ㄽᩥࡢせ᪨㢟 ┠ Adhesion Characteristics of Fuel Spray Impinging on Flat Wall for Gasoline Engine㸦ᖹᯈቨ㠃࡟⾪✺ࡍࡿ࢞ࢯࣜࣥᄇ㟝ࡢᾮ⭷ᙧᡂ࡟㛵ࡍࡿ◊✲㸧Ặྡ 㥪ὥு (Hongliang LUO)
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In the current study, the impinging spray on the wall by single-hole gasoline injector under non-evaporationand evaporation conditions were investigated experimentally. The high-speed video observation method (Miescattering) and Refractive Index Matching (RIM) were implemented under different engine dynamic
operation to visualize the spray and fuel adhesion, respectively. The characteristics of spray morphology suchas spray tip penetration, impinging spray height were compared during the injection process and the evolutionof fuel adhesion such as mass, area and thickness were analyzed after the injection processes in detail. The
effect of injection pressure (10, 20, 30 MPa) and ambient pressure (0.1, 0.5, 1.0 MPa) were paid attention to
firstly, and then the surface roughness of the impinging wall (Ra 2.5, Ra7.7), and impingement distances (28and 40 mm) were selected to acquire a better understanding about the impinging spray under non-evaporation
conditions. Furthermore, the effect of ambient temperatures (298 and 433 K) on fuel adhesion was considered,along with the effect of hole diameter (0.135 and 0.155 mm). Moreover, droplets behaviors before and after
impingement were discussed deeply by Particle Image Analysis (PIA) equipment. Additionally, therelationship between the fuel adhesion on the wall and the corresponding spray behaviors was investigatedunder the same conditions of the experiments as well. The main conclusions are summarizedThe motivation and significance of this study were introduced, and a review of the previous research inthis field was conducted to give more background information of the current study in Chapter1. After that,the experimental approaches applied in this research were introduced in very detail in Chapter 2. The
discussion and analysis about the results were in chapter 3-5. The main findings are classified as following.
1. The study on Non-evaporation Spray Evolution and Fuel Adhesion Formation (Chapter 3)
The characteristics of fuel spray and adhesion under different pressures, wall roughnesses andimpingement distances were investigated experimentally under non-evaporation condition in chapter 3. The
values of Rs, Hv, S, and Hi were acquired, and the fuel adhesion evolution was analyzed. Furthermore, theprobabilities of adhesion and thickness distribution were discussed. The major conclusions are as follows:
The fuel adhesion tip is shorter than the spray tip because fuel droplets splash above the wall after
impingement. Fuel droplets still exist in the air above the wall even after the end of injection. Owing to better
atomization with high injection pressure, the fuel adhesion on the wall increases. An increase in ambientpressure improves the uniformity of the fuel adhesion.
An increase in wall roughness decreases the spray tip penetration and increases the impinging spray height.
The fuel adhesion mass and area increase with time even after the end of injection. The fuel adhesion becomesslightly thicker in downstream for Ra2.5, whereas the thicker area moves upstream for Ra7.7. An increase inwall roughness increases the mass and area of the fuel adhesion. The ambient pressure decreases thedifferences between the two types of walls, whereas the injection pressure increases the differences. A higher
roughness results in a higher maximum thickness of the fuel adhesion. An increase in roughness deteriorates
the uniformity of the fuel adhesion. Wall roughness affects the fuel adhesion thickness along different lines.

For x0, the adhesion thickness for Ra7.7 is higher than that for Ra2.5 at the constant value stage, and thethickness uniformity for Ra7.7 is considerably inferior to that for Ra2.5. For y lines, the adhesion thickness
for Ra7.7 is higher than that for Ra2.5 in the upstream region, and the thickness uniformity for Ra7.7 is poor
compared to that for Ra2.5.
With a large impingement distance under ambient condition, the velocity of droplets decreases significantly,resulting in more droplets adhering to the wall instead of splashing out of the wall. As a result, Rs, Hv, and Hi
decrease with an increase in impingement distance. However, after impingement, owing to the stronger dragforce by the ambient gas and friction from the wall, S increases with the increase in impingement distance.
Both the high injection pressure and large impingement distance increase the fuel adhesion mass and area,
but the mechanisms are different. Owing to better atomization with high injection pressure, the fuel adhesionon the wall increases. At a large impingement distance, the lower velocity, bigger spray width, and better
atomization are the main reasons for increased fuel adhesion on the wall after impingement. Under the large
impingement distance condition, more fuel adheres on midstream and the thickness uniformity of fueladhesion becomes worse. Moreover, the maximum thickness of fuel adhesion increases with a large
impingement distance.
2. The study on Evaporating Spray Evolution and Fuel Adhesion Formation (Chapter 4)
The aim of this study in chapter 4 was to investigate the effect of high temperature on fuel adhesion undergasoline engine conditions to understand its mechanism. For this, toluene was injected via a single-holeinjector on the wall. Mie scattering and RIM methods were applied to observe the impinging spray structureand fuel adhesion on the wall. The spray tip penetration and impinging spray height were compared, and theevolution of fuel adhesion along with its mass, area, and thickness were studied. Finally, the mechanisms offuel adhesion formation were established in regions I and II. Moreover, due to the importance in the designof the injector hole diameter, especially for the characteristics of atomization, the effect of hole diameter thefuel adhesion was checked. RIM experiment was done to measure the fuel adhesion under different holediameters of gasoline injector. The main conclusions of this study are summarized as follows:High ambient temperature has a significant impact on the impinging spray and fuel adhesion on the wallsof the engine. A high ambient temperature favors the evaporation of fuel, thus decreasing the spray tip
penetration and impinging spray height of liquid phase. Moreover, it decreases the mass, area, and maximum
thickness of the fuel adhesion owing to the evaporation effect. Also, it increases the average thickness owing
to the decrease in ratio of fuel adhesion area being faster than that of fuel adhesion mass. The fuel adhesion
continues to increase even after the end of injection, because of droplets being re-deposited on the wall.
However, under Tamb = 433 K, the adhered fuel evaporates from the periphery of the impingement region
even where there are still some droplets being re-deposited on the wall, but the increased adhesion can only
be observed in region I. By comparing the evolution of fuel adhesion under different ambient temperatures,
it can be concluded that high ambient temperatures lead to more uniform fuel adhesion on the wall.
The distributions of adhesion mass were studied in regions I and II. Similar curves were observed in region
I under different ambient temperatures, whereas there was great variation in region II. Based on these results,
different mechanisms were described for the formation of fuel adhesion during and after injection. The
primary spray impinging on the wall contributed to the formation of fuel adhesion in region I, known as theprimary impingement region. The splashing droplets impinging next on the wall contributed to the formationof fuel adhesion in region II, known as the secondary impingement region. Furthermore, high ambient
temperature exerts more influence on the fuel adhesion formation in region II when compared to region I.
Decreasing the nozzle hole diameter can reduce the fuel adhesion mass, area, average thickness andmaximum thickness owing to the better atomization. However, the large hole diameter improves theuniformity of the thickness under both non-evaporation and evaporation conditions.
3. The study on Microscopic Spray Behaviors (Chapter 5)
The microscopic characteristics of impinging spray under gasoline conditions were studied in chapter 5.
PIA was applied to observe the microscopic spray structure, and droplets were detected by refined criteria.
The droplet size distributions and SMD were calculated and compared under various injection and ambientpressures. Furthermore, the correlation between droplets behaviors and fuel adhesion on the wall wasdiscussed in this chapter, too. The main conclusions of this study are drawn as follows:
Before impingement, large droplets and ligaments can be observed. Both injection and ambient pressuresincrease the droplet density by promoting the breakup process. However, under high injection and ambientpressures, the spray droplets are dense, and it is difficult to observe the ligaments and large droplets. Moreover,after impingement, the near-wall region becomes very dense as many droplets accumulate, whereas thedroplets far away from the wall are clear and easily observed. Before impingement, injection pressure has amore positive effect on the distribution of small droplets, and ambient pressure favors the breakup of largedroplets. Furthermore, after impingement, the probability of small droplets under Pinj = 20 MPa, Pamb = 0.1
MPa is higher than that under Pinj = 20 MPa, Pamb = 0.5 MPa. And the probability of large droplets under Pinj
= 10 MPa, Pamb = 0.5 MPa is higher than that under Pinj = 10 MPa, Pamb = 0.1 MPa, which demonstrates thecoalescence effect of ambient pressure.
Before impingement, the probability distribution of droplet number along the radial distance from the sprayaxis shows “M”-type curve. And the SMD distribution along the radial distance shows “ҍ”-type curve. Afterimpingement, the probability distribution of droplet number along the vertical distance shows similar “>”type curve. The SMD decreases from the near-wall region to the periphery under Pamb = 0.1 MPa, whereas areversal phenomenon can be observed under Pamb = 0.5 MPa. Both the breakup and coalescence behaviorsof droplets occur during the impinging spray. At low velocity, the coalescence phenomenon is more obvious
at the periphery of spray under high ambient pressure. However, it weakens at increased droplet velocity.
Key factor governing the spray-wall impingement behavior were found. The adhered fuel adhesion mass
increase with smaller Re, We, and K numbers. Although combination with the fuel adhesion mass and droplets
behavior has been done to find some partial conclusion, the gasoline spray-wall is totally complicated andneed more investigation have to be taken to identify the fuel adhesion formation and impingement process.