Boiling is used in a wide variety of industries, including electronics cooling, distillation, and power generation. Fundamental studies on the boiling process are needed for effective implementation. Key performance characteristics of boiling are the heat transfer coefficient, which determines the amount of heat flux that can be dissipated for a given superheat, and critical heat flux(CHF), the failure point that occurs when vapor blankets the surface. The wettability of a surface is one of the key parameters that affects boiling behavior. Wetting surfaces(e.g., hydrophilic surfaces), typically characterized by a static contact angle below 90°,have better critical heat flux due to effective rewetting, but compromised heat transfer coefficients due to increased waiting times between nucleation of each bubble. Meanwhile, nonwetting surfaces (e.g., hydrophobic surfaces), characterized by static contact angles greater than 90°, have better heat transfer coefficients due to improved nucleation characteristic, but reach critical heat flux early due to surface dry out. However, recent studies have shown that the static contact angle alone offers and incomplete, and sometimes inaccurate, description of this behavior, which is instead governed entirely by the dynamic wettability. Specifically, the receding contact angle impacts the size and contact area of bubbles forming on a surface during boiling, while the advancing contact angle determines how the bubble departs. With this more complete set of wettability descriptors, three characteristic wetting regimes define the boiling behavior: hygrophilic surfaces having advancing and receding contact angles both under 90°; hygrophobic surfaces having both these dynamic contact angles over 90°;and ambiphilic surfaces having a receding contact angle less than 90°, but an advancing contact angle greater than 90°.The goal of this thesis is to experimentally characterize and compare the behavior of boiling surfaces in each of these regimes, observe the contact line behavior, and explain the mechanisms for their differences in performance.

<div>A microheater and resistance temperature detector (RTD) are designed and fabricated for various applications. First, a hierarchical manifold microchannel heatsink with an integrated microheater and RTDs is demonstrated. Microfluidic cooling within the embedded heat sink improves heat dissipation, with two-phase operation offering the potential for dissipation of very high heat fluxes while maintaining moderate chip temperatures. To enable multi-chip stacking and other heterogeneous packaging approaches, it is important to densely integrate all fluid flow paths into the device. Therefore, the details of heatsink layouts and fabrication processes are introduced. Characterization of two-phase cooling as well as reliability of the microheater/RTDs are discussed. In addition, another application of microheater for mining particle detection using interdigitated capacitive sensor. While current personal monitoring devices are optimized for monitoring microscale particles, a higher resolution technique is required to detect sub-micron and nanoscale particulate matters (PM) due to smaller volume and mass of the particles. The detection capability of the capacitive sensor for sub-micron and nanoparticles are presented, and an incorporated microheater improved stable capacitive sensor reading under air flow and various humidity. </div><div>This paper also introduces the characterization of nanomaterials such as metallic nanowires (NWs) and single layer graphene. First, the copper nanowire (CuNW)/graphene hybrid networks for transparent conductors (TC) is investigated. Though indium tin oxide (ITO) has been widely used, demands for the next generation of TC is increasing due to a limited supply of indium. Thus, the optical and electrical properties of CuNW/graphene hybrid network are compared with other transparent conductive materials including ITO. Secondly, silver nanowire (AgNW) growth technique using electrodeposition is introduced. A vertically aligned branched AgNW arrays is made using a porous anodic alumina template and the optical properties of the structure are discussed.</div><div><br></div>

<div>This dissertation focuses on a consistent and conservative Phase-Field method for multiphase flow problems, and it includes both model and scheme development. The first general question addressed in the present study is the multiphase volume distribution problem. A consistent and conservative volume distribution algorithm is developed to solve the problem, which eliminates the production of local voids, overfilling, or fictitious phases, but follows the mass conservation of each phase. One of its applications is to determine the Lagrange multipliers that enforce the mass conservation in the Phase-Field equation, and a reduction consistent conservative Allen-Cahn Phase-Field equation is developed. Another application is to remedy the mass change due to implementing the contact angle boundary condition in the Phase-Field equations whose highest spatial derivatives are second-order. As a result, using a 2nd-order Phase-Field equation to study moving contact line problems becomes possible.</div><div><br></div><div>The second general question addressed in the present study is the coupling between a given physically admissible Phase-Field equation to the hydrodynamics. To answer this general question, the present study proposes the <i>consistency of mass conservation</i> and the <i>consistency of mass and momentum transport</i>, and they are first implemented to the Phase-Field equation written in a conservative form. The momentum equation resulting from these two consistency conditions is Galilean invariant and compatible with the kinetic energy conservation, regardless of the details of the Phase-Field equation. It is further illustrated that the 2nd law of thermodynamics and <i>consistency of reduction</i> of the entire multiphase system only rely on the properties of the Phase-Field equation. All the consistency conditions are physically supported by the control volume analysis and mixture theory. If the Phase-Field equation has terms that are not in a conservative form, those terms are treated by the proposed consistent formulation. As a result, the proposed consistency conditions can always be implemented. This is critical for large-density-ratio problems.</div><div><br></div><div>The consistent and conservative numerical framework is developed to preserve the physical properties of the multiphase model. Several new techniques are developed, including the gradient-based phase selection procedure, the momentum conservative method for the surface force, the boundedness mapping resulting from the volume distribution algorithm, the "DGT" operator for the viscous force, and the correspondences of numerical operators in the discrete Phase-Field and momentum equations. With these novel techniques, numerical analyses ensure that the mass of each phase and momentum of the multiphase mixture are conserved, the order parameters are bounded in their physical interval, the summation of the volume fractions of the phases is unity, and all the consistency conditions are satisfied, on the fully discrete level and for an arbitrary number of phases. Violation of the consistency conditions results in inconsistent errors proportional to the density contrasts of the phases. All the numerical analyses are carefully validated, and various challenging multiphase flows are simulated. The results are in good agreement with the exact/asymptotic solutions and with the existing numerical/experimental data.</div><div> </div><div><br></div><div>The multiphase flow problems are extended to including mass (or heat) transfer in moving phases and solidification/melting driven by inhomogeneous temperature. These are accomplished by implementing an additional consistency condition, i.e., <i>consistency of volume fraction conservation</i>, and the diffuse domain approach. Various problems are solved robustly and accurately despite the wide range of material properties in those problems.</div>

<p> With new technologies taking advantages of the rapid miniaturization of devices to microscale across emerging industries, there is an unprecedented increase in the heat fluxes generated. The relatively low phase-change thermal resistance associated with boiling is beneficial for dissipating high heat flux densities in compact spaces. However, for boiling heat transfer, a high degree of geometrical confinement significantly alters two-phase interface dynamics which affects the flow pattern, wetting dynamics, and moreover, the heat transfer rate of the boiling processes. Hence, it is crucial to have a deeper understanding of the mechanistic effects of confinement on two-phase heat dissipation and carefully examine the applicability of boiling correlations developed for unconfined pool boiling to predict and optimize design of extremely compact two-phase thermal management solutions. This dissertation develops and demonstrate a fundamental understanding of the impact of confinement on pool boiling. To elucidate the mechanisms that impact confined boiling, this study experimentally evaluates boiling characteristics through the quantification of boiling curves and high-speed visualization across a range of gap spacing smaller than the capillary length of the working fluid. </p> <p><br></p> <p> This work reveals the existence of two distinct boiling regime uniquely observed in boiling in confined configurations (namely, intermittent boiling and partial dryout). In contrast to pool boiling where the maximum heat transfer coefficient occurs below the critical heat flux limit, the intermittent boiling regime demonstrates the highest heat transfer coefficient in confined boiling. Then, this study provides a mechanistic explanation for the enhanced heat transfer rate due to geometrical confinement. Mainly, small residual pockets of vapor, termed ‘stem bubbles’ herein, remain on the boiling surface through a pinch-off process. These stems bubbles act as seeds for vapor growth in the next phase of the boiling process without the need for active nucleation sites. Furthermore, this dissertation develops a more accurate, mechanistic-based model for the phenomena that occur at CHF in confined configurations. The newly developed mechanistic understanding and model provides guidance on new directions for designing extremely compact two-phase thermal solutions.</p>

<p>The subcutaneous injection has emerged as a common approach for self-administration of biotherapeutics due to the patient comfort and cost-effectiveness. However, the available knowledge about transport and absorption of these agents after subcutaneous injection is limited. Here we aim to find drug distribution in the tissue and lymphatic uptake after subcutaneous (SC) injection. In the first part of the study, a mathematical framework to study the subcutaneous drug delivery from injection to lymphatic uptake is presented. A three-dimensional poroelastic model is exploited to find the biomechanical response of the tissue by taking into account tissue deformation during the injection. The results show that including tissue deformability noticeably changes tissue poromechanical response due to the significant dependence of interstitial pressure on tissue deformation. Moreover, the importance of the amount of lymph fluid at the injection site and injection rate on the drug uptake to lymphatic capillaries is highlighted. Finally, the variability of lymphatic uptake due to uncertainty in parameters, including tissue poromechanical and lymphatic absorption parameters, is evaluated. It is found that interstitial pressure due to injection is the major contributing factor in short-term lymphatic absorption, while the amount of lymph fluid at the site of injection determines the long-term absorption of the drug. Finally, it is shown that the lymphatic uptake results are consistent with experimental data available in the literature.</p><p>In the second part, drug transport and distribution in different tissue layers are studied. A single-layer model of the tissue as a base study was first explored. During injection, the difference between the permeability of the solvent and solute results in a higher drug concentration proportional to the inverse of the permeability ratio. Then the effects of layered tissue properties with primary layers, including epidermis, dermis, subcutaneous, and muscle layers, on tissue biomechanical response to injection and drug transport are studied. The drug distributes mainly in the SQ layer due to its lower elastic moduli. Finally, the effect of secondary tissue elements like the deep fascia layer and the network of septa fibers inside the SQ tissue is investigated. The Voronoi algorithm is exploited to create random geometry of the septa network. It is shown how drug molecules accumulate around these tissue components as observed in experimental SC injection. Next, the effect of injection rate on drug concentration is studied. Higher injection rates slightly increase the drug concentration around septa fibers. Finally, it is demonstrated that the concentration-dependent viscosity increases the concentration of biotherapeutics in the direction of septa fibers.</p><p>In the third part of this thesis, a poro-hyperelastic model of the tissue is exploited to find the biomechanical response of the tissue together with a transport model based on an advection-diffusion equation in large-deformation poro-hyperelastic Media. The process of mAbs transport to the lymphatic system is explored. This process has two major parts. First, the initial phase, where mAbs are dispersed in the tissue as a result of momentum exerted by injection. This stage last for only a few minutes after the injection. Then there is the second stage, which can take tens of hours, and as a result, monoclonal antibodies (mAbs) molecules are transported from the subcutaneous layer towards initial lymphatics in the dermis to enter the lymphatic system. In third chapter, both stages are studied. The process of plume formation, interstitial pressure, and velocity development is explored. Then the effect of the injection device, injection site, and sensitivity of long-term lymphatic uptake due to variability in permeability, diffusivity, viscosity, and binding of mAbs are investigated. Then the results are used to find an equivalent lymphatic uptake coefficient that is widely used in pharmacokinetic (PK) models to study the absorption of mAbs. We show that the injection rate is the least, and the injection site is the most important parameter in the uptake of mAbs. Injection depth and mAbs dose also significantly alter lymphatic absorption. Finally, the computational model is validated against experimental studies available in the literature.</p>

<p>  </p> <p>In gas turbines, the hot gas exiting the combustor can be as high as 2000 ^oC, and some of this hot gas enter into the space between the stator and rotor disks (wheelspace). Since the hot gas entering with its high temperatures could damage the disks, hot-gas ingestion must be minimized. This is done by using rim seals and by introducing a flow of cooler air from the compressor (sealing flow) into the wheelspace. </p> <p>Ingress and egress into rim seals are driven by the stator vanes, the rotor and its rotation, and the rotor blades. This study focuses on the first-stage turbine, where ingress could cause the most damage and has two parts. The first part focuses on understanding ingress and egress driven by the rotor and its rotation, known as rotationally-induced ingress, by studying ingress about an axial seal in a stator-rotor configuration without vanes and without blades. The second part focuses on understanding ingress and egress driven by stator vanes, known as externally-induced ingress, by studying a stator-rotor configuration with vanes but no blades, where the ratio of the external Reynolds number to the rotational Reynolds number is 0.538. For both parts, solutions were generated by wall-resolved large-eddy simulation (LES) based on the WALE subgrid model and by Reynolds-averaged Navier-Stokes (RANS) based on the SST model. For both stator-rotor configurations, the grid-independent solutions obtained were compared with available experimental data.   </p> <p>Results obtained for the configuration without vanes and blades show Kelvin-Helmholtz instability (KHI) to form even without swirl from the hot-gas flow and to create a wavy shear layer on the rotor. Also, Vortex shedding (VS) occurs on the backward-facing side of the seal and impinges on the rotor side of the seal. The KHI and VS produce alternating regions of high and low pressures about the rotor-side of the axial seal, which cause ingress to start on the rotor side of the seal. Results obtained for the configuration with vanes but no blades show both LES and RANS to correctly predict the coefficient of pressure, C_p, upstream of the axial seal. However, only LES was able to correctly predict the sealing effectiveness. This shows C_p by itself maybe is inadequate in quantifying externally-induced ingress. One reason why RANS was unable to predict sealing effectiveness is significantly under predicting the pressure drop on the rotor surface, which affected the pressure variation along the hot-gas path and hence the pressure difference across the axial seal, which ultimately drives ingress. </p>

<p>  </p> <p>Recent developments in radiative cooling paints have shown significant promise towards commercialization of the technology. Therefore, questions have been asked as to how the durability of these paints could be evaluated and improved, as well as how these paints could impact energy use and global climate change. In this work, a paint formulation was developed using nanoplatelet hBN pigments with an MP-101 binder from SDC Technologies, Inc. This formulation shows similar reflective properties to that of an hBN acrylic formulation (97.5% and 97.9% reflectance, respectively) while boosting a water droplet contact angle of as much as 120°, proving hydrophobicity and therefore self-cleaning properties. Additionally, a comprehensive study was conducted to understand the potential impact of the radiative cooling paints on the changing global climate. Three potential impacts of the paint were discussed, including capture and utilization of CO2 into the CaCO3 paint, the reduction of HVAC usage on buildings painted with the RC paints, and net cooling of the earth due to the solar reflection and thermal emission of the paint into deep space. It was discovered that all three parts had a positive impact on the global climate, regardless of which US climate zone the representative building was in. Additionally, it was found that the paints could reduce as much as an equivalent 539 lbs CO2eq from the atmosphere for each m2 of the paint applied.</p>

<p>  </p> <p>With economies shifting towards net-zero carbon emissions, there is an increased interest in carbon-free energy carriers. Hydrogen is a potential carbon-free energy source. However, it poses several production, infrastructural, and safety challenges. Ammonia blends have been identified as a potential hydrogen carrier and fuel for gas turbine combustion. Partially cracked ammonia mixtures consist of large quantities of hydrogen that help overcome the disadvantages of pure ammonia combustion. The presence of nitrogen in the fuel blends leads to increased NO_x emissions, and therefore lean premixed combustion is necessary to curb these emissions. Understanding the flame features, precursors, and dynamics of blowout of such blends due to lean conditions is essential for stable operation, lean blowout prediction, and control. </p> <p><br></p> <p>In this study, high-fidelity large eddy simulations for turbulent premixed ammonia/hydrogen/nitrogen-air flames in an axisymmetric, unconfined, bluff-body stabilized burner are performed to gain insights into lean blowout dynamics. Partially cracked ammonia (40% NH₃, 45% H₂, and 15% N₂, by volume) is chosen as fuel since its laminar burning velocity is comparable to CH4-air mixtures. A finite rate chemistry model with a detailed chemical kinetic mechanism (36 species and 247 reactions) is utilized to capture characteristics of various species during blowout. A comprehensive study of the flow field and flame structure for a weakly stable burning at an equivalence ratio of 0.5 near the blowout limit is presented. Further, the effects of blowout on the heat release rate, vorticity, distribution of major species, and ignition radicals are studied at four time instances at blowout velocity of 70 m/s. Since limited data is available on turbulent premixed combustion of partially cracked ammonia, such studies are essential in understanding flame behavior and uncertainties with regard to blowout.</p>

<p dir="ltr">Boiling processes have long had an important role in power generation and air conditioning applications. The efficient and reliable heat dissipation afforded through the phase change process in the boiling has led to their generation of a substantial body of work in this field over several decades. Despite decades of efforts, the heat transfer performance prediction in boiling has been highly empirical with models working only for a narrow range of surface/fluids or other operating conditions. The limitation in these models is a result of a lack of mechanistic understanding of the underlying heat and mass transfer process. Surface dryout or boiling crisis is a process wherein there is a spontaneous formation of vapor film on top of the surface causing a catastrophic increase in surface temperature. The heat flux at which this formation of vapor film occurs is called critical heat flux (CHF). The CHF demarcates the upper limit to the regime of stable nucleating bubbles called nucleate boiling. The mechanism causing dryout is under debate for over half a century and several conflicting theories that cause dryout have been suggested since the 1950s including hydrodynamic, irreversible dryspot expansion, macrolayer dryout/liftoff, critical bubble distributions, vapor-recoil based theories and more. The lack of consensus is due to limitation in the information collected on the dynamic multiscale and chaotic bubble interactions. Recent advances in high-fidelity spatiotemporal phase, temperature, and heat flux measurements now enable diagnostic tools that can be leveraged to understand the complex heat transfer processes emerging from bubble-surface interaction on the boiling surface. In this work, we develop such techniques to understand various transport mechanisms underlying boiling and its crisis.</p><p dir="ltr">In this work, an experimental technique for collecting synchronized through-substrate visual and infrared (IR) measurements of a boiling surface is developed. An IR and visually transparent sapphire substrate with an IR-opaque indium-tin-oxide (ITO) heater layer is used to measure the phase (liquid and vapor areas) and temperature of the ITO layer. The visual camera collects the light reflected off the substrate from a red LED and the images collected show a contrast between liquid and vapor areas that is used to generate binarized phase maps. The temperature from the IR camera is used as boundary condition to solve a conduction problem for heat fluxes going into the fluid. Four distinct heat flux signatures corresponding to liquid, contact line, vapor and rewetting regions are observed. A post-processing methodology utilizing synchronous phase measurements to identify and partition these regions is introduced. The high-fidelity phase measurements allow for detection of fine features that are not discernable using heat flux maps alone. Analysis of the heat flux and temperature maps of partitioned regions for HFE-7100 fluid on the ITO surface show qualitative agreement with the trends in mechanisms underlying those areas. The experiment and post-processing methodology introduced in this work is the first to provide partitioning of underlying heat transfer mechanisms for multi-bubbles throughout the entire range of the boiling curve during both steady and transient scenarios.</p><p dir="ltr">The technique developed is used to probe the mechanisms underlying the boiling crisis. Theories suggested in the literature for boiling crisis are carefully evaluated and evidence against hydrodynamic instability, macrolayer dryout, vapor recoil, irreversible expansion of dryspots, macrolayer liftoff model, and bifurcations from critical distributions is observed. The signature in the peak of the spatially averaged fluid heat flux is observed to precede any other signs of dryout. Beyond the peak heat flux an increase in superheat leads to reduced heat dissipated by boiling and further increases the temperature causing a thermal runaway in the substrate that eventually leads to dryout. Hence, the boiling crisis is found to be a consequence of a peak in the nucleate boiling curve. The cause for the peak in the boiling heat flux for the surface-fluid combination tested was due to degradation of heat transfer caused by the replacement of high-heat-transfer contact line region with lower-heat-transfer vapor covered regions, among the multiple competing mechanisms. Hence, we propose that mechanistically modeling the boiling crisis rests on prediction of the peak in the upper portion of the nucleate boiling curve by considering all underlying heat transfer mechanisms. A modeling framework based on heat flux partitioning, where the overall heat transferred during boiling is calculated as the sum of the heat transferred by individual mechanisms is demonstrated as potential pathway to predict the upper portion of the nucleate boiling curve and thereby critical heat flux. Based on the terms involved in summation for individual mechanisms, we propose that the boiling curve for any given surface be interpreted as a path on a multidimensional surface (boiling manifold). Estimation of such a boiling manifold allows for prediction of the boiling curve for any surface, given development of the relations between these parameters and surface-fluid properties, and can further be used to backtrack relevant thermophysical or nucleation properties for enhanced boiling performance.</p><p dir="ltr">Enhancement of pool boiling heat transfer performance using surface modifications is of major interest to applications and this work further delves into characterizing the boiling performance using traditional surface averaged measurements of microstructured surfaces using HFE-7100. We find that microlayer evaporation from the imbibed liquid layer underneath the growing vapor bubbles is the key mechanism of boiling heat transfer enhancement in microstructures. Further, this implies that characterization of microstructured surfaces for evaporative performance can serve as an important proxy to enable heat transfer coefficient enhancement prediction during pool boiling. Hence, we also developed an easily calculated Figure of Merit (FOM) that characterizes the efficacy of evaporation from microstructured surfaces.</p><p dir="ltr">To summarize, in this work we developed an experimental technique using synchronous through-substrate high-speed visual and IR imaging methods. New post-processing techniques for partitioning of different heat transfer mechanisms are proposed and used to analyze boiling on an ITO-coated sapphire substrate with HFE-7100 as the working fluid. We reveal thermal runaway in the substrate caused due to a negative-sloping boiling curve as the mechanism of dryout. Mechanistic modeling of the critical heat flux thus involves calculating the peak in the nucleate boiling curve. A framework to predict the nucleate boiling curve and subsequently critical heat flux is proposed based on the partitioning analysis. The experimental method developed lays the groundwork for measuring heat flux and superheats associated with various mechanisms, and hence, enables validation of future partitioning-based boiling heat transfer models that intrinsically enable prediction of the peak.</p>

<p dir="ltr">Addressing the pressing need for reduced carbon emissions, Turbulent Jet Ignition (TJI) emerges as a promising technology for ultra-lean combustion, offering enhanced thermal efficiencies and minimized cyclic variability in spark-ignited engines. To facilitate rapid testing and integration of this technology, a robust computational modeling framework is crucial. This study delves into the predictive capabilities of computational models for main-chamber ignition and premixed flame propagation using a single-cycle TJI rig measured by Biswas et al. (Applied Thermal Engineering, volume 106, 2016). Employing an open-source compressible flow simulation solver with Large Eddy Simulation (LES) for turbulence modeling, the investigation integrates the conventional Laminar Finite Rate Chemistry (LFRC) model alongside the transported Probability Density Method (PDF) for turbulence-chemistry interaction. A fully-consistent Eulerian Monte-Carlo Fields (EMCF) method is utilized to approximate the transported PDF, while Interaction by Exchange with Mean is employed to close micro-mixing terms in stochastic differential equations. A reduced chemical reaction mechanism with 21 species and 84 reactions (DRM-19) is used for solving chemical kinetics, and a double Gaussian energy deposition model is used to approximate the spark ignition in the pre-chamber. An unstructured O-grid mesh with 0.3 million cells in the pre-chamber and 1 million cells in the main chamber is employed. Results are divided into two phases: pre-chamber initialization and full TJI simulations. Validation of the predicted pre-chamber flame propagation and the lean ignition in the main-chamber is carried out by using available experimental data. Under quiescent conditions, both the LFRC and transported PDF methods largely underestimate the flame speed and subsequent pressure growth in the pre-chamber. A linear momentum forcing technique is applied to investigate the impact of initial turbulence in the pre-chamber, demonstrating a notable influence on flame propagation. Fine-tuning of the forcing coefficient reproduces the sudden pressure growth observed in the experiment. The experimentally validated pre-chamber simulation serves as the initial condition for the full TJI simulations. It is found that the LFRC model fails to predict lean-ignition in the main-chamber, resulting in a misfiring event. Incorporation of turbulence-chemistry interaction using the transported PDF method substantially improves the prediction of the ignition event in the main-chamber, achieving fair qualitative agreement and quantitative validation of combustion parameters within 10% of the reported experimental data. The rich simulation results consisting of a full set of statistical description of the thermo-chemical states enable us to gain deep insights into the ignition mechanisms in the main chamber, which is limited when done experimentally. A novel dual ignition phenomenon is revealed in the TJI rig for the first time. Initially, a primary ignition kernel is formed at a downstream location which eventually detaches from the main jet. As the jet momentum decreases, a secondary ignition event follows, this time at a more upstream location which eventually combines with the primary ignition kernel to form a single connected flame front. Investigation of these ignition sequences in chemical composition space reveal distinct differences between the two. The primary ignition event in the main-chamber is followed by a large concentration of active radicals from the pre-chamber jet, accelerating the chain-branching steps, characterizing what has been referred to as flame ignition. In contrast, the secondary ignition occurs in the absence of active radicals in the pre-chamber jet, hence characterized as jet ignition. Further analysis of the effect of pre-chamber jet characteristics on lean ignition in the main-chamber is conducted by setting up cases with different initial pressure ratios (p_r^o) between the two chambers, a non-dimensional parameter, ranging from 1.2 to 3.2. As the initial pressure ratio increases, jet momentum increases, with dual ignition observed in cases above p_r^o= 2.2. Case with p_r^o= 3.2 lead to misfiring. The effect of ignition sequence on global combustion characteristics of TJI is analyzed. Dual ignition events lead to non-monotonicity in combustion characteristics such as global reaction progress variable, flame penetration, and global heat release rate. In dual ignition events, although the rate of fuel consumption and global heat release rate is initially lower, the secondary ignition leads to a sudden increase in flame surface area, resulting in a sudden jump and promoting the overall performance of the TJI system.</p>