There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Suggested by the structure of the visual nervous system, a new algorithm is proposed for pattern recognition. This algorithm can be realized with a multilayered network consisting of neuron-like cells. The network, “neocognitron”, is self-organized by unsupervised learning, and acquires the ability to recognize stimulus patterns according to the differences in their shapes: Any patterns which we human beings judge to be alike are also judged to be of the same category by the neocognitron. The neocognitron recognizes stimulus patterns correctly without being affected by shifts in position or even by considerable distortions in shape of the stimulus patterns.

Neocognitron--A New Algorithm for Pattern Recognition Tolerant of Deformations and Shifts in Position

The editors have assembled a world-class group of contributors who address the questions the combustion diagnostic community faces. They are chemists who identify the species to be measured and the interfering substances that may be present; physicists, who push the limits of laser spectroscopy and laser devices and who conceive suitable measuremen

Applied Combustion Diagnostics

Laser diagnostic techniques play a large and growing role in combustion research and development. Here we highlight three areas where quantitative sensing based on laser absorption has had strong influence: chemical kinetics, propulsion, and practical energy systems. In the area of chemical kinetics, measurements in shock tubes of high-temperature reaction rate coefficients using species-specific laser absorption techniques have provided new and accurate answers to questions about combustion chemical processes. In the area of propulsion, wide-bandwidth measurements of flow temperatures, species concentrations, and velocity have provided engine designers with the necessary information to improve operation and performance. In the area of practical energy systems, real-time measurements of combustor operating conditions and emissions have enabled needed incremental improvements in large power plants and improved safety of operation. Yet, there is still more to be done, and opportunities for new applications will grow as laser sensors evolve. This review seeks to provide an overview of the current power and future potential of these modern diagnostic tools.

Applications of quantitative laser sensors to kinetics, propulsion and practical energy systems

conferencia sobre "Particle Image Velocimetry" de les 13:00-14:00 a la Sala de Juntes de l'FNB impartida pel professor Peter Bueken da l'Antwerp Maritime Acedemy (Belgica)

Particle Image Velocimetry

This review discusses the role of laser diagnostics in combustion science and technology. In its first part, it may guide understanding of advanced diagnostic methods, and is particularly helpful for non-specialized experimentalists. Various challenges for future developments and applications of optical combustion diagnostics are highlighted. In the second part of this review, flame-wall interactions are selected for a more in-depth discussion. Flame-wall interactions are scientifically interesting and are of great importance to any enclosed practical combustion process. Following a description of current understanding, the focus is on using optical diagnostics to probe thermal, fluidic, and chemical properties of head-on and sidewall quenching. The review ends with a discussion of issues and implications for future experimental research and specific diagnostic needs.

Advanced laser diagnostics for an improved understanding of premixed flame-wall interactions

Improved understanding of in-cylinder flows requires knowledge from well-resolved experimental velocimetry measurements and flow simulation modeling. Engine simulations using large eddy simulations (LES) are making large progress and the need for well documented velocimetry measurements for model validation is high. This work presents velocimetry measurements from PIV, high-speed PIV, stereoscopic PIV, and tomographic PIV to extensively describe the in-cylinder flow field in a motored optical engine operating at 800 RPM. These measurements also establish a comprehensive database designed for LES model development and validation. Details of the engine, engine accessory components, and well-controlled boundary conditions and engine operation are presented. The first two statistical moments of the flow field are computed and show excellent agreement among the PIV database. Analysis of statistical moments based on limited sample size is presented and is important for modeling validation purposes. High-speed PIV resolved the instantaneous flow field throughout entire engine cycles (i.e. 719 consecutive crank-angles), while tomographic PIV images are further used to investigate the 3D flow field and identify regions of strong vortical structures identified by the Q-criterion. Principle velocity gradient components are computed and emphasize the need to resolve similar spatial scales between experimental and modeling efforts for suitable model validation.

On the validation of les applied to internal combustion engine flows: Part 1: Comprehensive experimental database

High-speed particle image velocimetry has been applied to study the flow field of an optically accessible motored direct-injection spray-guided internal combustion engine. Based on recent improvements in all-solid-state diode-pumped laser- and CMOS camera-technology a large field of view (43 × 44 mm2) was achieved at 6 kHz resulting in a temporal resolution of 1° crank angle at 1,000 rpm. This allows the investigation of the temporal evolution of large-scale flow structures. The flow field was recorded during the latter half of the compression stroke for tumble flow conditions at 500, 1,000 and 2,000 rpm. An analysis of cycle-to-cycle variations has been performed from individual and ensemble-averaged cycles. The temporal evolution of the main vortex center and the kinetic energy shows a few individual cycles with strong variations from the mean caused by a substantially different flow regime. A quantification of cyclic variations using the kinetic energy is possible.

Flow field measurements in an optically accessible, direct-injection spray-guided internal combustion engine using high-speed PIV

Time-resolved particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF), both at 5 kHz, were applied simultaneously on extinguishing turbulent opposed jet flames. This repetition rate allowed tracking of transient extinction events in turbulent combustion. The additional information acquired about time history enabled a study of the evolution of vortex-flame interactions leading to extinction from individual events. A newly introduced multidimensional conditioning technique to avoid spatial- and temporal-smearing of important flow field information was developed in order to compare individual extinction events in a meaningful, statistical manner. The conditional statistics show that vortices tend to align around the flame and generate regions of high strain in the region where the flame is about to extinguish.

/pdf/time-resolved-conditional-flow-field-statistics-in-t3q40pjrpm.pdf

Time-Resolved Conditional Flow Field Statistics in Extinguishing Turbulent Opposed Jet Flames Using Simultaneous Highspeed PIV/OH-PLIF

In-cylinder measurements of the instantaneous 3D flow field are required for further understanding of turbulent mixing and combustion processes in internal combustion (IC) engines as well provide valuable data for the development of large eddy simulation (LES) models for combustion simulation. Tomographic particle image velocimetry (TPIV) is applied within a motored direct-injection spark-ignition (DISI) optical engine to measure the instantaneous volumetric flow field at selected crank-angle degrees (CAD) during the intake and compression stroke. Measurements were conducted using a double-pulse Nd:YAG laser with an average pulse energy of 375 mJ for illumination and four CCD cameras arranged circularly around the optically accessible cylinder. A volume of 47 × 35 × 4 mm 3 was imaged located centrally between the intake valves. The uncertainty of the 3D velocity data was addressed using the principle of mass conservation for the inlet flow. A precision within 9% was found for the calculation of the velocity gradient tensor and is comparable to experiments in generic configurations, indicating that TPIV measurements within a motored IC engine are feasible. Based on the volumetric velocity data, the average structure of the flow field was analyzed showing a clear orientation of the average velocity, which changes during the different phases of the cycle. The 3D turbulent kinetic energy (TKE) is computed and compared to the 2D-TKE determined from in-plane velocity components and reveals distinct regions of large out-of-plane velocity fluctuations. Results from volumetric velocimetry furthermore provides insight into the occurrence and orientation of vortical structures that here are identified by using the Q-criterion. Differences between flow structures during intake and compression strokes are discussed on basis of ensemble-averaged and individual cycle velocity maps as well as the full vorticity vector.

Benjamin Böhm

Papers

Advanced laser diagnostics for an improved understanding of premixed flame-wall interactions

On the validation of les applied to internal combustion engine flows: Part 1: Comprehensive experimental database

Flow field measurements in an optically accessible, direct-injection spray-guided internal combustion engine using high-speed PIV

Time-Resolved Conditional Flow Field Statistics in Extinguishing Turbulent Opposed Jet Flames Using Simultaneous Highspeed PIV/OH-PLIF

Investigation of the 3D flow field in an IC engine using tomographic PIV