Optical Chamber Research Articles

Combustion characteristics of ammonia-hydrogen mixture with turbulent jet ignition

Ammonia and hydrogen are promising zero-carbon fuels that can help combustion engines achieve the zero-carbon emissions target. However, ammonia features high ignition energy demand and slow flame propagation speed. Pre-chamber turbulent jet ignition, with high ignition energy and enhanced in-cylinder turbulence, shows potential for achieving efficient and stable engine combustion with low-reactivity fuels. The optical constant volume combustion chamber simulates the process of pressure environment in the engine cylinder during the compression stroke to push the unburned gas into the pre-chamber, and simulates the process of jet ignition during the pressure environment in the main combustion chamber at the end of the compression stroke. The effects of different parameters such as ambient pressure, hydrogen fraction, and orifice diameter on the turbulent jet ignition combustion were investigated. The results indicate that jet ignition is a more effective means than spark ignition to accelerate the ammonia-hydrogen mixture combustion. A hot jet carrying heat and active radicals is injected into the main chamber due to the pressure difference, and then ignites the ammonia-hydrogen mixture. With increased hydrogen volume fraction, the ignition process is advanced due to the earlier formation and higher reactivity of the hot jet. Meanwhile, the enhanced fuel reactivity and turbulent disturbance accelerate turbulent flame propagation with increased hydrogen addition. The ignition delay time and jet flame axial development are accelerated with increase in equivalence ratio from 0.6 to 1.0. With increased orifice diameter, the pre-chamber jet flame is observed due to the weakened quenching effect, leading to shortened ignition delay and extended combustion duration.

Ultra-compact dual-channel integrated CO2 infrared gas sensor

Expiratory CO2 concentrations can directly reflect human physiological conditions, and their detection is highly important in the treatment and rehabilitation of critically ill patients. Existing respiratory gas analyzers suffer from large sizes and high power consumption due to the limitations of the internal CO2 sensors, which prevent them from being wearable to track active people. The internal and external interference and sensitivity limitations must be overcome to realize wearable respiratory monitoring applications for CO2 sensors. In this work, an ultra-compact CO2 sensor was developed by integrating a microelectromechanical system emitter and thermopile detectors with an optical gas chamber; the power consumption of the light source and ambient temperature of the thermally sensitive devices were reduced by heat transfer control; the time to reach stabilization of the sensor was shortened; the humidity resistance of the sensor was improved by a dual-channel design; the light loss of the sensor was compensated by improving the optical coupling efficiency, which was combined with the amplitude trimming network to equivalently improve the sensitivity of the sensor. The minimum size of the developed sensor was 12 mm × 6 mm × 4 mm, and the reading error was <4% of the reading from −20 °C to 50 °C. The minimum power consumption of the sensor was ~33 mW, and the response time and recovery time were 10 s (@1 Hz), and the sensor had good humidity resistance, stability, and repeatability. These results indicate that the CO2 sensor developed using this strategy has great potential for wearable respiratory monitoring applications.

Commissioning of the MIGDAL detector with fast neutrons at NILE/ISIS

Many dark matter experiments are exploiting the Migdal effect, a rare atomic process, to improve sensitivity to low-mass (sub-GeV) WIMP-like dark matter candidates. However, this process is yet to be directly observed in nuclear scattering. The MIGDAL experiment aims to make the first unambiguous measurement of the Migdal effect in nuclear scattering. A low-pressure optical Time Projection Chamber is used to image in three-dimensions the characteristic signature of a Migdal event: an electron and a nuclear recoil track sharing a common vertex. Nuclear recoils are induced using fast neutrons from a D–D source, which scatter in the gaseous volume of the detector. The experiment is operated with 50 Torr of CF4 using two glass GEMs for charge amplification. Both light and charge are read-out, and these measurements are combined for track reconstruction. Commissioning data has been recorded with fast neutrons at the Neutron Irradiation Laboratory for Electronics (NILE) at Rutherford Appleton Laboratory in the UK. Results of the experiment’s commissioning and the performance of the detector with a high rate of highly ionising nuclear recoils are presented, along with results from low energy electrons. Initial results of light and charge read-out with low pressure noble gas mixtures are also presented.

Decay study of Be11 with an optical time-projection chamber

The β decay of one-neutron halo nucleus Be11 was investigated using the Warsaw Optical Time Projection Chamber (OTPC) detector to measure β-delayed charged particles. The results of two experiments are reported. In the first one, carried out in LNS Catania, the absolute branching ratio for β-delayed α emission was measured by counting incoming Be11 ions stopped in the detector and the observed decays with the emission of α particle. The result of 3.27(46)% is in good agreement with the literature value. In the second experiment, performed at the HIE-ISOLDE facility at CERN, bunches containing several hundreds of Be11 ions were implanted into the OTPC detector followed by the detection of decays with the emission of charged particles. The energy spectrum of β-delayed α particles was determined in the full energy range. It was analyzed in the R-matrix framework and was found to be consistent with the literature. The best description of the spectrum was obtained assuming that the two 3/2+ and one 1/2+ states in B11 are involved in the transition. The search for β-delayed emission of protons was undertaken. Only the upper limit for the branching ratio for this process of (2.2±0.6stat±0.6sys)×10−6 could be determined. This value is in conflict with the result published by Ayyad [] but does agree with the limit reported by Riisager []. Published by the American Physical Society 2024

Simultaneous sealing and bisection of porcine renal blood vessels, ex vivo, using a continuous-wave, infrared diode laser at 1470 nm

Electrosurgical and ultrasonic devices are used in surgical procedures for hemostatic sealing and bisection of vascular tissues. Previous benchtop studies alternatively demonstrated successful infrared laser sealing and cutting of blood vessels, in a sequential, two-step approach. This study describes a smaller, laparoscopic device compatible design, and simultaneous approach to sealing and bisection of vessels, with potential optical feedback. A 1470-nm infrared diode laser sealed and bisected 40 porcine renal arteries, ex vivo. A reciprocating, side-firing, optical fiber, housed in a transparent square quartz optical chamber (2.7 × 2.7 × 25 mm outer dimensions), delivered laser energy over an 11 mm scan length, with a range of incident powers (41–59 W) and treatment times (5–21 s). Vessel diameters ranged from 2.5 to 4.8 mm. Vessel burst pressure measurements were performed on each cut end (n = 80) with success indicated by pressures exceeding 360 mmHg. All vessel ends were successfully sealed and bisected (80/80). The highest incident power, 59 W, yielded short treatment times of 5–6 s. Peak temperatures on the external chamber surface reached 103 oC. Time to cool down to body temperature measured 37 s. Infrared lasers simultaneously seal and bisect blood vessels, with treatment times comparable to, and temperatures and cooling times lower than reported for conventional devices. Future work will focus on integrating the fiber and chamber into a standard 5-mm-outer-diameter laparoscopic device. Customization of fiber scan length to match vessel size may also reduce laser energy deposition, enabling lower peak temperatures, treatment times, and cooling times.

Secondary scintillation yield from GEM electron avalanches in - and --isobutane for CYGNO — Directional Dark Matter search with an optical TPC

CYGNO is an international collaboration with the aim of operating a ▪ optical time projection chamber (TPC) for directional Dark Matter (DM) searches and solar neutrino spectroscopy, to be deployed at the Laboratori Nazionali del Gran Sasso (LNGS). A ▪/▪ (60/40) mixture is used, along with a triple Gas Electron Multiplier (GEM) cascade to amplify the ionisation signal. The scintillation produced in the electron avalanches is read out using a scientific complementary metal–oxide–semiconductor (sCMOS) camera. This solution has proven to provide very high sensitivity to interactions in the few ▪ energy range. The inclusion of a hydrogen-based gas will offer an even lighter target, resulting in a more efficient energy transfer in a DM particle collision, and consequently, a lower detection threshold. Additionally, longer track lengths of light nuclear recoils are easier to detect with a clearer direction. However, the addition of such gas will contribute to quenching the scintillation, jeopardizing the TPC performance. In this work, we demonstrate the feasibility of adding 1% to 5% isobutane to the ▪/▪ (60/40) mixture by measuring the respective absolute scintillation yield output. The overall scintillation produced in the charge avalanches is not drastically suppressed by quenching due to the isobutane addition. The presence of Penning transfer from excited He atoms to isobutane molecules increases the number of electrons in the avalanches, partially compensating for the loss of scintillation due to quenching. For the highest applied GEM voltage, the total number of photons produced in the avalanche per ▪ deposited in the absorption region presents a decrease of only a factor of about three, from 2.30(20)×104 to 8.2(4)×103▪, as the isobutane content increases from 0 to 5%. The quantification of the visible component of the scintillation shows that isobutane quenches both visible and ultraviolet (UV) photons emitted by ▪/▪.

Scintillation of Ar/CF4 mixtures: glass-THGEM characterization with 1% CF4 at 1–1.5 bar

Argon gas doped with 1% wavelength-shifter (CF4) has been employed in an optical time projection chamber (OTPC) to image cosmic radiation. We present results obtained during the system commissioning, performed with two stacked glass thick gaseous electron multipliers (THGEMs) and an electron-multiplying charge coupled device (EMCCD camera) at 1 bar. Preliminary estimates indicate that the combined optical gain was of the order of 106 (ph/e), producing sharp and high-contrast raw images without resorting to any filtering or post-processing. A first assessment of the impact of pressurization showed no change in the attainable gains when operating at 1.5 bar.

A new underwater in-situ microplastics detection system based on micro-Raman spectroscopy: Development and sea trials

In-situ underwater observation for marine microplastics (MPs) study has long been desired but challenged by the difficulty in achieving continuous MPs enrichment and MPs analysis in underwater environments. Herein, a novel underwater system for in-situ detection of MPs was introduced. An innovative design with a filter mesh flipped 180° driven by a stepper motor was adopted to ensure the self-cleaning of the filter mesh and continuous MPs enrichment, reducing the frequency of manual maintenance required for the system. A special-designed optical detection chamber based on micro-Raman spectroscopy featured a 13 × 10 mm imaging field of view and a 50 µm imaging resolution was developed to gather morphology and composition information of MPs. During sea trials, the system successfully detected polypropylene (PP) microplastic and other suspended substances in seawater including microalgae, organic substances, and sands. This study lays the groundwork for future research into underwater in-situ investigation of marine MPs pollution.

Applicability to DEMO breeding blankets of neutron measurements techniques from fission reactors

Neutron measurements are routinely performed in fission reactors. A lot of experience has been gained at CEA in designing, prototyping and testing neutron sensors and associated acquisition systems in several nuclear facilities with a wide range of demanding conditions. In this paper, the applicability of this experience to neutron diagnostics in the breeding blankets of DEMO is addressed, as a complement to the already planned diagnostic strategy.The breeding blankets are a key component of a fusion reactor such as DEMO. The expected performances and operational constraints are demanding, nevertheless some of those, as the neutron flux range and high temperature, are close to what is encountered in sodium-cooled fast neutron reactors.The strengths and drawbacks of neutron sensors are presented with respect to the performances and constraints. Self-powered neutron detectors and fission chambers benefit from a vast return of experiment in fission reactors and received recent developments in the framework of studies for sodium-cooled fast neutron reactors. The innovative optical fission chamber is discussed for its electromagnetic immunity and high dynamic range demonstrated up to seven decades. Dosimetry with activation foils is also considered for its ability to provide an absolute calibration and spectral unfolding.

Experimental study of peripheral fuel injection for higher performance in diesel engines

In conventional diesel combustion (CDC), a centrally located multi-hole injector supplies fuel radially outwards. This study introduces and explores the concept of peripheral fuel injection (PeFI) to supply fuel from multiple locations on top of the combustion chamber using several single-hole injectors. The PeFI concept is designed to eliminate flame-wall and jet-wall interactions, and, ideally, to produce independent flames without any interference. PeFI is also intended to increase air entrainment in the near field and thus, reduce equivalence ratio at the lift-off length and subsequent soot formation. PeFI reduces wall heat transfer compared to CDC although this feature is not considered in the present study. The two methods of fuel injection are compared in a non-reacting optical chamber via high-speed imaging of the jets. N-heptane fuel at 1500 bar supply pressures is injected into a test chamber filled with nitrogen at engine relevant ambient densities of 23.0 and 18.5 kg/m3. Four configurations are trialed including a six-hole central injector and six, single-hole PeFI injectors with holes oriented at a layout angle, defined as the angle between the center of the fuel jet and chamber radius, of 0°, 15°, and 30°. Flow visualizations show jet-to-jet interactions at small layout angles for PeFI, but little to no jet-to-jet (or jet-wall) interference as the layout angle increases to 30°. Image analysis reveals that PeFI provides faster rate of injection, longer jet penetration length, greater width near the jet tip, and larger jet volume compared to those for the central injector. Overall, results demonstrate the potential of PeFI to simultaneously improve fuel efficiency and reduce emissions in diesel engines.

Effect of Impingement Angle on Flame Stability in a Non-Premixed Methane/Oxygen Diffusion Flame Burner

ABSTRACT The focus of this research was understanding the effect of varying the secondary flow impingement angle of a single coaxial injector in an experimental non-premixed flame burner on flame stability. The burner was a horizontally mounted, rectangular combustion chamber with retractable spark plug for ignition. Reactants were gaseous oxygen and methane as the primary and secondary flow, respectively. Three injectors were designed and fabricated with exit impingement angles of 15, 30, and 45 degrees with the primary flow. The diffusion flame behavior and flame standoff distance length was observed through optical chamber side windows parallel to the axis of the flame. Stability maps of the diffusion flame behavior based upon equivalence ratio, reactant Reynolds numbers, and injector impingement angle were created. It was observed that the 15 degree impingement angle generated the most stable, anchored diffusion flames for high equivalence ratios and low Reynolds numbers. As impingement angle increased, stable, anchored flames transitioned from existing at fuel-lean highly turbulent primary flows to fuel-rich, highly turbulent flows as well as from fuel-rich, low primary flows to no ignition under the same conditions. Therefore, secondary flow impingement angle can drastically influence the location and range of stable, anchored methane/oxygen diffusion flames.

Measurement and modelling signals from an optical fission chambers during reactor irradiation

Nowadays, fission chambers are commonly used for neutron diagnostic in industrial pressurized water reactors. However, with the diversity of emerging nuclear power plant prototypes such as fusion, fast neutron or high temperature reactors, innovative neutron diagnostic system are developed by the French Alternative Energies and Atomic Energy Commission (CEA). Indeed, in some case the operating range of existing fission chambers will not be adapted to the measuring conditions. Thus, the CEA is developing a technology called optical fission chambers, where photons are collected instead of charged particles. This paper presents a macroscopic model of the signal-to-noise ratio of optical fission chamber measuring in neutron and gamma fields. Due to the novelty of this study, we expect to have a better understanding about the intensity of the different light sources. Secondly we aim to validate the developed numerical model by comparing the simulated spectra to the experimental ones. Finally, we highlight some design features which may improves the signal to noise ratio of optical fission chamber.

Designing an optical gas chamber with stepped structure for non-dispersive infrared methane gas sensor

Compared to traditional semiconductor and electrochemistry gas sensors, the non-dispersive infrared (NDIR) gas detection technology presents notable advantages in terms of stability and selectivity. However, the high-performance NDIR gas sensor generally requires a long optical path, resulting in a large gas chamber. In this short communication, a simple and relatively small stepped optical gas chamber (45 mm × 20 mm × 30 mm) with long optical path (94.92 mm) is designed combining simulation method. Furthermore, the stepped optical gas chamber based on the simulation structure is fabricated by a computer number control technique, and used to fabricate a NDIR gas sensor. The results show that the NDIR gas sensor based on the stepped optical gas chamber can be successfully used for CH4 gas detection with a wide detection range and good repeatability. This work provides an optional reference for developing compact NDIR gas sensor.

Experimental study of lube oil pre-ignition in an optical gas engine test rig

Lean-premixed gas combustion is an attractive option for meeting future emission standards toward considerably lower particulate matter and emissions while obtaining an efficiency comparable to diesel combustion. However, ignition processes still pose considerable challenges, with pre-ignition being a major issue. The pre-ignition phenomenon might result from the self-ignition of lube oil in hot zones, making it challenging to observe in real engines. To study single or sparsely separated lube oil droplets under engine-like conditions, the “Flex-OeCoS” experimental test facility was used. To be able to induce such pre-ignitions artificially a novel piezo droplet injector was developed and manufactured, which enabled the metering of minor amounts of lubricating oil or even the injection of single droplets. High-speed cameras and specially developed and partially automatable and adaptive evaluation algorithms were used to record and track the behavior of the injected droplet using overlaid schlieren and OH* chemiluminescence. During the measurement campaigns, relevant operating parameters were varied, and optical investigations were carried out with an ignitable mixture on the Flex-OeCoS test facility under engine-relevant operating conditions. Spontaneous ignition of the vaporized lubricating oil was observed, which subsequently led to ignition of the whole air-fuel mixture in the optical combustion chamber. This was especially evident for lean methane-air mixtures up to an air-fuel ratio of 2.0. With this approach, information could be gathered about the necessary internal engine conditions that lead to pre-ignition in lean mixtures and where their limits lie.

Hydrogen concentration measurements using spark induced breakdown spectroscopy in a real engine

This study develops spark induced breakdown spectroscopy (SIBS) for measurements of direct injected hydrogen concentration in a multi-cylinder engine operated at real conditions. To this end, calibration is performed in the air excess ratio (λ) range of 2.1 ∼ 2.9 and simultaneously, high-speed schlieren imaging of laminar hydrogen flame propagation is performed in an optical high-pressure constant volume combustion chamber (CVCC). To achieve real engine applications, the SIBS is further developed using a modified conventional spark plug for sapphire window insertion onto the positive electrode and guided arc formation via a newly designed nipple type ground electrode. Specifically, the peak spectra intensity ratio of Hα (656 nm) to O (777 nm) is used for calibration, which shows a linear correlation with λ. For the first time, the calibrated SIBS is applied to a real engine operated at 46.2 ∼ 63.9 Nm load and 2000 rpm with 3.5 MPa hydrogen direct injection. The results show lower local λ than the global λ despite early injection timing of 165 crank angles before top dead centre, indicating a significant influence of in-cylinder flow motion on the spatial distribution of hydrogen-air mixtures.

Modeling hydrogen–diesel dual direct injection combustion with FGM and transported PDF

This work extends the transported probability density function (PDF) method to model hydrogen–diesel dual direct injection (H2DDI) combustion, where a H2 jet is ignited by a small pilot diesel jet flame. The work is motivated by previous H2DDI engine tests where stable compression ignition engine operation was reported with up to 90 % H2 supply by energy share. To help explain this high performance and provide a tool to help further engine optimization, the Eulerian Monte Carlo Fields (EMCF) solution method is employed with which a transported PDF equation is solved in combination with Flamelet Generated Manifold (FGM) for high accuracy and computational efficiency. In all cases, the pilot fuel ignites before interacting with the H2 jet and thus reaction rate and chemical composition are computed as the weighted average of the corresponding values taken for two separated FGM tables generated for the two fuels. Pressure measurements and high-speed schlieren imaging performed in a preburn-type optical constant volume combustion chamber (CVCC) with n-heptane (nC7H16) pilot fuel were used to validate the EMCF+FGM model. The application focus is how H2 ignition and combustion is affected when the nC7H16 is injected prior to or after the main H2 jet. EMCF+FGM computed heat release rate and flame structure were compared with experimental data and results from conventional FGM model based on presumed PDF. When applied to H2DDI combustion, the EMCF+FGM model successfully reproduces flame structures and heat release rate under different injection strategies, including the transition towards partially-premixed combustion when the nC7H16 pilot follows the main H2 injection. Moreover, analysis of heat release rate from different stochastic fields can provide a useful indication about cyclic variability and combustion stability.

Computational design of a smoke detector with high sensitivity considering three-dimensional flow characteristics

Early fire detection is essential for preventing catastrophic events, and fire detectors play a critical role in ensuring fire safety. Among the various types of fire detectors, photoelectric smoke detectors are widely used because of their ability to detect smoke at an early stage. The present study investigates the effects of changes in flow directions and inlet size on the smoke detection ability of a photoelectric smoke detector by conducting computational fluid dynamics (CFD) simulations. The results indicated that when the flow direction changes, the components in the optical chamber may hinder the smoke inflow and increase the detector activation time. Moreover, the smoke inlet size was found to affect the carbon monoxide concentration inside the chamber. The velocity magnitude distributions confirmed the correlation between the smoke velocity in the labyrinth structures entering the optical chamber and the detection ability of the smoke detector. These findings suggested that when optimizing the performance of a smoke detector, flow direction, inlet size, and amount of smoke introduced into the optical chamber should be considered. The current study suggested the modified design of the smoke detector to have superior detection ability in both directions compared to the base case in terms of activation time.

Development and Application of an Automated Raman Sensor for Bioprocess Monitoring: From the Laboratory to an Algae Production Platform.

Microalgae provide valuable bio-components with economic and environmental benefits. The monitoring of microalgal production is mostly performed using different sensors and analytical methods that, although very powerful, are limited to qualified users. This study proposes an automated Raman spectroscopy-based sensor for the online monitoring of microalgal production. For this purpose, an in situ system with a sampling station was made of a light-tight optical chamber connected to a Raman probe. Microalgal cultures were routed to this chamber by pipes connected to pumps and valves controlled and programmed by a computer. The developed approach was evaluated on Parachlorella kessleri under different culture conditions at a laboratory and an industrial algal platform. As a result, more than 4000 Raman spectra were generated and analysed by statistical methods. These spectra reflected the physiological state of the cells and demonstrate the ability of the developed sensor to monitor the physiology of microalgal cells and their intracellular molecules of interest in a complex production environment.

Comparison of quartz and sapphire optical chambers for infrared laser sealing of vascular tissues using a reciprocating, side-firing optical fiber: Simulations and experiments.

Infrared (IR) lasers are being tested as an alternative to radiofrequency (RF) and ultrasonic (US) surgical devices for hemostatic sealing of vascular tissues. In previous studies, a side-firing optical fiber with elliptical IR beam output was reciprocated, producing a linear IR laser beam pattern for uniform sealing of blood vessels. Technical challenges include limited field-of-view of vessel position within the metallic device jaws, and matching fiber scan length to variable vessel sizes. A transparent jaw may improve visibility and enable custom treatment. Quartz and sapphire square optical chambers (2.7 × 2.7 × 25 [mm3 ] outer dimensions) were tested, capable of fitting into a 5-mm-OD laparoscopic device. A 1470 nm laser was used for optical transmission studies. Razor blade scans and an IR beam profiler acquired fiber (550-µm-core/0.22NA) output beam profiles. Thermocouples recorded peak temperatures and cooling times on internal and external chamber surfaces. Optical fibers with angle polished distal tips delivered 94% of light at a 90° angle. Porcine renal arteries with diameters of 3.4 ± 0.7 mm (n = 13) for quartz and 3.2 ± 0.7 mm (n = 14) for sapphire chambers (p > 0.05), were sealed using 30 W for 5 s. Reflection losses at material/air interfaces were 3.3% and 7.4% for quartz and sapphire. Peak temperatures on the external chamber surface averaged 74 ± 8°C and 73 ± 10°C (p > 0.05). Times to cool down to 37°C measured 13 ± 4 s and 27 ± 7 s (p < 0.05). Vessel burst pressures (BP) averaged 883 ± 393 mmHg and 412 ± 330 mmHg (p < 0.05). For quartz, 13/13 (100%) vessels were sealed (BP > 360 mmHg), versus 9/14 (64%) for sapphire. Computer simulations for the quartz chamber yielded peak temperatures (78°C) and cooling times (16 s) similar to experiments. Quartz is an inexpensive material for use in a laparoscopic device jaw, providing more consistent vessel seals and faster cooling times than sapphire and current RF and US devices.

An ultra-small integrated CO2 infrared gas sensor for wearable end-tidal CO2 monitoring

Human physiological metabolic status can be obtained by monitoring exhaled CO2 concentration, but current CO2 sensors have disadvantages such as large size, high power consumption, and slow response time, which limit their application in wearable devices and portable instruments. In this article, we report a small size, good performance, and large range CO2 infrared gas sensor that integrates a high emissivity MEMS emitter chip, a high detectivity thermopile chip, and a high coupling efficiency optical chamber to achieve high efficiency optical-thermal-electrical conversion. Compared with typical commercial sensors, the size of the sensor can be reduced by approximately 80% to only 10mm×10mm×6.5mm, with the advantages of low power consumption and fast response speed. Further, a monitoring system for end-tidal CO2 concentration installed on a mask was developed using this sensor, and good results were achieved.