An Experimental Study of Diesel Spray Impingement on a Flat Plate: Effects of Injection Conditions

Abstract

Advanced injection strategies for internal combustion engines have been extensively studied although there still exists a significant fundamental knowledge gap on the mechanism for high-pressure spray interaction with the piston surface and chamber wall in the internal combustion engine. The current study focuses on providing qualitative and quantitative information on spray-wall impingement and its characteristics by expanding the range of operating parameters under engine-like conditions. Parameters considered in the experiment are ambient gas and fuel injection conditions. The test included the non-vaporizing spray at the different ambient density (14.8, 22.8 and 30 kg/m 3 ) and injection pressure (1200, 1500 and 1800 bar) with the isothermal condition (ambient, and plate temperatures of 423 K). The test was conducted in the constant-volume vessel with the 60-degree impinging spray angle relative to the plate. The free spray and impinged spray properties were qualitatively analysed based on Mie and schlieren images. The results showed that the lower ambient density and higher injection pressure tended to result in relatively higher impinged spray height. The expanding shape of the impinged spray on the wall showed the oval shape.Keywords free spray; impinged spray; wall-impinged expanding spray; flat plate Introduction Internal combustion engines (ICEs) have been the dominant power supply for automobiles since the 20 th century and will keep playing an important role in transportation sectors in the coming decades. Increasingly stringent fuel consumption and emission standards are driving automotive research. Advanced injection strategies such as increasing injection pressure, multiple injections, injection timing control, and many others can enhance fuel efficiency in the application of direct injection spark ignition (DISI) engines and direct injection (DI) diesel engines. The DISI and DI diesel engines are able to achieve such higher efficiencies by means of better spray atomization and air-fuel mixing. Besides injection parameters mentioned above, the spray-wall interaction plays a critical role in fuel spray dispersion and subsequent combustion event [1][2][3]. The fuels used in ICEs undergo the vaporization process and mix with air before combustion. However, the fuel spray may impinge on the engine surfaces before it is fully vaporized [4]. The non-vaporizing spray possibly impinges on the cylinder head or liner in DI engines and even on the inlet valves in port fuel injected (PFI) engines. The spray-wall impingement usually forms a liquid film on the wall, which is referred to wall-wetting phenomenon [5]. The fuel deposition on the wall may survive during the combustion phase, resulting in producing unburned hydrocarbon (HC) and particulate matter (PM) emissions [6][7][8]. Especially in cold operation (such as cold start and warm-up), the wall wetting in PFI engines becomes dominant mechanism for engine-out HC emissions [9][10][11][12][13]. When the spray droplets hit the wall, they may und...

Assessment of impinged flame structure in high-pressure direct diesel injection

“…Detailed information of the combustion vessel can be found in a previous study. 33 A single-hole, off-axis, Bosch LBZ diesel injector was adopted. The nozzle size is 200 µm in diameter.…”

“…axial/radial expansion distances at axial direction) were obtained by tracking the boundary of the spray expansion pattern in our previous study. 33 The procedure of boundary tracking method in this study is shown in Figure 5.…”

“…The expansion rate defined by the time derivative of SED illustrates initially an increment but later a decrement, which is similarly observed in the previous study. 33 Such a phenomenon indicates that the spray expansion starts to accelerate via the initial spray momentum but later decelerate via a combination of weakening spray momentum and increasing shear force which adversely acts on the spray movement.…”

The Experiment and Simulation on Impact Characteristics of AVGAS Spray Based on Impact Phenomenon

“…The angle of impact is also an important factor in spray characteristics [10], [11], [22]. Studies have shown that lower impact angles tend to result in faster spray penetration [10]- [12], [22], [23]. An optimal impact angle can provide better fuel distribution and higher combustion efficiency [4], [9].…”

Experiment and Simulation Investigation on the Characteristics of Diesel Spray Impingement Based on Droplet Impact Phenomenon

“…After spray hitting the wall, the spray radius and height is changed, which will affect the mixing of fuel and air, and further affect the engine performance and exhaust particulate emissions. Therefore, it is significant to study the phenomenon of spray impingement on diesel engine [1][2][3][4][5].…”