Diesel Spray Behavior Research Articles

Macroscopic and microscopic characteristics of a fuel spray impinged on the wall

An experimental study was performed to investigate the macroscopic behavior and atomization characteristics of a high-speed diesel spray impinged on the wall at various injection and impinging conditions. The development processes of sprays impinged on the wall were visualized using the spray visualization system composed of a Nd:YAG laser and an intensified charge-coupled device (ICCD) camera. The atomization characteristics of the impinged spray on the wall were also explored in terms of mean droplet diameter and velocity distributions by using a phase Doppler particle analyzer (PDPA) system. The results provide the effects of injection parameters, wall conditions, and the other various experimental conditions on the macroscopic behavior and atomization characteristics of the impinged sprays on the wall.

IMAGING OF VAPOR/LIQUID DISTRIBUTIONS OF SPLIT-INJECTED DIESEL SPRAYS IN A TWO-DIMENSIONAL MODEL COMBUSTION CHAMBER

The ultraviolet-visible laser absorption-scattering (LAS) technique was extended to simultaneous imaging of two-dimensional vapor/liquid mass distributions in a nonaxisymmetric evaporating diesel spray such as that injected into a two-dimensional model combustion chamber of direct-injection diesel engines. The main error for vapor measurement is incurred by the temperature dependence of molar absorption coefficients (TDMAC) of the test fuel. Thus, selecting a test fuel of negligible TDMAC can greatly increase the measurement accuracy. By means of this extended LAS technique, the overall mass, as well as the mass distribution of vapor and liquid phase per projection area perpendicular to the laser beam, was obtained, and then the behavior of split-injection diesel spray in a two-dimensional model combustion chamber in a high-temperature high-pressure constant-volume vessel was observed. Finally, the effects of injection mass ratios on the distributions of vapor and droplets and characteristics of fuel/air mixing were examined.

高圧ディーゼル噴霧の壁面衝突後の成長挙動(ディーゼル噴霧とその燃焼,内燃機関の燃焼化学と排出物制御)

高圧ディーゼル噴霧の壁面衝突後の成長挙動(ディーゼル噴霧とその燃焼,内燃機関の燃焼化学と排出物制御)

高圧ディーゼル噴霧の発達と液滴の蒸発挙動(エンジンの新しい計測技術とモデリング(2),エンジンの新しい計測技術とモデリング)

Effects of ambient temperature and injection pressure on evaporating process and droplet behavior of diesel spray was investigated by using a magnified nano-spark photography method and a rapid compression machine. Spray tip penetration becomes short with increasing ambient temperature. When ambient temperature rises up to 950K, penetration of liquid core becomes short. Magnified photographs reveal the detailed structure of evaporating spray. Droplets begin to evaporate near middle stream region of the spray. Some droplets fly while evaporating, and the droplets leave streamline at the back. The evaporation is promoted by injection pressure. Under the condition of high injection pressure, observed droplet size is small and the spray evaporation progresses strongly due to introducing high temperature ambient gas. Consequently, high-pressure injection produces wide gas phase region near the spray tip.

ディーゼル噴霧特性に関する実験的研究 噴霧到達距離の無次元表示

An experimental work has been carried out to explain the Diesel spray behavior. The measurement is per-formed for the spray tip penetration and the spray angle with three different injection pressures and ambient gas density. The change of ambient gas density has been done with pressured N2 gas and a high density SF6 gas. The density of SF6 gas is about 5.3 times N2 gas at room conditions. The obtained results for spray tip penetration are simplified with non-dimensional form. The form is based on Break-up length and time. As a result, the non-dimensional data with N2 gas fit to a curve that is unaffected with different injection pressure and ambient gas density. Moreovere, the measurement result (penetration and angle) with SF6 gas has been shown same result with N2 gas. Therefore, the potential of the non-dimensional expression method for the spray tip penetration is confirmed.

Diesel spray image segmentation with a likelihood ratio test

To characterize the macroscopic behavior of Diesel sprays and to validate and extend for current high-pressure injection systems the correlations existent in the literature, it is necessary to determine the spray geometry accurately, at least in terms of spray tip penetration and cone angle. These parameters are measured by analyzing Diesel spray images and are highly sensitive to the correct edge determination. An algorithm for segmentation of color images based on a likelihood ratio test is presented. This algorithm is compared with others available in the literature and has been validated, even for adverse experimental conditions. The experimental facilities, optical layouts, and image-processing algorithms are described.

Effect of Air Flow and Chamber Shape on Fuel Spray Configuration in a DI Diesel Engine.

The requirements of meeting increasingly stringent emission regulations dictate increasing complexities in diesel engines and new thinking in the engine design. In this respect investigation of the diesel spray and mixture formation within the combustion chamber have attracted much attention. The diesel spray behavior has usually been investigated photographically in a pressurized vessel at ambient temperature. This paper presents the results of the fuel spray behavior for a modified direct injection diesel engine with a square piston of different combustion chambers. It was found that a strong squish affects the top side of spray significantly at early injection timings, higher engine speeds and narrow head clearances. The round lip in a reentrant type combustion chamber contributes to a better confinement of fuel and concave shape of the bottom surface helps the spray to reach to the air rich zone of the combustion chamber and mixture formation improves.

Image Analysis of a Diesel Spray Impinging on a Wall

Behavior of diesel spray moving along a flat wall was experimentally investigated for further understanding of a mixing process between diesel spray and surroundings. Internal structures of impinging spray injected into a high-pressure atmosphere were visualized by YAG laser. Inclined angle of wall against the spray axis was varied from 4 to 90 deg. In order to estimate the substantial penetration of impinging spray, spray path length was defined and it was measured as a function of time. Density of spray in a photograph was analyzed by an image processing. When the impingement angle was small, a stratified flow of dense spray was remained along the wall. The inflection point of the spray penetration rate was not affected by the impingement. These phenomena led to a decrease of momentum exchange between spray and surroundings. On the other hand, in the case of deep impingement, the spray behavior changed from axial to radial jet on the wall. The inflection point of the spray penetration rate was fixed on the impingement point and coherent structure of the dense spray appeared on the wall.

Behavior of Diesel Spray Penetrating along a Wall.

In this paper, behaviors of diesel spray injected along a wall were experimentally investigated. In order to clarify the wall effect on spray structure, the geometry of the wall and its relative position to the spray axis were varied. Structures of spray injected into a high-pressure atmosphere were recorded by high-speed photographs. Results shows that the asymmetrically large vortexes in the spray were induced by the wall effect, and the spray penetrating along the wall was deviated to the wall surface. This phenomenon is called the Coanda effect in the field of fluid dynamics. The growth orientation of spray was defined by image analysis. Maldistribution ratio of spray area was defined for the quantitative estimation of the spray deviation behavior. The spray deviating conditions such as the geometry of the wall and its relative position to the spray axis were fined.

Behavior of diesel spray impinging on a wall.

The behavior of unvaporizing diesel spray impinging on a plane wall were investigated by the image analysis of shadow photographs of fuel spray. The following results were obtained : (1) The mixing between fuel and ambient gas is promoted by the spray impingement. (2) The quantity of ambient gas entrained into spray is increased by the spray impingement. (3) The empirical relations for the spray development after impingement on the plane wall were obtained.