An Imaging Study of Compression Ignition Phenomena of Iso-Octane, Indolene, and Gasoline Fuels in a Single-Cylinder Research Engine

2008 ◽  
Vol 130 (5) ◽  
Author(s):  
Bradley T. Zigler ◽  
Stephen M. Walton ◽  
Dimitris Assanis ◽  
Elizabeth Perez ◽  
Margaret S. Wooldridge ◽  
...  
Keyword(s):  
Heat Release ◽  
High Speed ◽  
Blue Emission ◽  
Primary Objective ◽  
Valuable Insight ◽  
Compression Ignition ◽  
Imaging Data ◽  
High Speed Imaging ◽  
Single Cylinder ◽  
Hcci Combustion

High-speed imaging combined with the optical access provided by a research engine offer the ability to directly image and compare ignition and combustion phenomena of various fuels. Such data provide valuable insight into the physical and chemical mechanisms important in each system. In this study, crank-angle resolved imaging data were used to investigate homogeneous charge compression ignition (HCCI) operation of a single-cylinder four-valve optical engine fueled using gasoline, indolene, and iso-octane. Lean operating limits were the focus of the study with the primary objective of identifying different modes of reaction front initiation and propagation for each fuel. HCCI combustion was initiated and maintained over a range of lean conditions for various fuels, from ϕ=0.69 to 0.27. The time-resolved imaging and pressure data show that high rates of heat release in HCCI combustion correlate temporally to simultaneous, intense volumetric blue emission. Lower rates of heat release are characteristic of spatially resolved blue emission. Gasoline supported leaner HCCI operation than indolene. Iso-octane showed a dramatic transition into misfire. Similar regions of preferential ignition were identified for each of the fuels considered using the imaging data.

A Comparison of Imaging of Compression Ignition Phenomena of Iso-Octane, Indolene, and Gasoline Fuels in a Single-Cylinder Research Engine

2006 ◽  
Author(s):  
Bradley T. Zigler ◽  
Stephen M. Walton ◽  
Dimitris Assanis ◽  
Elizabeth Perez ◽  
Margaret S. Wooldridge ◽  
...  
Keyword(s):  
Heat Release ◽  
High Speed ◽  
Blue Emission ◽  
Primary Objective ◽  
Valuable Insight ◽  
Compression Ignition ◽  
Imaging Data ◽  
High Speed Imaging ◽  
Single Cylinder ◽  
Hcci Combustion

High-speed imaging combined with the optical access provided by a research engine offer the ability to directly image and compare ignition and combustion phenomena of various fuels. Such data provide valuable insight into the physical and chemical mechanisms important in each system. In this study, crank-angle resolved imaging data were used to investigate homogeneous charge compression ignition (HCCI) operation of a single-cylinder four-valve optical engine fueled using gasoline, indolene, and iso-octane. Lean operating limits were the focus of the study with the primary objective of identifying different modes of reaction front initiation and propagation for each fuel. HCCI combustion was initiated and maintained over a range of lean conditions for various fuels, from φ = 0.77 to 0.27. The time-resolved imaging and pressure data show high rates of heat release in HCCI combustion correlate temporally to simultaneous, intense volumetric blue emission. Lower rates of heat release are characteristic of spatially-resolved blue emission. Gasoline supported leaner HCCI operation than indolene. Iso-octane showed a dramatic transition into misfire. Similar regions of preferential ignition were identified for each of the fuels considered using the imaging data.

A Multi-Axis Imaging Study of Spark-Assisted Homogeneous Charge Compression Ignition Phenomena in a Single-Cylinder Research Engine

2007 ◽  
Author(s):  
Bradley T. Zigler ◽  
Stephen M. Walton ◽  
Darshan M. Karwat ◽  
Dimitris Assanis ◽  
Margaret S. Wooldridge ◽  
...  
Keyword(s):  
High Speed ◽  
Homogeneous Charge Compression Ignition ◽  
Imaging Study ◽  
Operating Conditions ◽  
Valuable Insight ◽  
Compression Ignition ◽  
Imaging Data ◽  
High Speed Imaging ◽  
Single Cylinder ◽  
Homogeneous Charge

High-speed imaging combined with the optical access provided by a single-cylinder research engine offer the ability to directly study ignition and combustion phenomena. Such data provide valuable insight into the physical and chemical mechanisms important in advanced engine combustion strategies. In this study, crank-angle resolved chemiluminescence imaging data both orthogonal to and along the piston axis were used to investigate homogeneous charge compression ignition (HCCI) operation of a single-cylinder four-valve optical engine fueled using indolene. This preliminary study focused on identifying how multi-axis imaging can contribute to understanding the effects of spark-assist on HCCI performance. Operating conditions of advanced spark ignition timing for extending the lean limits of bulk charge compression ignition were used. The experiments were performed at a fixed equivalence ratio of φ = 0.56, with fixed intake conditions (wide open throttle with air preheat). The multi-axis imaging provides a clear indication of the propagation of a reaction front from the spark kernel. The combination of orthogonal and axial views may provide valuable information spatially resolving volumetric heat release, thereby providing an indication of the fractional energy release due to the spark assist compared to the energy released by auto-ignition.

High Speed Imaging of Forced Ignition Kernels in Non-Uniform Jet Fuel/Air Mixtures

2017 ◽  
Author(s):  
Sheng Wei ◽  
Brandon Sforzo ◽  
Jerry Seitzman
Keyword(s):  
Heat Release ◽  
High Speed ◽  
Air Flow ◽  
Cetane Number ◽  
High Energy ◽  
Liquid Fuels ◽  
High Speed Imaging ◽  
Ignition Probability ◽  
Turbine Engine ◽  
Planar Laser

This paper describes experimental measurements of forced ignition of prevaporized liquid fuels in a well-controlled facility that incorporates non-uniform flow conditions similar to those of gas turbine engine combustors. The goal here is to elucidate the processes by which the initially unfueled kernel evolves into a self-sustained flame. Three fuels are examined: a conventional Jet-A and two synthesized fuels that are used to explore fuel composition effects. A commercial, high-energy recessed cavity discharge igniter located at the test section wall ejects kernels at 15 Hz into a preheated, striated crossflow. Next to the igniter wall is an unfueled air flow; above this is a premixed, prevaporized, fuel-air flow, with a matched velocity and an equivalence ratio near 0.75. The fuels are prevaporized in order to isolate chemical effects. Differences in early ignition kernel development are explored using three, synchronized, high-speed imaging diagnostics: schlieren, emission/chemiluminescence, and OH planar laser-induced fluorescence (PLIF). The schlieren images reveal rapid entrainment of crossflow fluid into the kernel. The PLIF and emission images suggest chemical reactions between the hot kernel and the entrained fuel-air mixture start within tens of microseconds after the kernel begins entraining fuel, with some heat release possibly occurring. Initially, dilution cooling of the kernel appears to outweigh whatever heat release occurs; so whether the kernel leads to successful ignition or not, the reaction rate and the spatial extent of the reacting region decrease significantly with time. During a successful ignition event, small regions of the reacting kernel survive this dilution and are able to transition into a self-sustained flame after ∼1–2 ms. The low aromatic/low cetane number fuel, which also has the lowest ignition probability, takes much longer for the reaction zone to grow after the initial decay. The high aromatic, more easily ignited fuel, shows the largest reaction region at early times.

scholarly journals High-Speed Imaging of Forced Ignition Kernels in Nonuniform Jet Fuel/Air Mixtures

2018 ◽  
Vol 140 (7) ◽  
Author(s):  
Sheng Wei ◽  
Brandon Sforzo ◽  
Jerry Seitzman
Keyword(s):  
Heat Release ◽  
High Speed ◽  
Air Flow ◽  
Cetane Number ◽  
High Energy ◽  
Liquid Fuels ◽  
High Speed Imaging ◽  
Ignition Probability ◽  
Turbine Engine ◽  
Planar Laser

This paper describes experimental measurements of forced ignition of prevaporized liquid fuels in a well-controlled facility that incorporates nonuniform flow conditions similar to those of gas turbine engine combustors. The goal here is to elucidate the processes by which the initially unfueled kernel evolves into a self-sustained flame. Three fuels are examined: a conventional Jet-A and two synthesized fuels that are used to explore fuel composition effects. A commercial, high-energy recessed cavity discharge igniter located at the test section wall ejects kernels at 15 Hz into a preheated, striated crossflow. Next to the igniter wall is an unfueled air flow; above this is a premixed, prevaporized, fuel–air flow, with a matched velocity and an equivalence ratio near 0.75. The fuels are prevaporized in order to isolate chemical effects. Differences in early ignition kernel development are explored using three synchronized, high-speed imaging diagnostics: schlieren, emission/chemiluminescence, and OH planar laser-induced fluorescence (PLIF). The schlieren images reveal rapid entrainment of crossflow fluid into the kernel. The PLIF and emission images suggest chemical reactions between the hot kernel and the entrained fuel–air mixture start within tens of microseconds after the kernel begins entraining fuel, with some heat release possibly occurring. Initially, dilution cooling of the kernel appears to outweigh whatever heat release occurs; so whether the kernel leads to successful ignition or not, the reaction rate and the spatial extent of the reacting region decrease significantly with time. During a successful ignition event, small regions of the reacting kernel survive this dilution and are able to transition into a self-sustained flame after ∼1–2 ms. The low-aromatic/low-cetane-number fuel, which also has the lowest ignition probability, takes much longer for the reaction zone to grow after the initial decay. The high-aromatic, more easily ignited fuel, shows the largest reaction region at early times.

A new heat release rate (HRR) law for homogeneous charge compression ignition (HCCI) combustion mode

2009 ◽  
Vol 29 (17-18) ◽  
pp. 3654-3662 ◽  
Author(s):  
Miguel Torres García ◽  
Francisco José Jiménez-Espadafor Aguilar ◽  
Tomás Sánchez Lencero ◽  
José Antonio Becerra Villanueva
Keyword(s):  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Homogeneous Charge Compression Ignition ◽  
Compression Ignition ◽  
Combustion Mode ◽  
Hcci Combustion ◽  
Homogeneous Charge

Optical Investigation of the Effects of Ethanol/Gasoline Blends on Spark-Assisted HCCI

2013 ◽  
Author(s):  
Mohammad Fatouraie ◽  
Margaret S. Wooldridge
Keyword(s):  
Heat Release ◽  
High Speed ◽  
Engine Performance ◽  
Optical Investigation ◽  
Release Rates ◽  
High Speed Imaging ◽  
Engine Operation ◽  
Spark Timing ◽  
Combustion Properties ◽  
Ethanol Blends

Spark assist (SA) has been demonstrated to extend the operating limits of homogeneous charge compression ignition (HCCI) modes of engine operation. This experimental investigation focuses on the effects of 100% indolene and 70% indolene/30% ethanol blends on the ignition and combustion properties during SA HCCI operation. The spark assist effects are compared to baseline HCCI operation for each blend by varying spark timing at different fuel/air equivalence ratios ranging from ϕ = 0.4–0.5. High speed imaging is used to understand connections between spark initiated flame propagation and heat release rates. Ethanol generally improves engine performance with higher IMEPn and higher stability compared to 100% indolene. SA advances phasing within a range of ∼5 CAD at lower engine speeds (700 RPM) and ∼11 CAD at higher engine speeds (1200 RPM). SA does not affect heat release rates until immediately (within ∼5 CAD) prior to autoignition. Unlike previous SA HCCI studies of indolene fuel in the same engine, flames were not observed for all SA conditions.

Optical Investigation of the Effects of Ethanol/Gasoline Blends on Spark-Assisted HCCI

2014 ◽  
Vol 136 (8) ◽  
Author(s):  
Mohammad Fatouraie ◽  
Margaret Wooldridge
Keyword(s):  
Heat Release ◽  
High Speed ◽  
Engine Performance ◽  
Optical Investigation ◽  
Release Rates ◽  
High Speed Imaging ◽  
Engine Operation ◽  
Auto Ignition ◽  
Spark Timing ◽  
Combustion Properties

Spark assist (SA) has been demonstrated to extend the operating limits of homogeneous charge compression ignition (HCCI) modes of engine operation. This experimental investigation focuses on the effects of 100% indolene and 70% indolene/30% ethanol blends on the ignition and combustion properties during SA HCCI operation. The spark assist effects are compared to baseline HCCI operation for each blend by varying spark timing at different fuel/air equivalence ratios ranging from Φ = 0.4–0.5. High speed imaging is used to understand connections between spark initiated flame propagation and heat release rates. Ethanol generally improves engine performance with higher net indicated mean effective pressure (IMEPn) and higher stability compared to 100% indolene. SA advances phasing within a range of ∼5 crank angle degrees (CAD) at lower engine speeds (700 rpm) and ∼11 CAD at higher engine speeds (1200 rpm). SA does not affect heat release rates until immediately (within ∼5 CAD) prior to auto-ignition. Unlike previous SA HCCI studies of indolene fuel in the same engine, flames were not observed for all SA conditions.

scholarly journals Three-dimensional flow and lift characteristics of a hovering ruby-throated hummingbird

2014 ◽  
Vol 11 (98) ◽  
pp. 20140541 ◽  
Author(s):  
Jialei Song ◽  
Haoxiang Luo ◽  
Tyson L. Hedrick
Keyword(s):  
High Speed ◽  
Three Dimensional ◽  
Leading Edge ◽  
Dynamics Simulation ◽  
Vertical Force ◽  
Imaging Data ◽  
High Speed Imaging ◽  
Three Dimensional Flow ◽  
Dimensional Flow ◽  
Wake Interaction

A three-dimensional computational fluid dynamics simulation is performed for a ruby-throated hummingbird ( Archilochus colubris ) in hovering flight. Realistic wing kinematics are adopted in the numerical model by reconstructing the wing motion from high-speed imaging data of the bird. Lift history and the three-dimensional flow pattern around the wing in full stroke cycles are captured in the simulation. Significant asymmetry is observed for lift production within a stroke cycle. In particular, the downstroke generates about 2.5 times as much vertical force as the upstroke, a result that confirms the estimate based on the measurement of the circulation in a previous experimental study. Associated with lift production is the similar power imbalance between the two half strokes. Further analysis shows that in addition to the angle of attack, wing velocity and surface area, drag-based force and wing–wake interaction also contribute significantly to the lift asymmetry. Though the wing–wake interaction could be beneficial for lift enhancement, the isolated stroke simulation shows that this benefit is buried by other opposing effects, e.g. presence of downwash. The leading-edge vortex is stable during the downstroke but may shed during the upstroke. Finally, the full-body simulation result shows that the effects of wing–wing interaction and wing–body interaction are small.

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