Wide Range Of Ambient Conditions Research Articles

A Respiratory Simulator for the Study of Pathogen Transmission in Indoor Environments

Detailed investigation of pathogen transmission by respiratory droplets requires extensive experimental datasets with high spatial–temporal resolution in a wide range of ambient conditions. Respiratory simulators are attractive tools for those measurements, because they improve repeatability, endurance, and control of experimental conditions with respect to studies on human subjects. They also enable the use of powerful experimental techniques, which may raise health concerns if employed on humans. In this paper, we design and present a respiratory simulator, which is capable of accurately reproducing physiological flow rate profiles and allows the investigation of the spatial and temporal features of the exhaust flow by background‐oriented schlieren (BOS) and particle image velocimetry (PIV). We use laser interferometry and high‐magnification shadowgraphy to verify the size distributions of the emitted droplets, and we quantify the evolution of the droplet concentration during cough events by Mie scattering analysis. The experiments demonstrate the ability of the respiratory simulator to generate highly reproducible cough events with precise and controllable droplet size distributions over a wide range of flow rates.

Performance analysis of a novel dual-evaporation-temperature combined-effect absorption chiller for temperature and humidity independent control air-conditioning

Temperature and humidity independent control (THIC) air-conditioning (AC) systems are promising alternatives to conventional AC systems. A novel dual-evaporation-temperature combined-effect (DETCE) absorption chiller for THIC AC application is proposed. It can produce high-temperature (16–18 °C) and low-temperature (7 °C) chilled water with a thermal coefficient of performance (COP) above 1 by the deep utilization of heat source at around 100–120 °C. Theoretical models were established to investigate effects of generation temperature (Tgen), evaporation temperature and high-temperature cooling capacity ratio (HCR) on thermal performance of the novel chiller. The results show that the COP of the proposed chiller (COPch,prop) is largely affected by Tgen and HCR. The COPch,prop is 24.1 %-50.4 % larger than that of the conventional single-effect absorption chiller (SEABC) under typical HCRs (0.5–0.7). Performance comparison of the DETCE absorption chiller-based THIC AC system and the conventional SEABC-based AC system was also conducted under different room sensible heat ratios (RSHR), fresh air ratios (FR) and ambient conditions. It is found that the proposed system has a greater energy-saving potential when applied in an air-conditioned space with a large RSHR and FR. Under typical RSHRs (0.6–0.8), both the thermal energy saving rate (ESR) and the heating fluid saving rate of the novel system are over 20 %. Besides, the proposed system can achieve an average ESR of around 30 % under a wide range of ambient conditions. This study provides a novel solution for the deep utilization of solar energy or waste heat at around 100–120 °C to achieve efficient and environmentally friendly THIC AC.

Improving efficiency of transcritical CO2 cycles through a magnetic refrigeration subcooling system

Subcooling methods for transcritical CO2 plants are being studied in order to improve the behaviour of these systems in hot climates, where basic configurations are not competitive enough. To achieve important improvements in the transcritical CO2 performance, it is necessary to perform the subcooling with a refrigeration cycle working with a Coefficient of Performance higher than that of the CO2 system without subcooling. Magnetic refrigeration devices can achieve high Coefficient of Performance values when the temperature difference between the hot sink and cold source is small, and therefore they meet the requirements to be applied as a CO2 subcooling method. This work presents the coupling of two refrigeration technologies: vapour compression and magnetocaloric refrigeration, which has not yet been presented in the literature. The magnetic refrigeration system is, based on the experimental results of the existing prototype, analysed semi-empirically and further evaluated, as a subcooling method for a transcritical CO2 cycle in a wide range of ambient conditions. Gas-cooler pressure, subcooling degree and operating parameters of the magnetic refrigerator were optimized for each condition to obtain the maximum Coefficient of Performance. We show that subcooling with the existing prototype of magnetic refrigeration system can enhance the overall Coefficient of Performance of transcritical CO2 cycle by up to 9%.

Observable signatures of enhanced axion emission from protoneutron stars

We perform general relativistic one-dimensional supernova (SN) simulations to identify observable signatures of enhanced axion emission from the pion-induced reaction $\pi^- + p \rightarrow n + a$ inside a newly born protoneutron star (PNS).We focus on the early evolution after the onset of the supernova explosion to predict the temporal and spectral features of the neutrino and axion emission during the first 10 s. Pions are included as explicit new degrees of freedom in hot and dense matter. Their thermal population and their role in axion production are both determined consistently to include effects due to their interactions with nucleons. For a wide range of ambient conditions encountered inside a PNS, we find that the pion-induced axion production dominates over nucleon-nucleon bremsstrahlung processes. By consistently including the role of pions on the dense matter equation of state and on the energy loss, our simulations predict robust discernible features of neutrino and axion emission from a galactic supernova that can be observed in terrestrial detectors. For axion couplings that are compatible with current bounds, we find a significant suppression with time of the neutrino luminosity during the first 10 s. This suggests that current bounds derived from the neutrino signal from SN 1987A can be improved and that future galactic supernovae may provide significantly more stringent constraints.

Deposition of Fuel Impurities Within Thermal Barrier Coatings in Gas Turbine Hot Gas Paths

Abstract For the reliable operation of modern gas turbines, thermal barrier coatings (TBCs) need to withstand a wide range of ambient conditions resulting from impurities in inlet air or fuels. When analyzing the deposition of detrimental hot gas constituents, previous efforts largely focus on the investigation of solid and molten deposit interaction with TBCs. Recent literature and observations in gas turbines indicate that not only liquids can penetrate porous TBCs, but the deposition from gas phase inside of pores and cracks is also an aspect of TBC degradation. To investigate this vapor deposition process, a diffusion model has been coupled with a thermodynamic equilibrium solver. The diffusion model calculates vapor transport of trace elements through pores and gaps in the TBC, where the thermodynamic equilibrium solver calculates local thermodynamic equilibria to predict whether deposition takes place. In this work, the model is applied to discuss the deposition properties of calcium. In recent literature, calcium has—in some cases—been reported to deposit inside of TBCs as pure anhydrite (CaSO4). An actual anhydrite finding in the TBC of a stationary gas turbine blade was reproduced applying the introduced model. The vapor deposition is shown to occur within and on top of the TBC, depending on several factors, such as pressure, temperatures, calcium-to-silicon ratio, and calcium-to-sulfur ratio. The successful alignment of conditions in real engines with model results will allow addressing the increasing demand for more fuel- and operational flexibility of current and future gas turbines.

IMPROVING THE CALCULATION OF EVAPORATING SPRAYS FOR MEDIUM-SPEED MARINE-ENGINE-LIKE CONDITIONS

In order to reduce maritime transportation's greenhouse gas and pollutant emissions, marine engine manufacturers need to deepen the fundamental understanding of the injection and spray process. But little knowledge is openly available on marine engine fuel sprays, and their numerical simulation. In this paper, two-dimensional unsteady-state Reynolds-averaged Navier-Stokes simulations were performed to study evaporating high-pressure marine engine sprays, in which an injector with a nozzle diameter of 0.44 mm was used. The proposed approach was first validated using measurement data of Spray A and Spray D from the Engine Combustion Network. A satisfactory agreement with the Engine Combustion Network data demonstrated that the simulation can correctly capture the spray processes. However, a discrepancy was found when simulating the marine engine sprays. After summarizing and analyzing the values of the turbulence model constant (C1 of the standard k-ε model) used from the published literature, a lower value of C1 was adopted, and good agreement under a wide range of ambient conditions (density varying from 7.6 to 22.5 kg/m3, and temperature varying from 700 to 950 K) was achieved. Also, the disagreement that was noted for the liquid penetration for a low-temperature case could be explained by the ligament detachment phenomenon which was captured by the computational fluid dynamics simulation.

Numerical study of the effect of atomic mass of the ambient gas on the expansion and the lateral interactions of LBO plumes

The characteristics of the lateral interaction of two LBO plasma plumes in argon Ar ambient gas at high pressures were reported in a recent publication (Yadav et al 2017 J. Phys. D: Appl. Phys. 50 355201). Further, we have investigated the interaction characteristics of plumes in He, Ne, Ar and Xe gases to see the effect of atomic mass on the interaction. The present work illustrates the applicability of the present model for theoretical understanding of dynamics, structure, density variation, shock wave formations and their interactions of two propagating plasma plumes in a wide range of ambient conditions. The formation of interaction region, geometrical shape and strength of the shock fronts and subsequent regular and Mach reflections in accordance with the nature and pressure of ambient gas are successfully captured in the simulations.

Metamorphosis in Insect Muscle: Insights for Engineering Muscle-Based Actuators.

One of the major limitations to advancing the development of soft robots is the absence of lightweight, effective soft actuators. While synthetic systems, such as pneumatics and shape memory alloys, have created important breakthroughs in soft actuation, they typically rely on large external power sources and some rigid components. Muscles provide an ideal actuator for soft constructs, as they are lightweight, deformable, biodegradable, silent, and powered by energy-dense hydrocarbons such as glucose. Vertebrate cell lines and embryonic cultures have allowed critical foundational work to this end, but progress there is limited by the difficulty of identifying individual pathways in embryonic development, and the divergence of immortal cell lines from these normal developmental programs. An alternative to culturing muscles from embryonic cells is to exploit the advantages of species with metamorphic stages. In these animals, muscles develop from a predefined pool of myoblasts with well-characterized contacts to other tissues. In addition, the endocrine triggers for development into adult muscles are often known and tractable for experimental manipulation. This is particularly true for metamorphic muscle development in holometabolous insects, which provide exciting new avenues for tissue engineering. Using insect tissues for actuator development confers additional benefits; insect muscles are more robust to varying pH, temperature, and oxygenation than are vertebrate cells. Given that biohybrid robots are likely to be used in ambient conditions and changing environments, this sort of hardiness is likely to be required for practical use. In this study, we summarize key processes and signals in metamorphic muscle development, drawing attention to those pathways that offer entry points for manipulation. By focusing on lessons learned from in vivo insect development, we propose that future culture designs will be able to use more systematic, hypothesis-driven approaches to optimizing engineered muscle. Impact statement This review summarizes our current understanding of metamorphic muscle development in insects. It provides a framework for engineering muscle-based actuators that can be used in robotic applications in a wide range of ambient conditions. The focus is on identifying key processes that might be manipulated to solve current challenges in controlling tissue development such as myoblast proliferation, myotube formation and fusion, cytoskeletal alignment, myotendinous attachment and full differentiation. An important goal is to gather findings that cross disciplinary boundaries and to promote the development of better bioactuators for nonclinical applications.

Assessment of engine combustion network recommendations for measurement of ignition and lift-off length

The engine combustion network recommends two different imaging-based diagnostics for the measurement of diesel spray ignition delay and lift-off length, respectively. To measure ignition delay, high-speed imaging of broadband luminosity, spectrally filtered to limit collected wavelengths below 600 nm, is recommended. This diagnostic is often referred to as broadband natural luminosity. For lift-off length measurements, the engine combustion network recommends imaging of OH* chemiluminescence. This diagnostic requires using an image-intensified camera to detect narrowly filtered light around 310 nm. Alternatively, it has been shown that the lift-off length can be measured using broadband natural luminosity, avoiding the need for an intensifier and ultraviolet-transmitting optics. However, care is needed in the collection and processing of this diagnostic to accurately isolate the chemiluminescence signal. Particularly, standard intensity thresholding techniques are not sufficient for isolating the chemiluminescence signal in broadband natural luminosity images. Thus, an intensity-histogram-based thresholding method is introduced. This article assesses the feasibility and practicality of measuring lift-off length using broadband natural luminosity using a detailed comparison to OH* chemiluminescence measurements. It is shown that lift-off length measurements using broadband natural luminosity are prone to user bias error in the optical setup and data processing, especially under moderate- to high-sooting conditions. We conclude that while OH* imaging provides the most reliable and accurate measurement of lift-off length at a wide range of ambient conditions, an intensity-histogram analysis can help discriminate the high-temperature chemiluminescence signal from others in a broadband natural luminosity image at higher-sooting operating conditions than demonstrated in current literature.

Effects of ambient conditions on concurrent-flow flame spread over a wide thin solid in microgravity

Two-dimensional numerical simulations were performed to study concurrent-flow flame spread over a thin solid in microgravity. The main variable is the ambient flow velocity. Results were validated against recent microgravity experiments (Saffire) where samples 41 cm wide were burned in two different flow velocities. The numerical results showed that, when flow velocity increases, the average radiative heat flux out of the solid surface in the pyrolysis region remains constant. The average convective heat flux decreases and the average radiative heat flux into the solid surface increases. The average net heat flux remains approximately constant. Additional simulations using different ambient pressures and oxygen percentages further showed that, while away from extinction conditions, the average net heat flux in the sample pyrolysis region and hence the average solid mass burning rate are insensitive to the ambient conditions (i.e., oxygen percentage, flow speed, pressure). Furthermore, the steady-state flame length is mainly controlled by the rate of oxygen entrainment into the gas-phase reaction zone and the average solid mass burning rate. Based on these observations, analytical model was developed to correlate the flame spread rate and flame length to ambient conditions. It predicts that, for concurrent-flow flame spread at steady state, the flame length and flame spread rate have linear dependency on the ambient pressure and the forced flow velocity, and a second order dependency on the ambient oxygen percentage. The proposed correlations were tested against numerical simulations as well as a collection of data from previous microgravity experiments in a wide range of ambient conditions.

A study on the mechanism reduction and evaluation of biodiesel with the change of mechanism reduction factors

This study aims to confirm the effect of changing the various factors with the directed relation graph error propagation–based methods and to adopt a new approach of the mechanism evaluation in the reduction of biodiesel mechanism. The factors considered in this study were a threshold value, target species, ambient conditions, and the evaluation formula consists of the reduction rates and the maximum error rate of ignition delay to objectively compare the skeletal mechanisms generated under different conditions. For a threshold value, the automatic mechanism reduction process was used to select the appropriate threshold value by applying the relative tolerance and absolute tolerance; so relative tolerance and absolute tolerance represent the factor of the threshold value. Also, the seven steps of mechanism reduction process consist of directed relation graph error propagation, directed relation graph error propagation with sensitivity analysis, peak concentration analysis, full species sensitivity analysis, and A-factor modification. As a result of the mechanism reduction, different relative tolerance and absolute tolerance values should be applied to each step to select the appropriate threshold value. For target species, considering polycyclic aromatic hydrocarbon species as target species shows higher efficiency of mechanism reduction. Also, considering the negative temperature coefficient region as ambient conditions helps the mechanism be reduced efficiently than a wide range of ambient conditions. Finally, the reduced mechanism which had 247 species and 1129 reactions was generated, and the maximum error rate of ignition delay was about 30%. For the applicability of three-dimensional computational fluid dynamics and verification of the reduced mechanism, the compression ignition engine simulation was performed. As a result of three-dimensional computational fluid dynamics, the predicted cylinder pressure, rate of heat release, indicated mean effective pressure, and power were similar to the experimental results. However, the results of carbon monoxide and nitrogen oxide emissions did not match the experimental results.

Fresh air humidification in winter using desiccant wheels for cold and dry climate regions: Optimization study of humidification processes

• Analyzing efficient fresh air humidification methods for buildings in cold and dry climate regions. • Multi-stage desiccant wheels with separate dehumidification air improve system performance. • Control strategies are discussed, showing an over 95 % satisfactory rate, under Urumchi condition. • When natural gas boilers are used, heating system efficiency can be around 2 with heat recoveries. Efficient fresh air humidification methods for buildings located in cold and dry climate regions are discussed in this paper. Air handling units that use desiccant wheels to realize air humidification are studied. Optimization analysis is carried out for three types of air handling units under different ambient humid ratios and effects of desiccant wheel facial area ratios ( A r ) between dehumidification air and humidification air, air flow rate ratio between dehumidification air and humidification air ( F r ), rotation speed ( RS ), stage number etc., are discussed. Based on the optimization results, an air handling unit that has 3 stages desiccant wheels and 3 streams dehumidification air is proposed. For this device, A r is 3 for each desiccant wheel and F r can be adjusted from 1 to 9. It can satisfy fresh air humidification in a wide range of ambient conditions. Based on this device, two control strategies are discussed based on Urumchi winter ambient conditions. The satisfactory rate is over 95%.

Low-Emission Operation of Aeroderivative Gas-Turbine Combustor over a Wide Range of Ambient Conditions

The capabilities of controlling a low-emission combustor (LEC) over a wide range of ambient conditions are analyzed. The LES is intended for a GTU-16P gas turbine that is a derivative of the PS-90A aircraft engine by the UEC Aviadvigatel company. The LEC is of premix swirl stabilized type based on GTE-110 prototype. Its burner consists of pilot and main burners. The main burner has two fuel supply channels that allow controlling the quality of the air-fuel mixture. The low-emission operation range of the LEC can be extended to 70% load at negative ambient temperatures by bleeding air to the compressor inlet.

Design, development, and scientific performance of the Raman Laser Spectrometer EQM on the 2020 ExoMars (ESA) Mission

AbstractThe Raman Laser Spectrometer (RLS) is one of the three Pasteur Payload instruments located within the rover analytical laboratory drawer (ALD), for ESA's Aurora exploration programme, ExoMars 2020 mission. The instrument will analyse the crushed surface and subsurface samples that are positioned below the Raman optical head by the ALD carousel.The RLS engineering and qualification model (EQM) was delivered to ESA at the end of 2017, after a wide technical and scientific test characterization campaign. The scientific campaign comprised instrument calibration and detailed evaluation of the scientific requirements and overall performance. For spectral calibration, continuous emission standard lamps (such as Hg‐Ar, Ne, and Xe) were utilized, as well as Raman spectra of pure liquids typically used as standards (cyclohexane and carbon tetrachloride (CCl4)). In addition, Raman spectra of the RLS calibration target (CT), a small disc of polyethylene terephthalate (PET) were obtained at various temperatures. This target, placed inside the rover, will be used for both Instrument health checks and calibration activities throughout Mars operations. For the scientific requirements and performance evaluations, several liquid and solid samples were analysed under a wide range of ambient conditions. The obtained spectral band parameters (peak position, relative peak intensity, peak width, and peak profile) were evaluated. Also, the instrument response (in terms of SNR) was characterized at different integration times and detector operating temperatures. In this paper, we provide a description of the development, verification, functional test, and overall scientific performance of the RLS instrument developed for ExoMars. Particular attention is placed on the performance of the EQM, which is the most representative instrument, in terms of engineering and functionality, of the flight model (FM) and in addition is used for performing all the mechanical, thermal, and radiation tests necessary for space qualification (for planetary applications). The data presented and analysed here, comprise part of the overall dataset obtained during the full instrument characterization campaign conducted at INTA before and during delivery and integration of the EQM in the rover ALD at TAS‐I facilities (Torino, Italy). The results obtained confirm that the full functionality and scientific performance of the RLS instrument was maintained after integration.

Self-Powered, Rapid-Response, and Highly Flexible Humidity Sensors Based on Moisture-Dependent Voltage Generation.

Most advanced humidity sensors are powered by batteries that need regular charging and replacement, causing environmental problems and complicated management issues. This paradigm has been overcome through the development of new technology based on the concept of simple, self-powered, rapid-response, flexible humidity sensors enabled by the properties of densely packed titanium dioxide (TiO2) nanowire networks. These sensors eliminate the need for an external power source and produce an output voltage that can be readily related to ambient humidity level over a wide range of ambient conditions. They are characterized by rapid response and relaxation times (typically 4.5 and 2.8 s, respectively). These units are mechanically flexible and maintain a constant voltage output after 10 000 bending cycles. This new type of humidity sensor is easily attached to a human finger for use in the monitoring of ambient humidity level in the environment around human skin, near wet objects, or in the presence of moist materials. The unique properties of this new self-powered wearable humidity sensor technology open up a variety of new applications, including the development of electronic skin, personal healthcare products, and smart tracking in the future Internet-of-things.

Combined water desalination and electricity generation through a humidification-dehumidification process integrated with photovoltaic-thermal modules: Design, performance analysis and techno-economic assessment

Abstract Humidification-dehumidification (HDH) processes have proved to be a promising solution for small-scale desalination, appropriate for water production in off-grid locations where the water demand does not justify the installation of conventional large-scale systems. With this contribution, we investigate the design and operation of an HDH process coupled with photovoltaic-thermal (PVT) solar modules for the simultaneous generation of clean water and electricity. The HDH system consists of established technologies, namely a humidification column and a heat exchanger, and is simulated through a commercial software accounting for heat and mass transfer limitations. On the other hand, PVT modules are a relatively new technology and their performance is determined experimentally to characterize the simultaneous generation of electricity and heat under realistic operating conditions. Based on the maximum-efficiency ratio of water to air mass flow rates, the optimal design of the system is determined for a wide range of ambient conditions by evaluating the impact of saline water flow rate, PVT configuration and HDH size on the amount of clean water produced. Then, the optimal operation of the system is characterized as function of the ambient conditions for a fixed system design. The state of the system is represented by the maximum process temperature, at the outlet of the PVT modules, whereas the performance is evaluated in terms of clean water and electricity generation. Finally, a techno-economic assessment is carried out to compare the proposed technology against conventional solar-driven HDH units, which use thermal and photovoltaic panels, for a wide range of electricity price, ambient conditions, amount of yearly water produced and size of the HDH process.

Inverse design of wind turbine blade sections for operation under icing conditions

A methodology is developed to determine the shape of the two dimensional section of wind turbine blades considering the operation of wind turbine under icing conditions. An inverse design process provides the blade shape from a prescribed pressure or velocity distribution, and then the icing of the blade section obtained is simulated under different ambient conditions. The aerodynamic performances of the bare blade and the iced blade are evaluated and compared, which serves as the basis for involving a correction factor in the inverse design process. This correction factor modifies the prescribed velocity distribution so that the blade shape provided by the inverse design process will be applicable under some icing conditions that are chosen according to the prevailing meteorological conditions of the location where the wind turbine is installed. The procedure presented will contribute towards the design of blade shapes that can enable wind turbines to operate under a wide range of ambient conditions satisfactorily.

Extension of Fuel Flexibility by Combining Intelligent Control Methods for Siemens SGT-400 Dry Low Emission Combustion System

Extension of gas fuel flexibility of a current production SGT-400 industrial gas turbine combustor system is reported in this paper. A SGT-400 engine with hybrid combustion system configuration to meet a customer's specific requirements was string tested. This engine was tested with the gas turbine package driver unit and the gas compressor-driven unit to operate on and switch between three different fuels with temperature-corrected Wobbe index (TCWI) varying between 45 MJ/m3, 38 MJ/m3, and 30 MJ/m3. The alteration of fuel heating value was achieved by injection or withdrawal of N2 into or from the fuel system. The results show that the engine can maintain stable operation on and switching between these three different fuels with fast changeover rate of the heating value greater than 10% per minute without shutdown or change in load condition. High-pressure rig tests were carried out to demonstrate the capabilities of the combustion system at engine operating conditions across a wide range of ambient conditions. Variations of the fuel heating value, with Wobbe index (WI) of 30 MJ/Sm3, 33 MJ/Sm3, 35 MJ/Sm3, and 45 MJ/Sm3 (natural gas, NG) at standard conditions, were achieved by blending NG with CO2 as diluent. Emissions, combustion dynamics, fuel pressure, and flashback monitoring via measurement of burner metal temperatures, were the main parameters used to evaluate the impact of fuel flexibility on combustor performance. Test results show that NOx emissions decrease as the fuel heating value is reduced. Also note that a decreasing fuel heating value leads to a requirement to increase the fuel supply pressure. Effect of fuel heating value on combustion was investigated, and the reduction in adiabatic flame temperature and laminar flame speed was observed for lower heating value fuels. The successful development program has increased the capability of the SGT-400 standard production dry low emissions (DLE) burner configuration to operate with a range of fuels covering a WI corrected to the normal conditions from 30 MJ/N·m3 to 49 MJ/N·m3. The tests results obtained on the Siemens SGT-400 combustion system provide significant experience for industrial gas turbine burner design for fuel flexibility.

Measured Saturation Vapor Pressures of Phenolic and Nitro-aromatic Compounds.

Phenolic and nitro-aromatic compounds are extremely toxic components of atmospheric aerosol that are currently not well understood. In this Article, solid and subcooled-liquid-state saturation vapor pressures of phenolic and nitro-aromatic compounds are measured using Knudsen Effusion Mass Spectrometry (KEMS) over a range of temperatures (298-318 K). Vapor pressure estimation methods, assessed in this study, do not replicate the observed dependency on the relative positions of functional groups. With a few exceptions, the estimates are biased toward predicting saturation vapor pressures that are too high, by 5-6 orders of magnitude in some cases. Basic partitioning theory comparisons indicate that overestimation of vapor pressures in such cases would cause us to expect these compounds to be present in the gas state, whereas measurements in this study suggest these phenolic and nitro-aromatic will partition into the condensed state for a wide range of ambient conditions if absorptive partitioning plays a dominant role. While these techniques might have both structural and parametric uncertainties, the new data presented here should support studies trying to ascertain the role of nitrogen containing organics on aerosol growth and human health impacts.

Scaling combustion recession after end of injection in diesel sprays

While soot and NOx emissions tend to be lower for partially-premixed compression ignition (PPCI) strategies compared to more conventional conditions, a common theme amongst PPCI strategies are the excessive unburned hydrocarbons (UHC) that originate from overly lean mixtures near the nozzle due to end-of-injection entrainment. The focus of this work is on combustion recession, which governs the outcome of near-nozzle UHC and has been identified as a process that is strongly influenced by end-of-injection transients in addition to in-cylinder thermodynamic conditions and injection parameters. Combustion recession is the process whereby the initially lifted reaction zone retreats back towards the nozzle following end-of-injection thus consuming UHC that would otherwise remain near the nozzle and persist into the expansion stroke. In an effort to link end-of-injection combustion transients to ambient thermodynamic conditions and injector parameters, a scaling methodology to predict the likelihood of combustion recession in diesel sprays was developed. This methodology relates ignition timescales during steady injection to mixing timescales after end-of-injection. Reasonable agreement between the predicted scaling and measured combustion recession data is shown over a very wide range of ambient conditions, injector parameters, and end-of-injection transients. The success of this scaling suggests that combustion recession is autoignition dominated, heavily influenced by injector design, and that the mixing-limited vaporization assumption can be extended to the study of end-of-injection phenomena. This work also suggests that combustion recession is a more robust parameter for correlation to UHC than ignition dwell.