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Technical Paper

Measurement of Droplet Diameter and Fuel Concentration in a Non-Evaporating Diesel Spray by Means of an image Analysis of Shadow Photographs

1984-02-01
840276
A new method was developed which measures the atomization characteristics of a non-evaporating, axisymmetric diesel spray: The film image density of the high speed focused shadow photographs of a spray was analyzed based on the incident light extinction principle, and the Sauter mean diameter and the fuel concentration distribution were calculated from the image data and the measured injection rate with the help of the onion peeling model. The measured Sauter mean diameter showed good agreement with the diameter measured by the conventional immersion method, and also the measured fuel concentration distribution along the spray axis was proved to coincide well with the predicted result by Che one dimentional quasi-steady jet model except at a region near the spray tip.
Technical Paper

Two–Dimensional Imaging of Formaldehyde Formed During the Ignition Process of a Diesel Fuel Spray

2000-03-06
2000-01-0236
The time of, and location where ignition first occurs in a diesel fuel spray were investigated in a rapid compression machine (RCM) using the two–dimensional techniques of silicone oil particle scattering imaging (SSI), and the planar laser induced fluorescence (LIF) of formaldehyde. Formaldehyde has been hypothesized to be one of the stable intermediate species marking the start of oxidation reactions in a transient spray under compression ignition conditions. In this study, the LIF images of the formaldehyde formed in a diesel fuel spray during ignition process have been successfully obtained for the first time by exciting formaldehyde with the 3rd harmonic of the Nd:YAG laser. SSI images of the vaporizing spray, and the LIF images of formaldehyde were obtained together with the corresponding time record of combustion chamber pressures at initial ambient temperatures ranging from 580 K to 790 K.
Technical Paper

LDA Measurement and a Theoretical Analysis of the In-Cylinder Air Motion in a DI Diesel Engine

1985-02-01
850106
The swirl velocity in the combustion bowl of a DI diesel engine was measured by means of laser doppler anemometry, varying the swirl intensity and engine speed. At the same time an axisymmetrical two dimensional laminar model for simulating the in-cylinder air motion was presented. The boundary condition of the flow near the wall was investigated by a comparison of predicted and measured swirl velocity, and as a result the free slip condition was found to be suitable for the present model. A comparison between measured and theoretical swirl velocity revealed that the secondary flow in the combustion bowl induced by an interaction between the squish and swirl flow transfers swirl velocities from points to points, causing a complex time variation of the swirl velocity at an observing point.
Technical Paper

Prediction of the Rate of Heat Release of an Axisymmetrical Diesel Flame in a Rapid Compression Machine

1984-02-01
840519
A phenomenological model for predicting the rate of heat release of an axisymmetrical diesel flame which was achieved in a rapid compression machine has been proposed: Basing on the experimental observations, authors have introduced a new expression about the effects of abrupt thermal expansion due to the initial combustion on the air entrainment. A simple probability density function was also employed to express the distribution of the local equivalence ratio in the flame. The predicted rate of heat release showed good agreement with the experimental results in the diffusion combustion phase.
Technical Paper

Measurement of Flame Temperature Distribution in a D.I. Diesel Engine by Means of Image Analysis of Nega-Color Photographs

1981-02-01
810183
A new technique was proposed for measuring instantaneous distributions of flame temperature and KL factor of luminous flames. Here the principle of the two-color method was used to calculate flame temperature and KL factor from the two-color densities of a film image taken on a nega-color film. We applied this technique to the high speed nega-color photographs of flames in a D. I. diesel engine operated with varying swirl ratios, and discussed the measured results of instantaneous distributions of flame temperature and KL factors.
Technical Paper

Stratification of Swirl Intensity in the Axial Direction for Control of Turbulence Generation During the Compression Stroke

1991-02-01
910261
Control of turbulence during the compression stroke is suggested by both theoretical calculations and experimental results obtained with an LDV measurement in a motored engine. The authors have found experimentally that when an axial distribution of swirl intensity exists, a large-scale annular vortex is formed inside the cylinder during the compression stroke and this vortex generates and transports turbulence energy. A numerical calculation is adopted to elucidate this phenomenon. Then, an axial stratification of swirl intensity is found to generate a large-scale annular vortex during the compression stroke by an interaction between the piston motion and the axial pressure gradient. The initial swirl profile is parametrically varied to assess its effect on the turbulence parameters. Among calculated results, turbulence energy is enhanced strongest when the swirl intensity is highest at the piston top surface and lowest at the bottom surface of the cylinder head.
Technical Paper

Quantitative Measurement of Fuel Vapor Concentration in an Unsteady Evaporating Spray via a 2-D Mie-Scattering Imaging Technique

1993-10-01
932653
The cross-sectional distribution of fuel vapor concentration in an evaporating spray was measured quantitatively by a new scattering imaging technique, silicone particle scattering imaging method, which was proposed in a previous paper[1]. When fuel containing silicone oil injected into a nitrogen environment at high temperature, the volatile base fuel in the droplets vaporized rapidly, leaving behind small droplets of silicone oil suspended in the vapor-gas mixture. The silicone oil droplets were illuminated by a thin laser sheet, and the scattered light was imaged by a CCD camera. The cross-sectional distribution of vapor concentration was estimated from the scattering image of the silicone oil droplets by Mie scattering theory. The results demonstrated clearly the inhomogeneity of the fuel vapor concentration. The distribution of vapor concentration was discontinuous, and islands of rich mixture with a scale of several millimeters existed in the center region of the spray.
Technical Paper

Mixing Enhancement in Diesel-Like Flames via Flame Impingement on Turbulence-Generating Plates

1992-10-01
922210
Soot concentration is very high in the periphery near the head of an unsteady spray flame which is achieved in a quiescent atmosphere in a rapid compression machine. To reduce soot concentration in this region, it was intended to improve fuel-air mixing by letting the flame impinge on a turbulence-generating plate. Two types of turbulence-generating plates, one donut-type, the other cross-type, were tested. Soot concentration in the flame was imaged using the laser shadow technique. The effect of injection pressure on soot reduction by the flame impingement was also investigated. The overall soot concentration is reduced significantly in the case when the flame impinges on the cross-type turbulence-generating plate at 50 mm (333 nozzle diameters) from the nozzle exit. The flame impingement on the cross-type turbulence-generating plate at 333 nozzle diameters makes soot reduction little dependent on injection pressures.
Technical Paper

2-D Soot Visualization in Unsteady Spray Flame by means of Laser Sheet Scattering Technique

1991-02-01
910223
The two-dimensional distribution of a soot cloud in an unsteady spray flame in a rapid compression machine(RCM) was visualized using the laser sheet scattering technique. A 40 mm x 50 mm cross section on the flame axis was illuminated by a thin laser sheet from a single pulsed Nd:YAG laser(wavelength 532 nm). Scattered light from soot particles was taken by a CCD camera via a high speed gated image intensifier. The temporal variation of the scattered light images were presented with the injection pressure as a parameter. The results showed that scattered light was intense near the periphery of the flame tip and that the scattered light becomes weaker significantly and disappears fast after the end of injection as injection pressure is increased. This technique was also applied to the visualization of the two-dimensional distribution of liquid droplets in the non-evaporating spray to correlate it with the soot concentration distribution.
Technical Paper

A Study of the Structure of Diesel Sprays Using 2-D Imaging Techniques

1992-02-01
920107
The structure of dense sprays was investigated using 2-D imaging techniques. To investigate the mechanism of atomization, the liquid phase in a non-evaporating spray was visualized by a thin laser sheet formed by a single pulse from a Nd:YAG laser at the distance from 4 to 19 mm from the nozzle orifice with the injection pressure and the surrounding gas density as parameters. A new technique for the visualization of vapor phase in an evaporating spray, the SSI (Silicone particle Scattering Imaging) method, was proposed to investigate the structure of the vapor phase regions of the spray.
Technical Paper

A Study on Soot Formation in Unsteady Spray Flames via 2-D Soot Imaging

1992-02-01
920114
The formation and oxidation processes of soot particles in unsteady spray flames were investigated in a quiescent atmosphere using 2-D laser sheet visualization. The mid-plane of a flame was illuminated twice during a short time-interval by a laser sheet from a double-pulsed YAG laser. An image pair of the scattered light from soot particles was taken by two intensified gated cameras in succession. The velocity vectors of soot clouds at various location in the sooting region were estimated using the spatial correlation between the image pair. The results of temporal and spatial variation of velocity and scattering intensity in the evolving soot clusters made it clear that soot is mainly formed in the periphery of the flame tip where the air entrainment is less and flame temperature favors soot formation.
Technical Paper

Simultaneous 2-D Imaging of OH Radicals and Soot in a Diesel Flame by Laser Sheet Techniques

1996-02-01
960834
The OH and soot in an unsteady flame, which was achieved in a rapid compression machine, were visualized simultaneously by the laser-induced fluorescence and laser-induced scattering techniques. The fuel mixture consisting of 90% paraffin hydrocarbon (reference fuel) and 10% polypropylene-glycol was used to reduce the optical attenuation caused by dense soot cloud. The simultaneous images of the fluorescence from OH and scattering from soot show that the soot and OH exist separately from each other in the leading portion of the spray flame, and the OH is formed earlier than the soot in the near field region of spray flame.
Technical Paper

Numerical Simulation of Turbulent Dispersion of Fuel Droplets in an Unsteady Spray via Discrete Vortex Method

1995-10-01
952433
The turbulent dispersion of particles in an unsteady two dimensional particle-laden jet was simulated by a discrete vortex method coupling with a model of gas/particles interaction. Numerical analysis of a spray yielded the distributions of vorticity, fuel mass concentration and local Sauter mean diameter (SMD) of droplets in a spray. The predicted distribution of local SMD of droplets in a spray demonstrated that the size of droplets in the spray periphery is larger than that of droplets in the center region of spray. This trend of distribution of drop size coincided with that of measured one. The predicted distributions of drop size and vorticity revealed that the larger droplets are easily centrifuged to the periphery of the spray. The effects of the pattern of injection rate on the mixing process in a transient spray were also investigated.
Technical Paper

A Study on Soot Formation and Oxidation in an Unsteady Spray Flame via Laser Induced Incandescence and Scattering Techniques

1995-10-01
952451
Two kinds of planar soot imaging techniques, laser induced incandescence (LII) and laser induced scattering (LIS) techniques were applied simultaneously to an unsteady free spray flame achieved in a rapid compression machine. An analysis of LII and LIS images yielded three kinds of qualitative images of soot concentration, size of soot particles, and number density of soot in the flame. These images revealed the fact that the soot is formed mainly in the center region of a flame resulting in an appearance of soot cloud with high number density and small particle size in this region, and then the soot size increases and the number density decreases while soot is conveyed downstream.
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