Plasma assisted combustion: Dynamics and chemistry

http://engine.princeton.edu/Publications/Ombrello_2010-2.pdf

Flame propagation enhancement by plasma excitation of oxygen. Part I: Effects of O3

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

A review of livestock monitoring and the need for integrated systems

This paper presents a method aimed at recognizing environmental sounds for surveillance and security applications. We propose to apply one-class support vector machines (1-SVMs) together with a sophisticated dissimilarity measure in order to address audio classification, and more specifically, sound recognition. We illustrate the performance of this method on an audio database, which consists of 1015 sounds belonging to nine classes. The database used presents high intraclass diversity in temps of signal properties and some kind of interclass similarities. A large discrepancy in the number of items in each class implies nonuniform probability of sound appearances. The method proceeds as follows: first, the use of a set of state-of-the-art audio features is studied. Then, we introduce a set of novel features obtained by combining elementary features. Experiments conducted on a nine-class classification problem show the superiority of this novel sound recognition method. The best recognition accuracy (96.89%) is obtained when combining wavelet-based features, MFCCs, and individual temporal and frequency features. Our 1-SVM-based multiclass classification approach overperforms the conventional hidden Markov model-based system in the experiments conducted, the improvement in the error rate can reach 50%. Besides, we provide empirical results showing that the single-class SVM outperforms a combination of binary SVMs. Additional experiments demonstrate our method is robust to environmental noise.

Using One-Class SVMs and Wavelets for Audio Surveillance

A small, uncooled plasma torch was developed and used in combination with an injector designed to study ignition and flameholding in hydrogen-fueled supersonic flows. The plasma torch was operated on mixtures of hydrogen and argon with total flows of 10 to 70 scfh. The fuel injector design consisted of five small upstream pilot fuel injectors, a rearward facing step for recirculation, and three main fuel injectors downstream of the step. The plasma torch was located in the recirculation region, and all injection was perpendicular to the Mach 2 stream. Both semi-freejet and ducted tests were conducted. The experimental results indicate that a low power plasma torch operating on a 1:1 volumetric mixture of hydrogen and argon and located in the recirculation zone fueled by the upstream pilot fuel injectors is a good igniter for flow conditions simulating a flight Mach number of 3.7. The total temperature required to autoignite the hydrogen fuel for this injector geometry was 2640 R. The injector configuration was shown to be a good flameholder over a wide range of total temperature. Spectroscopic measurements were used to verify the presence of air total temperatures below 1610 R.

Plasma torch igniter for scramjets

An experimental study was performed in the Virginia Polytechnic Institute and State University supersonic wind tunnel on a simplified and revised multiport aerodynamic-ramp injector array in a supersonic flow. The new aerodynamic-ramp injector consisted of four flush-walled holes, in contrast to the original nine-hole versions. For comparison, a single, low downstream-angled circular injector hole was examined. Test conditions included sonic air injection into a Mach 2.4 air cross stream with an average Reynolds number of 4.2 x 10 7 /m at jet-to-freestream momentum flux ratios from 1.1 to 3.3. Shadowgraphs and surface oil-flow visualization pictures were taken in the vicinity of the injectors to gain a qualitative assessment of the injector flowfields. Quantitative measurements of the pressure field on the surface near injectors and in a cross-stream plane downstream were conducted using pressure-sensitive paint and pitot/cone-static probes, respectively. The mixing characteristics of the injectors at three downstream stations were quantified using total temperature probes and a combination of heated and unheated injected air profiles to generate a mixing analog to concentration. Results showed that the aerodynamic-ramp mixed faster and had a larger plume area than the single-hole injector, while sustaining somewhat higher pressure losses due to increased blockage and a higher downstream-angled injector arrangement.

Improved Aerodynamic-Ramp Injector in Supersonic Flow

An active noise control system using a compact sound source is effective to reduce aircraft engine duct noise. The fan noise from a turbofan engine is controlled using an adaptive filtered-x algorithm. Single, multi channel control systems are used to control the fan blade passage frequency (BPF) tone and the BPF tone and the first harmonic of the BPF tone for a plane wave excitation. The multi channel control system is used to control fan tones and a high pressure compressor BPF tone simultaneously, and any spinning mode. A compact sound source is employed to generate the control field. This compact sound source consists of an array of identical thin, cylindrically curved panels (125) with an inner radius of curvature corresponding to that of the engine inlet. These panels are flush mounted inside the inlet duct (Inlet Wall) and sealed on all edges to prevent leakage around the panel.

/pdf/active-control-of-aircraft-engine-inlet-noise-using-compact-5ce37oq65y.pdf

Active control of aircraft engine inlet noise using compact sound sources and distributed error sensors

A three-channel active control system is applied to an operational turbofan engine to reduce tonal noise produced by both the fan and the high-pressure compressor. The control approach is the feedforward filtered-x least-mean-square algorithm implemented on a digital signal processing board. Reference transducers mounted on the engine case provide blade passing and harmonics frequency information to the controller. Error information is provided by large area microphones placed in the acoustic far field. To minimize the error signal, the controller actuates loudspeakers mounted on the inlet to produce destructive interference. The sound pressure level of the fundamental tone of the fan was reduced using the three-channel controller by up to 16 dB over a +/- 30-deg angle about the engine axis. A single-channel controller could produce reduction over a +/- 15-deg angle. The experimental results show the control to be robust. Outside of the areas contolled, the levels of the tone actually increased due to the generation of radial modes by the control sources. Simultaneous control of two tones is achieved with parallel controllers. The fundamental and the first harmonic tones of the fan were controlled simultaneously with reductions of 12 and 5 dBA, respectively, measured on the engine axis. Simultaneous control was also demonstrated for the fan fundamental and the high-pressure compressor fundamental tones.

Active control of fan noise from a turbofan engine

A hydrocarbon-fuel injection and ignition/e ame-holding system consisting of an aerodynamic-ramp injector and a DC plasma torch was designed for a scramjet vehicle operating from Mach 4 to Mach 8. It was tested in an unheated Mach 2.4 e ow for initial evaluation. The injector consisted of two rows of two holes, angled downstream, and toed in to create additional vorticity and enhance mixing. The plasma torch was placed downstream of the injector at three different locations. The experiments involved ethylene injection through the aeroramp at jet-to-freestream momentum-e ux ratios from 1.4 to 3.2. Methane and nitrogen were used as the main feedstocks for the plasma torch. The power output of the plasma torch varied from 1500 to 3000 W. Results showed that nitrogen outperformed methane, and increasing the oxygen content at the plasma/fuel-plume interface signie cantly improved the potential for ignition and e ame propagation. The methane and nitrogen feedstocks performed best at the closest and middle downstream torch stations relative to the ethylene-fuel plume, respectively. Because of the low static freestream temperature (131 K), very little heat release was produced under these cold-e ow conditions. Tests in a model scramjet combustor with hot e ow are needed to complete the evaluation of this system. In addition, at all three torch stations, the counter-rotating vortex motion of the fuel-injector plume lifted up the plasma-torch plume. As a result, the downstream temperature-plume cores were 2.5 and 3.5 times higher at injector jet-to-freestream momentum-e ux ratios of 1.5 and 3.0, respectively, compared to the torch alone.

Walter F. O'Brien

Papers

Plasma torch igniter for scramjets

Improved Aerodynamic-Ramp Injector in Supersonic Flow

Active control of aircraft engine inlet noise using compact sound sources and distributed error sensors

Active control of fan noise from a turbofan engine

Integration of an Aeroramp Injector/Plasma Igniter for Hydrocarbon Scramjets