Ahsan Choudhuri

Combustion characteristics of hydrogen-hydrocarbon hybrid fuels

A comparative study of the flame structure and characteristics of diffusion flames of the mixture of hydrogen–hydrocarbon (natural gas and propane) hybrid fuel in a slow co-flowing stream of air is presented. The volumetric content of natural gas and propane in the mixture was varied from 0–35%. The burner exit Reynolds number was varied from 150–3000. Measurements include flame length, radiative fraction of heat release, pollutant emission indices and in-flame profiles of composition and temperature. Results indicate: the increase of natural gas or propane in the hydrogen–hydrocarbon mixture increases the flame luminosity and flame length, increases the radiative heat loss fraction and soot concentration, decreases both NO and NOx emission indices, increases the CO emission index, and decreases the peak temperature in the near burner, mid flame and far-burner regions. The changes are quantified in the paper.

Characteristics of hydrogen-hydrocarbon composite fuel turbulent jet flames

The characteristics (flame length, pollutant emission, radiative heat loss fraction, and volumetric soot concentration) of hydrogen–hydrocarbon composite fuel turbulent jet diffusion flames are presented. A correlation of flame length with hydrogen concentration in the fuel mixture is shown. The reactivity of fuel mixture increases with the increase of hydrogen concentration, which ultimately shortens the combustion time, and thereby reduces the overall flame length. Convective time scale decreases with the increase of hydrogen content in the mixture. The measured and predicted flame lengths show a similar trend; however, the predicted values are 1.4 times higher than the measured values. Axial soot concentration decreases, the CO emission index decreases, but, NO and NOx emission indices increase at higher hydrogen concentrations in the mixture.

Concept and Model of a Metamaterial-Based Passive Wireless Temperature Sensor for Harsh Environment Applications

Wireless passive temperature sensors are receiving increasing attention due to the ever-growing need of improving energy efficient and precise monitoring of temperature in high-temperature energy conversion systems, such as gas turbines and coal-based power plants. Unfortunately, the harsh environment, such as high temperature and corrosive atmosphere present in these systems, has significantly limited the reliability and increased the costs of current solutions. Therefore, this paper presents the concept and design of a low cost, passive, and wireless temperature sensor that can withstand high temperature and harsh environments. The temperature sensor was designed following the principle of metamaterials by utilizing closed ring resonators in a dielectric ceramic matrix. The proposed wireless, passive temperature sensor behaves like an

Stability of Hydrogen/Hydrocarbon Blended Fuel Flames

LC

Flame Extinction Limits of H2‐CO Fuel Blends

circuit, which has a temperature-dependent resonance frequency. Full-wave electromagnetic solver Ansys Ansoft HFSS was used to validate the model and evaluate the effect of different geometry and combination of split ring resonator structures on the sensitivity and electrical sizes of the proposed sensor. The results demonstrate the feasibility of the sensor and provide guidance for future fabrication and testing.

Effects of Fuel Compositions on the Structure and Yield of Flame Synthesized Carbon Nanotubes

Anexperimentalandnumericalinvestigationispresented todelineatetheeffectson thestability ofnaturalgasjet e ames when hydrogen is added. It is observed that the e ame liftoff height decreases nonlinearly with the addition of hydrogen in a natural gas e ame. Blowout velocity sharply increases with theincrease of hydrogen content in the mixture. It is evident that hydrogen fuel dominates the stability behavior of the mixed fuel. The turbulent mixing rate of nonreacting hydrogen/hydrocarbon hybrid fuel was computed numerically. The Favre averaged Navier ‐ Stokes equations were solved numerically, and the local concentrations of hydrogen and hydrocarbon fuels were calculated for different inlet mixture conditions. The signie cance of the local concentration on the e ame stability mechanism is presented. Nomenclature BH = function of mass diffusivity of atom H BO = function of mass diffusivity of atom O BOH = function of mass diffusivity of radical OH Cr = concentration of the reactant mixture DH = binary diffusion coefe cient of H atom DO = binary diffusion coefe cient of O atom DOH = binary diffusion coefe cient of OH radical dj = burner diameter H = characteristic e ame length, Eq. (4) h = e ame length k 0 = general rate of reaction for hydrocarbon fuel L H = normalized liftoff height RH = Reynolds number based on characteristics e ame length H Re j = jet exit Reynolds number r = multiplication factor .SL/max = maximum laminar e ame speed for pure fuel Ub = blowout velocity Un = normalized blowout velocity

Investigation of Combustion Instability Effects on the Flame Characteristics of Fuel Blends

The flame extinction limits of syngas (H2‐CO) flames were measured using a twin-flame counterflow burner. Plots of extinction limits (%f: volumetric percent of fuel in air) versus global stretch rates were generated at different fuel blend compositions and were extrapolated to determine the flame extinction limit corresponding to an experimentally unattainable zero-stretch condition. The zero-stretch extinction limit of H2‐CO mixtures decreases with the increase in H2 concentration in the mixture. The average difference between the measured flame extinction limit and the Le Chatelier’s calculation is around 7% of the mean value. The measured OH chemiluminescence data indicates that regardless of blend composition the OH radical concentration reduces to a critical value prior to the flame extinction. The measured laminar flame velocity close to the extinction indicates that regardless of fuel composition, the premixed flame of hydrogen fuel blends extinguishes when the mixture laminar flame velocity falls below a critical value.

Laminar flame velocity of syngas fuels

Abstract Flame synthesis of carbon nanostructures including nanotubes on galvanized steel was investigated utilizing laminar diffusion flames of different types of fuel. Methane (CH4), propane (C3H8) and acetylene (C2H2) were used as fuels. Distinctive carbon nanostructures were produced depending on fuel types and fuel flow rates. The qualitative and quantitative analysis of many transmission electron microscope (TEM) and scanning electron microscope (SEM) images were performed. Methane produced thin multi wall carbon nanotubes as well as nanorods and nanofibers within the fuel flow rate range of 7.18E‐07 m3/s to 9.57E‐07 m3/s. Propane yielded nanotubes only at the fuel flow rate of 4.20E‐07 m3/s. The nanotubes synthesized by acetylene flames were of different types that included helically coiled and twisted nanotubes.

Experimental Investigation of Transient Forced Convection of Liquid Methane in a Channel at High Heat Flux Conditions

The flashback propensity and flame extinction combustion instabilities are investigated in hydrogen based fuel blends (ranging from 0 ‐ 25% volumetric composition) of CH 4 ‐ H 2 and CO ‐ H2. A one-dimensional counterflow twin flame burner is engineered to investigate the flame extinction trends. A burner system with interchangeable burner exits of various diameters is designed to investigate the flashback propensity. S uch a system allows in analyzing the effect of burner exit diameter on the flashback propensity of fuel blends. The high burning velocity of hydrogen increases the flashback propensity in fuel blends. However, the presence of hydrogen in fuel blends strengthens the flame surfaces and prov ides greater flame stability. These flames tend to extinct at much leaner air-fuel ratios at a given s tretch rate. The presence of external oscillations enhances the flame instabilities, both in flashback propensity and flame extinction processes. Higher the frequency or amplitude of these external oscill ations, greater is the flame instabilities.

An investigation on the mixing and flame behavior of microcombustors

The paper presents the experimental measurements of the laminar burning velocity of H2 -CO mixtures. Hydrogen (H2 ) and carbon monoxide (CO) are the two primary constituents of syngas fuels. Three burner systems (nozzle, tubular, and flat flame) are used to quantify the effects of burner exit velocity profiles on the determination of laminar flame propagation velocity. The effects to N2 and CO2 diluents have been investigated as well, and it is observed that the effects of N2 and CO2 on the mixture burning velocity are significantly different. Finally, the burning velocity data of various syngas compositions (brown, bituminous, lignite and coke) are presented.Copyright