Heavy-duty natural gas engines offer air pollution and energy diversity benefits. However, current homogeneous-charge lean-burn engines suffer from impaired efficiency and high unburned fuel emissions. Natural gas direct-injection engines offer the potential of diesel-like efficiencies, but require further research. To improve understanding of the autoignition and emission characteristics of natural gas direct-injection compression-ignition combustion, the effects of key operating parameters (including injection pressure, injection duration, and pre-combustion temperature) and gaseous fuel composition(including the effects of ethane, hydrogen and nitrogen addition) were studied. An experimental investigation was carried out on a shock tube facility. Ignition delay, ignition kernel location, and NOx emissions were measured. The results indicated that the addition of ethane to the fuel resulted in a decrease in ignition delay and a significant increase in NOx emissions. The addition of hydrogen to the fuel resulted in a decrease in ignition delay and a significant decrease in NOx emissions. Diluting the fuel with nitrogen resulted in an increase in ignition delay and a significant decrease in NOx emissions. Increasing pre-combustion temperature resulted in a significant reduction in ignition delay, and a significant increase in NOx emissions. Modest increase in injection pressure reduced the ignition delay; increasing injection pressure resulted in higher NOx emissions. The effects of ethane, hydrogen, and nitrogen addition on the ignition delay of methane were also successfully predicted by FlameMaster simulation. OH radical distribution in the flame was visualized utilizing Planar Laser Induced Fluorescence (PLIF). Single-shot OH-PLIF images revealed the stochastic nature of the autoignition process of non-premixed methane jets. Examination of the convergence of the ensemble-averaged OH-PLIF images showed that increasing the number of repeat experiments was the most effective way to achieve a more converged result. A combustion model, which incorporated the Conditional Source-term Estimation(CSE) method for the closure of the chemical source term and the Trajectory Generated Low-Dimensional Manifold (TGLDM) method for the reduction of detailed chemistry, was applied to predict the OH distribution in a combusting non-premixed methane jet. The model failed to predict the OH distribution as indicated by the ensemble-averaged OH-PLIF images, since it cannot account for fluctuations in either turbulence or chemistry.

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This work is about the study of the turbulent round jet to low Reynolds number in the outlet of a nozzle due to the countless uses in the industrial field. The objectives of the thesis are the verification of the Particle Image Velocimetry (PIV) data with other methods and authors and the analysis of the near and transition region of the flow. The method has been divided in three parts: processing of the PIV data that has been the normalization and union of the data; validation of the PIV measurement in comparison with other related studies; and the analysis of the near and intermediate field with the known data. Once that this part has been realized, the results and the discussion of the same have been presented. The preparation of the data has been made with a big accuracy how it has been demonstrated in the report. The verification of the PIV data has been affirmative with a big similitude for every magnitude that have been compared with other authors. Several patterns and an equation checked have been obtained in the analysis of the potential and transition region of the turbulent flow. In the near field, a model has been found in the self-similarity turbulence intensity. In the intermediate field, the inverse streamwise mean velocity have been proved that follow a lineal function depending the parameters of the Reynolds number and nozzle geometry. Also, self-similarity streamwise velocity has evolved similar to Gaussian distribution. Finally, an evaluation of the principal point to eddy will be development has been made. Turbulent kinetic energy and vector fields have demonstrated that vortices are created in the intersection between near and intermediate zone.

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It is well known that high-speed liquid jetting is one of the most powerful techniques available to cut or penetrate material. Recently, it has been conjectured that high-speed liquid jets may be beneficial in improving combustion in such applications as SCRAM jets and direct injection diesel engines. Although there are practical limitations on maximum jet velocity, a fundamental study of the characteristics of high-speed liquid fuel jets and their auto-ignition feasibility is necessary. Important benefits could be increased combustion efficiency and enhanced emission control from improved atomisation. The generation of high-speed liquid jets (water and diesel fuel) in the supersonic to hypersonic ranges by use of a vertical single stage powder gun is described. The effect of the projectile velocity and projectile mass on the jet velocity is found experimentally. Jet exit velocities from a range of different nozzle inner profiles and nozzle hardness are thoroughly examined. The characteristics and behaviour of the high-speed liquid jet and its leading bow shock wave have been studied with the aid of a shadowgraph technique. This provides a clearer picture of each stage of the generation of hypersonic liquid jets. It makes possible the study of hypersonic diesel fuel jet characteristics and their potential for auto-ignition. The fundamental processes by which a supersonic liquid jet is generated by projectile impact have been investigated. The momentum transfer from the projectile to the liquid and the shock wave reflection within the nozzle cavity are the key items of interest. A new one-dimensional analysis has been used in order to simplify this complex and difficult problem. The impact pressure obtained from the projectile was firstly derived. Then, an investigation of the intermittent pressure increase in a closed end cavity and a simple stepped, cross-sectional nozzle were carried out. The nozzle pressure and final jet velocity were estimated and compared to a previous method and to experimental results. Some interesting characteristics found in the experiments relate well to those anticipated by the analysis. The characteristics of a hypersonic diesel fuel jet and its leading edge shock wave were assessed for their potential for auto-ignition using fuel with cetane numbers from 50-100. The investigations were performed at normal ambient air and at elevated air (110 ???C) temperature. So far, there is no sign of auto-ignition that may occur because of the temperature rise of the induced shock.

This thesis reports on the structure of the flow inside a nozzle which produces a naturally oscillating jet flow. The nozzle consists of a short cylindrical chamber with a concentric triangular-inlet orifice at one end and a circular exit lip at the other end. This triangular-jet nozzle was developed from the “fluidic-precessing-jet” (FPJ) nozzle, which has a similar arrangement of components, but has a circular rather than a triangular inlet. For reliably oscillating flow, the FPJ nozzle should have an inlet-to-chamber expansion ratio of at least 5.0, a chamber lengthto- diameter ratio between 2.6 and 2.8, and an exit-lip height of about 0.1 chamber diameters. The triangular-jet nozzle produces a continuously and aperiodically oscillating jet flow which is different from the FPJ flow. The oscillation occurs at smaller inlet-to-chamber expansion ratios (2.1 ≲ D /de₁ ≲ 3.5) and over a wider range of chamber lengths (2.0 ≲ L /D ≲ 2.5). The initial spreading angle of the jet flow is smaller, but is still much larger than that of non-oscillating, axisymmetric turbulent-jet flows. In addition, the external “oscillating-triangular-jet” (OTJ) flow has preferred azimuthal directions which are aligned with the three corners of the orifice. The kinetic-energy-loss coefficient of the OTJ nozzle is much smaller than that of the FPJ nozzle because oscillation occurs at much smaller inlet-to-chamber expansion ratios. For a narrow range of length-to-diameter ratios (1.00 ≲ L/D ≲ 1.25), the triangular-inlet nozzle can also produce a non-oscillating or “stationary deflected triangular jet” (SDTJ) which reattaches asymmetrically to the inside surface of the cylindrical chamber. The SDTJ has a weak tendency to oscillate, which suggests that flow patterns required for self-excited oscillation are already present in the SDTJ flow. Surface-flow visualisation and surface-pressure measurements in the SDTJ nozzle have provided the location of critical points and bifurcation lines on the chamber wall, and from this the topology of the SDTJ flow is deduced. Some details of the flow such as a jet-reattachment node near the chamber exit and a strong swirl adjacent to the inlet orifice are known from previous studies of the FPJ flow, but there are many newly observed features. The most easily identified of these are two sink-focus separation points, one on each side of the reattachment node but closer to the inlet plane. The foci counter rotate and are of unequal size. Reverse flow through the exit plane of the chamber is attracted to the larger focus. The vortex core rising from each focus is entrained by the reattaching-jet (SDTJ) flow and is drawn out of the chamber. A backward-facing pressure probe placed in the OTJ “reattaching-flow” region of chamber wall can be used as a reliable detector of jet-flow oscillation. Cross-correlating the signal from this detector probe with simultaneous static-pressure measurements elsewhere on the chamber wall gives a conditionally-averaged pressure on the wall of the OTJ chamber. The OTJ wall-pressure distribution has the same features as the SDTJ surface-pressure distribution, but it has greater asymmetry about a mirror plane drawn through the chamber axis and the detector probe. An array of three backward-facing pressure probes has been used as an “event detector” for conditionally-sampled (PIV) measurements of non-axial velocity components in cross-sections of the OTJ nozzle. The event-detection scheme responds only to a preselected (counter-clockwise) direction of motion of the oscillating-jet flow. The streamline patterns constructed from the conditionally-sampled measurements confirm the presence of the jet-reattachment node, the swirl and the sink foci identified from the SDTJ surface-flow visualisation. The shear-layer interaction between the jet from the triangular orifice and the swirl (adjacent to the inlet plane) produces strong longitudinal vortices in the ensemble-averaged flow. The jet flow distributes these vortices through the length of the chamber. Vortex cores representing the vortices are reconstructed by tracking streamline foci from one PIV cross-section plane to another. The tracking process includes the connection and termination of vortex cores in a manner which is consistent with the Helmholtz vortex law. In this flow field, the vortex core produced by the swirl and the vortex core rising from the larger sink-focus vortex on the chamber wall are connected to form a loop. The extent to which this vortex loop is contained within the chamber determines whether or not the flow is oscillating. If only a small fraction (e.g. 8%) of the vortex circulation passes through the exit plane of the nozzle, the loop is trapped inside the chamber and the deflected jet oscillates. If the length of the chamber is halved, about 35% of vortex circulation escapes from the nozzle and the oscillation stops. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1353005 / Thesis (Ph.D.) - University of Adelaide, School of Mechanical Engineering, 2009

This thesis reports on the structure of the flow inside a nozzle which produces a naturally oscillating jet flow. The nozzle consists of a short cylindrical chamber with a concentric triangular-inlet orifice at one end and a circular exit lip at the other end. This triangular-jet nozzle was developed from the “fluidic-precessing-jet” (FPJ) nozzle, which has a similar arrangement of components, but has a circular rather than a triangular inlet. For reliably oscillating flow, the FPJ nozzle should have an inlet-to-chamber expansion ratio of at least 5.0, a chamber lengthto- diameter ratio between 2.6 and 2.8, and an exit-lip height of about 0.1 chamber diameters. The triangular-jet nozzle produces a continuously and aperiodically oscillating jet flow which is different from the FPJ flow. The oscillation occurs at smaller inlet-to-chamber expansion ratios (2.1 ≲ D /de₁ ≲ 3.5) and over a wider range of chamber lengths (2.0 ≲ L /D ≲ 2.5). The initial spreading angle of the jet flow is smaller, but is still much larger than that of non-oscillating, axisymmetric turbulent-jet flows. In addition, the external “oscillating-triangular-jet” (OTJ) flow has preferred azimuthal directions which are aligned with the three corners of the orifice. The kinetic-energy-loss coefficient of the OTJ nozzle is much smaller than that of the FPJ nozzle because oscillation occurs at much smaller inlet-to-chamber expansion ratios. For a narrow range of length-to-diameter ratios (1.00 ≲ L/D ≲ 1.25), the triangular-inlet nozzle can also produce a non-oscillating or “stationary deflected triangular jet” (SDTJ) which reattaches asymmetrically to the inside surface of the cylindrical chamber. The SDTJ has a weak tendency to oscillate, which suggests that flow patterns required for self-excited oscillation are already present in the SDTJ flow. Surface-flow visualisation and surface-pressure measurements in the SDTJ nozzle have provided the location of critical points and bifurcation lines on the chamber wall, and from this the topology of the SDTJ flow is deduced. Some details of the flow such as a jet-reattachment node near the chamber exit and a strong swirl adjacent to the inlet orifice are known from previous studies of the FPJ flow, but there are many newly observed features. The most easily identified of these are two sink-focus separation points, one on each side of the reattachment node but closer to the inlet plane. The foci counter rotate and are of unequal size. Reverse flow through the exit plane of the chamber is attracted to the larger focus. The vortex core rising from each focus is entrained by the reattaching-jet (SDTJ) flow and is drawn out of the chamber. A backward-facing pressure probe placed in the OTJ “reattaching-flow” region of chamber wall can be used as a reliable detector of jet-flow oscillation. Cross-correlating the signal from this detector probe with simultaneous static-pressure measurements elsewhere on the chamber wall gives a conditionally-averaged pressure on the wall of the OTJ chamber. The OTJ wall-pressure distribution has the same features as the SDTJ surface-pressure distribution, but it has greater asymmetry about a mirror plane drawn through the chamber axis and the detector probe. An array of three backward-facing pressure probes has been used as an “event detector” for conditionally-sampled (PIV) measurements of non-axial velocity components in cross-sections of the OTJ nozzle. The event-detection scheme responds only to a preselected (counter-clockwise) direction of motion of the oscillating-jet flow. The streamline patterns constructed from the conditionally-sampled measurements confirm the presence of the jet-reattachment node, the swirl and the sink foci identified from the SDTJ surface-flow visualisation. The shear-layer interaction between the jet from the triangular orifice and the swirl (adjacent to the inlet plane) produces strong longitudinal vortices in the ensemble-averaged flow. The jet flow distributes these vortices through the length of the chamber. Vortex cores representing the vortices are reconstructed by tracking streamline foci from one PIV cross-section plane to another. The tracking process includes the connection and termination of vortex cores in a manner which is consistent with the Helmholtz vortex law. In this flow field, the vortex core produced by the swirl and the vortex core rising from the larger sink-focus vortex on the chamber wall are connected to form a loop. The extent to which this vortex loop is contained within the chamber determines whether or not the flow is oscillating. If only a small fraction (e.g. 8%) of the vortex circulation passes through the exit plane of the nozzle, the loop is trapped inside the chamber and the deflected jet oscillates. If the length of the chamber is halved, about 35% of vortex circulation escapes from the nozzle and the oscillation stops. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1353005 / Thesis (Ph.D.) - University of Adelaide, School of Mechanical Engineering, 2009