Ultra-high Injection Pressure Research Articles

Large-Eddy Simulation Study of Ultra-High Fuel Injection Pressure on Gasoline Sprays

The development of gasoline spray at ultra-high injection pressures was analyzed using Large-Eddy simulation (LES). Two different nozzle hole geometries, divergent and convergent shape, were considered to inject the fuel at injection pressures ranging from 200 to 1500 bar inside a constant volume spray chamber maintained at atmospheric conditions. The discrete droplet phase was treated using a Lagrangian formulation together with the standard spray sub-models. The numerical results were calibrated by reproducing experimentally observed liquid penetration length and efforts were made to understand the influence of ultra-high injection pressures on the spray development. The calibrated model was then used to investigate the impact of ultra-high injection pressures on mean droplet size and droplet size distribution. In addition, the spray-induced large-scale eddies and entrainment rate were evaluated at different ultra-high injection pressures. Overall, simulation results showed a good agreement with available measurement data. At ultra-high injection pressures mean droplet sizes were significantly reduced and comprised very high velocities. Integral length scales of spray-induced turbulence and air entrainment rate into the spray were larger at higher injection pressure compared to lower ones.Graphic abstract

Diesel spray and combustion of multi-hole injectors with micro-hole under ultra-high injection pressure – Non-evaporating spray characteristics

Increasing the injection pressure and reducing the nozzle hole diameters can increase the thermal efficiency of diesel engines (DI). To understand the spray characteristics under ultra-high injection pressure, the spray characteristics of multi-hole injectors with different diameters were investigated under different injection pressures. The results show that the injector with a larger hole diameter has a larger injection delay and a longer injection rate rise and fall time. The injection pressure has a small effect on the injection delay. As the injection pressure increases, the injection rate rise and fall time decreases. Increasing the injection pressure and the hole diameter increases the instability of the spray. The penetration of the injectors with different hole diameters is similar in the initial stage of injection. The penetration increased with the increase of the injection pressure. However, the effect of the high injection pressure on the increase of the penetration becomes weak. The injectors with a larger nozzle hole diameter displayed a larger penetration, spray angle, spray cone angle, and spray area. The micro-hole injector under the ultra-high injection pressure, the expansion of the middle of the spray caused a larger spray angle and spray area. A larger nozzle hole diameter and injection pressure promotes an increase in the gas mass rate. But the injector with the micro-hole diameter has a better ṀA/ṀF ratio and a lower average spray equivalent ratio under ultra-high injection pressure. Naber and Siebers’ penetration model and Inagaki and Mizuta's spray angle model with modified parameters showed the better prediction effect under all experimental conditions.

Numerical study on turbulent dispersion of diesel sprays under ultrahigh injection pressure using large eddy simulation

ABSTRACT The modern diesel engines equipped with an advanced fuel injection system up to ultrahigh injection pressure of 300 MPa are under development at present. The impact of injection pressure on fuel spray characteristics such as spray penetration and spray cone angle has been widely concerned in previous studies. However, it is still lack of the detailed investigation on the turbulent dispersion of small droplets produced by a high-pressure injector due to the limited capability of optical diagnostic techniques to simultaneously measure the two phases. Droplet dispersion due to turbulence plays a major role in high-velocity fuel spray mixing and combustion processes involving group evaporation of droplets. Thus, the effect of different injection pressures on droplet dispersion in nonevaporating diesel sprays was investigated using the Euler-Lagrange framework with large eddy simulation (LES) implemented in an open-source code OpenFOAM. Size-dependent instantaneous radial motion and dispersion characteristics of droplets dominated by large-scale turbulent structures within a polydisperse downstream spray were analyzed in detail. Results show that increasing injection pressure can modestly promote the radial dispersion of most droplets with diameter of 2 ~ 12 µm further downstream at the late stage of injection. This could be the result of the increasing interaction time of droplets with larger turbulent structures due to the increase of spray penetration with increasing injection pressure. However, increasing injection pressure has no significant impact on the strength of droplet-turbulence interaction in terms of slip velocity between droplet and gas phases and this could be quantitatively explained by the droplet Stokes number (St) estimated in this study. The most droplets with 0.1 < St < 10 tend to move and concentrate further radially outward, leading to droplet clustering. Thus, the effect of injection pressure on droplet-turbulence interaction is much less than its influence on droplet size for high-velocity fuel sprays, indicating that the ultrahigh injection pressure has much less important impact on the spatial inhomogeneity of droplet distribution than its influence on the evaporation rate of individual droplets.

Air Motion Induced by Ultra-High Injection Pressure Sprays for Gasoline Direct Injection Engines

The fuel injection pressures used in gasoline direct injection (GDI) engines have increased in recent years to improve fuel efficiency and reduce emissions. Current GDI engines use injection pressures of up to 350 bar, and there is evidence that even higher fuel injection pressures could yield further improvements in atomization. Higher injection pressures could also improve mixture formation by increasing the spray velocity; however, the research with higher injection pressures over 1000 bar is limited due to a limit of mechanical components. This manuscript summarizes experimental investigations into the effect of injection pressure, injection mass, and nozzle shape on spray-induced air motion with ultrahigh injection pressure over 1000 bar. Fuel sprays were generated at a range of injection pressures with different injection masses and nozzle geometries, and Particle Image Velocimetry (PIV) was performed using a Charge-coupled device (CCD) camera and an Nd:YAG (neodymium-doped yttrium aluminium garnet) laser to characterize the vector fields in the surrounding air and the rate of air entrainment into the sprays. Sprays generated with higher injection pressures and injection masses induced stronger large-scale air motion: an injection pressure of 1500 bar with an injection mass of only 5 mg caused almost the same amount of air entrainment as an injection pressure of 200 bar with an injection mass of 27 mg. However, the spray-induced air motion dissipated within 5 ms after the end of injection (EOI) in all cases. The air entrainment rate was also increased by using a divergent nozzle rather than a convergent one. Interactions between the spray and the surrounding air are thus strengthened by using a high injection pressure and a divergent nozzle.

Combustion Characteristic of Offset Orifice Nozzle under Multi Pulse Ultrahigh Pressure Injection and PCCI Combustion Conditions

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;CI engines provide higher thermal efficiency compared to other internal combustion engines. On the other hand large amounts of smoke and NO&lt;sub&gt;x&lt;/sub&gt; are produced during combustion. Smoke and NO&lt;sub&gt;x&lt;/sub&gt; can be reduced by applying Premixed Charge Compression Ignition (PCCI) combustion. Unfortunately, the problems of PCCI combustion include unstable start of combustion and limited operating range. The multi-pulse ultrahigh pressure injection allows fuel to control PCCI combustion. The objective of offset orifice nozzle is to improve mixture formation and shorten spray penetration in order to increase thermal efficiency and control PCCI combustion. The offset orifice nozzle was designed by shift orifice aliment from into the sac center to edge of sac follow swirl direction. Counter bore design was applied to offset orifice nozzle in order to keep the constant orifice length as standard nozzle. This paper investigates the effect of nozzle orifice design on combustion characteristics under multi pulse ultra high pressure injection and PCCI combustion conditions. The experiments were carried out on a single cylinder engine at 0.55 MPa gross IMEP at 1,750 rpm. The injection pulses were 3 pulses equally mass main injection at 150, 200, 250, 300 and 350 MPa injection pressure. In case of standard nozzle orifice, 1&lt;sup&gt;st&lt;/sup&gt;, 2&lt;sup&gt;nd&lt;/sup&gt; pulse are PCCI followed by diffusive combustion in every injection pressure. For offset orifice nozzle orifice at 150 and 200 MPa 1&lt;sup&gt;st&lt;/sup&gt;, 2&lt;sup&gt;nd&lt;/sup&gt; pulse are also PCCI combustion. However when injection pressure is over 200 MPa, the 2nd pulse of rate of heat release become diffusive combustion. The offset orifice nozzle resulted in increased thermal efficiency, NO&lt;sub&gt;x&lt;/sub&gt; and smoke. However significant differences between the smoke of offset orifice nozzle and standard nozzle were not found under injection pressure 300 and 350 MPa. The offset orifice nozzle also resulted in decrease CO and THC.&lt;/div&gt;&lt;/div&gt;

The Development Characteristics of Diesel Spray and Flame with Ultra-high Pressure Injection

The Development Characteristics of Diesel Spray and Flame with Ultra-high Pressure Injection

Investigation on Effect of Offset Orifice Nozzle under Multi Pulse UltrahighPressure Injection and PPC Combustion Conditions

Investigation on Effect of Offset Orifice Nozzle under Multi Pulse UltrahighPressure Injection and PPC Combustion Conditions

Particulate and gaseous emissions from a direct-injection spark ignition engine fueled with bioethanol and gasoline blends at ultra-high injection pressure

In this study, the effects of bioethanol mixing with gasoline on the emission of particulates and gaseous emissions at ultra-high pressure injection up to 50 MPa were investigated in a gasoline direct-injection (GDI) engine. A 398 cc single-cylinder engine fueled with bioethanol blends was used for the experiment. The gaseous emission was measured by an emission bench, and particle number (PN) was counted by a PPS-M device. Experiments were carried out under the conditions of maximum injection pressure of 50 MPa and constant intake flow rate with various injection conditions. Gasoline and bioethanol-blended fuel was used, with the blending ratio varied from 10% to 50% by volume. The results indicated that, as the injection pressure and bioethanol content increased, the PN decreased by 93.6% and 78.9%, respectively. PN emission is proportional to bioethanol contents in case of PN emitted from wall film. Effect of bioethanol addition with ultra-high pressure injection over 35 MPa is not significant on PN, since atomization enhancement due to the increased injection pressure is saturated. Total hydrocarbon and nitrogen oxide emissions decreased up to 34.5% and 35.6% with increasing oxygenated fuel, bioethanol, contents at ultra-high pressure injection over 35 MPa and were remarkably influenced by injection timing.

Investigation on an Injection Strategy Optimization for Diesel Engines Using a One-Dimensional Spray Model

Common rail systems have been widely used in diesel engines due to the stricter emission regulations. The advances in injector technology and ultrahigh injection pressure greatly promote the development of multiple-injection strategy, leading to the shorter injection duration and more variable injection rate shape, which makes the mixing process more significant for the formation of pollutant emission. In order to study the mixing process of diesel sprays under variable injection rate shapes and find the optimized injection strategy, a one-dimensional spray model was modified in this paper. The model was validated by the measured spray penetrations based on shadowgraphy experiments with the varying injection rate. The simulations were performed with five injection rate shapes, triangle, ramping-up, ramping-down, rectangle and trapezoid. Their spray penetrations, entrainment rates and equivalence ratios along spray axial distance are compared. The potentials of multiple-injection and gas-jet after end-of-injection (EOI) to improve mixing process and emission reduction are discussed finally. The results indicated that ramping-up injection rate obtains the highest entrainment rate after EOI, and it needs 1.5 times of injection duration for the entrainment wave to arrive at the spray tip. For the other four injection rates, the sprays can be treated as a steady-like state, needing twice of injection duration from EOI to the time the entrainment wave reaches the spray tip. The multiple-injection with proper injection rate shape enhanced the entrainment rate, and the gas-jet after EOI affected the mixture distribution and entrainment rate in spray tail under ramping-down injection rate.

Effects of hydrogen addition on the combustion characteristics of diesel fuel jets under ultra-high injection pressures

Many applications use hydrogen addition and high-pressure fuel injection technology to improve combustion performance. In this study, spray atomization and combustion characteristics of a diesel fuel jet, under the injection pressure of 350 MPa, injecting into a constant volume combustion vessel filled with air-hydrogen mixture at the diesel engine relevant condition are investigated by simulation method. A simplified mechanism of the n-heptane (C7H16) oxidation chemistry mechanism consisting of 26 reactions and 25 species integrated with the Kéromnès-2013 hydrogen combustion mechanism and EDC combustion model are utilized to predict the diesel fuel spray auto-ignition and combustion. The ambient gas is the mixture of air and hydrogen range in volume fraction from 0% to 10%. The ambient temperature and pressure is set to 1000 K and 3.5 MPa, respectively. The results indicate that as the hydrogen volume fraction is 2%, the minimum overall droplet SMD (Sauter Mean Diameter) is approximately 0.95 μm, which is obviously smaller than that of the case with the conventional high injection pressure. In cases that H2 v/v% larger than 4%, the maximum gaseous temperature increased significantly up to 2700 K. There are two peaks in the temperature growth rate curves as the hydrogen fraction of 8% and 10%. The high temperature at the outer edge of the spray is clearly seen due to its high value when the hydrogen fraction is larger than 4%. The hot reaction layer is the main location of CO formation. The H, OH radicals are formed at the edge of the spray where the temperature is high. The hydrogen species obviously promotes the oxidation and combustion of diesel fuel.

Experimental study on effects of ethanol-diesel fuel blended on spray characteristics under ultra-high injection pressure up to 350 MPa

In the present study, the atomization characteristics of ethanol-diesel blends fuel spray and shock waves were investigated by using experimental methods under ultra-high injection pressure in the range 200Mpa–350 MPa. A high-speed camera and Schlieren technology were used to visualize the fuel spray morphology and shock waves. The spray tip penetration, velocity and shock wave angle were determined via experimental approaches. Furthermore, the special spray shape under ultra-high injection pressure, such as liquid tail, expanded body and bifurcated structures, was analyzed. To validate the classical spray empirical models, predicted spray penetration results based on two typical models (Dent's and Hiroyasu's model) were compared with experimental data. The results indicated that fuel injection pressure and ethanol volume fraction presented significant effects on the spray evolution. With increasing injection pressure, the spray tip penetration became faster and the induced attached shock waves reveal clearer. The fuel spray jets achieved the larger penetration velocity and more induced shock waves under higher injection pressure or lower ethanol volume fraction.

Comparison of Ultra-High Rail Pressures and Postinjections for Soot Reduction With Massive Exhaust Gas Recirculation

In this study, the application of ultra-high fuel injection pressure (up to 300 MPa) is compared with that of a post injection strategy for the reduction of soot at medium load conditions with exhaust gas recirculation (EGR) rates greater than 40%. Emissions were predominantly studied at the engine's maximum brake torque speed of 1600 rpm. A 4.5-L, four-cylinder diesel engine with series turbochargers and a high-pressure EGR loop was used for all tests. Results indicate that, ultra-high injection pressures may not have large effects on hydrocarbons (HC) or CO emissions. Small soot reductions were achieved at the expense of increased NOx emissions. Post injections resulted in larger soot reductions for a small increase in NOx while allowing lower fuel pressures to be utilized. The increase in NOx emissions with a post injection was observed to be comparatively less at increased engine speeds. For operation at high EGR, post injections were observed to be more effective at reducing soot than ultra-high injection pressures. Both injection pressure and post injections were observed to have small to negligible effects on engine fuel consumption, leaving EGR and injection timing as the primary efficiency drivers at the conditions studied.

Hydraulic analysis of a GDI injector operation with close multi-injection strategies

The increase of injection pressure in GDI engines represents a proven development trend in the effort of limiting raw particulate emission, which is one of the most severe concerns for this kind of combustion system. Since increasing injection pressure level tends to cause significant issues in terms of spray penetration control, in parallel with ultra-high injection pressure multi-event strategies are being considered to improve the air-fuel mixture formation management. The adoption of these advanced injection strategies can potentially affect the injection system hydraulic behavior, hence an adequate control of each event fuel quantity is mandatory for a proper engine optimization.When the injector is operated according to a multi-event strategy, complex hydraulic and electro-magnetic phenomena may occur. Pressure waves triggered by each injection can eventually influence the subsequent events, modifying the injected volume compared to the expected, isolated event value. This hydraulic phenomenon is well-known for Diesel applications and is investigated in the present paper in a typical GDI configuration evidencing the effect of the dwell time value between consecutive events both in terms of injected volume and injection rate profile using a proprietary injection analyzer. Further, when consecutive injections are remarkably close, the succeeding injection event is likely to be influenced by a different, electro-magnetic phenomenon in addition to pressure waves propagation in the system pipes. With reduced dwell time strategies, the current profile driving the injector can be modified by a previous close-coupled actuation due to residual magnetization in the solenoid circuit. This phenomenon determines for the succeeding injection event a steeper transient of the solenoidal current, causing a faster injector needle rise and correspondingly a significantly increased injected quantity.In this paper, an innovative methodology is proposed to investigate in multi-injection strategies the effects of close injector actuations, evidencing the influence of hydraulic phenomena and of current profile modifications, respectively. The developed approach, named ETboost, consists in a double injection with a first dummy command. To this end, a short ETboost command is required not causing the injector needle opening and thus no triggering pressure waves that might influence the second injection. Using this analysis approach, the residual magnetization effects on a production GDI injector were experimentally investigated in terms of mean injected volume and instantaneous flow rate. The results obtained with reduced dwell-time were compared with the standard operation mode (single injection), evidencing a significant increment of the injected volume in particular in the ballistic operation where the actual injected quantity can be more than doubled if compared to standard actuation. The dependence of the injected volume on ETboost and dwell time was explored for different operating conditions, evidencing how reducing the dwell time and increasing the ETboost duration the injected volume is enlarged and the shot-to-shot dispersion is significantly reduced.

Dynamic spray development of 2-methylfuran compared to ethanol and isooctane under ultra-high injection pressure

Understanding spray behaviors is key for the successful employment of high injection pressure systems and biofuels such as 2-methylfuran (MF) and ethanol (ETH) in modern direct-injection gasoline engines. In this present work, the MF spray characteristics in the near-field (up to 1.6 mm) and far-field (up to 48 mm) were experimentally investigated under ultra-high injection pressure of 30, 40 and 50 MPa compared to those of ETH and isooctane (ISO). The effects of injection pressure and fuel properties on the spray morphology, tip penetration and cone angle development have been analyzed. The results showed that MF had a unique spray tip structure with a bubble attached to a mushroom tip at 30 and 40 MPa. The formation of this mushroom tip and bubble was closely related and strongly influenced by the Weber number. Among the three fuels tested, MF presented the lowest spray tip velocity at both near-field and far-field due to its large density. Compared to ETH, MF and ISO always had wider macro cone angles due to their lower viscosity.

Effect of ultra-high injection pressure up to 50 MPa on macroscopic spray characteristics of a multi-hole gasoline direct injection injector fueled with ethanol

This research systematically studied the effect of injection pressure on macroscopic spray characteristics of a five-hole gasoline direct injection (GDI) injector fueled with ethanol, especially under ultra-high injection pressure up to 50 MPa. The front and side views of sprays were photographed by the schlieren method using a high-speed camera. Various parameters, including spray development stages, cone angle, penetration, area and irregular ratio, were fully analyzed to evaluate macroscopic characteristics of the whole spray and spray core with varying injection pressure. The results demonstrated that the effect of ultra-high injection pressure on macroscopic spray characteristics was significant. As injection pressure increased from 10 MPa to 50 MPa, the occurrence time of branch-like structure decreased; the cone angle increased little; the area increased significantly; the area ratio dropped by 6.4 and 5.8 percentage points on average for the front view and side view spray, respectively. There was a significant increase in the trend for penetration as the injection pressure rose from 10 MPa to 30 MPa. However, this trend became weak when the injection pressure further increased. The penetration ratio under ultra-high injection pressure was slightly higher than it was under 10 or 20 MPa. Ultra-high injection pressure would not obviously raise the possibility of spray/wall impingement, but led to the impingement quantity increasing to some extent. Increasing injection pressure could enhance the vortex scale, finally resulting in better air/fuel mixing quality. Ultra-high injection pressure was a potential way to improve air/fuel mixture homogeneity for a GDI injector fueled with ethanol.

Particle and Gas Flow Modeling of Wall-impinging Diesel Spray under Ultra-high Fuel Injection Pressures

Advanced models of spray breakup and droplet collision are implemented in OpenFOAM code for comparing the flat-wall impinging and free fuel sprays under ultra-high pressure direct injection diesel engines. The non-evaporating spray and ambient gas flow characteristics are analyzed by a combination of Eulerian and Lagrangian methods for continuous and dispersed phase, respectively. Various injection pressures and two different impinging distances are used. Reynolds Averaged Navier Stokes (RANS) equations are solved using standard k-ε turbulence model. Computational domain and grid size are determined based on a mesh study. Numerical results are validated by published experimental data for free and wall-impinging sprays. The robustness and accuracy of the proposed scheme are confirmed by comparing the main characteristics of spray and surrounding gas against published experimental data. To accomplish this, spray shape, penetration and gas velocity vectors are compared with experimental data and insightful understanding of the spray characteristics are provided. In comparison with free spray, tip penetration has been limited in impinging sprays. Turbulent flow in impinging sprays leads to more induced air motion. Also, impinging spray leads to more pushed-out gas velocity. The obtained results indicate that the numerical findings are generally in good agreement with experimental data in case of ultra-high injection pressures and micro-hole injectors.

Numerical research on micro diesel spray characteristics under ultra-high injection pressure by Large Eddy Simulation (LES)

The Large Eddy Simulation model was introduced to study the micro spray characteristics under ultra-high injection pressure (>220MPa). 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 (180MPa, 240MPa) and nozzle diameters (0.1mm, 0.16mm). 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 0.25mm 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 240MPa are more intensive than that of 180MPa, 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 0.16mm, and also the values of velocity in the spray center is higher than that of the diameter of 0.1mm; 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 (240MPa) 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.

Effects of micro-hole nozzle and ultra-high injection pressure on air entrainment, liquid penetration, flame lift-off and soot formation of diesel spray flame

Increasing the injection pressure and downsizing the nozzle orifice diameter have been major measures for diesel engines to facilitate fuel–ambient gas mixture formation and combustion processes. The objective of this investigation is to carry out a quantitative analysis on the effects of micro-hole nozzle and ultra-high injection pressure on the mixing and combustion characteristics of diesel spray flame. Hence, laser-induced fluorescence and particle image velocimetry technique was employed to quantitatively access the gas entrainment of diesel spray emerging from nozzle with orifice diameter down to 80 µm under injection pressure up to 300 MPa, together with OH* chemiluminescence imaging and two-color pyrometry techniques to resolve the combustion and soot formation processes. Additionally, numerical simulation on the multi-phase flow inside injector nozzle was conducted to obtain information on internal flow dynamics. Experimental results show that over 80% of the ambient gas entrained into a spray pl...

Applying Different Strategies within OpenFOAM to Investigate the Effects of Breakup and Collision Model on the Spray and in-Cylinder Gas Mixture Attribute

In the current study, a 3-D numerical simulation of two-phase flow has been conducted in a direct injection CI engine using the Eularian-Lagrangian approach and a new breakup model. The newly modified breakup scheme has been implemented for simulating the ultra-high pressure diesel injection. The effects of droplet breakup and collision model on the spray and in-cylinder gas characteristics have been examined using the open source code OpenFOAM. Spray penetration and cone angle are investigated as spray properties and surrounding gas motion are studied by in-cylinder gas velocity and pressure distribution for non-evaporating conditions. In addition, vapor penetration of the evaporating spray is presented to study the effects of current scheme on the evaporating condition. The continuous field is described by RANS equations and dynamics of the dispersed droplet is modeled by Lagrangian tracking scheme. Results of the proposed modified KHRT model are compared against other default methods in OpenFOAM and favorable agreement is achieved. Robustness and accuracy of different breakup schemes and collision models are also verified using the published experimental data. It is demonstrated that the proposed breakup scheme and Nordin collision model display very accurate results in the case of ultra-high pressure injection.

Experimental study on spray characteristics under ultra-high injection pressure for DISI engines

In order to provide comprehensive information on gasoline spray characteristics under ultra-high fuel injection pressure for direct-injection spark-ignition engines, the macroscopic characteristics of gasoline sprays for both liquid and vapor phases, including overall spray structures, spray tip penetrations, and spray angles, were determined simultaneously via Laser Absorption-Scattering technique under non-vaporizing and vaporizing conditions. Empirical correlations of spray tip penetration for transient gasoline sprays were obtained and compared with those for diesel sprays. Experimental results showed that under non-vaporizing conditions, spray tip penetration was approximately proportional to time. Under vaporizing conditions, the spray plumes were compressed axially and expanded radially; fuel vapor was concentrated in the spray head, while fuel droplets in the tail. Vapor phase spray tip penetration shared similar values and temporal variations with liquid phase but with a subtle and regular difference. In contrast with diesel sprays, gasoline spray penetration of liquid phase showed larger dependence on ambient gas density and smaller dependence on fuel pressure drop through injector. Compared with liquid phase, vapor phase penetration showed a larger growth rate with time and presented a smaller falling slope against ambient gas temperature.