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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.
Technical Paper

Development of a Rapid Compression-Expansion Machine Simulating Diesel Combustion

1995-10-01
952514
A rapid compression-expansion machine was developed, which can simulate intake, compression, expansion and exhaust strokes in a single Diesel cycle by an electrically controlled and hydraulically actuated driving system. The whole system which is composed of a hydraulic actuator, fuel injector and a valve driving device, is sequentially controlled by a micro-computer. The machine features; 1) accurate control of piston position at TDC, 2) no effect of lubricant on HC emission due to the use of dry piston rings; 3) independent control of local wall temperature; and 4) high power output to drive heavy piston at high frequency. The single cycle operation permits Diesel combustion experiments under a wide range of operating conditions and easy access of optical diagnostics with minimized amount of test fuel. The performance test showed that the machine can drive a DI Diesel type piston with a 100 mm bore at a maximum frequency of 16.7 Hz at a maximum compression pressure of 15 MPa.
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

Ignition, Combustion and Emissions in a DI Diesel Engine Equipped with a Micro-Hole Nozzle

1996-02-01
960321
In an attempt to achieve lean combustion in Diesel engines which has a potential for simultaneous reduction in no and soot, the authors developed a micro-hole nozzle which has orifices with a diameter as small as 0.06 mm. Combustion tests were carried out using a rapid compression-expansion machine which has a DI Diesel type combustion chamber equipped with the micro-hole nozzle. A comparison with the result of a conventional nozzle experiment revealed that the ignition delay was shortened by 30 %, and in spite of that, both peaks of initial premixed combustion and diffusion combustion increased significantly. The combustion in the case of the micro-hole nozzle experiment was accompanied with a decrease in soot emission, whereas an increase in NO emission.
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

High Temperature Diesel Combustion in a Rapid Compression-Expansion Machine

1991-09-01
911845
According to previous papers on the combustion process in LHR diesel engines the combustion seems to deteriorate in LHR diesel engines. However it has been unclear whether this was caused by the high temperature gas or high temperature combustion chamber walls. This study was intended to investigate the effect of gas temperature on the rate of heat release through the heat release analysis and other measurements using a rapid compression-expansion machine. Experiments conducted at high gas temperatures which was achieved by the employment of oxygen-argon-helium mixture made it clear that the combustion at a high gas temperature condition deteriorated actually and this was probably due to the poorer mixing rate because of the increase in gas viscosity at a high gas temperature condition.
Technical Paper

A New Technique for the Measurement of Sauter Mean Diameter of Droplets in Unsteady Dense Sprays

1989-02-01
890316
A new technique is developed for the in-situ measurement of Sauter mean diameter of droplets in non-evaporating transient dense sprays. This method analyzes the image of a shadowpicture of a spray based on the incident light extinction principle, and allows the sizing of Sauter mean diameter of whole droplets in a transient spray with any shape. In addition, this method allows the measurement of the local droplet size in a quasi-steady region of an axisymmetric spray if the conservation equations regarding mass and momentum are included in the calculation and data analysis. A calibration was carried out using glass beads as test particles: this was proved to have an accuracy of Sauter mean diameter measurement within 10%, on average. Applications of the new technique to both diesel and gasoline (EFI) sprays have been made.
Technical Paper

Particulate Formation and Flame Structure in Diesel Engines

1989-02-01
890436
The present paper describes the particulate formation in diesel flames considering the flame structure and its similarity to that of gaseous turbulent diffusion flames. A comparison of spatial variations of soot concentration, equivalence ratio and flame temperature between diesel flames and turbulent diffusion flames reveals the facts that soot particles are mostly farmed in a region where the equivalence ratio is near stoichiometric and the flame temperature is the highest in both flames, and that in diesel flames this region exists generally near the flame tip. A close inspection of high speed photographs of diesel flames suggests the three major routes of soot emission from diesel engines: quenching of flamelets detached from the flame tip due to 1) the flame impingement onto the wall; and 2) cooling of the flamelets by the bulk air; and 3) survival of soot containing flamelets inside the flame.
Technical Paper

Development of a Rapid Compression-Expansion Machine to Simulate Combustion in Diesel Engines

1988-10-01
881640
A rapid compression-expansion machine which can simulate the combustion processes in diesel engines is developed. The configuration of the combustion chamber is a 100 mm bore and a 90 mm stroke, and the compression ratio is 15. The piston is driven by an electro-hydraulic system with a thrust of 90 kN and the maximum frequency of 20 Hz. The whole system composed of a hydraulic actuator, a fuel injection system, and a valve driving unit is sequentially controlled by a computer. The reproducibility of the stop position of the piston at the end of compression is achieved with an accuracy of ±0.1 mm by employing a hydraulic-mechanical brake mechanism. The experiment shows that the combustion in the expansion stroke is achieved, and that the combustion characteristics such as the rate of heat release and indicated output as well as the exhaust emission can be measured.
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

A Study on the Time and Space Resolved Measurement of Flame Temperature and Soot Concentration in a D. I. Diesel Engine by the Two-Color Method

1979-02-01
790491
The two-color method regarding the visible wavelength radiation from soot particles in flames was closely studied in order to establish it as a measuring technique of the flame temperature and soot concentration in diesel engines. The accuracy of the temperature calibration of the measuring equipment was assured by a newly developed high temperature black body furnace and a standard tungsten lamp. The emissivity of diesel flames, which is the most important value in this method, was investigated through both the spectroscopic analysis of soot sampled from a diesel flame and the comparative measurements between the two-color method and the emission-absorption method. The examined two-color method was applied to a direct injection diesel engine. The time and space resolved values of temperature and soot concentration were obtained for the first time.
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

2-D Imaging of Fuel Vapor Concentration in a Diesel Spray via Exciplex-Based Fluorescence Technique

1993-10-01
932652
To measure the fuel vapor concentration in an unsteady evaporating spray injected into nitrogen atmosphere, the exciplex-forming method, which produces spectrally separated fluorescence from the liquid and vapor phase, was applied in this study. Two experiments were conducted to investigate the qualitative and quantitative applicability of the technique in a high temperature and high pressure atmosphere during the fuel injection period. One is to examine the thermal decomposition of TMPD dopant at a high temperature and a high pressure nitrogen atmosphere during a short period of time. The other is to calibrate the relationship between fluorescence intensity and vapor concentration of TMPD at different vapor temperatures. And then, the qualitative measurement of fuel vapor concentration distributions in diesel sprays was made by applying the technique.
Technical Paper

High Combustion Temperature for the Reduction of Particulate in Diesel Engines

1988-02-01
880423
Experiments on the effects of temperature T and equivalence ratio ϕ on soot formation at high pressures up to 5 MPa were conducted. The soot formation region is mapped on ϕ-T diagram using the results obtained in the experiments and the published data. NO formation region is also determined by the Zeldovich equations and is plotted on the same diagram. The time histories of ϕ and T of the flame in a DI diesel engine which was obtained by a gas sampling study, are plotted on the ϕ-T diagram to form a trajectory. Discussion of the trajectory in relation to both soot and NO formation region gives suggestion of a possibility of high temperature - rich mixture combustion to reduce particulate formation in diesel engines.
Technical Paper

A Study on Precise Measurement of Diesel Fuel Injection Rate

1992-02-01
920630
An experimental evaluation of the reliability of the Zeuch's method was carried out. The following were derived: 1) cavitation limits the minimum back pressure available; 2) the injection rate measured by the Zeuch's method agrees with that by the W.Bosch's method; 3) the effect of dynamic pressure of the injected fuel jet has a negligible effect on the pressure sensor which is attached to the chamber wall; and 4) the high-frequency noise after the end of injection observed in the Zeuch's measurement can be effectively removed by either a low-pass filter or an inverse Fourier transform processing.
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

Fast Burning and Reduced Soot Formation via Ultra-High Pressure Diesel Fuel Injection

1991-02-01
910225
The relation between the characteristics of a non-evaporating spray and those of a corresponding frame achieved in a rapid compression machine was investigated experimentally. The fuel injection pressure was changed in a range of 55 to 260 MPa and the other injection parameters such as orifice diameter and injection duration were changed systematically. The characteristics of the non-evaporating spray such as the Sauter mean diameter and the mean excess air ratio of the spray were measured by an image analysis technique. The time required for a pressure rise due to combustion was taken as an index to characterize the flame. It was concluded that the mean excess air ratio of a spray is the major factor which controls the burning rate and that the high injection pressure is effective in shortening the combustion duration and reducing soot formation.
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

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.
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