited antimicrobial responses on both gram positive and gram negative bacteria as well as exhibiting antifungal properties.

Biparametric assessment of the combustion stability in an industrial gas turbine combustor

Here we propose a generalized procedure for a two-parameter assessment of the Combustion stability (CS) of industrial gas turbines. In evaluating the CS, this procedure employs two parameters of measured dynamic pressure data: the Root-mean-square (RMS) pressure as the primary parameter and the damping ratio as a secondary parameter. The former tells the time-averaged level of the dynamic pressure, and, the latter, the degree of acoustic energy loss. A data point pairing the two parameters, which are evaluated at a specific instance of a combustion process, identifies Instantaneous combustion stability (ICS) by its location on a 2-D domain of both parameters. Collective representation of the ICS points on the domain produces a CS map of the combustion process. The locus of the ICS point on the map represents the temporal variation of CS during the combustion process. The biparametric assessment procedure divides the CS map into three regimes (i.e., stable, transitional and unstable) by utilizing two threshold values for the RMS pressure and one for the damping ratio. The feasibility of the proposed procedure was tested with the dynamic pressure data from a model gas turbine combustor burning synthetic natural gas. Then the technique was applied experimental data obtained from a laboratory-scale lean premixed combustor to identify the three regimes of the combustion process of a reported case. We found that the procedure is able to provide gas turbine operators with valuable information on CS during a combustion process, especially on the transitional regime.