Spatio-Temporal Progression of Two-Stage Autoignition for Diesel Sprays in a Low-Reactivity Ambient: n-Heptane Pilot-Ignited Premixed Natural Gas

[EN] The spatial and temporal locations of autoignition depend on fuel chemistry and the temperature, pressure, and mixing trajectories in the fuel jets. Dual-fuel systems can provide insight into fuel-chemistry aspects through variation of the proportions of fuels with different reactivities, and engine operating condition variations can provide information on physical effects. In this context, the spatial and temporal progression of two-stage autoignition of a diesel-fuel surrogate, n-heptane, in a lean-premixed charge of synthetic natural gas (NG) and air is imaged in an optically accessible heavy-duty diesel engine. The lean-premixed charge of NG is prepared by fumigation upstream of the engine intake manifold. Optical diagnostics include: infrared (IR) imaging for quantifying both the in-cylinder NG concentration and the pilot-jet penetration rate and spreading angle, high-speed cool-flame chemiluminescence imaging as an indicator of low-temperature heat release (LTHR), and high-speed OH* chemiluminescence imaging as an indicator high-temperature heat release (HTHR). To aid interpretation of the experimental observations, zero-dimensional chemical kinetics simulations provide further understanding of the underlying interplay between the physical and chemical processes of mixing (pilot fuel-jet entrainment) and autoignition (two-stage ignition chemistry). Increasing the premixed NG concentration prolongs the ignition delay of the pilot fuel and increases the combustion duration. Due to the relatively short pilot-fuel injections utilized, the transient increase in entrainment near the end of injection (entrainment wave) plays an important role in mixing. To achieve desired combustion characteristics, i.e., ignition and combustion timing (e.g., for combustion phasing) and location (e.g., for reducing wall heat-transfer or tailoring charge stratification), injection parameters can be suitably selected to yield the necessary mixing trajectories that potentially help offset changes in fuel ignition chemistry, which could be a valuable tool for combustion design.This research was sponsored by the U.S. Department of Energy (DOE) Office of Energy Efficiency and Renewable Energy (EERE). Optical engine experiments were conducted at the Combustion Research Facility of Sandia National Laboratories in Livermore, CA. Sandia National Laboratories is a multimission laboratory 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's National Nuclear Security Administration (NNSA) under contract DE-NA0003525. We gratefully acknowledge the contributions of Keith Penney and Dave Cicone for their assistance in developing research tools and maintaining the optical engine.Rajasegar, R.; Niki, Y.; García-Oliver, JM.; Li, Z.; Musculus, M. (2021). Spatio-Temporal Progression of Two-Stage Autoignition for Diesel Sprays in a Low-Reactivity Ambient: n-Heptane Pilot-Ignited Premixed Natural Gas. SAE International. 1-16. https://doi.org/10.4271/2021-01-052511

Verification of diesel spray ignition phenomenon in dual-fuel diesel-piloted premixed natural gas engine

[EN] Dual-fuel (DF) engines, in which premixed natural gas and air in an open-type combustion chamber is ignited by diesel-fuel pilot sprays, have been more popular for marine use than pre-chamber spark ignition (PCSI) engines because of their superior durability. However, control of ignition and combustion in DF engines is more difficult than in PCSI engines. In this context, this study focuses on the ignition stability of n-heptane pilot-fuel jets injected into a compressed premixed charge of natural gas and air at low-load conditions. To aid understanding of the experimental data, chemical-kinetics simulations were carried out in a simplified engine-environment that provided insight into the chemical effects of methane (CH4) on pilot-fuel ignition. The simulations reveal that CH4 has an effect on both stages of n-heptane autoignition: the small, first-stage, cool-flame-type, low-temperature ignition (LTI) and the larger, second-stage, high-temperature ignition (HTI). As the ratio of pilot-fuel to CH4 entrained into the spray decreases, the initial oxidization of CH4 consumes the OH radicals produced by pilot-fuel decomposition during LTI, thereby inhibiting its progression to HTI. Using imaging diagnostics, the spatial and temporal progression of LTI and HTI in DF combustion are measured in a heavy-duty optical engine, and the imaging data are analyzed to understand the cause of severe fluctuations in ignition timing and combustion completeness at low-load conditions. Images of cool-flame and hydroxyl radical (OH*) chemiluminescence serve as indicators of LTI and HTI, respectively. The cycle-to-cycle and spatial variation in ignition extracted from the imaging data are used as key metrics of comparison. The imaging data indicate that the local concentration of the pilot-fuel and the richness of the surrounding natural-gas air mixture are important for LTI and HTI, but in different ways. In particular, higher injection pressures and shorter injection durations increase the mixing rate, leading to lower concentrations of pilot-fuel more quickly, which can inhibit HTI even as LTI remains relatively robust. Decreasing the injection pressure from 80 MPa to 40 MPa and increasing the injection duration from 500 mu s to 760 mu s maintained constant pilot-fuel mass, while promoting robust transition from LTI to HTI by effectively slowing the mixing rate. This allows enough residence time for the OH radicals, produced by the two-stage ignition chemistry of the pilot-fuel, to accelerate the transition from LTI to HTI before being consumed by CH4 oxidation. Thus from a practical perspective, for a premixed natural gas fuel-air equivalence-ratio, it is possible to improve the "stability" of the combustion process by solely manipulating the pilot-fuel injection parameters while maintaining constant mass of injected pilot-fuel. This allows for tailoring mixing trajectories to offset changes in fuel ignition chemistry, so as to promote a robust transition from LTI to HTI by changing the balance between the local concentration of the pilot-fuel and richness of the premixed natural gas and air. This could prove to be a valuable tool for combustion design to improve fuel efficiency or reduce noise or perhaps even reduce heat-transfer losses by locating early combustion away from in-cylinder walls.This research was sponsored in part by the U.S. Department of Energy (DOE) Office of Energy Efficiency and Renewable Energy (EERE). Optical engine experiments were conducted at the Combustion Research Facility of Sandia National Laboratories in Livermore, CA. Sandia National Laboratories is a multi-mission laboratory 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's National Nuclear Security Administration (NNSA) under contract DE-NA0003525.Niki, Y.; Rajasegar, R.; Li, Z.; Musculus, MP.; García-Oliver, JM.; Takasaki, K. (2022). Verification of diesel spray ignition phenomenon in dual-fuel diesel-piloted premixed natural gas engine. International Journal of Engine Research. 23(2):180-197. https://doi.org/10.1177/146808742098306018019723

Distribution of sediment nutrients of Vellar estuary in relation to shrimp farming

153-156Sediment composition, organic carbon, total phosphorus and total nitrogen content of sediments in Vellar estuary were studied in relation to shrimp farming. Data collected over a 2 year period showed that the nutrient rich water (due to settling of unfed feed particle) discharged periodically from the shrimp farms, did not influence much the sediment nutrients of the estuary

Fundamental insights on ignition and combustion of natural gas in an active fueled pre-chamber spark-ignition system

[EN] Pre-chamber spark-ignition (PCSI), either fueled or non-fueled, is a leading concept with the potential to enable diesel-like efficiency in medium-duty (MD) and heavy-duty (HD) natural gas (NG) engines. However, the inadequate scientific base and simulation tools to describe/predict the underlying processes governing PCSI systems is one of the key barriers to market penetration of PCSI for MD/HD NG engines. To this end, experiments were performed in a heavy-duty, optical, single-cylinder engine fitted with an active fueled PCSI module. The spatial and temporal progress of ignition and subsequent combustion of lean-burn natural gas using PCSI system were studied using optical diagnostic imaging and heat release analysis based on main-chamber and pre-chamber pressure measurements. Optical diagnostics involving simultaneous infrared (IR) and high-speed (30 kfps) broadband and filtered OH* chemiluminescence imaging are used to probe the combustion process. Following the early pressure rise in the pre-chamber, IR imaging reveals initial ejection of unburnt fuel-air mixture from the pre chamber into the main-chamber. Following this, the pre-chamber gas jets exhibit chemical activity in the vicinity of the pre-chamber region followed by a delayed spread in OH* chemiluminescence, as they continue to penetrate further into the main-chamber. The OH* signal progress radially until the pre-chamber jets merge, which sets up the limit to a first stage, jet-momentum driven, mixing-controlled (temperature field) premixed combustion. This is then followed by the subsequent deceleration of the pre-chamber jets, caused by the decrease in the driving pressure difference (AP) as well as charge entrainment, resulting in a flame front evolution, where mixing is not the only driver. Chemical-kinetic calculations probe the possibility of flame propagation or sequential auto-ignition in the second stage of combustion. Finally, key phenomenological features are then summarized so as to provide fundamental insights on the complex underlying fluid-mechanical and chemical-kinetic processes that govern the ignition and subsequent combustion of natural gas near lean-limits in high-efficiency lean-burn natural gas engines employing PCSI system.This research was sponsored by the U.S. Department of Energy (DOE) Office of Energy Efficiency and Renewable Energy (EERE) . Optical engine experiments were conducted at the Combustion Re-search Facility of Sandia National Laboratories in Livermore, CA. Sandia National Laboratories is a multi-mission laboratory man-aged and operated by National Technology and Engineering So-lutions of Sandia, LLC., a wholly owned subsidiary of Honey-well International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration (NNSA) under contract DE-NA0003525. We gratefully acknowledge the contributions of Keith Penney and Dave Cicone for their assistance in developing research tools and maintaining the optical engine. Jose M. Garcia-Oliver ac-knowledges the support of the Generalitat Valenciana government in Spain through Grant #Best/2019/176 during his scientific visit to the Combustion Research Facility.Rajasegar, R.; Niki, Y.; García-Oliver, JM.; Li, Z.; Musculus, MP. (2021). Fundamental insights on ignition and combustion of natural gas in an active fueled pre-chamber spark-ignition system. Combustion and Flame. 232:1-20. https://doi.org/10.1016/j.combustflame.2021.111561S12023

Influence of pilot-fuel mixing on the spatio-temporal progression of two-stage autoignition of diesel-sprays in low-reactivity ambient fuel-air mixture

[EN] The spatial and temporal locations of autoignition for direct-injection compression-ignition engines depend on fuel chemistry, temperature, pressure, and mixing trajectories in the fuel jets. Dual-fuel systems can provide insight into both fuel-chemistry and physical effects by varying fuel reactivities and engine operating conditions. In this context, the spatial and temporal progression of two-stage autoignition of a diesel-fuel surrogate, n-heptane, in a lean-premixed charge of synthetic natural-gas (NG) and air is imaged in an optically accessible heavy-duty diesel engine. The lean-premixed charge of NG is prepared by fumigation upstream of the engine intake manifold. Optical diagnostics include high-speed (15kfps) cool-flame chemiluminescenceimaging as an indicator of low-temperature heat-release (LTHR) and OH * chemiluminescence-imaging as an indicator high-temperature heat-release (HTHR). NG prolongs the ignition delay of the pilot fuel and increases the combustion duration. Zero-dimensional chemical-kinetics simulations provide further understanding by replicating a Lagrangian perspective for mixtures evolving along streamlines originating either at the fuel nozzle or in the ambient gas, for which the pilot-fuel concentration is either decreasing or increasing, respectively. The zero-dimensional simulations predict that LTHR initiates most likely on the air streamlines before transitioning to HTHR, either on fuel-streamlines or on air-streamlines in regions of near-constant phi. Due to the relatively short pilot-fuel injection-durations, the transient increase in entrainment near the end of injection (entrainment wave) is important for quickly creating auto-ignitable mixtures. To achieve desired combustion characteristics, e.g., multiple ignition-kernels and favorable combustion phasing and location (e.g., for reducing wall heat-transfer or optimizing charge stratification), adjusting injection parameters could tailor mixing trajectories to offset changes in fuel ignition chemistry. (C) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.Support for this research at the Combustion Research Facility, Sandia National Laboratories, Livermore, CA, was provided by the U.S. Department of Energy (DOE), Office of Energy Efficiency and Renewable Energy. Sandia is a multi-mission laboratory operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. DOE's National Nuclear Security Administration under contract DE-NA0003525Rajasegar, R.; Niki, Y.; Li, Z.; García-Oliver, JM.; Musculus, MPB. (2021). Influence of pilot-fuel mixing on the spatio-temporal progression of two-stage autoignition of diesel-sprays in low-reactivity ambient fuel-air mixture. Proceedings of the Combustion Institute. 38(4):5741-5750. https://doi.org/10.1016/j.proci.2020.11.0055741575038

An experimental and one-dimensional modeling analysis of turbulent gas ejection in pre-chamber engines

[EN] Experimental results from a study on the evolution of gas jets ejected through the orifices of a pre-chamber in a heavy-duty optical engine are presented. The work examines conditions without fuel inside the main-chamber, which helps to describe the dynamics of the ejected gas jets without the interference of subsequent combustion in the main-chamber. Experimental diagnostics consist of high-speed visible intensified imaging and low-speed infrared imaging. Additionally a one-dimensional gas jet model is used to characterize the spatial distribution of the ejected flow, including parameters such as tip penetration, which are then validated based on experimental results. Different stages in the ejection of pre-chamber jets are identified, with chemical activity restricted to a maximum distance of 5 to 10 orifice diameters downstream of the orifice as indicated by the recorded visible radiation. Sensitivity of cycle-to-cycle variations in pre-chamber jet development to the air-to-fuel ratio in the pre-chamber observed in the experiments is in most part attributed to the variations in the timing of combustion initiation in the pre-chamber. The influence of the ejection flow on the penetration of the gas jet on a cycle-tocycle basis is presented using the one-dimensional model. The one-dimensional model also indicates that the local flow exhibits highest sensitivity to operating conditions during the start of ejection until the timing when maximum flow is attained. Differences that exist during the decreasing mass-flow ejection time-period tend to smear out in part due to the transient slowdown of the ejection processThis research was sponsored by the U.S. Department of Energy (DOE) Office of Energy Efficiency and Renewable Energy (EERE). Optical engine experiments were conducted at the Combustion Research Facility, Sandia National Laboratories, Livermore, CA. Sandia National Laboratories is a multi-mission laboratory 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's National Nuclear Security Administration under contract DE-NA0003525. Jose M Garcia-Oliver acknowledges the support of the Generalitat Valenciana government in Spain through Grant Best/2019/176 for his scientific visit to the Combustion Research Facility. P. J. Martinez-Hernandiz is partly supported by an FPI contract (FPI-S2-19-21993) of the "Programa de Apoyo para la Investigacion y Desarrollo (PAID05-19)" of the Universitat Politecnica de ValenciaGarcía-Oliver, JM.; Niki, Y.; Rajasegar, R.; Novella Rosa, R.; Gómez-Soriano, J.; Martínez-Hernándiz, PJ.; Li, Z.... (2021). An experimental and one-dimensional modeling analysis of turbulent gas ejection in pre-chamber engines. Fuel. 299:1-15. https://doi.org/10.1016/j.fuel.2021.12086111529

Random amplified polymorphic DNA analysis of the moth orchids, Phalaenopsis (Epidendroideae: Orchidaceae)

10.1007/s10681-005-4814-yEuphytica1411-211-22EUPH