Non-reacting Conditions Research Articles

Schlieren and mie-scattering visualization of an evaporating spray under marine diesel engine conditions

Due to the critical influence on combustion, extensive research has been carried out to deepen the understanding of diesel spray evolution. However, for the greater share of land-based diesel engines, most of the studies have focused on the injectors with small nozzle diameter and rare studies can be found on marine diesel engines, which has a larger mass flow rate and longer injection duration with large nozzle diameter. In this study, the influence of injection pressure, ambient temperature, ambient density and nozzle diameter on spray morphology for medium speed marine diesel engine injectors (with nozzle diameter up to 0.53 mm) were investigated under various non-reacting but evaporative conditions. The experiments were performed via a highly enhanced constant volume chamber (highest temperature of 900 K and highest pressure of 8 MPa) with an optical window diameter of 205 mm. Liquid and vapor penetration of sprays were recorded by Mie-scattering and schlieren optical configurations respectively. Results show that the vapor penetration velocity is mainly affected by injection pressure. Ambient temperature has the most significant effect on liquid penetration length, but less effect can be found on the vapor penetration velocity. Given the obvious deviation from heavy duty engine sprays, the empirical correlations for liquid penetration length and vapor spray evolution are updated to fit the spray characteristics of medium speed marine diesel engine injectors, which is helpful to understand the spray behavior for large nozzle diameter injector under marine diesel engine conditions.

Effects of varying the liquid fuel type and air co-flow conditions on the microscopic spray characteristics in an atmospheric annular co-flow spray burner

The atomization process is critical for combustion systems since it directly influences emissions and performance. Thus injection system should provide the spray required structure and characteristics, e.g., angle and droplet size distribution. Therefore, this work investigates the effects of varying the fuel type, air co-flow rates, fuel mass flow rate and air co-flow temperature on the spray characteristics (e.g., droplet size distribution and droplet velocity) in an annular co-flow spray burner. These effects were investigated by measuring droplet sizes and velocities at different radial and axial positions of n-Heptane, n-Decane and n-Dodecane sprays under non-reacting conditions at a room pressure of 1 atm and temperature of 298K and using the Microscopic Diffused Back-illumination (MDBI) technique. In addition, the Sauter mean diameter (SMD) for different flow conditions were predicted using three well-known correlations and compared to experimental measurements. The outcomes of this research provided a fair understanding of the influence of varying these parameters on the droplet sizes and velocity through a wide test matrix. Finally, the findings reported here will support future research into the function of phase change in flame stability.

Identification of flow structures in a closed chamber in the presence of a needle plasma actuator

This study deals with the experimental characterization of the induced flow dynamics by a disk-needle-type plasma actuator driven by a sinusoidal generator and located in a rectangular cross-section burner. Flow characterization was performed using different plasma actuation conditions and standoff distances. Experiments were conducted under non-reactive flow conditions. Electrical characterization was carried out. Airflow behavior was also analyzed using smoke flow visualization. Smoke flow visualization showed the dynamic behavior of the plasma-induced flow. Post-processing of high-quality images was performed by using Proper Orthogonal Decomposition (POD) technique to recognize the dominant flow vortexes and coherent structures. This could support the design of plasma actuation devices in real combustors and be useful for the implementation of numerical models. Moreover, it has been concluded that flow dynamics can be controlled by a variation of the plasma power or the gap distance between two electrodes. Laser Droplet Velocimetry (LDV) was used to investigate the distribution of flow velocities and turbulent kinetic energy (TKE) at different plasma power values of the sinusoidal alternating current generator and standoff distances. From POD and LDV analyses, it has been observed that there is quite a linear relation between the POD energy of the first mode and the maximum TKE. The POD method could be used to identify motions in the flow field carrying the most TKE. TKE peaks are present in the area with the most energetic flow structures, as identified by the POD.

Characterization of ammonia spray combustion and mixture formation under high-pressure, direct injection conditions

Ammonia has the potential to replace fossil fuels in internal combustion engines (ICEs). However, ammonia is characterized by unfavorable combustion characteristics and a propensity to form pollutants during combustion. The pilot-ignited high pressure, direct-injection of ammonia is promising regarding its prospective performance with ammonia as fuel. In this work, optical investigations (Mie-scattering (MS), shadowgraphy (SG), OH* chemiluminescence (CL)) and heat release rate (HRR) analysis are complemented by 1-D spray modeling to provide fundamental insight into distinctive features of ammonia spray combustion and mixture formation under engine-relevant conditions in a rapid-compression-expansion-machine (RCEM). CL measurements reveal that ammonia spray flames do not stabilize after ignition by a diesel pilot injection. Instead, the lift-off length gradually increases until the end of injection and beyond. To aid in the interpretation of the lift-off behavior, a 1-D, mixing-limited spray model is validated by experimental results for ammonia spray penetration and stationary liquid length (LL) under non-reactive conditions. Modeling results reveal that ammonia sprays are marked by low temperatures close to the nozzle exit, followed by a rapid decrease in mean equivalence ratios well below 1. Based on a mechanism that suggests flame stabilization by product re-entrainment and subsequent auto-ignition, the inhibition of flame stabilization in ammonia sprays is explained by high mixing requirements with combustion products to undergo auto-ignition. Implications of the lack of a self-stabilized flame on combustion characteristics are discussed and diesel post-injections, fuel pre-heating and reduction of the natural lift-off length are suggested as measures to avoid extensive pollutant formation in regions upstream of the lift-off length after the end of ammonia injection.

Biodiesel derived from waste cooking oil in blends with ultra-low sulphur diesel and its spray macroscopic properties under split injection strategy

There is a significant interest to evaluate alternative injection strategies in order to improve the performance of biofuels and its blends in internal combustion engines as a way to decarbonize the transport sector, particularly in high potence demand niche. Biodiesel is the renewable analogue for petroleum diesel but the performance assessment of its blends from related to their spray macroscopical properties is scarce in the literature. This article evaluates the effect of Waste Cooking Oil Biodiesel (WCO) produced at semi-industrial scale in blends (B05, B10, B20) with commercial Ultra Low Sulphur Diesel (ULSD) on the fuel spray macroscopic properties such as penetration, angle, and area when a split injection strategy is used in a constant volume chamber under non-reactive and evaporative conditions using an injection and back pressure of 120 MPa and 5 MPa, respectively. These results were analysed in conjunction with relevant physicochemical properties of the fuels to identify the optimum diesel-WCO biodiesel blend, that could be implemented in a conventional diesel engine. It was observed that the increase of density and viscosity directly influences spray tip penetration, whereas surface tension affects spray angle. The values of spray penetration and spray area of all fuels during the second injection were higher than those of the first injection. Accordingly, the first injection event provokes an improvement mixing process of the second injection event in all cases. The values of spray penetration and area corresponding to B10 and B20 were higher than those of B5 and ULSD in both injection events at all times. Therefore, the split injection could be an effective strategy to improve the mixing process of biodiesel blends as well as the efficiency and emission performance in conventional diesel engines.

Droplet cluster evolution and collective gasification of droplet groups in a fuel spray: A comparative study under non-reacting and reacting conditions

In this paper, the goal is to understand the influence of spray combustion on the evolution of droplet clusters and collective gasification processes of droplet groups in a fuel spray. Experiments were conducted in an acetone spray from a pressure swirl injector under both non-reacting and reacting conditions for the same fuel flow rate through the injector. The PIV technique was employed to capture Mie-scattering images of the spray and to measure droplet velocity, while droplet sizing was achieved by application of the ILIDS technique. Voronoi analysis of the PIV images facilitated identification of droplet clusters. Accordingly, the cluster length scale and local droplet number density within clusters could be obtained. In addition, the Group evaporation/combustion number (G) for individual clusters was also evaluated. Either in the presence or absence of spray combustion, wide range of cluster size exists in the spray which highlights multi-scale clustering of droplets. Accordingly, G varies in a broad range that indicates multi-mode evaporation/combustion of the droplet clusters. Distinct behavior of droplet clusters is identified depending on the cluster size relative to the mean cluster area. While the evolution of small clusters is not sensitive to the presence of the spray flame, the length scale of the large-scale clusters and gasification process of such groups of droplets are modified due to spray combustion compared to the non-reacting condition.

Experimental diesel spray characterization of the medium-duty injector with single- and multi-hole nozzle configurations under non-reacting, non-vaporizing conditions

Characteristics of diesel sprays injected through Cummins medium-duty ISB injectors were studied experimentally in an optically accessible constant-volume combustion vessel. The experiments were performed with ultra-low-sulfur diesel (ULSD) under non-reacting and non-vaporizing conditions, including different ambient gas densities (23–65 kg/m3), injection pressures (500–1,500 bar), and injection duration times (0.5–1.5 ms). The ambient temperature of the vessel was maintained at a room temperature of 313 K for all the tests. A systematic comparison was made between single-hole (SH) and multi-hole (MH) injector configurations. A plume-to-plume variation in spray penetration length was observed for various operating conditions. A substantial deviation was observed for a specific hole against the averaged plume, indicating that arbitrary selection of the plume index may result in inaccurate spray characterization of the MH injector. The penetration length of the MH injector was shorter than that of the SH injector under the same operating conditions, indicating that a spray model calibrated on SH injector data may not accurately predict the transient spray behavior of the MH injector in practical engine simulations. A square-root correlation of the spray penetration length was applied for both the SH and MH injectors. The spray penetration length and dispersion angles of the ISB SH injector were also compared with those of the heavy-duty Cummins ISX SH injector. While the ISX SH injector showed a faster penetration than the ISB SH injector, the dispersion angle was similar. The differences in spray penetration between ISB and ISX injectors followed the expected trend based on their nozzle hole diameters.

Conjugate heat transfer characteristics of effusion cooling under realistic swirl flow in a three-sector gas turbine model combustor

• Convective heat transfer inside effusion holes contributes greatly to the heat removal even the film layer is damaged. • The full-coverage cooling film is developed and reachable after swirl flow-cooling jets intense interaction. • The swirl flow impinging location is not influenced by amount of main and cooling flows. · Increment of coolant. Conjugate heat transfer characteristics of the effusion cooling applied on the swirl-stabilized combustor liner is experimentally and numerically investigated in a three-nozzle gas turbine model combustor at non-reacting flow conditions. The interaction between the strong swirl main flow and multi-hole cooling jets inclined at 30° is stressed by varying the pressure drop across the nozzle ( Δ P m = 3–5%) and effusion plate ( Δ P e = 0–2%). The expanding swirl flow impinges on the liner wall and thus inhibits the injection of coolant via effusion holes locally, causing non-uniform cooling protection along both streamwise and lateral directions. The overall cooling effectiveness in the impingement region is much lower than other regions on the cooled plate. Despite of the detrimental effect of the main flow impingement on the formation of the effusion film, the cooling function doesn’t totally collapse due to the great capability of heat removal through convection heat transfer inside the cooling holes. Superposition effect induced full coverage of film on the wall is distinguished at further downstream. Enhancing the cooling air amount weakens the consequence of the mainstream impingement and lead the full coverage initial location to move upwards.

Effect of buoyancy on dispersion of reactive pollutants in urban canyons

In this paper, we aim to investigate the interplay between chemistry, flow dynamics and temperature using high fidelity computational fluid dynamics (CFD) models in an urban environment. A detailed numerical model based on large eddy simulation (LES) is developed considering the temperature and buoyancy effect and the non-equilibrium chemical processes. The model is used to study flow and reaction inside experimental and real-size street canyons. Street canyons are chosen for this study, as they represent the smallest unit of urban environments where detailed flow simulations combined with chemical reactions can be performed with high numerical accuracy. The effect of thermal driven flow is studied in reacting and non-reacting conditions to understand the role of buoyancy in accurately modeling pollutant reaction and dispersion. It is shown that buoyancy has a significant effect on the dynamics of the flow, by altering the main vortex structure inside the canyon and by increasing turbulent kinetic energy. It is also found that the chemical reactions strongly affect final concentrations of pollutants, which indicates the potential need for implementation of more advanced chemical models in future work. The importance of correct boundary conditions to accurately predict pollutant concentrations are discussed. Finally, by comparing the LES results with experimental field measurements in a real street canyon, the limitation of using periodic boundary conditions, as it is commonly used in the literature, is discussed. Moreover, it is shown that implementation of a variable photolysis rate is likely needed.

Lean blowout characteristics of spray flame in a multi-swirl staged combustor under different fuel decreasing rates

Lean Blow Out (LBO) poses a significant safety hazard when occurring in aero-engines. Understanding the lower stability limits of gas turbine combustors and the characteristics of spray flame close to LBO are imperative for safe operation. The objective of this work is to evaluate the effects of fuel decreasing rates and pressure drops of the injector on LBO performances in a multi-swirl staged combustor equipped with an airblast injector. A set of hardware and control system was developed to realize a user-defined fuel supply law. High-speed imaging was applied to record complete LBO processes under the conditions of linear fuel reduction and stable airflow. Partical Image Velocimetry (PIV) and Planar Mie (PMie) scattering were used to acquire the flow fields and spray fields under non-reacting conditions. Experimental results have shown that LBO limits extend to leaner conditions as the pressure drop of the injector increases. With an increase of the fuel decreasing rate, the exhaust temperature before flame extinction increases, and the LBO Fuel-to-Air-Ratio (FAR) decreases. The time evolution of the integral CH* intensity conforms to a linear function during the LBO process. Proper Orthogonal Decomposition (POD) was used to analyze the dynamic characteristics of lean-burn flames. Under different fuel decreasing rates and pressure drops of the injector, flames close to LBO present similar modal spatial distributions, alternately appearing axial, radial, high-order axial, and high-order radial oscillations.

Effect of Spanwise Hole-to-Hole Spacing on Overall Cooling Effectiveness of Effusion Cooled Combustor Liners for a Swirl-Stabilized Can Combustor

Abstract One of the most effective ways to cool the combustor liner is through effusion cooling. Effusion cooling (also known as full-coverage effusion cooling) involves uniformly spaced holes distributed throughout the combustor liner wall. Effusion cooling configurations are preferred for their high effectiveness, low-pressure penalty, and ease of manufacturing. In this article, experimental results are presented for effusion cooling configurations for a realistic swirl driven can combustor under reacting (flame) conditions. The can combustor was equipped with an industrial engine swirler and gaseous fuel (methane), subjecting the liner walls to engine representative flow and combustion conditions. In this study, three different effusion cooling liners with spanwise spacings of r/d = 6, 8, and 10 and streamwise spacing of z/d = 10 were tested for four coolant-to-main airflow ratios. The experiments were carried out at a constant main flow Reynolds number (based on combustor diameter) of 12,500 at a total equivalence ratio of 0.65. Infrared thermography (IRT) was used to measure the liner outer surface temperature, and detailed overall effectiveness values were determined under steady-state conditions. The results indicate that decreasing the spanwise hole-to-hole spacing (r/d) from ten to eight increased the overall cooling effectiveness by 2–5%. It was found that reducing the spanwise hole-to-hole spacing further to r/d = 6 does not affect the cooling effectiveness implying the existence of an optimum spanwise hole-to-hole spacing. Also, the minimum liner cooling effectiveness on the liner wall was found to be downstream of the impingement location, which is not observed in the existing literature for experiments done under nonreacting conditions.

Prediction of Heat Transfer and Fluid Flow Effects on Entropy Generation in a Monolithic Catalytic Converter Using Large-Eddy Simulation.

In the present work, heat transfer and fluid flow and their effects on entropy generation in a realistic catalytic converter of a Lada Niva 21214 vehicle are studied using large eddy simulation. At first, the pressure drop over the catalytic converter is measured for dry air at constant temperature ( K), different volumetric flow rates, and extrapolated to large volumetric flow rates for dry air ( K) and for the exhaust gas under realistic engine conditions ( K) using the Darcy–Forchheimer relation. Then, coupled heat and fluid flow phenomena inside the catalytic converter are analyzed for nonreacting isothermal conditions and nonreacting conditions with conjugate heat transfer by using the large-eddy simulation. The predicted pressure drop agrees well with the measured and extrapolated data. Based on the obtained numerical results, the characteristic flow features are identified, namely: the impinging flow with stagnation, recirculation, flow separation and laminarization within the fine ducts of the monolith, which depends on the heat transfer through temperature-dependent thermophysical properties of exhaust gas. Moreover, due to high-velocity gradients at the wall of the narrow ducts in the monolith, entropy production by viscous dissipation is observed predominantly in the monolith region. In contrast, entropy production due to heat transport is relatively small in the monolith region, while it overwhelms viscous dissipation effects in the pipe regions.

Investigation of colorless distributed combustion regime using a high internal recirculative combustor

This study aims at investigating the combustion characteristics of methane and a hydrogen-rich fuel on distributed regime in a combustor with high internal recirculation as distributed regime can achieve with highly internal entrainment. The model validation was first taken place with the existing experimental results under non-reacting conditions, and it is demonstrated that the mean velocity profiles predicted are in satisfactorily good agreement with the existing data in the combustor. Then, the methane and the hydrogen-rich fuel were consumed at an equivalence ratio of 0.8 and a thermal power of 10 kW under distributed conditions which means that oxygen concentration in the oxidizer is reduced from 21% to 15% along with internal entrainment for each fuel used. The results showed that the velocity magnitudes increased in the combustor with decrease in oxygen concentration because of diluent introduction. Moreover, distributed regime enabled uniformly temperature field inside the combustor together with the ultra-low NO X values with introducing the diluent. In addition, one can say that the maximum temperature and the outlet NO X values (1800 K and 27.60 ppm at 21% O 2 – 1450 K and 0.05 ppm at 15% O 2 for methane, 2000 K and 32.47 ppm at 21% O 2 – 1700 K and 0.19 ppm at 15% O 2 for the hydrogen-rich fuel) were relatively higher while combusting the hydrogen-rich fuel compared to those of methane due to the presence of hydrogen. However, It is concluded that distributed regime provided uniformly temperature fields and ultra-low NO X levels even the hydrogen-rich fuel is used. • Colorless distributed combustion was investigated using a recirculative combustor. • External/internal recirculation zones were obtained in the combustor. • Velocity profiles were highly affected with highly internal recirculation. • More uniform thermal fields and ultra-low NO X emissions were achieved.

Characterization of flow field and combustion dynamics in a novel pressurized side-wall quenching burner using high-speed PIV/OH-PLIF measurements

A novel, pressurized side-wall quenching (SWQ) burner test rig enabling investigations on flame-wall interactions (FWI) of a fully premixed V-shaped flame at conditions mimicking some characteristics of practical devices, e.g. increased pressures and Reynolds numbers, is introduced within this study. Two operating cases featuring turbulent flow conditions at atmospheric and 3 bar operating pressure are defined and characterized based on velocity fields and flame front positions provided by simultaneous high-speed particle image velocimetry (PIV) and planar laser-induced fluorescence of the OH radical (OH-PLIF). For non-reacting conditions, profiles of mean velocities and mean velocity fluctuations are measured in addition to near-wall flow fields at locations where FWI occurs for chemically reacting conditions. For reacting conditions, near-wall flows are characterized in the vicinity of the quenching zone. Based on measured fluctuations of the streamwise velocity component, the turbulent flame is classified at the transition from the wrinkled to the corrugated flamelet regime. Using the derived flame front positions, the instantaneous flame-wall interaction is classified into SWQ-like, head-on quenching (HOQ)-like and multi-zone quenching events and the transition between these scenarios is identified by means of OH-PLIF image sequences. A statistical analysis of the flame front topology is performed based on the flame brush and deduced frequency distributions. Statistically significant differences between both operating cases are confirmed by chi-squared homogeneity tests.

Effect of acoustic perturbation on particle dispersion in a swirl-stabilized pulverized fuel burner: Cold-flow conditions

Inter-particle distance and particle dispersion during gasification of biomass have been found to significantly affect soot emission. Consequently, enhanced particle dispersion decreases energy losses and the risk for blockages of downstream equipment, increasing the efficiency and reliability of entrained flow reactors (EFRs). In this work, we investigated the interactions between imposed acoustic oscillations and particle dispersion under non-reacting conditions in a co-axial burner for a lab-scale EFR. A flow of air, laden with pulverized stem wood particles (Norwegian Spruce) of three different sizes (63–112 μm, 200–250 μm, and 500–600 μm), was forced axially through the burner center tube at Reynolds numbers ranged from 800 to 1700, and loading ratio of 0.7–4.2. The influences on particle dispersion from variations of the Strouhal number (0.12–0.6), the pressure amplitude at synthetic jet cavity (0.5–4.0 kPap-p), the swirl number (0–2.3), and the center jet velocity (1.9–3.9 m s−1) were investigated. Post-processed shadowgraph images revealed the influence of acoustic perturbations, which generate large structures with high particle concentration for both swirling and non-swirling conditions. Time-averaged contour maps showed a significantly higher particle dispersion, quantified as dispersion angle, for higher values of forcing amplitude and swirl numbers, with a stronger influence from the forcing amplitude, especially at lower Stokes number.

Investigation into Thermal-Fluid interaction of ammonia turbulent swirling flames under various Non-Premixed burner conditions

This study deals with flow and turbulence interaction of an ammonia flame in a non-premixed burner. Numerical investigations have been performed on the velocity field, thermal field and the turbulence parameters for various oxidizers. In order to validate the simulations and select the most favorable turbulence model, some modeling have first been performed under non-reacting conditions, and the predictions are compared with the measurements. Although the predicted results obtained by using all k-epsilon models are in acceptable consistency with the experimental values, the predictions acquired through RNG k-epsilon model have showed more consistent results with the experimental measurements since there are swirling flows in the flow-field. The further modeling results under the reacting conditions showed the main flow and the external recirculation regions occurred in the flow-field. However, a central recirculation zone was not observed for all cases studied. It is revealed that the predicted axial velocity values for ammonia-air combustion are higher than those of oxy-conditions in the reaction zone. The radial and the tangential velocity values are lower than axial velocity values for all cases. Besides, the tangential velocity component is much lower in case of the ammonia-oxy combustion. It was observed that high turbulence intensity values (about % 350 and % 290 for oxy- and air-combustion) occurred in the mixing zone due to mean velocity affecting velocity fluctuations. Moreover, a consistency between the temperature and the velocity profiles has been predicted in the main flow zone.

Observational comparative study in Kühni and ORC agitated columns for the mechanism and performance of molybdenum extraction under various hydrodynamic conditions

The present work is expressed to interpret the hydrodynamic parameters of rotation extraction columns in the reactive and non-reactive systems. The solvent extraction technique has been utilized for optimizing the transportation of molybdenum ions to the organic phase in two agitated columns (ORC and Kühni columns). Dispersed phase volume fraction, average droplet diameter, slip velocity, size distribution, and ions permeability of the aqueous phase have been investigated in terms of changing the operational variables including the agitation rate, flow rate of the inlet dispersed and continuous phases, column geometry, and reaction conditions. By considering the reactive and non-reactive conditions, the responses investigated indicated that the alteration in the agitation rate and reaction systems on the hydrodynamic parameters is considerable in comparison with the column geometry as well as both phase flow rates. Previous experimental research works for anticipating the drop behavior, holdup values, and slip velocity of droplets in different rotary columns have been reviewed and several new models have been derived by considering the geometric parameters and reactive or physical systems. The solvent extraction findings showed that the rotary extraction columns could be utilized as a suitable mass transfer device for chemical reaction systems.

Influence of wall mounted ramps on DLR strut scramjet combustor under non-reacting flow field

The scramjet technology is considered to be the advanced engine for high-speed transportations. The present numerical examination addresses the influence of double ramp's implications in the scramjet engine combustor walls accompanied by strut injection technique under non-reacting flow conditions. The numerical analyses are performed using simulation software, ANSYS Fluent 18.0. Computational problems have been modeled using Reynolds averaged Navier-Stokes (RANS) equations. The inlet flow condition of the model is Mach (Ma) 2 and sonic speed hydrogen fuel from the strut is driven along the flow direction. The characteristics of flow for the two-dimensional (2D) combustor models are studied using shadowgraph images and Mach number contours. Numerical solutions are analogized with the published experimental outcome for validation. The wall static pressure values are higher at the vicinity of the strut ramps regions due to the additional shock interactions generated from the ramps compared to the DLR scramjet model. The subsonic zones are created due to additional shock waves and enhance air–fuel mixing for ramp-mounted combustors. The total pressure loss across the combustor increases as the ramps are positioned downstream of the strut.

Simulation on non-ideal behaviour of plug flow bioreactor based on the growth study of Lactobacillus species

ABSTRACT The physical properties of a biological system vary with time due to the growth of biomass, and thus the flowability of such a medium inside any bioreactor also changes with time. The present study aims to study the non-ideal behaviour of a plug flow bioreactor (PFBR) under non-reactive conditions for a biological system. Different physical parameters of this study have been incorporated from the batch growth study of Lactobacillus sp. The growth of bacteria culture was simulated using a PVA solution to conduct residence time distribution (RTD) experiments in pulse and step mode. Different parameters of the dispersion model were measured, and the non-zero variance indicated that dispersion always occurred along the path of reaction which led to turbulence and diffusion. The Peclet No was non-infinite; thus, PFBR always deviates from the ideal behaviour of the plug flow reactor. During the velocity distribution study, it had also been established that the Peclet number was decreased with the increase of Reynolds Number at a certain medium viscosity. Moreover, the non-ideality of PFBR further increased due to the change of physical properties of the medium. Here, a polynomial relation had been established between the Peclet number and medium viscosity. Therefore, the current study might be a value addition towards the designing of the plug flow bioreactor.

Influence of thermal wall boundary condition on scalar statistics during flame-wall interaction of premixed combustion in turbulent boundary layers

The influence of thermal wall boundary conditions on the behaviour of scalar statistics during flame-wall interaction (FWI) of premixed flames within turbulent boundary layers has been investigated. Three-dimensional direct numerical simulations (DNS) of two different flow configurations for flames interacting with chemically inert isothermal as well as adiabatic walls in fully developed turbulent boundary layers have been performed. The first configuration is an oblique wall interaction (OWI) of a V-flame in a turbulent channel flow and the second configuration is representative of head-on interaction (HOI) of a planar flame in a turbulent boundary layer. The turbulence in the non-reacting conditions for these simulations is representative of a friction velocity based Reynolds number of Reτ=110 while the combustion characteristics are representative of stoichiometric methane–air mixture under atmospheric conditions. Differences in the mean behaviours of the progress variable and non-dimensional temperature have been observed for the two configurations in response to different wall boundary conditions. Mean scalar variance of the progress variable and temperature and their respective scalar dissipation rates have been investigated and it is found that the variances of the progress variable and temperature remain coupled in the case of adiabatic walls, while significant differences exist between these quantities in the vicinity of the wall under isothermal wall conditions for both flow configurations. The mean scalar dissipation rates of progress variable and temperature during FWI decrease towards the wall in both flow configurations under different thermal wall boundary conditions, but in the case of isothermal wall conditions a higher scalar dissipation rate for the non-dimensional temperature is observed when compared with the scalar dissipation rate for the progress variable. The behaviours of the mean turbulent scalar fluxes of progress variable and the non-dimensional temperature suggest that the scalar fluxes can show both gradient and countergradient type behaviour depending on the flow configuration and also on the proximity of the flame to the wall. In the case of V-flame OWI, the choice of the wall boundary condition has a significant influence on the behaviour of the scalar fluxes, whereas in the case of turbulent boundary layer HOI, no significant differences in the scalar fluxes are observed for different wall boundary conditions.