Thesis Chapters by Awanish Pratap Singh
Laser-Induced Breakdown Ignition and Combustion Diagnostics Using Optical Methods
PhD Thesis (15AE91R01), 2019
By using the laser-induced spark ignition method, the challenges associated with environmental po... more By using the laser-induced spark ignition method, the challenges associated with environmental pollutants and the production of clean energy can be possibly addressed. In this regard, the method was applied using two lasers (one with low pulse energy (LPE) of 270 𝜇J/pulse, and another with high pulse energy (HPE) of 50 mJ/pulse) to investigate the ignition phenomenon of the atomized ethanol-air spray. With the LPE, no display of ignition was observed even though it fulfils the threshold conditions. Therefore, the experiment with LPE raises some questions to our current understanding. This study answers these questions by highlighting some points raised by pioneers in this field. These answers were further supported by providing experimental evidence while applying a HPE. It was observed that the breakdown created by the LPE was unable to ignite ethanol-air spray mixture because the lifetime of the plasma kernel was very small (in microseconds). While performing the study with HPE, it was observed that the breakdown becomes a sufficient condition for ignition only when the lifetime of the kernel lasts for few milliseconds. If the kernel does not continue for milliseconds, then ignition will not occur even after energy deposition, the energy left with plasma kernel is higher than minimum ignition energy (MIE). To clearly understand the interaction of the breakdown plasma and the fuel spray this study provides some important additional data of laser-induced breakdown (LIB) in ambient air. This additional data led to an enhanced physical understanding of blast wave, third lobe, and plasma kernel. In addition, this understanding aided in answering the questions regarding requirements for initiation of ignition by LPE. To make a useful guideline for designing practical laser ignition system, this study has proposed the favourable conditions for initiating ignition after LIB, which also summarises the overall phenomenon into three chronological stages with their physical time of occurrence. Knowledge of the proposed conditions is not only important for the fundamental understanding of the laser-ignition process, but it can also play a vital role in the selection of lasers, optical windows, and beam delivery system for the design of a practical laser ignition system. A new framework is presented in this study to explain a previously unexplained (generation of third-lobe) and newly observed physical phenomena (generation of fourth-lobe and multiple shock-waves). Additionally, this study also presents the role of the third lobe to help ignition, a new two temperature photoionization equation based on Saha ionization equation, relativistic approach for calculation of shockwave expansion, spray formation process with their effect on spray velocity and spray ignition, and successive laser energy deposition to enhance the lifetime of the plasma kernel.
In automotive technology, an intake manifold is the component of an engine that transports the ai... more In automotive technology, an intake manifold is the component of an engine that transports the air-fuel mixture to the engine cylinders. The main purpose of the intake manifold is to evenly distribute the combustion mixture to each intake port of the engine cylinder. Even distribution is important to optimize the volumetric efficiency and performance of the engine, but the major problem in the thesis was to identify that; to achieve the even distribution of flow at each cylinders, to select the best turbulence model for the analysis of manifold using computational fluid dynamics, to achieve the maximum mass flow rate through the restricted size C-D nozzle, to maintain the equal pressure throughout the plenum, to propagate back the higher pressure column of air to intake port within the duration of the intake valve’s closure. To achieve the even flow of distribution and improve the volumetric efficiency, author divided his analysis into three different part restrictor, plenum, and cylinder runner and then analyzed the final intake manifold. Dividing the work into three different part and then combine them as single manifold part provide the greater refinement in the result and act as meshing of manifold.
To select the best turbulence model for this study, author took the design data of existing experimental model and find that Spalart-Allmaras model was approximately same as the experimental model. For designing the nozzle, author selected the four design variables; nozzle inlet diameter, inlet curvature radius, diffuser half angle and diffuser length with five level of each variable. With these four variable and five level of each variable, author had need to perform 625 experiments, but he design the matrix by the help of Taguchi method using statistical tool “Minitab” and perform only 25 experiment in CFD package “Ansys Fluent”, to find the best result for restrictor, author again use the statistical tool to analyze the design matrix, and then predict the best result for restrictor. To propagate back the higher pressure column of air to intake port within the duration of the intake valve’s closure, author use the Ram Theory and Helmholtz theory to calculate the runner length and diameter as well as total distance traveled by the pressure column during the intake valve closure. To find out the pressure variation in cylinder runner due to intake valve opening and closing, author design virtual engine of the same specification of Kawasaki Ninja ZX-6R by using leading engine designing software “Ricardo Wave”, and then use these pressure data to develop the transient boundary condition in “Ansys Fluent”. To achieve the static pressure inside the plenum and distribute the combustible air evenly to each intake runner, author select two design variables; plenum shape (rectangular, circular, elliptical and curved) and plenum size (2.0litre, 2.25litre, 2.5litre, 2.75litre and 3.0litre). To find the best result for plenum, author perform the experiment in Ansys Fluent for all possible experiment and find the curved and elliptical shape plenum were providing higher volumetric efficiency, static plenum pressure and even flow of distribution to each cylinder.
For designing final intake manifold author select the best design from all three part; restrictor, cylinder runner, plenum; and perform the experiment using computational fluid dynamics software Ansys Fluent, and in result he find that plenum with 2.5litre size curved shape with restrictor of 48mm nozzle inlet diameter, 41mm inlet curvature radius, 152mm diffuser length, and 30and 70 diffuser half angle.
Keywords: Intake Manifold, Plenum, Restrictor, Cylinder Runner, Volumetric Efficiency, Computational Fluid Dynamics
Papers by Awanish Pratap Singh
Intake Manifold Design Using Computational Fluid Dynamics
In automotive technology, an intake manifold is the component of an engine that transports the ai... more In automotive technology, an intake manifold is the component of an engine that transports the air-fuel mixture to the engine cylinders. The main purpose of the intake manifold is to evenly distribute the combustion mixture to each intake port of the engine cylinder. Even distribution is important to optimize the volumetric efficiency and performance of the engine, but the major problem in the thesis was to identify that; to achieve the even distribution of flow at each cylinders, to select the best turbulence model for the analysis of manifold using computational fluid dynamics, to achieve the maximum mass flow rate through the restricted size C-D nozzle, to maintain the equal pressure throughout the plenum, to propagate back the higher pressure column of air to intake port within the duration of the intake valve’s closure. To achieve the even flow of distribution and improve the volumetric efficiency, author divided his analysis into three different part restrictor, plenum, and cylinder runner and then analyzed the final intake manifold. Dividing the work into three different part and then combine them as single manifold part provide the greater refinement in the result and act as meshing of manifold. To select the best turbulence model for this study, author took the design data of existing experimental model and find that Spalart-Allmaras model was approximately same as the experimental model. For designing the nozzle, author selected the four design variables; nozzle inlet diameter, inlet curvature radius, diffuser half angle and diffuser length with five level of each variable. With these four variable and five level of each variable, author had need to perform 625 experiments, but he design the matrix by the help of Taguchi method using statistical tool “Minitab” and perform only 25 experiment in CFD package “Ansys Fluent”, to find the best result for restrictor, author again use the statistical tool to analyze the design matrix, and then predict the best result for restrictor. To propagate back the higher pressure column of air to intake port within the duration of the intake valve’s closure, author use the Ram Theory and Helmholtz theory to calculate the runner length and diameter as well as total distance traveled by the pressure column during the intake valve closure. To find out the pressure variation in cylinder runner due to intake valve opening and closing, author design virtual engine of the same specification of Kawasaki Ninja ZX-6R by using leading engine designing software “Ricardo Wave”, and then use these pressure data to develop the transient boundary condition in “Ansys Fluent”. To achieve the static pressure inside the plenum and distribute the combustible air evenly to each intake runner, author select two design variables; plenum shape (rectangular, circular, elliptical and curved) and plenum size (2.0litre, 2.25litre, 2.5litre, 2.75litre and 3.0litre). To find the best result for plenum, author perform the experiment in Ansys Fluent for all possible experiment and find the curved and elliptical shape plenum were providing higher volumetric efficiency, static plenum pressure and even flow of distribution to each cylinder. For designing final intake manifold author select the best design from all three part; restrictor, cylinder runner, plenum; and perform the experiment using computational fluid dynamics software Ansys Fluent, and in result he find that plenum with 2.5litre size curved shape with restrictor of 48mm nozzle inlet diameter, 41mm inlet curvature radius, 152mm diffuser length, and 30and 70 diffuser half angle. Keywords: Intake Manifold, Plenum, Restrictor, Cylinder Runner, Volumetric Efficiency, Computational Fluid Dynamics
Laser-induced deformation and fragmentation of droplets in an array
International Journal of Multiphase Flow
Video: On the dynamics of vortex droplet co-axial interaction
73th Annual Meeting of the APS Division of Fluid Dynamics - Gallery of Fluid Motion
On the radiative heat loss and axis-switching phenomena of a decaying laser spark
Plasma Sources Science and Technology
A three-dimensional numerical simulation of a decaying laser spark in gaseous nitrogen has been c... more A three-dimensional numerical simulation of a decaying laser spark in gaseous nitrogen has been carried out in Cartesian co-ordinate. The simulation starts with the introduction of a laser pulse in the domain. Thermal equilibrium has been assumed throughout the numerical simulation involving the species N2, N, N+, e−. The boundary conditions are treated following characteristic property of the waves to ensure smooth transmission of the blast wave out of the computational domain. The previously unexplained axis-switching phenomenon of the breakdown region has been explained, and a qualitative comparison of the same with experimental schlieren images has been made. The total radiation loss, including the loss during the breakdown, has been calculated. The variation of inverse Bremsstrahlung radiation, black body radiation, and spectral radiation of atomic nitrogen with time have been shown separately. Additionally, the temporal variation of radiation intensity of atomic nitrogen over ...
Video: Atomization of levitated droplets via laser-induced breakdown
Video: Aerodynamic breakup of droplets in a shock-induced flow
Droplet-droplet interactions is ubiquitous in various applications ranging from medical diagnosti... more Droplet-droplet interactions is ubiquitous in various applications ranging from medical diagnostics to enhancing and optimizing liquid jet propulsion. We employ an experimental technique where the laser pulse interacts with a micron-sized droplet and causes optical breakdown. The synergy of a nanosecond laser pulse and an isolated spherical droplet is accurately controlled and manipulated to influence the deformation and fragmentation of an array of droplets. We elucidate how the fluid dynamic response (such as drop-drop and shock-drop interactions) of an arrangement of droplets can be regulated and optimally shaped by laser pulse energy and its interplay with the optical density of liquid target. A new butterfly type breakup is revealed, which is found to result in controlled and efficient fragmentation of the outer droplets in an array. The spatio-temporal characteristics of a laser-induced breakdown dictate how shock wave and central droplet fragments can influence outer droplets...
On the dynamics of shock-droplet interaction
Numerical Simulation of Laser-Induced Spark by Single and Double Pulse in Quiescent Air
Video: Mechanism of shock-induced aerobreakup of a droplet
74th Annual Meeting of the APS Division of Fluid Dynamics - Gallery of Fluid Motion
Journal of Fluid Mechanics
The multiscale dynamics of a shock–droplet interaction is crucial in understanding the atomisatio... more The multiscale dynamics of a shock–droplet interaction is crucial in understanding the atomisation of droplets due to external airflow. The interaction phenomena are classified into wave dynamics (stage I) and droplet breakup dynamics (stage II). Stage I involves the formation of different wave structures after an incident shock impacts the droplet surface. These waves momentarily change the droplet's ambient conditions, while in later times they are mainly influenced by shock-induced airflow. Stage II involves induced airflow interaction with the droplet that leads to its deformation and breakup. Primarily, two modes of droplet breakup, i.e. shear-induced entrainment and Rayleigh–Taylor piercing (RTP) (based on the modes of surface instabilities) were observed for the studied range of Weber numbers $(We\sim 30\text{--}15\,000)$ . A criterion for the transition between two breakup modes is obtained, which successfully explains the observation of RTP mode of droplet breakup at hi...
Journal of Fluid Mechanics
Interaction of droplets with vortical structures is ubiquitous in nature, ranging from raindrops ... more Interaction of droplets with vortical structures is ubiquitous in nature, ranging from raindrops to a gas turbine combustor. In this work, we elucidate the mechanism of co-axial interaction of a droplet with a vortex ring of different circulation strengths ( $\varGamma = 45\text {--}161\ \textrm {cm}^2\ \textrm {s}^{-1}$ ). We focus on both the droplet and the vortex dynamics, which evolve in a spatio-temporal fashion during different stages of the interaction, as in a two-way coupled system. Vortex rings of varying circulation strengths are generated by injecting a slug of water into a quiescent water-filled chamber. Experimental techniques such as high-speed particle image velocimetry, planner laser-induced fluorescence imaging and high-speed shadowgraphy are used in this work. In the droplet dynamics, different regimes of interaction are identified, including deformation (regime-I), stretching and engulfment (regime-II) and breakup of the droplet (regime-III). Each interaction re...
Spatio-temporal effect of the breakdown zone in the laser-initiated ignition of atomized ethyl alcohol-air mixture
Applied Energy
Abstract Laser initiated ignition would play a vital role in future gas turbine combustors. Two l... more Abstract Laser initiated ignition would play a vital role in future gas turbine combustors. Two lasers of 270 μJ and 50 mJ pulse energy are used to study the laser-induced spark ignition of atomized ethyl alcohol-air mixture. With the low-energy pulse of 270 μJ energy, no display of ignition is observed even though it fulfills the threshold conditions to create breakdown. However, with the high-energy pulse of 50 mJ energy, ignition is observed if the plasma kernel was following certain conditions after the occurrence of the breakdown. It is observed that breakdown created by the low-energy pulse was unable to ignite the atomized ethanol-air mixture because the lifetime of the plasma kernel was very small (in microseconds). While performing the study with high-energy pulse, it is observed that the breakdown becomes a sufficient condition for ignition only when the lifetime of the kernel is couple of milliseconds. Additionally, the spatial location of the laser spark is found to play a vital role in successful ignition of the mixture. This work also discusses the spray formation process with its effect on ignition and the role of the third lobe on rapid development of the plasma kernel. The process of laser energy deposition to full scale combustion is categorized into three events. Finally, based on the experimental observations, this work has proposed some favourable conditions for initiating ignition with a laser spark. Knowledge of the proposed conditions can play a vital role for designing a practical laser ignition system.
LES of Laser Initiation of Combustion of Gaseous Fuel-Air Mixture
Bulletin of the Lebedev Physics Institute
Large Eddy Simulation has been carried out to understand the laser initiation of combustion of le... more Large Eddy Simulation has been carried out to understand the laser initiation of combustion of lean hydrogen-air mixture in homogeneous isotropic turbulence. Initially, the blast wave from the breakdown zone sweeps out most the mixture surrounding the hot core zone at high velocity preventing formation of burning zone. The combustion initiates only if the core zone contains enough heat to sustain a steady flame thereafter.
Two-dimensional numerical simulations on laser energy depositions in a supersonic flow over a semi-circular body
International Journal of Heat and Mass Transfer, 2017
Abstract Two-dimensional numerical simulations are carried out to investigate the effect of laser... more Abstract Two-dimensional numerical simulations are carried out to investigate the effect of laser energy deposition (single pulse, 10 mJ, 50 mJ, and 100 mJ of absorbed energy) ahead of a semicircular body immersed in a Mach 3.45 free-stream. The temperature, pressure, and species composition of the laser energy deposition zone after cessation of the laser pulse is determined by a new and easy method based on Helmholtz free-energy minimization. Either five (O 2 , O, N 2 , N, and NO) or seven species (O 2 , O, N 2 , N, NO, NO + , and electron (e − )) are assumed to exist in the energy deposition zone after cessation of the pulse. It is observed that the energy deposition zone quickly separates itself into a hot core region and a near circular blast wave which travels radially outward while being convected by the flow. Upon interaction of the blast wave and the hot core region with the bow shock ahead of the body, lensing of the bow shock is observed. A small region of reverse velocity field (opposite to the free-stream flow direction) in the interaction region is found to be responsible for the lensing. The pressure jump across the lensed portion of the bow shock decreases and the streamlines passing through the lensed portion with a lower pressure jump is found to be responsible for the wave drag reduction on the body. The hot core region divides itself into two counter-rotating vortices and gets convected by the flow. The line contours of pressure, temperature, Mach number, species concentrations, and vorticity along with numerical schlieren images during the evolution of the energy deposition zone and its interaction with the body bow shock are given. The time histories of nose static pressure, wave drag on the body for the three cases of laser energies are plotted. The average wave drag on the body is found to decrease with increase in laser energy within 10–100 mJ. Some important points on the difference between the existing experimental data (in the open literature) and the results from the present simulations are highlighted.
Journal of Applied Physics, 2022
The interaction of high-temperature plasma with matter has several potential applications. In thi... more The interaction of high-temperature plasma with matter has several potential applications. In this study, we generated laser-induced plasma through single and successive laser energy deposition. The lifetime of the plasma is of paramount importance in most practical applications. However, this cannot be achieved with a single high-energy pulse due to some practical challenges. Therefore we carried out experimental and numerical investigations on the successive laser energy deposition and demonstrated its importance compared to the single pulse energy deposition. It has been observed that during successive energy deposition, the absorption of energy from the second pulse is nonlinear, and the reason for such behaviour is explained in this study. Due to the nonlinear absorption from the second pulse, this study therefore aims to present the pulse interval configuration between the successive pulses with which it is effective for practical use. In this study, some interesting and first...
Two-dimensional numerical simulations on laser energy depositions in a supersonic flow over a semi-circular body
Two-dimensional numerical simulations are carried out to investigate the effect of laser energy d... more Two-dimensional numerical simulations are carried out to investigate the effect of laser energy deposi-tion (single pulse, 10 mJ, 50 mJ, and 100 mJ of absorbed energy) ahead of a semicircular body immersed in a Mach 3.45 free-stream. The temperature, pressure, and species composition of the laser energy depo-sition zone after cessation of the laser pulse is determined by a new and easy method based on Helmholtz free-energy minimization. Either five (O 2 , O, N 2 , N, and NO) or seven species (O 2 , O, N 2 , N, NO, NO + , and electron (e À)) are assumed to exist in the energy deposition zone after cessation of the pulse. It is observed that the energy deposition zone quickly separates itself into a hot core region and a near circular blast wave which travels radially outward while being convected by the flow. Upon interaction of the blast wave and the hot core region with the bow shock ahead of the body, lensing of the bow shock is observed. A small region of reverse velocity field (opposite to the free-stream flow direction) in the interaction region is found to be responsible for the lensing. The pressure jump across the lensed portion of the bow shock decreases and the streamlines passing through the lensed portion with a lower pressure jump is found to be responsible for the wave drag reduction on the body. The hot core region divides itself into two counter-rotating vortices and gets convected by the flow. The line contours of pressure, temperature, Mach number, species concentrations, and vorticity along with numerical schlieren images during the evolution of the energy deposition zone and its interaction with the body bow shock are given. The time histories of nose static pressure, wave drag on the body for the three cases of laser energies are plotted. The average wave drag on the body is found to decrease with increase in laser energy within 10–100 mJ. Some important points on the difference between the existing experimental data (in the open literature) and the results from the present simulations are highlighted.
—Two-dimensional numerical simulations have been carried out to elucidate the flow field when two... more —Two-dimensional numerical simulations have been carried out to elucidate the flow field when two successive laser pulses are applied in the quiescent air. A second pulse is introduced successively in the previously produced breakdown zone of air in first pulse at the same spatial location as the first pulse. The time interval between the two pulses are kept at 1.13µs and 7µs in the present simulation. The dissociation and recombination of air at the high temperature breakdown zone is modeled by five species (O2, O, N2, N, NO) and eleven elementary reactions. The breakdown zone is assumed to absorb an energy of 31mJ/mm 3 from a single laser pulse. The result shows that a layer of shock wave propagates when repetitive pulse is applied instead of single pulse. When the delay between pulses increased from 1.13µs to 7µs the evolution of second blast wave around the breakdown zone is more prominent and propagates with more speed. The result shows the density field perturbations varies according to the time interval between pulses. The roll up motion around the breakdown zone is observed from the numerical schlieren imaging. A prediction is made about the energy available for ignition of a combustible mixture.
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Thesis Chapters by Awanish Pratap Singh
To select the best turbulence model for this study, author took the design data of existing experimental model and find that Spalart-Allmaras model was approximately same as the experimental model. For designing the nozzle, author selected the four design variables; nozzle inlet diameter, inlet curvature radius, diffuser half angle and diffuser length with five level of each variable. With these four variable and five level of each variable, author had need to perform 625 experiments, but he design the matrix by the help of Taguchi method using statistical tool “Minitab” and perform only 25 experiment in CFD package “Ansys Fluent”, to find the best result for restrictor, author again use the statistical tool to analyze the design matrix, and then predict the best result for restrictor. To propagate back the higher pressure column of air to intake port within the duration of the intake valve’s closure, author use the Ram Theory and Helmholtz theory to calculate the runner length and diameter as well as total distance traveled by the pressure column during the intake valve closure. To find out the pressure variation in cylinder runner due to intake valve opening and closing, author design virtual engine of the same specification of Kawasaki Ninja ZX-6R by using leading engine designing software “Ricardo Wave”, and then use these pressure data to develop the transient boundary condition in “Ansys Fluent”. To achieve the static pressure inside the plenum and distribute the combustible air evenly to each intake runner, author select two design variables; plenum shape (rectangular, circular, elliptical and curved) and plenum size (2.0litre, 2.25litre, 2.5litre, 2.75litre and 3.0litre). To find the best result for plenum, author perform the experiment in Ansys Fluent for all possible experiment and find the curved and elliptical shape plenum were providing higher volumetric efficiency, static plenum pressure and even flow of distribution to each cylinder.
For designing final intake manifold author select the best design from all three part; restrictor, cylinder runner, plenum; and perform the experiment using computational fluid dynamics software Ansys Fluent, and in result he find that plenum with 2.5litre size curved shape with restrictor of 48mm nozzle inlet diameter, 41mm inlet curvature radius, 152mm diffuser length, and 30and 70 diffuser half angle.
Keywords: Intake Manifold, Plenum, Restrictor, Cylinder Runner, Volumetric Efficiency, Computational Fluid Dynamics
Papers by Awanish Pratap Singh