Flame experiments at the Advanced Light Source: New insights into soot formation processes

Hansen N, Skeen SA, Michelsen HA, Wilson KR, Kohse-Höinghaus K. Flame experiments at the Advanced Light Source: New insights into soot formation processes. JOURNAL OF VISUALIZED EXPERIMENTS. 2014;87(87):E51369

Development of limited-view tomography for measurement of Spray G plume direction and liquid volume fraction

Abstract The method for direct injection of fuel in the cylinder of an IC engines is important to high-efficiency and low-emission performance. Optical spray diagnostics plays an important role in understanding plume movement and interaction for multi-hole injectors, and providing baseline understanding used for computational optimization of fuel delivery. Traditional planar or line-of-sight diagnostics fail to capture the liquid distribution because of optical thickness concerns. This work proposes a high-speed (67 kHz) extinction imaging technique at various injector rotations coupled to computed tomography (CT) for time-resolved reconstruction of liquid volume fraction in three dimensions. The number of views selected and processing were based on synthetic (modeled) liquid volume fraction data where extinction and CT adequately reconstructed each plume. The exercise showed that for an 8-hole, symmetric-design injector (ECN Spray G), only three different views are enough to reproduce the direction of each plume, and particularly the mean plume direction. Therefore, the number of views was minimized for experiments to save expense. Measurements applying this limited-view technique confirm plume–plume variations also detected with mechanical patternation, while providing better spatial and temporal resolution than achieved previously. Uncertainties due to the limited view within pressurized spray chambers, the droplet size, and optically thick regions are discussed. Graphic abstrac

Internal and near nozzle measurements of Engine Combustion Network "Spray G" gasoline direct injectors

[EN] Gasoline direct injection (GDI) sprays are complex multiphase flows. When compared to multi-hole diesel sprays, the plumes are closely spaced, and the sprays are more likely to interact. The effects of multi-jet interaction on entrainment and spray targeting can be influenced by small variations in the mass fluxes from the holes, which in turn depend on transients in the needle movement and small-scale details of the internal geometry. In this paper, we present a comprehensive overview of a multi-institutional effort to experimentally characterize the internal geometry and near-nozzle flow of the Engine Combustion Network (ECN) Spray G gasoline injector. In order to develop a complete pictitre of the near-nozzle flow, a standardized setup was shared between facilities. A wide range of techniques were employed, including both X-ray and visible-light diagnostics. The novel aspects of this work include both new experimental measurements, and a comparison of the results across different techniques and facilities. The breadth and depth of the data reveal phenomena which were not apparent from analysis of the individual data sets. We show that plume-to-plume variations in the mass fluxes from the holes can cause large-scale asymmetries in the entrainment field and spray structure. Both internal flow transients and small-scale geometric features can have an effect on the external flow. The sharp turning angle of the flow into the holes also causes an inward vectoring of the plumes relative to the hole drill angle, which increases with time due to entrainment of gas into a low-pressure region between the plumes. These factors increase the likelihood of spray collapse with longer injection durations.The X-ray experiments were performed at the 7-BM and 32-ID beam lines of the APS at Argonne National Laboratory. Use of the APS is supported by the U.S. Department of Energy (DOE) under Contract No. DE-AC02-06CH11357. Research was also performed at the Combustion Research Facility, Sandia National Laboratories, Livermore, California. Sandia National Laboratories is managed and operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy National Nuclear Security Administration under contract DE-NA-0003525.Duke, DJ.; Kastengren, AL.; Matusik, KE.; Swantek, AB.; Powell, CF.; Payri, R.; Vaquerizo, D.... (2017). Internal and near nozzle measurements of Engine Combustion Network "Spray G" gasoline direct injectors. Experimental Thermal and Fluid Science. 88:608-621. https://doi.org/10.1016/j.expthermflusci.2017.07.015S6086218

Inter-plume aerodynamics for gasoline spray collapse

The collapse or merging of individual plumes of direct-injection gasoline injectors is of fundamental importance to engine performance because of its impact on fuel–air mixing. However, the mechanisms of spray collapse are not fully understood and are difficult to predict. The purpose of this work is to study the aerodynamics in the inter-spray region, which can potentially lead to plume collapse. High-speed (100 kHz) particle image velocimetry is applied along a plane between plumes to observe the full temporal evolution of plume interaction and potential collapse, resolved for individual injection events. Supporting information along a line of sight is obtained using simultaneous diffused back illumination and Mie-scatter techniques. Experiments are performed under simulated engine conditions using a symmetric eight-hole injector in a high-temperature, high-pressure vessel at the “Spray G” operating conditions of the engine combustion network. Indicators of plume interaction and collapse include changes in counter-flow recirculation of ambient gas toward the injector along the axis of the injector or in the inter-plume region between plumes. The effect of ambient temperature and gas density on the inter-plume aerodynamics and the subsequent plume collapse are assessed. Increasing ambient temperature or density, with enhanced vaporization and momentum exchange, accelerates the plume interaction. Plume direction progressively shifts toward the injector axis with time, demonstrating that the plume interaction and collapse are inherently transient. </jats:p

High-speed formaldehyde planar laser-induced fluorescence and schlieren to assess influences of injection pressure and oxygen concentration on Spray A flames

The present study investigates the effect of injection pressure and ambient oxygen concentration variations on the Engine Combustion Network Spray A flame. The two-stage ignition and combustion processes for individual injections are characterized using a high-speed planar laser-induced fluorescence (PLIF) and schlieren imaging diagnostic at high pressure (near 6 MPa). For PLIF measurements, we use a pulse-burst-mode Nd:YAG laser capable of producing a 6 ms long 355-nm pulse-train with 300 pulses at 70 mJ/pulse, separated by 20 µs. The PLIF imaging at high-acquisition rate offers unique insights into understanding the spatiotemporal distribution of formaldehyde (CH2O) and polycyclic aromatic hydrocarbons (PAH). High-speed line-of-sight schlieren with a pulsed infrared light emitting diode (LED) is applied simultaneously with PLIF to visualize the spray penetration, low- and high-temperature ignition, and turbulent flame dynamics, while in-vessel pressure is used in concert with the optical diagnostics to assess the ignition delay time of the high-temperature ignition events. The PLIF and line-of-sight measurements, documenting the position and timing for formation and consumption of CH2O and the inception and distribution of PAH downstream with changes in ambient oxygen concentration and injection pressure, provide a unique database for detailed evaluation of single-event (e.g. LES) or ensemble-average CFD

Detailed measurements of transient two-stage ignition and combustion processes in high-pressure spray flames using simultaneous high-speed formaldehyde PLIF and schlieren imaging

The low- and high-temperature ignition and combustion processes in a high-pressure spray flame of n-dodecane were investigated using simultaneous 50-kHz formaldehyde (HCHO) planar laser-induced fluorescence (PLIF) and 100-kHz schlieren imaging. PLIF measurements were facilitated through the use of a pulse-burst-mode Nd:YAG laser, and the high-speed HCHO PLIF signal was imaged using a non-intensified CMOS camera with dynamic background emission correction. The experiments were conducted in the Sandia constant-volume preburn vessel equipped with a new Spray A injector. The effects of ambient conditions on the ignition delay times of the two-stage ignition events, HCHO structures, and lift-off length values were examined. Consistent with past studies of traditional Spray A flames, the formation of HCHO was first observed in the jet peripheries where the equivalence ratio (Φ) is expected to be leaner and hotter and then grows in size and in intensity downstream into the jet core where Φ is expected to be richer and colder. The measurements showed that the formation and propagation of HCHO from the leaner to richer region leads to high-temperature ignition events, supporting the identification of a phenomenon called “cool-flame wave propagation” during the transient ignition process. Subsequent high-temperature ignition was found to consume the previously formed HCHO in the jet head, while the formation of HCHO persisted in the fuel-rich zone near the flame base over the entire combustion period

Arbeitskampfrecht VII : Leistungsstörungen durch Arbeitskampf

In a collaborative effort to identify key aspects of heavy-duty diesel injector behavior, the Engine Combustion Network (ECN) Spray C and Spray D injectors were characterized in three independent research laboratories using constant volume pre-burn vessels and a heated constant-pressure vessel. This work reports on experiments with nominally identical injectors used in different optically accessible combustion chambers, where one of the injectors was designed intentionally to promote cavitation. Optical diagnostic techniques specifically targeted liquid- and vapor-phase penetration, combustion indicators, and sooting behavior over a large range of ambient temperatures—from 850 K to 1100 K. Because the large-orifice injectors employed in this work result in flame lengths that extend well beyond the optical diagnostics’ field-of-view, a novel method using a characteristic volume is proposed for quantitative comparison of soot under such conditions. Further, the viability of extrapolating these measurements downstream is considered. The results reported in this publication explain trends and unique characteristics of the two different injectors over a range of conditions and serve as calibration targets for numerical efforts within the ECN consortium and beyond. Building on agreement for experimental results from different institutions under inert conditions, apparent differences found in combustion indicators and sooting behavior are addressed and explained. Ignition delay and soot onset are correlated and the results demonstrate the sensitivity of soot formation to the major species of the ambient gas (i.e., carbon dioxide, water, and nitrogen in the pre-burn ambient versus nitrogen only in the constant pressure vessel) when holding ambient oxygen volume percent constant