Multi-hole Gasoline Direct Injection Research Articles

Near-field plume-to-plume interaction of multi-hole GDI injector under elevated ambient density conditions

Spray collapse can occur in the multi-hole injector under elevated ambient density conditions due to the plume-to-plume interaction. Numerous studies have investigated spray collapse in high ambient density conditions, but limited literature is available regarding the near-field plume-to-plume interaction triggering the spray collapse due to the optical density of the spray in the near field. In this study, an X-ray phase-contrast imaging (XPCI) technique that can visualize the spray structure and dynamics in the near field is applied to resolve the optical difficulties. With this method, the plume-to-plume interaction of a multi-hole gasoline direct injection injector is analyzed by measuring the transverse spray droplet size and axial velocity distributions under various ambient densities and injection pressures. The results showed that in the high ambient density condition with the low injection pressure, the spray droplet size started to increase, and the axial velocity remained stagnant from around 3 mm axial location as a result of plume-to-plume interaction and following spray collapse. The region of large droplets appeared asymmetric based on the hole arrangement. As the injection pressure increased in the high ambient density condition, the plume-to-plume interaction was suppressed in the near field and the spray collapse appeared farther downstream. Through the results, the spray collapse phenomenon and associated mechanism in the near field were discussed considering the droplet collision/coalescence and pressure structure in the spray.

Simulations of ammonia spray evaporation, cooling, mixture formation and combustion in a direct injection compression ignition engine

This study investigates the novel approach of direct liquid ammonia injection into the combustion chamber of a compression ignition engine. Unlike traditional gaseous ammonia port injection, this method shows promise in reducing ammonia slip and emissions. To simulate and analyze the behavior of the liquid ammonia spray, we employed numerical models based on existing literature on flashing and non-flashing spray simulations, as well as recent experimental studies on ammonia spray characteristics using a gasoline direct injection (GDI) injector. Our approach utilized a Lagrangian discrete phase modelling technique to perform a series of three-dimensional computational fluid dynamics (CFD) simulations. The primary objectives of this research were to evaluate the evaporation process of ammonia and its cooling effect, as well as to gain insights into mixture formation within the engine cylinder under different operating conditions. The simulations encompassed the entire engine cycle, considering a multi-hole GDI ammonia spray in conjunction with pilot n-heptane, a diesel surrogate, in equal proportions on an energy basis. Three distinct injection timings for ammonia were examined, leading to varying thermodynamic conditions within the combustion chamber during each spray formation. Consequently, different modelling parameters and initial conditions were necessary to accurately replicate the spray behavior. To address this, we proposed a systematic procedure for assigning pre-defined spray angles. The non-reacting, evaporating spray simulations yielded valuable insights into the mixture formation process, which guided our analysis. Finally, reacting conditions were considered to evaluate engine performance and resulting exhaust gas emissions. This study provides a comprehensive overview of critical aspects related to direct ammonia injection in internal combustion engine (ICE) systems. Moreover, it uncovers performance trends that can serve as a foundation for future investigations in this field.

Effects of in-nozzle flow and low-pressure zone on spray targeting of multi-hole gasoline direct injection injector

The purpose of this study is to reveal the effect of In-nozzle flow and low-pressure zone near the nozzle exit on the spray targeting of a multi-hole gasoline direct injection injector using a numerical simulation. The change in spray targeting owing to in-nozzle flow and the distribution of the liquid phase at the hole exit were analyzed through a multi-phase flow simulation. A volume of fluid (VOF) model was used to effectively distinguish between the liquid flow and cavitation region. Results of the numerical simulation at the internal and near-field show that cavitation occurred at a sharp corner with a high flow velocity. Moreover, the low liquid rebounded at the hole wall, and the flow was bent in the direction of cavitation. The results of the spray simulation indicated that an increase in the injection pressure reduced the minimum pressure in the low-pressure zone. By contrast, the increase in ambient pressure not only decreased the pressure in the low-pressure zone, but also caused the low-pressure zone to form closer to the hole exit. In most cases, the low-pressure zone had a greater effect on plume bending than on in-nozzle flow, which was further enhanced as the ambient pressure increased.

NUMERICAL STUDY OF DIRECT INJECTION SPRAY BEHAVIOR OF GASOLINE AND METHANOL-GASOLINE BLENDS UNDER SPLIT-INJECTION STRATEGY IN ENGINE-LIKE CONDITIONS

Several studies have shown that the split-injection strategy has improved the shortcomings of the high particulate matter emissions and cycle-to-cycle variations in homogeneous and stratified combustion modes of gasoline direct injection (GDI) engines. However, the spray behavior under the split injection strategy is poorly understood. This study uses computational fluid dynamics (CFD) simulations in Converge software to investigate the spray characteristics of gasoline and methanol-gasoline blends under a split-injection strategy. The simulation studies were performed for a multihole GDI injector in a constant volume spray chamber, replicating the ambient conditions similar to a GDI engine's homogeneous and stratified combustion modes. Appropriate models for simulating different spray phenomena, such as spray breakup, collision, and coalescence, were used. The CFD model was validated using the experimental spray penetration length provided in the engine combustion network database. The results showed that the split-injection reduced the Sauter mean diameter (SMD) of fuel spray droplets and liquid fuel mass content than a single injection case. The dwell time of 2 ms was found suitable for homogeneous mode conditions, while its effect was insignificant in stratified mode conditions. Further, a split ratio of 80:20 resulted in smaller SMD during the injection period and a higher fuel evaporation rate. The effect of methanol addition was also explored under the split-injection mode. M85 showed higher deviations in the liquid spray penetration, SMD, and liquid spray mass content than G100.

Spray–wall impingement in a multi-hole GDI injector for split injection at elevated wall temperature and ambient conditions

Post wall-impingement characteristics of pulsatile and split injection sprays in multi-hole Gasoline Direct Injection (GDI) are investigated. A combined experimental and numerical approach is adopted, to examine the influence of wall temperature as well as gas temperature and pressure on spray evolution. For fuel injection condition, split proportion and wall stand-off distance are not varied. The single injection case is also studied for comparison. The experiments were conducted under atmospheric conditions but for different wall temperatures, and the fuel spray was visualized using high-speed shadowgraph technique. The three-dimensional Eulerian–Lagrangian spray simulations were validated against the measured post-impingement plume width and height. Simulations were carried out to analyse spray–wall interaction process under elevated ambient temperature and pressure conditions also. Considerably smaller radial and vertical spread of the spray plume is obtained for split injection, highlighting its benefits over the single injection case. Both plume and wall film characteristics are strongly influenced by the ambient gas density and temperature rather than the wall temperature. However, time evolutions of the mass, thickness and temperature of the film are similar for both single and split cases at different operating conditions, exhibiting some interesting trends. For split injection, the vapour plumes from the two injection pulses interact. At high ambient temperatures, the peak equivalence ratio values are lower for split injection due to lower injected mass per pulse, in comparison to the single injection strategy. • GDI spray–wall interaction is investigated experimentally and computationally. • The measured post-impingement plume height/width corroborate well with the predictions. • The plume characteristics are primarily dependent on gas phase density. • The wall film thickness reduces considerably for split-injection compared to single injection. • For split-injection and elevated ambient temperature, the initial wall film vaporizes prior to 2nd injection.

Characterizing under-expansion behaviors induced by rapid phase change of flash-boiling jets

Flash-boiling sprays issued from multi-hole gasoline direct injection (GDI) injectors could collapse, which is recently proved to be caused by under-expansion, but very few experimental data are available on this sort of under-expansion. In this study, high-speed microscopic Schlieren photography was used to capture the near-field shock structures in flash-boiling n-hexane jets. The tests were carried out in a constant volume vessel with ambient pressures (Pamb) from 10 to 101 kPa, fuel temperatures (Tfuel) from 30 to 170 ℃, and injection pressures (Pinj) from 2 to 20 MPa. The shock structure was carefully analyzed in terms of shock width and length. Generally, both the shock width and length decreased with the increase in Pamb. With the increase in Tfuel, the shock length was relatively stable and the shock width overall increased, but a decreasing trend in shock width could be observed at 170 ℃, possibly caused by the near-critical behaviors. Further analysis showed that the shock width shows a strong linear correlation with Δμ·Pamb−0.5 (Δμ denoting chemical potential of phase change) for a given Pinj, and the shock length shows a strong quadratic polynomial relationship with ηinj (injection pressure ratio, defined as the ratio of Pinj to Pamb). Additionally, some new shock structures without Mach disk were observed, indicating that the phase change induced under expansion is different from the typical gaseous under-expansion.

On Modeling of Spray G ECN Using ROI-Based Eulerian-Lagrangian Simulation

A numerical study has been carried out to understand the effects of Unsteady Reynolds Averaged Navier-Stokes (standard k ― ε and RNG k ― ε model) and large eddy simulations (LES) on a multi-hole gasoline direct injection (GDI) system. The fuel injector considered in this study is the Spray G nozzle from the Engine Combustion Network (ECN). A blob injection model, based on empirical rate of injection (ROI) profile, is considered in this study. The latest data on spray penetrations from Engine Combustion Network is used for model validation along with experimental findings on suction velocity and local droplet diameter. The spray breakup is simulated by using the KH-RT breakup length model. The turbulence model constant Cε1, is tuned to match with the experimental data of liquid and vapor penetrations in simulations while using the standard k-ε turbulence model. On the other hand, the Kelvin-Helmholtz breakup model time constant (B1) and Rayleigh Taylor breakup length constant (Cbl) are tuned for the RNG k ― ε turbulence model. From this work it is observed that by increasing the breakup length model constants (Cbl), the radial dispersion of the spray increases, and the extent of breakup is lowered. The set of optimized model parameters used with RNG k - ε is also used for LES modeling studies with different sub-grid models. The spray penetrations with standard k ― ε turbulence (Cε1=1.44) model are reported underpredicting, and the RNG k ― ε and LES sub-grid models predicted well with the latest and recommended data from ECN. In terms of gas axial velocity comparison, the standard k-ε(Cε1=1.44) simulation setup does not perform as well as the simulation setups using RNG k-ε and LES turbulence models (with breakup parameters: Cbl = 16 and B1 = 32). However, the standard k-ε(Cε1=1.44) simulation setup perform better than the simulation setups using RNG k-ε and LES turbulence models (with breakup parameters: Cbl = 16 and B1 = 32) when it comes to predicting local droplet diameter at 15 mm downstream of the injector tip. A parametric study is also performed considering the geometry of the stepped holes in the computational domain. The rate of injection based simulation is initiated at the end of the smaller hole. The case including the stepped holes led to over-prediction compared to the case with the usual computational domain (i.e., without the stepped holes), in terms of spray penetrations, but exhibited higher levels of fluctuations in the spray morphology. Finally, parametric studies were carried out to understand the relative importance of the individual spray sub-models (breakup, evaporation and collision) and the results are conclusive that for a spray simulation the breakup models are the dominant factors.

Experiment methods and apparatus for finely controlled partial needle lift measurements with a gasoline direct injector

In this study, an experiment method and apparatus are developed which allow exploration of partial-lift spray in a production gasoline direct injection (GDI) injector. For this injector, discretizing the needle’s stroke into a series of steady partial-lift tests seems a viable approach for quantifying transient behavior, where spray performance is often inferior from the perspective of emissions. However, performing such tests is not trivial due to manufacturing challenges and material limitations making it difficult to isolate any particular lift at pressure. To explore the applicability of fixed partial-lift tests, the following are performed: (1) An inward-opening multi-hole GDI injector is minimally modified with an apparatus to finely control needle lift by limiting the needle’s stroke with a fine micrometer head. (2) An experiment process is developed to associate the micrometer set-point with the imposed needle lift, compensating for pressure induced component flex. This flex is significant and of a similar magnitude to the needle’s stroke. (3) In-nozzle flow is simulated using computational fluid dynamics (CFD) within the AVL FIRE software to compare a stationary and moving needle. The comparison reveals a relative insignificance of needle velocity for the majority of the needle’s stroke (>5 μm). The nozzle hole flow rates and effective exit velocities are similar, suggesting fixed partial-lift spray well approximates the normally moving needle spray. This new experiment method can be used on current injectors to quantify spray performance during needle transients by discretizing the stroke into steps as small as 2 μm, exceeding the control in any current published literature.

Spray dynamics and atomization characteristics of multi-hole GDI injectors under flash boiling conditions

• About 100 points on the 30 mm plane below the injector was measured by using PDPA. • The effect of hole angle and air entrainment on spray atomization was analyzed. • The atomization uniformity of flash boiling spray in the space was improved. In the gasoline direct injection (GDI) engine, spray atomization contributes significantly to the formation of a uniform mixture and the effective combustion of the spray. In this study, a phase Doppler particle analyzer (PDPA) was used to measure the spray atomization characteristics of two five-hole GDI injectors with different hole arrangements under subcooled and mild flash-boiling conditions (superheated degree = 20 °C). Based on the spray patterns of the two injectors on a plane 30 mm below the injector tip, the two injectors were called triangle-patterned and pentagon-patterned injectors. A total of 100 measuring points were selected on a plane 30 mm below the injector tip, and the spray droplet diameter and velocity at these points were measured to understand the overall atomization characteristics of the spray in space. The experimental results indicated that as the spray transitioned from subcooled to flash boiling conditions, a polarization phenomenon occurred in which the velocity in the center of the plume increased and the velocity in the peripheral region of the plume decreased. However, the spray droplet diameter significantly decreased under flash-boiling conditions. The average Sauter mean diameter (SMD) of the two injectors on a plane 30 mm below the injector tip decreased by approximately 4 μm, and the uniformity of the spatial distribution of the SMD also increased. Compared with the triangle-patterned injector (injector A), the average SMD of the pentagon-patterned injector (injector B) was slightly smaller; this was attributed to the stronger air entrainment inside the spray and the enhanced air flow caused by the larger plume spacing of the pentagon-patterned injector.

Investigation of the effects of cavitation on near nozzle dynamics in multi-hole gasoline direct injection sprays

Investigation of the effects of cavitation on near nozzle dynamics in multi-hole gasoline direct injection sprays

Modelling and prediction of cavitation erosion in GDi injectors operated with E100 fuel

Ethanol (E100) can be utilised in spark ignition engines for passenger car vehicles. This brings a challenge to the durability of the fuel injection system components since its use can result in corrosion, further enhanced by cavitation-induced erosion. This work reports computational fluid dynamics (CFD) predictions for both the flow development and the locations prone to cavitation erosion in multi-hole gasoline direct injection (GDi) injectors operated with E100. The compressible form of the Navier–Stokes equations is solved numerically considering the motion of the injector’s needle valve. Thermodynamic and mechanical equilibrium is assumed between the liquid, vapour and non-condensable gas; E100 liquid and vapour are considered as a barotropic fluids where the corresponding variation in density with pressure and the speed of sound are estimated via a relevant equation of state; an additional transport equation is solved for simulating the non-condensable air entrainment into the injector during the dwell time between successive injections. Turbulence is modelled using both large eddy simulation (LES) and Unsteady Reynolds-averaged Navier–Stokes (URANS) considering a sector and the full nozzle geometry, respectively. Various cavitation erosion indices reported in the literature are evaluated against new durability tests of surface erosion damage obtained after 400 M injection cycles. The relevant nozzle wall erosion images are found to correlate well with the accumulated erosive power predicted from the computational model.

Spray dynamics and evaporation in a multihole GDI injector for pulsatile and split injection at elevated ambient pressure and temperature conditions

The evolution of pulsatile and split injection spray from a multihole, Gasoline Direct Injection (GDI) atomizer at different ambient conditions is examined experimentally and computationally. The fuel is injected at 80 bar for a duration of 1.2 ms (for single injection) and also for different split proportions (ranging from 0.3 ms to 0.9 ms for the first injection and 0.9 ms to 0.3 ms for the second injection). The influence of different split proportions on the spray characteristics such as spray penetration length, cone angle and droplet size is studied in detail, and they are compared against those of single injection case to highlight the differences. Experiments were conducted in a constant volume chamber for elevated ambient pressures. The fuel spray was visualized using high-speed shadowgraph technique. Three-dimensional spray simulations were carried out using ANSYS FLUENT 16.1. The RANS-DPM coupled simulations were performed for higher ambient pressure and temperature conditions. Good agreement between the experiments and simulations is achieved with respect to spray penetration length and cone angles for both single and split injection strategies. For larger proportion of the first injection, the interaction of the second spray with the rear of the first spray was prominent at higher chamber pressure. The spray penetration length was found to reduce for split injection strategy for all ambient pressure conditions. The spatio-temporal evolution of vapour plumes in terms of equivalence ratio highlights the possibility of attaining near homogeneous, rich mixture or a stratified mixture depending on the split proportion and dwell time.

Experimental study on flash-boiling spray structure of multi-hole gasoline direct injection injector in a constant volume chamber

The macroscopic and microscopic characteristics of flash-boiling spray were experimentally investigated with various optical measurement techniques. The effects of ambient pressure and fuel temperature on flash-boiling characteristics in multi-hole gasoline direct injection injector were analyzed. The analysis was focused on the spray structure and atomization droplet size distributions. In order to increase the understanding of the flash-boiling spray targeting, three injectors with different spray patterns were investigated under strong flash-boiling condition. The results show that ambient pressure and fuel temperature have significant influence on flash boiling. Both lower ambient pressure and higher fuel temperature could accelerate the flash-boiling process. For the macroscopic characteristics, similar influences could be found with the ambient pressure decreased by 0.4 bar and the fuel temperature increased by 10°C. Further, significant difference could be found within cold-jet spray and strong flash-boiling spray, such as the spatial structure. The spray structure always turns from hollow cone into solid when flash boiling occurs. With a higher fuel superheat degree, the spray droplet distribution moves toward smaller sizes and let the larger droplets reduce due to the promotion of atomization. For the strong flash-boiling spray, the Sauter mean diameter has decreased by 50% compared with cold-jet spray. There is a corresponding relationship between collapsed flash-boiling spray target and weighted geometric center of the injector. Spray collapse could be avoided by increasing the plume distance.

Dynamic Thermal Behavior of a GDI Spray Impacting on a Heated Thin Foil by Phase-Averaged Infrared Thermography

<div class="section abstract"><div class="htmlview paragraph">The regulations about pollutant emissions imposed by Community’s laws encourage the investigation on the combustion optimization in modern engines and in particular in those adopting the gasoline direct injection (GDI) or direct injection spark-ignited (DISI) configuration. It is known that the piston head and cylinder surface temperatures, coupled with the fuel injection pressure, strongly influence the interaction between droplets of injected fluid and the impinged wall. In the present study, the Infrared (IR) thermography is applied to investigate the thermal footprint of an iso-octane spray generated by a multi-hole GDI injector impinging on a heated thin foil. The experimental apparatus includes an Invar foil (50 μm in thickness) heated by Joule effect, clamped within a rigid frame, and the GDI injector located 11 mm above the surface. Thermal images of the impinging spray are acquired from the dry side of the foil at several time delays after the impact instant at two different injection pressures (10 and 20 MPa). The temperature difference distributions are employed to describe the unsteady dynamics of the impingement.</div></div>

Application of an Equilibrium-Phase Spray Model to Multicomponent Gasoline Direct Injection

An Equilibrium Phase (EP) spray model has been recently proposed for modeling high-pressure diesel fuel injection, which is based on jet theory and a phase equilibrium assumption. In this approach, the non-equilibrium processes of drop breakup, collision and surface vaporization are neglected, assuming that spray vaporization is a mixing-controlled equilibrium process. A liquid-jet model and a gas-jet model are also intro-duced to improve grid-independency. In the current study, the EP model is applied in simulations of multi-hole gasoline direct injection (GDI). The model is validated at ambient densities from 3 to 9 kg/m3 and ambient temperatures from 400 K to 900 K, for two different GDI injectors, i.e. the Engine Combustion Network (ECN) Spray G injector and a GM injector. Iso-octane is used as the surrogate in consistency with available experi-ments. The results show good agreement in terms of liquid/vapor penetration, shape of the vapor envelope, and the velocity evolution along the injector centerline. Then, a 10-component gasoline surrogate fuel is used to demonstrate the capability of this model for multi-component spray simulations, which is essential for engine combustion and emission predictions.

Prediction of spray collapse in multi-hole gasoline direct-injection fuel injectors

A parametric study was conducted to predict the conditions leading to spray collapse in multi-hole gasoline direct-injection fuel injectors using computational fluid dynamics simulations. The computational fluid dynamics simulations were performed using an in-house multi-dimensional code that accounts for thermal non-equilibrium and entrainment of the non-condensable gas and coupled with primary atomization. The simulations were performed for a fixed injection pressure and fuel temperature on nine different six-hole injectors. The parameters were varied to include the effects of the ratio of the ambient pressure to the saturation pressure (Pa/Ps), the drill angle, and the diameters of the nozzle and the counter bore, respectively, on the spray. The findings indicate that spray collapse results from a combination of the nozzle geometry, the thermodynamic conditions of the fuel, and the ambient pressure. Spray collapse was observed in injectors with a narrow arrangement of the nozzle holes under extreme flash-boiling conditions with very low ambient pressures and in the case of non-flash-boiling conditions with very high ambient pressures.

Spray morphology transformation of propane, n-hexane and iso-octane under flash-boiling conditions

Spray collapse has been widely observed under both flash-boiling and non-flash-boiling conditions when multi-hole gasoline direct injection (GDI) injectors with compact nozzle configurations were used. The main objective of this study is to further understand the collapse mechanisms by using liquids with appreciably different properties (propane, n-hexane and iso-octane). The tests were carried out in a constant volume vessel with ambient pressures ranging from 0.6 bar to 11.0 bar and fuel temperatures from 30 °C to 110 °C. Flashing propane sprays presented a non-collapse feature under elevated-ambient-pressures but flash-boiling conditions. By close-up examination of flashing propane sprays over a wide range of liquid temperatures and ambient pressures, it was found that there should be an ambient pressure threshold between 1.0 and 3.0 bar between the collapsed and the non-collapse sprays for propane. The spray collapse occurred as the ambient pressure is below the threshold. The non-collapse feature for flashing propane sprays under the ambient pressures beyond the threshold was attributed to the prohibition of nucleation and bubble growth under elevated ambient pressures.

Multi-hole gasoline direct injection:In-nozzle flow and primary breakup investigated in transparent nozzlesand with X-ray

The contribution describes the flow field inside modern gasoline direct-injection nozzles and sprays. Starting from the internal nozzle flow, results from transparent real-size nozzles are shown, w...

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.

Air Entrainment in High Pressure Multihole Gasoline Direct Injection Sprays

Air Entrainment in High Pressure Multihole Gasoline Direct Injection Sprays