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(2021)ThesisNatural kidney filtration is a compact, multi-step filtration process which passes wastes and exceeded fluids via microscale vessels in glomerulus and tubules. The principal renal replacement therapy (RRT), commonly called dialysis, is a single-step filtration process based on diffusion to replace kidney failure. Conventional dialysis is limited in its effectiveness (not a continuous treatment), its impact on quality of life (typically requiring patients to spend several days per week in a clinic), and its cost (large systems, requiring frequent membrane replacement). This thesis is an investigation into the feasibility of using microfluidics and membrane technology to create portable alternatives to dialysis systems. It starts with a comprehensive review of the state-of-the-art in portable artificial kidneys, microfluidics, membrane science, and other related fields. An innovative, multi-step process was designed to mimic kidney filtration using two membranes; one to filter out large particles and one to remove urea and recycle water, thus mitigating the need for a dialysate system. The underlying physics (the mixing and shear stress) of the mechanisms which could enhance filtration performance at microscale was then studied. It was found that by adding microspacers into narrow-channel flows, it is possible to significantly enhance filtration. Optimized 3D-printed spacer designs (e.g., a ‘gyroid’ spacer) showed flux enhancement of up to 93% (compared to a plain channel) when using a plasma mimicking solution. The use of different blood and plasma mimicking solutions also suggested a prior step to separate large biological components (e.g., cells, proteins) is helpful to reduce cell contact and fouling in membrane filtration. The potential use of microfluidic diode valves and micropumps for pressure and flowrate regulation in the proposed small-format system was discussed. Membrane processes which mimic the filtration function of the tubules and have the potential for integration into portable systems (e.g., reverse osmosis and membrane distillation) are demonstrated to be useful potential alternatives to dialysis in toxin removal and in returning clean water to the blood stream.
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(2021)ThesisUnderwater sound can have a detrimental effect on marine animals due to the ever-increasing noise levels in their pristine habitat. It has also been commonly used to detect underwater floating objects via a sonar system. To absorb unwanted underwater sound, polymers (e.g., rubber), which have similar impedance to that of water, are widely used for sound absorption in water. Nanocomposites have attracted considerable attention due to their ability to improve sound absorption properties of polymer-based sound absorption materials. This project aims to develop a thin-layer nanocomposite with high underwater sound absorption at low frequency and high pressure. A water-filled impedance tube, an essential facility to test new materials developed in this PhD thesis, was designed and constructed. The established research facility consists of four main components: a stainless steel tube and its supporting devices, a sound source (a projector) and its associated electronics, an underwater sound pressure measurement system, and a water pressurized system. Subsequent calibrations and measurements showed that the established apparatus could be used to measure the underwater sound absorption coefficient in a frequency range of 1500 Hz to 7000 Hz and under hydrostatic pressure in a range of 0 to 1.5 MPa. Carbon nanotubes (CNTs) reinforced polydimethylsiloxane (PDMS) nanocomposites were designed, fabricated, and tested. This development comprised of two stages. In the first stage, PDMS was selected as the material matrix, surfactant and carboxyl functionalized multi-walled carbon nanotubes (MWCNT-COOH) as inclusions, and a new nanocomposite, namely PSM (PDMS/surfactant/MWCNT-COOH), was then developed. Effects of the added surfactant and MWCNT-COOH on the mechanical properties, chemical properties, and morphology were investigated, which indicated the nanocomposite’s potential for sound absorption improvement. Underwater acoustic tests showed high underwater sound absorption coefficients (>0.8) in the most frequency range 1500 Hz to 7000 Hz. However, it was observed that a significant drop in the underwater sound absorption performance under high hydrostatic pressure. It was found that the high compression of PSM was the cause of poor performance under high hydrostatic pressure. In the second stage, a core-shell structure was designed to maintain the high sound absorption coefficient of PSM under high hydrostatic pressure. A novel structure of a 2-mm-thick hard shell with a 2-mm-thick soft layer was developed to encapsulate the PSM sample so that its deformation can be minimized and its superior sound absorption property was improved under high pressure. Experimental results on the water-filled impedance tube demonstrated that the new structure offered a promising solution to the demand for advanced underwater materials, which are thin and have high sound absorption performance under high hydrostatic pressures. In summary, this study has developed a polymer-based nanocomposite. Mechanical properties, chemical properties, morphology, and underwater acoustic properties of the nanocomposite have been studied. The nanocomposite is thinner than existing underwater acoustic materials and has excellent underwater sound absorption performance in the frequency range of 1.5 to 7 kHz and under atmospheric pressure. For applications in high hydrostatic pressure up to 1.5 MPa, the proposed new structure with a total thickness of 14 mm, in comparison to 50 mm or more thickness of other developed materials for marine applications, showed good sound absorption results and potentially addressing the on-going technical challenge of poor sound absorption performance of acoustic materials under high hydrostatic pressure.
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(2020)ThesisOver the past few decades, various types of filler materials have been employed to develop the advanced resin-based dental composites, enhancing the lifetime of the restorations. However, further effort in the research on the multi-functional composite that is comparable to dental tissue in mechanical strength, as well as offering the improved antibacterial function and the better aesthetics, is continuously required. In this thesis, micro-sized short S-glass fibres and halloysite nanotubes (HNTs) are employed to serve as excellent load-carrying filler members and antibacterial agent in the dental composites. The mechanical reinforcement mechanism and the interfacial behaviours between filler and resin matrix have been precisely investigated through the multiscale analysis from atomistic to macro by utilising the combined experimental, theoretical, and computational methods. The surface modification process on the short S-glass fibres, named selective atomic-level metal etching, has been developed, which enables to strengthen the interfacial bond between resin matrix and glass fibre by increasing the surface roughness and reactive sites on the fibre. The influence of the surface treatment on the interfacial strength and mechanical properties of the resulted composites were examined through the single-fibre pull-out tests. Also, the modified Lewis-Nielsen model has been developed, where the effective fibre length factor is applied to accurately predict the modulus of the short fibre reinforced composites. For better understanding of the atomistic interfacial bonding and fracture behaviours between glass fibre and resin matrix, molecular dynamics simulations were conducted. The numerical results of the single fibre pull-out and the uniaxial composite tension simulations were validated with the experimental findings. The optimised computational design and analysis methods were established for developing new dental and bio-composites with the accurate prediction on the mechanical performances. The surface modification process on the HNTs was developed to promote the mechanical reinforcement effect and to add an antimicrobial functionality in the composites. The composite reinforced with 2.0 wt.% of chitosan grafted HNTs showed an increased efficacy in flexural strength and modulus up to 8.1% and 14.1%, respectively, and exhibited an improved antibacterial functionality against S. mutans with 39% reduction, making it a desirable dental material.
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(2020)ThesisA comprehensive literature review on the development of 3D inkjet printing technologies has revealed that inkjet printing is an effective method for additive manufacturing with advantages in specific applications such as microstructures and printable electronics. However, the knowledge of the flow development of the inkjet from the flow formation inside the nozzle to the dropping process is in severe dearth, so are the predictive models for the printing process. A CFD (computational fluid dynamics) model is presented to study the jetting and dropping characteristics for needle-valve inkjets. The model is developed by using a dynamic mesh method and experimentally verified for both a low viscosity fluid typified by a distilled water, and a relatively high viscosity PEDOT:PSS polymer nano-particle containing ink. The model-calculations show a good agreement with the experimental data under the corresponding conditions for the both types of inks. The results from the model show that the parameter window for generating a single droplet from the low viscosity fluid is narrower than that using the high viscosity ink. It also reveals that the droplet size increases with the nozzle diameter and a droplet with a diameter slightly smaller than the nozzle diameter can be achieved with a low viscosity ink under a low dropping velocity. The verified CFD model is then used to study the flow and dropping characteristics of an ink containing organic conductive polymer (PEDOT:PSS) nano-particles. It is revealed that three types of droplet defects can occur in the needle-valve ink jetting process, e.g. excess liquid suction, liquid accumulation, and satellite droplet formation. It is further found that an increase in the valve striking time, nozzle diameter or valve seat inclination results in a dramatic decrease in the droplet velocity, while an increase in the valve stroke or inlet air pressure causes an increase in the droplet velocity. The droplet volume and equilibrium deposition diameter increase with an increase in the valve stroke or inlet air pressure, but decrease with an increase in nozzle diameter or valve seat inclination. It is found that the droplet diameter is greater than the nozzle diameter and the droplet trajectory can be easily disturbed to become unstable when the droplet diameter is close to the nozzle diameter. A deposition diameter as small as 1.43 times the nozzle diameter has been achieved in this work. An experimental study of the needle-valve inkjet printing process is carried out to assess the characteristics of dots and strips printed in a single-pass process. It is revealed that the voltage waveform plays a significant role in affecting the printing performance. The minimum to maximum strip width ratio for single layer printing can go as small as 0.6. Predictive models for the various relevant printing performance measures, such as the deposited drop diameter, strip width and strip width variation, have been developed, which provide a mathematical basis for the selection of process parameters to achieve the desired printed features in practice.
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(2021)ThesisThis thesis presents an experimental investigation of air, argon and helium sonic under-expanded jets transversely injected through a turbulent boundary layer into a supersonic Mach 3 flow. The aims of the thesis are to demonstrate the steady and unsteady flow features of Transverse Jets In Supersonic Crossflow (TJISC), to present the shear layer vortex shedding frequency and the related controlling parameters, to extract the dominating coherent structures, and to present the mean and fluctuating pressure loads on the wall around the jet port beneath the TJISC. The flow field was visualized using two types of schlieren methods, meanwhile, the mean and pressure fluctuation distributions beneath the TJISC were measured by Pressure-Sensitive Paint (PSP) and a high-speed pressure transducer array, respectively. Besides the general flow features, instantaneous schlieren images reveal the unsteady nature of the TJISC. The quasi-periodically shedding shear layer vortices interact with the adjacent shock system and cause intense quasi-periodical deformation of the shock system. The Mach disk and the barrel shock presented in the air and argon cases are absent in the helium cases. In the convective frame for the helium cases, these shear layer vortices travel at supersonic speed and generate a series of moving shock waves that are propagating along the shear layer. The penetration depth of the helium TJISC is slightly higher than the air and argon cases due to these moving shocks. Power Spectral Density (PSD) of schlieren image pixel light intensity shows that the peak frequency of vortex shedding is inversely proportional to the momentum flux ratio J and this may be due to the level of compressibility. At the same J, the peak vortex shedding frequencies of the air and argon TJISC are similar, while the frequency of the helium TJISC is approximately double. Spectral Proper Orthogonal Decomposition (SPOD) and Dynamic Mode Decomposition (DMD) were applied to the schlieren data and coherent structures were extracted. The SPOD results show that the modal energy peak frequencies are consistent with the shear layer vortex shedding frequency, and the first mode that represents the shear layer vortices contains most of the modal energy. The SPOD results indicate that the flow field is relatively low-rank, and the shed vortices in the shear layer are dominant. Pressure fluctuations along the centre line beneath the jet illustrate that signals of the most upstream transducer (upstream of jet port) are dominated by the separated boundary layer. The signals of the second upstream transducer are dominated by the fluctuations of the shear layer vortices and shock structures in the air and argon cases, while the signals of the helium cases are relatively broadband. At the most downstream locations, the PSD of the pressure fluctuations presents peaks that are generated by the wake structures near the wall. Pressure-sensitive paint results identify the high-pressure regions upstream of the jet port that are caused by the separation shock and the bow shock. A symmetric low-pressure region, a collision shock, and the wake structures are observed downstream of the jet port. In conclusion, the TJISC is an unsteady flow field with complex fluid mechanics that are closely linked to the injectant gas properties. The peak shear layer vortex shedding frequency is inversely proportional to the J. This conclusion is confirmed by the SPOD and DMD data and the extract modes are addressed. Pressure loads beneath the jets were presented and linked to the unsteady flow structures and injected gas properties. This thesis provides detailed information on the TJISC and can provide some insights on designing scramjet engines.
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(2021)ThesisGear wear is an inevitable phenomenon during gear service life. Its propagation would impair the durability of gear tooth and reduce the remaining useful life of gear transmission system. Therefore, monitoring and predicting gear wear progression can bring significant benefits to industrial practice. Vibration analysis responds immediately to changes in the machine state (health and operating condition) and can therefore be used for gear monitoring. However, vibration-based techniques for gear wear monitoring are rather rare, even though techniques have been well established for detection and diagnosis of common gear faults such as gear tooth root cracks and tooth breakage. Therefore, in this research, a vibration-based integrated system is developed for gear wear monitoring and prediction. The developments were carried out in two stages: (i) wear mechanism identification using measured vibrations, and (ii) wear propagation monitoring and prediction using the integration of models, measurements and model updating approaches. In the first stage, the correlation between surface features and vibration characteristics is investigated. Then, use of cyclostationary properties of vibrations, a vibration-based online gear wear mechanism identification methodology is developed. Moreover, the evolution of fatigue pitting and abrasive wear (micro-level) are tracked using an indicator of second-order cyclostationarity of vibrations in specific spectral bands. In the second stage, a digital-twin system is developed by the integration of (i) a dynamic model to simulate the dynamic responses of gear system; (ii) two tribological (wear) models for estimation of wear depth and pitting density, and (iii) model updating through comparing simulation and measured vibrations. The integration of dynamic model and tribological models allow a knowledge-based wear prediction of the gear profile change (determined by the wear depth) and pitting density. With the regularly model updating using measured vibrations, the wear process can be well monitored, and the best possible prediction of remaining useful life can be achieved. The above developments provide effective and efficient tools for monitoring and prediction of gear wear, in particular, the profile change and pitting density, which is critical for making appropriate maintenance decisions to maximise the useful life of gears and to avoid catastrophic failures and unexpected economic losses.
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(2022)ThesisAdhesively bonded joints have been widely used to manufacture aircraft components. However, its application to single load-path airframe structure is costly to certify as extensive validation testing is required. Certification of bonded joints or patch repairs for primary aircraft structures requires demonstration of damage tolerance. In recent years, a damage slow growth management strategy has been considered acceptable by Federal Aviation Administration to reduce the maintenance cost. This thesis evaluates the applicability of a damage slow growth management strategy to bonded joints/patch repairs of primary aircraft structures through both experimental and computational study. The investigation was carried out first by 2-D strip specimen assessment and finally using 3-D analysis of wide bonded metal joint. This research was a collaborative project between ARC Training Centre for Automated Manufacture of Advanced Composites (AMAC) at the University of New South Wales (UNSW) and Defence Science and Technology (DST) Group. The double overlap tapered end specimen (DOTES) specimen which represents both disbond tolerant zone and safe-life zone in bonded patch repair was investigated first through a detailed computational and experimental investigation. The residual static strength of the joint as a function of disbond length was established using finite element modelling based on the characteristic distance approach. The virtual crack close technique (VCCT) approach was utilised to assess the strain energy release rates (SERRs) as a function of disbond crack length. Fatigue tests of the DOTES coupon specimen were conducted to investigate the entire process of disbond growth from initiation up to ultimate failure of the joint. The measured disbond growth rates were correlated with the SERRs using a modified Paris law that enabled prediction of joint fatigue life. The fatigue test results indicated that for a joint having a sufficient static strength safety margin under a typical fatigue loading that would propagate disbond, the disbond growth would remain stable within a particular length range. Thus, the slow growth approach would be feasible for bonded joints/patch repairs if the patch is designed to be sufficiently large to allow extended damage propagation. Cohesive zone element (CZE) technique was utilised to assess the SERRs and estimate the disbond growth of 3-D wide bonded metal joint analysis. The impact of local or partial width disbond (load shedding effect) was investigated in detail. The results indicate that for a local or part width disbond, some load was redistributed to the adjacent regions (load shedding effect) that causes a slower disbond growth and accordingly longer fatigue life compared to the full width disbond. The key outcomes from this research are: (a) accurate prediction of the disbond growth behaviour in bonded patch repairs through the developed generic patch repair specimen i.e DOTES, (b) fatigue life prediction of the joints has been established through modified Paris law, by conducting numerical integration and (c) the effect of initial disbond size in 3-D wide bonded metal joint specimen was investigated through computational assessment using a cohesive fatigue model.
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(2021)ThesisEmerging membrane technologies such as forward osmosis (FO) and membrane distillation (MD) can provide alternative engineering approaches to current water-treatment membrane technologies, but without the high-pressure requirements. Currently, greater industrial implementation of these technologies is hindered by limitations with low flux, flow polarisation issues, design optimisation and issues with membrane deformation. An experimental and numerical assessment of a plate-and-frame (PF) FO module, revealed significant occlusion of the draw-channel under applied transmembrane-pressure (TMP), at points up to 70% while under an applied TMP of 1.45bar. Subsequently, 3D computational fluid dynamics (CFD) simulations were performed and validated against pressure loss data under TMP, to reveal the impact of flow indicators known to affect concentration polarisation (CP), such as Reynolds number, velocity profiles and shear strain. The pressure-loss method was then applied to a range of commercially available modules, found to occlude a cross-sectional area from 12-16% for the spiral would (SW) types and 49% 1.45bar for the PF module. CP models were then developed in conjunction with flux data to establish the degree of CP occurring in the modules. The CP data was then related to a CFD characterisation to establish detailed relationships on the impact of TMP on CP effects. Finally, a solar vacuum-membrane distillation (solar-VMD) system was developed and assessed experimentally to apply the lessons learned from the FO investigation in another emerging membrane technology. Lab-scale experiments were used to develop and validate a CFD model, using predictive hydrodynamic factors such as Reynolds number and shear strain, to mitigate temperature polarisation (TP) using turbulence promoters. A parametric analysis of the CFD data revealed the flux improvements and TP mitigation available through the addition of a baffle, combined with an economic analysis for real world use (demonstrating a viable decentralised drinking and hot-water supply). Flux performance of the MD system was found at >8LMH in solar conditions of ~800W/m2, with a payback period of 2.06 years. Overall, this thesis provides a detailed assessment of the impacts of applied TMP in FO processes, as well as potential design optimisation pathways by furthering the knowledge of CFD analysis in emerging membrane technologies.
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(2022)ThesisGears are widely used in industrial machinery, and gear failure is a main cause of machine failure. Since gear wear is often the initial stage of gear failure, its monitoring and prediction are key to minimising machine downtime, maintenance costs, and safety risks. However, existing gear wear monitoring and prediction techniques face some ongoing technical challenges, including providing direct wear information and wear assessment and prediction in a cost-effective and efficient manner. To tackle the challenges, this research aims to develop a set of advanced techniques for gear wear monitoring and prediction. The four objectives of the research and their corresponding methodologies and outcomes are summarised as follow. (a) To develop a method to obtain direct and comprehensive wear information without disassembling the gearbox. This objective was realised by combining surface replication with image analysis, allowing easy acquisition of high-resolution mould images showing wear evolution on a tooth flank. (b) To investigate the relationship between the features of worn gear surfaces and those of wear debris. To further understand the role of wear debris analysis in wear assessment, a study on various features of macropits and wear particles in the same fatigue process was conducted and provided new insights into gear pitting and its monitoring. (c) To develop an automated system for gear wear assessment. Deep learning models were developed to identify wear mechanisms and severities using gear mould images and wear debris images. High classification accuracies were achieved, and comparisons between the two image sources were made. (d) To develop a gear wear prediction model using direct wear information. A deep generative model was developed and trained on time series of gear mould images. Tests showed that the model using the state-of-the-art AI technology can generate realistic and accurate predictions. Overall, this research addressed the main limitations of existing methods and provided a direct and evidence-based tool for monitoring and predicting gear wear. Its specific contributions include a new moulding-imaging method for monitoring gear wear evolution, a detailed comparison between worn gear surfaces and wear debris in a wear process, and AI and image-based gear wear assessment and prediction models for the first time. The techniques could be performed during regular inspections of machines and used with online methods for increased robustness.
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(2021)ThesisThe gasoline compression-ignition (GCI) concept has been proposed in recent years to circumvent the typical diesel engine NOx and soot emissions trade-off, whilst maintaining high engine efficiency. The GCI concept is commonly realised in a conventional diesel engine with heated intake air, utilising a conventional injection system and a single low-reactivity gasoline-like fuel. Combustion phasing is controlled through the injection timing, while the fast and lean combustion enables very high brake efficiency in excess of 50% with low NOx/particulate emissions across a wide range of engine loads. Additionally, this combustion mode can utilise economical and potentially widely available low-grade gasoline fuels (naphtha) with octane numbers in the range of 70-80. Despite many advantages, the ignition timing and combustion rate of GCI are very sensitive to both fuel chemistry and engine operating conditions. The lack of a fundamental understanding of ignition and combustion behaviours limits the optimisation of GCI engines. The aim of this thesis was to advance the fundamental understanding of the GCI combustion process. Characteristics of fuel-oxidiser mixing, ignition and combustion processes for gasoline-like fuels with a range of octane rating at compression-ignition (CI) engine relevant conditions were investigated. Experiments were conducted in an optically accessible constant-volume combustion chamber (CVCC), featuring well-characterised quiescent charge throughout the injection and combustion events. A single-hole axial-drilled diesel injector mounted on the back wall of the CVCC was used for fuel injections. The first part aims to assess the combustion characteristics of iso-octane (a gasoline surrogate) at CI conditions. CVCC featured an ambient gas density of 22.8 kg/m3 and an O2 concentration of 21 vol.\%. Optical techniques including natural flame luminosity, OH* chemiluminescence and shadowgraph imaging were performed to compare the combustion characteristics over ambient gas temperatures from 1000 K to 1120 K Measurements were also performed for n-heptane (a diesel surrogate) for reference purposes. Formaldehyde (CH2O) planar laser-induced fluorescence (PLIF) imaging was performed to confirm the presence of low-temperature reactions across the jet head, prior to the high-temperature ignition of iso-octane. From the measurement results, the lift-off lengths (LOLs), ignition delays (IDs) and their corresponding uncertainties for both fuels are observed to increase with lowering ambient temperature conditions. The LOLs, IDs and their uncertainties for the iso-octane flames are also consistently measured to be higher than that of n-heptane, across the tested ambient temperature range. The results reveal that the highest variability detected for the flame stabilisation distance of the iso-octane flame at the lowest tested ambient temperature condition 1000 K is attributable to the long transient stabilisation phase that it exhibits after ignition. Additional tests performed using a single-injection test case with lower octane number fuel, as well as split-injection strategies with neat iso-octane as fuel, demonstrate their potential to reduce the transient stabilisation phase of the test flames when compared with single-injection test case with neat iso-octane as fuel. The second part aims to investigate the effect of laser-induced plasma ignition (LI) on combustion behaviours of iso-octane at compression-ignition conditions. A high-energy laser was used to force the fuel ignition at a quiescent-steady environment inside the CVCC with 900 K ambient gas temperature, 22.8 kg/m3 ambient gas density and 21 vol.% O2 concentration. The diesel surrogate (n-heptane) was tested at a lower charge temperature of 735 K to offset its higher fuel reactivity than the iso-octane, such that the flames of both fuels can have a similar lift-off length. Forced laser ignition was introduced either before or after the natural autoignition timing of the fuels. The laser was focused at the jet axis 15 mm and 30 mm from the nozzle. High-speed schlieren imaging, heat release analysis and flame luminosity measurement were applied to the flames. The high-speed schlieren imaging was used to monitor the flame structure evolution of the natural ignition and LI cases. Due to laser ignition, the flame lift-off lengths decrease, with which the uncertainties in the lift-off distances reduce by more than 80 %. The laser-affected flame bases return back to the natural flame base locations. The uncertainties in the lift-off lengths also increase, as the flame stabilisation locations approach the natural lift-off distances. Under the test conditions of this work, the rates at which the iso-octane flames shift downstream are slower than in the n-heptane cases. The heat release rate profiles show high heat release from the flames following the LI events, before transitioning to lower steady values. The flame luminosity measurements indicate a strong correlation between the LI affected lift-off length and increased soot formation. The luminosity levels decrease as the flame base shifts downstream over time. The third part aims to investigate the underlying processes governing ignition and flame stabilisation in CI engine-relevant conditions. Primary reference fuels (PRFs), including PRF100 (neat iso-octane), PRF80 (a blend of 80 vol.% iso-octane and 20 vol.% n-heptane) and PRF0 (neat n-heptane), were tested to simulate changes in fuel ignition quality inside a quiescent steady environment with an ambient density of 22.8 kg/m3 and an O2 concentration of 15 vol. %. The ambient gas temperatures were controlled at 1150 K (PRF100), 1120 K (PRF80) and 900 K (PRF0), in order to adapt to the fuel reactivity so that a constant ignition delay of 1.15 ms can be achieved for all blends. This approach was employed in order to substantially reduce the effect of fuel-oxidiser mixing prior to ignition while highlighting the effect of fuel chemistry on the ignition process and flame evolution. Under the test conditions of this study, optical imaging reveals that the blends with higher iso-octane content exhibit a faster spreading of combustion after ignition and establish a steady lifted flame that is closer to the nozzle. Imaging by CH2O-PLIF indicates that blends with higher iso-octane content produce CH2O that is distributed across larger portions of the jet at an earlier timing when compared to neat n-heptane that shows a propagating first-stage ignition through the fuel jet. Supporting unsteady flamelet calculations are presented to investigate the effect of chemistry and turbulent mixing. The flamelet calculations agree qualitatively in several respects to the experiments, especially in the spatial and temporal trends for CH2O production and consumption. Synthesis of the flamelet and experimental results suggests that for the iso-octane-containing fuels, CH2O is formed via single-stage ignition reactions rather than exhibiting the typical two-stage ignition behaviour which is found in the pure n-heptane fuel case. Furthermore, the flamelet calculations suggest high-temperature ignition occurs first in lean mixtures in the iso-octane-containing fuel cases, but in rich mixtures for the PRF0 case. If autoignition is the mode of flame stabilisation, this provides an explanation for why the PRF100 and PRF80 cases stabilise further upstream, since lean mixtures have longer residence times, experience lower scalar dissipation rate, and maybe more likely to be exposed to a supporting peripheral reservoir of hot products, should one exist. Overall, this study provides insights into the roles of fuel chemistry and turbulent mixing on the ignition and combustion behaviour of PRFs under engine-relevant conditions.