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Thermal purge is an effective method for rapidly de-icing proton exchange membrane fuel cell (PEMFC) flow channels. This study investigates the impact of purge speed, temperature, and surface wettability on the melting of ice droplets in flow channels through a combination of experiments and simulations. The results demonstrate that purge speed primarily affects the movement time of the ice droplet. From a speed increase of 5 m/s to 15 m/s, the movement time decreases from 5.48 s to 1.26 s, accompanied by a gradual reduction in the melting rate. Purge temperature predominantly influences the change in ice droplet melting rate. When the temperature increases from 313.15 K to 353.15 K, the melting rate increases from 0.18 to 0.41. The surface wettability has little effect on the movement time and melting rate of the ice droplets. The response surface methodology is used to obtain the optimum conditions for the shortest purge time and maximum melting rate of ice droplets. The corresponding conditions are a purge speed of 10.48 m/s, a purge temperature of 346.82 K, and a surface contact angle of 82.47°. • A three-phase coupling model of solid-liquid-gas flow in channels was established. • A thermal purge melting experimental bench for ice droplets was constructed. • The purge speed impacts both the movement of ice droplets and their melting rate. • The optimal conditions for the process of ice droplet purge melting are formulated. [ABSTRACT FROM AUTHOR]

Hydrogen fuel cell sightseeing vehicles (HFCSVs) are usually driven in densely populated areas; the release of hydrogen may pose a threat to the safety of people. In this study, we explore the effects of the locations and heights of hydrogen storage tanks and the modes of parking on hydrogen diffusion and combustion in open space by activating the thermally activated pressure relief device (TPRD) of the hydrogen storage tanks. The results show that the diffusion distance of combustible hydrogen clouds is the largest when the hydrogen storage tank is in front; when the hydrogen storage tank is in the middle, the diffusion distance of combustible hydrogen clouds is the smallest, the time to reach the maximum is the shortest, and the minimum safety range is the smallest. The lower the height of the hydrogen storage tanks, the smaller the maximum volume of combustible hydrogen cloud and the larger the flame spreading range. When parking at 60°, 45°, and 30°, the maximum length of the combustible hydrogen cloud is almost the same. Under 30° parking, the right vehicle always has no flame distribution and will not activate TPRD due to a jet flame; this parking is the safest. • Established a CFD model for an open space hydrogen fuel cell sightseeing vehicle. • Explored the impact of hydrogen tank layout and parking modes on diffusion and combustion. • The diffusion distance of hydrogen is minimum when the hydrogen tank is in the middle. • The lower the height of the hydrogen storage tank, the larger the flame spreading range. • Compared to other parking modes, 30° parking is the safest. [ABSTRACT FROM AUTHOR]

A series of experiments are carried out to investigate the combustion, emissions characteristics and fuel consumption of a diesel engine equipped with elliptical nozzle. The elliptical holes, which are made with an aspect ratio of 1.5, have a similar flow area as that of the references. In-cylinder pressure, exhaust emissions and fuel consumption are measured with varied fuel injection timing under a constant speed and different loads. The elliptical nozzles are characterized by shorter ignition delays, lower maximum rates of heat release and in-cylinder average temperature, and longer combustion durations. The NOx emission of the ICE with an elliptical nozzle is lower and while Soot emission higher. Under variable fuel injection timing, the NOx-Soot trade-off are affected by the nozzle shape. A substantial improvement in the fuel consumption-NOx emission trade-off is obtained for elliptic nozzles at three different loads. Employing moderate earlier injection couple with elliptical nozzle can reduce fuel consumption 2.5% while NOx and Soot emission remain unchanged at 25% load, and NOx emission reduce by 8.3% and 12.7%, and Soot emission reduce by 5.7% and 10.9%, and fuel consumption reduce by 2.4% and 1.7% at 50% and 75% load respectively. • The combustion performances were studied by using elliptical diesel nozzle. • The elliptical nozzles are characterized by shorter ignition delay. • The NOx emission of elliptical nozzle is lower and Soot emission is higher. • The use of elliptical orifices can improvement in NOx-Soot trade-off. [ABSTRACT FROM AUTHOR]

The design and operation of embedded reactors involve chemical reaction efficiency issues, with the main consideration being heat and mass transfer characteristics. The contact area of the porous catalytic coating with methanol is affected by the reactor structure, to improve the hydrogen yield and reveal the mechanism of the channel structure on the hydrogen production performance, the hydrogen production performance of circle-triangle, circle-square, square-circle, square-square, and triangle-circle channels was investigated. The reasons for the differences in methanol conversion, hydrogen, and carbon monoxide selectivity were analyzed from the perspective of heat and mass transfer using a three-rate reaction mechanism. The results showed that the circle-triangle channel performed outstandingly in the hydrogen production from methanol steam reforming with 98.61 % methanol conversion, 88.74 % hydrogen selectivity, and 29.06 % CO selectivity. The shapes and sizes of the different channel structures affect the fluid flow pattern and velocity distribution, which in turn affect the mass transfer efficiency and lead to differences in hydrogen production performance. The circle-triangle channel exhibits superior heat transfer and material transport performance, which can improve the hydrogen production efficiency of methanol steam reforming and help provide an important reference for the embedded reactor design. [ABSTRACT FROM AUTHOR]

The internal flow in nozzle and macroscopic spray characteristics of diesel and biodiesel, by employing a validated numerical model and a laser-based Mie-scattering technique, are investigated. The results indicate that both the mass flow rate and the orifice exit average velocity of diesel are larger than those of biodiesel. Also, that diesel consistently produced higher cavitation intensity and turbulence kinetic energy confirms diesel can boost the naissance of cavitation and the turbulence disturbance inside the nozzle. Meanwhile, the cavitation intensity and the turbulence kinetic energy increase dramatically as the injection pressure increases; the cavitation domain is consistent with the domain of high turbulence kinetic energy. Furthermore, the radial velocity of diesel is significantly higher than biodiesel under the same injection pressure, while the radial velocities of both fuels increase as the injection pressure increase. Moreover, the spray tip penetration of biodiesel is longer than that of diesel, while the aerodynamic spray cone angle of biodiesel is narrower that of diesel under the same injection pressure. Higher surface tension and viscosity of biodiesel resulted in smaller cavitation intensity, turbulence kinetic energy and radial velocity at the nozzle exit, which in turn contribute to the narrowing of the aerodynamic spray cone angle. [ABSTRACT FROM AUTHOR]

The Large Eddy Simulation model was introduced to study the micro spray characteristics under ultra-high injection pressure (>220 MPa). EFS8400 spray test platform was set up to verify the accuracy of the numerical model. The mechanisms of micro spray characteristics were studied intensively under different injection pressures (180 MPa, 240 MPa) and nozzle diameters (0.1 mm, 0.16 mm). The results indicated that the micro turbulence vortex structures can be captured, especially in the liquid spray core area. Large Eddy Simulation model combined with the small grid size of 0.25 mm show a huge advantage in studying the micro spray characteristics under ultra-high injection pressure; The turbulence vorticity and spray velocity for injection pressure of 240 MPa are more intensive than that of 180 MPa, and also the ultra-high injection pressure can contribute to strong turbulence disturbance between spray and surrounding air, which is helpful to improve the quality of spray; The spray velocity field extended wider for the diameter of 0.16 mm, and also the values of velocity in the spray center is higher than that of the diameter of 0.1 mm; The entrainment vortex appeared at the edge of the large velocity gradient between spray and surrounding air, and the higher velocity gradient for ultra-high injection pressure (240 MPa) between the spray and air is easier to increase the generation of entrainment vortex in the downstream of the spray, which can significantly increase the quality of spray and atomization. [ABSTRACT FROM AUTHOR]

[Display omitted] • Structural characteristics and adsorption capacity of the particulate matter are investigated. • Methanol/biodiesel particulate matter shows adsorption capacity in relation to structure. • Blending ratio and working conditions have significant effects on particle structural characteristics. Methanol and biodiesel are oxygenated alternative fuels with potential applications. Structural characteristics of the particulate matter have an important influence on the application and regeneration of DPF. The particulate matter were collected and measured under different methanol/biodiesel blending ratios (0 %, 10 %, 20 %), engine loads (50 %, 75 %, 100 %) and speeds (2700 r/min, 3600 r/min). The results showed that the particulate matter possesses adsorption capacity and corresponds to structure. The pore radius is distributed between 8 and 80 nm, classified as mesoporous and microporous. When the methanol blending ratio increased from 0 % to 20 %, the average particle size of particulate matter decreased by 14 nm, the specific surface area increased by 8.05 m2/g, the average pore radius decreased by 3.113 nm and the pore volume increased by 0.016 mL/g. As the load increased, the average particle size and the average pore radius decreased, while the specific surface area and pore volume increased. As the speed increased, the average particle size, specific surface area and pore volume of the particles increased, while the average pore radius decreased. Overall, the adsorption capacity of particulate matter tended to increase with increasing blending ratio, engine load and speed. [ABSTRACT FROM AUTHOR]

To explore ice-melting process in a perforated gas diffusion layer and an effective and efficient GDL structure to enhance ice melting performance, a three-dimensional ice-melting model was established via lattice Boltzmann method based on enthalpy. The modified curved boundary condition was used in the model to consider complex carbon fiber surface. The influence of the hole shape parameters on ice melting was investigated. The main finding of the work is that the ice in a perforated gas diffusion layer can be melted faster than that in a conventional gas diffusion layer, which means that perforated gas diffusion layer has better ice melting ability. The width mainly influences the enhancement area of heat transfer. When the Fourier number is 0.1, as the width increases, the melting rate increases from 0.55 to 0.62. If the hole depth is larger than 0.5 times the thickness of the gas diffusion layer, the hole can act to enhance the ice melting. The maximum ice melting rate at a Fourier number of 0.1 is only 0.59. The increasing number of holes makes the temperature more evenly distributed. When the Fourier number is 0.1, as the number increases, the ice melting rate increases from 0.55 to 0.62. [ABSTRACT FROM AUTHOR]

The non-circular orifice has potential ability to increase the fuel spray and mixing quality. While the application of non-circular orifice in the GDI injection system hasn't been reported yet. The inner flow behaviors have great impact on the spray and mixing quality. Therefore, Volume of Fluid (VOF) and Large Eddy Simulation (LES) method are introduced to investigate the effects of non-circular orifices cross section shapes of GDI injector on the inner flow patterns and nozzle exit flow parameters. From the results, the total vapor phase volume fraction of the elliptical orifice is smaller than that in the circular one. The vapor phase fraction of elliptical orifice decreases with the increase of aspect ratio, and the vapor phase volume fraction of the elliptical E4 orifice is the smallest. In addition, the critical cavitation point of circular orifice is earlier than that of elliptical orifice, which indicated that the circular orifice is more prone to cavitate than the elliptical one. Finally, the discharge coefficient of circular orifice is the smallest among all orifices. The velocity coefficient of elliptical E4 orifice is the minimum under the cavitation conditions, while the elliptical E4 orifice held the largest area coefficient among other orifices. [ABSTRACT FROM AUTHOR]

To improve the drag reduction performances of the proton exchange membrane fuel cell (PEMFC), a three dimensional numerical investigation about the water removal in a lotus-like PEMFC flow channel is carried out. The effects of the microstructure shape parameters (height, radius and spacing) are investigated. The investigation revealed that the liquid water can be effectively removed by the lotus-like flow channel from the channel wall surface. The appropriate height of lotus-like channel can effectively reduce the water coverage ratio on the top wall of the lotus-like flow channel. As height increases, the average drag reduction ratio increases firstly and decreases finally. When the radiuses are 25 μm and 50 μm, the average drag reduction ratios of these cases are higher than those of the other cases obviously. The spacing of the lotus-like channel has a few effects on the water removal and water coverage ratio. The lotus-like flow channel with the height of 50 μm, the radius of 50 μm and the spacing of 150 μm has a high drag reduction and anti-corrosion performance. The work in this study provides a new choice for the flow channel and has certain guiding significance for the design of the flow channel for anti-corrosion and drag reduction. • A three-dimensional numerical simulation of water behavior was carried out. • The lotus-like flow channel can accelerate the water removal. • As the height increases, the average drag reduction ratio increases. • The radius of the microstructure has influence on the droplet flow velocity. • The spacing has an inapparent effect on droplet movement. [ABSTRACT FROM AUTHOR]

The using of an elliptical nozzle has been considered as a potential method for improving the air-fuel mixing and atomization quality. The present paper focuses on the transverse jet breakup behaviors and droplet size distribution for circular and elliptical orifices in supersonic crossflow on a pulse wind tunnel test platform, and the laser based pulsed laser background imaging method and high-speed spray particle size analyzer were adopted. The results show that the jet penetration depth of elliptical 4 (Aspect ratio of 4) orifice is always smaller than that of the circular orifice. Another interesting finding is that the difference of the jet penetration depth between the circular and elliptical 4 orifices decreases with the increase of injection pressure. Moreover, the jet surface wave number of the elliptical orifice is more than that of the circular jet, and the elliptical jet surface wave length is smaller than that of circular one. Additionally, the spray Sauter Mean Diameter (SMD) of elliptical 4 nozzle is 14.5% smaller than the circular spray at injection pressure of 5 MPa, and the elliptical 4 spray also has the smallest Dv50 and Dv90 among other orifices. Because elliptical 4 jet held larger windward surface area, which is helpful to increase the shear action of supersonic crossflow. Furthermore, the elliptical 4 spray produces the smallest droplet diameter at the largest volume fraction, and also the elliptical 4 spray has the smallest span of droplet diameter distribution than other orifices. • Transverse jet behaviors and droplet size were studied at supersonic crossflow. • The large windward area of elliptical jet resulted in short penetration depth. • The elliptical transverse jet has smaller SMD than that of circular jet. • The application of elliptical orifice improves mixing and atomization quality. [ABSTRACT FROM AUTHOR]

Based on the differential requirements for friction performance of wet clutch coupling pair under hydrodynamic, mixed and boundary lubrication states, a design of concave-convex composite texture on steel sheet surface is proposed and a theoretical lubrication model is established. Simulation results indicate that suitable composite texture can regulate and control tribological performance during the engagement process. Experimental results demonstrate that the concave-convex composite texture design can reduce friction coefficient by about 5.0%− 5.5% during the early engagement with high-speed sliding, while increase it by approximately 37.4%− 47.7% at the later engagement phase with low-speed sliding. This validates the comprehensive effect of composite texture in reducing film shear friction during hydrodynamic lubrication stage and increasing friction due to anchoring during boundary lubrication stage. [ABSTRACT FROM AUTHOR]

This paper presents an inquiry into the internal flow and spray behavior of diesel and biodiesel in a triangular orifice, using experimental and numerical methods. The inner flow was analyzed through the implementation of Large Eddy Simulation model. Furthermore, two high-speed cameras were utilized to capture spray images of the major and minor axes of the triangle-shaped nozzle simultaneously. The investigation revealed that, in comparison to diesel, biodiesel exhibited a higher discharge coefficient. Additionally, the vorticity magnitudes and turbulence vortex structures for biodiesel were consistently lower than those for diesel. The use of biodiesel can hinder the occurrence of cavitation. Moreover, it was observed that the triangular spray cone angle displayed axis-switching phenomena for both fuels. The axis-switching phenomenon is suppressed by using biodiesel. The research also discovered that the triangular biodiesel spray has a longer spray tip penetration and a smaller angle in all view planes. This could be attributed to the higher viscosity and surface tension of biodiesel, as well as the inhibition of the spray axis-switching during the injection, leading to an increase in the spray tip penetration and a decrease in the spray cone angle for biodiesel. • Higher discharge coefficient for biodiesel in triangular orifice. • Biodiesel utilization mitigates cavitation initiation. • Biodiesel curbed the occurrence of spray axis-switching phenomenon. • Biodiesel showed prolonged spray penetration and reduced angle in all planes. [ABSTRACT FROM AUTHOR]

Abstract The present research work presented an experimental comparison of the fuel-air mixing quality and macro spray behaviors for the equilateral triangular and circular sprays between diesel and biodiesel, through Mie-scattering method based on a laser beam system, at different high injection pressures (120 MPa, 140 MPa, 160 MPa) and backpressures (1 MPa, 3 MPa). The results indicated that the biodiesel spray had longer spray tip penetration than the diesel spray, and also the spray tip penetration of the circular one was consistently longer than that of the equilateral triangular spray for both fuels and injection conditions. The spray tip velocity of biodiesel was higher than that of the diesel fuel, and the spray tip velocity decreases with increasing backpressure. The biodiesel spray cone angles were always smaller than the diesel spray in both major and minor planes. The spray cone angle of the circular orifice was consistently smaller than that of the equilateral triangular spray. Besides, the equilateral triangular spray discharging axis-switching phenomenon for both fuels even under the high injection pressure conditions. The increase of backpressure will decrease the number of interactions of spray cone angles in major and minor planes, while the increase of injection pressure will increase the number of interactions. Moreover, the spray axis-switching occurred earlier at the higher injection pressure, which illustrated the increase of the injection pressure was helpful to increase the equilateral triangular spray instability and deformation. The biodiesel spray was more difficult to undergo the spray axis-switching as compared to the diesel spray. Furthermore, the biodiesel spray projection area was smaller than the diesel spray in all view planes. The spray projection area of equilateral triangular spray was higher than that of the circular spray for both fuels. Meanwhile, the diesel spray had more mass of the entrained air than the biodiesel spray. The mass of the entrained air of equilateral triangular spray was higher than that of the circular spray. The combination of high injection pressure and using an equilateral triangular nozzle can mitigate the poor spray quality of biodiesel significantly. [ABSTRACT FROM AUTHOR]

The nozzle orifice geometry has great impact on the internal flow and spray characteristics, and thus affects the fuel-air mixture quality for diesel engines. This paper presents experimental and numerical research on the internal flow and spray behaviors with biodiesel for elliptical orifice with large aspect ratio and circular orifice of diesel nozzles, under high injection pressure and backpressure conditions. Large Eddy Simulation (LES) and Schnerr and Sauer cavitation model were adopted to study the internal flow, and the numerical models were validated firstly in terms of the mass flow rate, center line pressure and cavitation morphology. The elliptical spray images at the minor and major planes were acquired simultaneously with two CCD cameras through shadowgraph method. The results showed that the discharge coefficient of elliptical orifice was higher than that of circular orifice, which indicated that the elliptical orifice has better flow performance as compared to circular orifice. In addition, the vapor volume fraction at the circular orifice exit was larger than that of elliptical orifice, while the vorticity magnitudes were consistent lower than that of elliptical nozzle at the same injection pressure. And also, the elliptical orifice has more turbulence vortex structures near the nozzle exit than that of circular orifice, and the number of turbulence vortex structures increased as the injection pressure increases. Moreover, the cavitation distribution in the elliptical orifice in the direction of major axis shows longer length than that in the minor axis direction. The cavitation morphology at the elliptical orifice exit showed a unique horseshoe shape, while the cavitation morphology for circular orifice was still distributed symmetrically. Another important point is that the cavitation domain was similar with distribution of the turbulence vortex structures. Furthermore, the variation trend of elliptic spray cone angle proved that the elliptical spray underwent axis-switching even under high injection pressure and backpressure. Finally, the circular orifice spray held longer spray tip penetration in comparison to elliptical spray, while the elliptical exhibited much larger spray cone angle in all view planes. Because the elliptical spray underwent greater air dynamic drag induced by larger spray surface area. And the higher vorticity magnitude and more turbulence vortex structures at the elliptical orifice exit could also promote the initial spray breakup and thus inhibit the development of spray tip penetration. The axis-switching of elliptical spray can also increase the air entrainment ratio, which was conductive to increase the spray cone angle. [ABSTRACT FROM AUTHOR]

The triangular spray has a potential to accelerate air-fuel mixing rate and undergo axis-switching during the injection process, which both are beneficial for improving the atomization quality. This paper presents an experimental investigation on the macro-spray characteristics and the mechanism of axis-switching with diesel and biodiesel emerging from equilateral triangular orifice of diesel nozzle, by using shadowgraph technique, under various injection pressures (50 MPa, 70 MPa, 90 MPa) and backpressures (1 MPa, 2 MPa, 3 MPa). Two CCD cameras were set to capture the macro spray images at the minor and major view planes simultaneously. Macro spray characteristics values were processed from the spray images in different view planes by MATLAB. The results indicated that the spray width of biodiesel was larger than that of diesel at all conditions from all view planes. In addition, both diesel and biodiesel emerging from equilateral triangular orifice underwent axis-switching during the spray progress even under the typical diesel engine operation conditions. Moreover, the difference of equilateral triangular spray widths between minor plane and major plane decreases as the backpressure increases for both fuels, it is expected that the increasing of backpressure enhances the aerodynamic effects, resulting in inhibiting the spray axis-switching. Furthermore, the difference of diesel spray widths between the major plane and minor plane was much higher than that of biodiesel. Because the higher surface tension and viscosity of biodiesel can cause smaller surface-instabilities and also resist the spray deformation, which are conductive to suppress the biodiesel spray axis-switching, and thus ultimately lead to narrowing the difference of biodiesel spray widths between minor plane and major plane. Finally, the spray tip penetration of biodiesel was consistent longer than that of diesel, while the spray cone angle of biodiesel was smaller than that of diesel, and also there was an interaction between major and minor view planes for diesel spray cone angle values at the backpressure of 1 MPa, but it didn’t happen for biodiesel during the whole injection process. The present results indicated that the diesel spray was much easier to undergo axis-switching. The higher probability of axis-switching, larger spray cone angle and spray width of diesel demonstrated better air-fuel mixing quality than biodiesel. [ABSTRACT FROM AUTHOR]

The elliptical orifice diesel nozzle has potential beneficial for improving spray and air-fuel mixing quality, which has great impact on combustion and emission performances for diesel engine. This paper presents experimental studies on the macro spray characteristics and the mechanism of axis-switching for elliptical and circular orifice diesel nozzles with same cross section area, with biodiesel fuel by using shadowgraph technique, under various injection pressures (50 MPa, 70 MPa, 90 MPa) and backpressures (1MPa, 2 MPa, 3 MPa). Two CCD cameras were adopted to acquire the macro spray images at the minor and major view planes simultaneously. Macroscopic spray characteristics from different view planes of spray were processed by MATLAB. The results indicated that the spray width of the elliptical spray was greater than that of the circular spray in all the view planes. Elliptical orifice spray exhibited axis-switching phenomenon during the injection process even at high injection pressure and backpressure. The increasing of backpressure enhances the aerodynamic effects, resulting in suppressing axis-switching of elliptical spray. However, increasing the injection pressure is beneficial for improving the axis-switching frequency, because the higher spray inertia resulting from higher injection pressure can cause greater spray surface-instabilities, which are conductive to enhance the axis-switching. Moreover, the spray width at the downstream increases as the backpressure increases, and for all geometrical orifices exhibited greater spray width under the higher injection pressure. In addition, the spray tip penetration of circular orifice was longer than that of elliptical orifice during the whole injection process. This is due to the larger spray surface of elliptical spray resulting in larger aerodynamic drag. Furthermore, the spray cone angle of the circular orifice is consistently smaller than that of elliptical orifice under typical diesel engine conditions. Because the axis-switching phenomenon of elliptical spray is helpful to improve the air entrainment ratio and thus resulting in larger spray cone angle. Finally, the present experiment results indicate that elliptical sprays are conductive to increase air entrainment ratio and air–fuel mixing quality as compared to circular sprays, due to the axis-switching phenomenon, larger spray cone angle and width. [ABSTRACT FROM AUTHOR]

• The cavitation intensity and vorticity magnitude of ethanol is smaller than gasoline. • The swallowtail-like spray structure only appeared in the major view plane for gasoline spray. • Using ethanol can inhibit the formation of swallowtail-like spray structure. • The gasoline spray tip branching angle increased with the increase of back pressure. Alternative fuels have significant effects on the nozzle inner flow and spray behaviors. The present research works focus on the gasoline and ethanol impact the inner flow and spray behaviors with elliptical GDI injector. The inner flow patterns were performed with numerical modeling method, while the spray characteristics were measured by high-speed shadowgraph technique. Results indicated that the cavitation intensity of ethanol is smaller than that of gasoline, while the mass flow rate of ethanol is higher than gasoline. Also, the gasoline is giving more turbulence vortex structures in the minor axis direction of elliptical GDI injector and higher vorticity magnitude at nozzle exit compared to ethanol. The nozzle exit velocity for gasoline is consistent higher than ethanol. Additionally, the unique swallowtail-like spray structure discharging from elliptical GDI injector for gasoline only appeared in the major view plane. However, this unique spray structure did not appear in the spray tip with ethanol. Finally, gasoline spray tip penetration and spray cone angle are larger than that of ethanol spray, and the spray tip branching angle increased with the increase of back pressure for gasoline spray. [ABSTRACT FROM AUTHOR]

The application of non-circular elliptical orifice is recognized to increase the fuel spray and mixing quality, which has potential ability for modern gasoline direct injection (GDI) engines. In this research work, a single-hole elliptical GDI injector with aspect ratio of 4 was adopted. Numerical simulation and experimental spray test are both introduced to study the inner flow patterns and spray characteristics. The results indicated that the cavitation is mainly distributed on the minor axial plane of the elliptical GDI injector, and the cavitation domain decreases gradually with the increase of back pressure. Additionally, the unique swallowtail-like spray structure discharging from the elliptical GDI injector with aspect ratio of 4 was captured for the first time, and the swallowtail-like spray structure only appeared on the major view plane of the elliptic spray. Moreover, the GDI elliptical spray tip branching length reduced with the increase of the back pressure, and the high back pressure can inhibit the formation of swallowtail-like spray structure. Finally, the branching angle at the spray tip increased with the increase of back pressure, because high back pressure will enhance the effect of high aerodynamic force. • The swallowtail-like spray structure was captured in the major view plane. • The spray tip branching length reduced with the increase of the back pressure. • High back pressure can inhibit the formation of swallowtail-like spray structure. • The spray tip branching Angle increased with the increase of back pressure. [ABSTRACT FROM AUTHOR]