GDI Injector Research Articles

Lemon peel oil as an alternative fuel for GDI engines: A spray characterization perspective

Lemon peel oil (LPO: C10H16O0.082) shows very similar calorific value, stoichiometric air to fuel ratio as isooctane, an ideal reference fuel for a gasoline engine, and also possesses very good anti-knock tendency and octane number rating (RON = 80) making it possible alternative fuel for gasoline engines. The present study investigates the suitability of LPO for direct injection spark ignition application by contrasting the spray characteristics of LPO with reference fuel isooctane for simulated engine-like conditions. Experiments were performed in a constant volume spray chamber under various engine-like pressure and temperature conditions. A six-hole GDI injector was used to study the spray behavior of LPO and then compared to standard reference fuel, isooctane. The ambient conditions in the chamber were derived using the crank resolved pressure data of the GDI engine. The selected chamber conditions are a) 1.5 bar, 329 K; b) 2.5 bar, 371 K; c) 6.0 bar, 453 K simulating in-cylinder conditions for three different injection timings. Phase Doppler particle analyzer and Mie scatter imaging techniques were employed for spray characterization. Spray morphology along with joint probability distribution for droplet size and axial velocity, cumulative volume fraction and Weber and Reynolds number ranges were used to contrast the two sprays for LPO and isooctane. Results showed that ambient pressure and temperature have a significant effect on spray behavior and late injection in compression stroke is proposed to be ideal for LPO to match the engine performance with that of isooctane based on the spray quality comparison.

Applicability of high-pressure direct-injected methane jet for a pure compression-ignition engine operation

Natural gas has been suggested as an alternative fuel for compression ignition (CI) engines because it generates significantly less pollutants and has a smaller carbon footprint, while maintaining the cycle efficiency. However, the high auto-ignition temperature of natural gas typically requires the use of a quasi-compression ignition method such as homogenous charge compression ignition (HCCI) or a dual-fuel mode. Yet, methods such as these are unable to realize the full potential of high efficiency and low emissions. This motivated us to evaluate the applicability of a high-pressure direct-injected natural gas jet for a pure CI engine under various engine load, injection timing, and injection pressure conditions using a single cylinder CI engine with a compression ratio of 15.5. The intake temperature was raised to 400 °C to achieve the auto-ignition temperature of methane after compression and a multi-hole GDI injector capable of operating at a pressure of 400 bar was used for fuel injection.As a result, CI operation was possible, but ignition occurred after the end of the injection in the form of a partially premixed flame rather than a diffusion flame for all conditions under which the engine was operated. A sufficient equivalence ratio of 0.8 was achieved at an injection pressure of 300 bar and injection duration of 1.6 ms with the multi-hole GDI injector, and the GMEP value varied from 2 bar to 5.5 bar according to the equivalence ratio. However, at an equivalence ratio of 0.7 or higher, the combustion efficiency decreased drastically because of the limit of the volume fraction of the piston bowl at TDC and the narrow nozzle distribution of the GDI injector. Measurement of the pollutants indicated that the total number of particles from methane CI operation exceeded that of diesel at an equivalence ratio of 0.74 in the same engine setup because of incomplete combustion; however, the total mass of the particulate matter (PM) was approximately 15% of the diesel because the average particle size from methane CI was approximately one third smaller than that of diesel. However, the high post-compression temperature for the auto-ignition of methane gas resulted in a high peak temperature, which resulted in the production of approximately 2000 ppm NOx under all test conditions. The results of the parametric study showed that, as the injection timing retarded, the ignition timing was almost equally retarded, thus the combustion was still observed in the form of a diffusion flame. As the injection pressure increased, the ignition delay became shorter and the emission of PM could be further reduced, but the NOx emission increased.

Interaction between under-expanded flashing jets: A numerical study

In this research, n-hexane flashing jets discharged from two-hole GDI injectors were studied numerically with different superheat levels and inter-hole angles. The mutual interaction between under-expanded flashing jets was discussed in terms of its effect and mechanism. It was found that under certain conditions, the jets deflected towards each other and merged into one jet which moved along the central axis, indicating the occurrence of spray collapse. The spray collapse is ascribed to the pressure drop in the central area between the two jets, which is an effect of the low-pressure cores within individual jets. The pressure drop in the central area is mainly determined by two effects, i.e. the intensity and volume of the low-pressure cores in individual jets, and the formation of the secondary cell which protects the central area from being affected by the ambience. In the transitional stage from non-collapse to fully-collapse, the pressure drop was enhanced with the rise of superheat level or the decrease of inter-hole angle, and the extent of spray collapse increased. Besides, unique shock structures similar to those of under-expanded gaseous twin-jets were formed at high superheat levels, which consist of two primary cells and a secondary cell.

Study of Liquid and Vapor Phases of a GDI Spray

ABSTRACTGasoline direct injection (GDI) systems have become dominant in passenger cars due to their flexibility in the fuel managing and the consequent advantages in the fuel economy. With the increasingly stringent emission regulations and concurrent requirements for enhanced engine thermal efficiency, a comprehensive characterization of the fuel spray behavior has become essential. Characteristics of free-evolving and impinging spray of iso-octane fluid, using a GDI injector from the Engine Combustion Network (ECN) circuit, were investigated by a hybrid Mie-scattering and schlieren optical technique. The experiments provided the spatial distribution and time-resolved evolution of the free, as well as the post-impingement, characteristics of the spray under various operating conditions. A customized processing algorithm, able to catch the contours of both liquid and vapor/atomized phases, was used to extract the diffusion and evaporation parameters that characterized the fuel spray. Aim of this study is a detailed understanding of a GDI spray evolution under engine-like conditions, by studying both the liquid and the vapor phases as the ambient and injection conditions varies in a controlled environment.

Morphology analysis on the effect of injection pressure on jet trajectory deviation of multi-jet sprays

Fuel spray behaviors play an important role in mixture formation, efficiency and emission of internal combustion engines. In this study, the effect of injection pressure on spray jet trajectory was investigated by using an asymmetric five-hole GDI injector. With schlieren imaging method, the ethanol spray development was captured under superheat degrees from 0.46 to 9.48, and the ambient pressure was fixed at 101.3 kPa. For the non-flash-boiling cases, the jet trajectory gradually deviated inward in the far field with the increase of injection pressure. For the flash boiling cases, the jet trajectory near the nozzle exit deviated outward under the relatively low injection pressures and deviated inwards with the increase of injection pressure. The outward deviation under relatively low injection pressure was attributed to the non-uniform vapor formation inside the nozzle orifice. The disappearance of near-field deviation under flash boiling conditions under high injection pressures could be attributed to the reduced time for nucleation and bubble growth inside the nozzle. Additionally, under both non-flash-boiling and flash-boiling conditions, the far-field deviation under high injection pressures could be attributed to the increased jet speed and the stronger jet-to-jet interaction. Compared with non-flash-boiling cases, the far field deviation under flash boiling conditions were more intense because of the enhanced atomization and it is believed that the smaller droplets were more inclined to move inwards. The remarkable effect of injection pressure on jet interaction of flash boiling sprays shows the potential of flexible jet targeting control at different engine loads.

Understanding spray and atomization characteristics of butanol isomers and isooctane under engine like hot injector body conditions

Spray characterization of GDI injectors is of significant importance as it influences the overall engine performance and its emissions. Spray morphology under various engine like conditions influences engine design. Vapor bubbles are formed inside liquid droplets when hot fuel is injected into the sub-saturation pressure conditions leading to flash boiling of GDI sprays. This dramatically alters the spray morphology and therefore needs to be understood thoroughly. A spray undergoing flash boiling experiences catastrophic breakup of the liquid jet resulting in fine atomization which in turn enhances droplet evaporation. However, spray structure is significantly altered under such conditions. In the present work, effect of hot injector body was studied to understand flash boiling behaviour of alcohol fuels and which were then compared to isooctane spray characteristics under similar conditions. Experiments were performed at five different injector temperatures: 298 K, 373 K, 423 K, 473 K and 523 K. Significant difference in spray morphology was observed when the fuel temperature was increased. Reduction in overall spray cone angle was observed with increase in temperature for all the fuels considered in this study. Vapour penetration lengths increased with increase in temperature, whereas liquid penetration initially increased and then decreased significantly due to higher evaporation rate. PDPA data showed significant reduction in SMD and AMD when the temperature was raised from 298 K to 423 K. SMD for n-butanol, isobutanol and isooctane reduced by 58.45%, 54.51% and 64.87%, respectively. Similarly, AMD reduced by 65.58%, 57.12% and 74.24%, respectively.

Modelling and understanding deposit formation and reduction in combustion engines – Application to the concrete case of internal GDI injector deposit

Deposits, which form within various parts of internal combustion engines, can affect normal engine operation and result in diverse negative effects. Versatile research over the last decades revealed that the formation and reduction of deposits is the result of a complex interaction between the physical boundary conditions at the place of interest and of the fuel properties. To appropriately catch this complexity, an abstract, generalized kinetic model for deposit formation and reduction mechanisms is developed within this publication. It accounts both for the chemical and physical properties of the fuel mixture on a single component basis and for the physical boundary conditions at the site of interest. Due to an included explicit time dependence, it is also able to describe the effect of boundary condition changes and hence dynamic engine operation. In the second part of this publication the model is applied to the concrete case of internal deposit formation of a GDI injector during continuous engine operation, where the fuel flow drift caused thereby is used as the measure for the deposit amount. The deposit formation tendencies within the engine map, i.e. various engine speed and load points, are investigated and the results are interpreted by evaluating the impact of the operation point changes on the deposit kinetics. In a last step, selected desposit formation and reduction phenomenons during engine operation are discussed, which show the necessity for a model with a component basis of both fuel and deposit composition.

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.

Characteristics of trans-critical propane spray discharged from multi-hole GDI injector

This paper is to investigate the characteristics of trans-critical propane spray compared with the flash boiling spray ejected from a multi-hole injector in a constant volume chamber by using the Schlieren and backlit imaging methods. The fuel temperature (Tf) is set from 30 °C to 120 °C, injection pressure (pf) from 60 bar to 120 bar and ambient pressure (pa) from 0.2 bar to 10 bar.The results show that the trans-critical spray has longer vapor penetration and shorter liquid penetration than the flash boiling spray, but those two sprays have similar curve liquid boundaries near the nozzle. Several discernable collapsed shock structures near the nozzle are observed at Tf = 120 °C, pf=120 bar, pa = 1 bar, but they disappear when pf drops to 60 bar for the transition path may not enter the two-phase region, and the liquid phase hardly occurs. The Mach disk distance of trans-critical spray in this study is larger than that of the under-expanded ideal gas jet because of the collapse phenomenon. At Tf = 120 °C, pf = 120 bar, the liquid length decreases when paincreases from 0.2 bar to 2.5 bar and increases when pa continues to rise.

Estimating velocity in Gasoline Direct Injection sprays using statistical pattern imaging velocimetry

Statistical pattern imaging velocimetry (SPIV) is a new technique for the estimation of the planar velocity field from the high-speed videos. SPIV utilizes an ensemble of either backlit or side lit videos to obtain full planar velocities in sprays and flames. Unlike conventional particle imaging velocimetry, statistical pattern imaging velocimetry does not require well-resolved images of particles within turbulent flows. Instead, the technique relies of patterns formed by coherent structures in the flow. Therefore, SPIV is well suited for the estimating planar velocities in sprays and turbulent flames, both of which have well-defined patterns embedded in the flow videos. The implementation of the SPIV technique is relatively quite straightforward since high-speed videos can be readily obtained either in a laboratory or production floor setting. The biggest challenge for the SPIV techniques is that the procedure is computationally expensive even with an ordinary mega-pixel camera. To improve the computation speed, a successive partitioning scheme was employed. In addition, to improve spatial resolution to subpixel dimensions, a weighted central averaging scheme was used. With these two enhancements, the SPIV method was used to obtain planar radial and axial velocities in a spray emanating from a GDI injector. Sprays from GDI injectors are very dense (with obscuration levels close to the injector being greater than 99%), and velocity measurements are difficult. However, further away from the nozzle, a Phase Doppler Anemometer can be used to obtain velocity measurements. The velocities obtained using these two methods showed reasonable agreement.

Retraction notice to Mechanism of flash boiling and spray analysis with gasoline, iso-octane, n-pentane and ethanol from a novel heated tip GDI injector

Retraction notice to Mechanism of flash boiling and spray analysis with gasoline, iso-octane, n-pentane and ethanol from a novel heated tip GDI injector

Near-nozzle spray dynamics of 6-hole GDI injector under subcooled and superheated conditions

The flash boiling of fuel sprays can occur in engines when the fuel is injected into the ambient gas which pressure is lower than the saturation vapor pressure of the fuel. Recently, the flash boiling has attracted many engine researchers’ interest due to its superior spray atomization performance. It has been discussed that the formation of the flash boiling sprays is governed by the bubble dynamics in the fuel such as bubble nucleation, growth, and burst. However, the detailed bubble dynamics and its effects on near-nozzle spray dynamics have remained a mystery due to great difficulties in the observation of flow characteristics inside and near the nozzle. The current study investigates the near-nozzle dynamics of flash boiling sprays from a 6-hole gasoline-direct-injection injector using an X-ray imaging technique. Various Rp (ratio of saturated vapor pressure to ambient gas pressure) conditions were applied by altering the ambient pressure under the fixed fuel temperature. The results showed that the flash boiling did not alter significantly the emerging flow velocity at the nozzle exit. The center of flash-boiling sprays did not decelerate in the near-nozzle region while that of the subcooled spray showed a gradual deceleration. The radial velocity of the flash boiling sprays increased at the edge of the spray as Rp increased while that in the spray center was near zero regardless of Rp condition. The radial velocity of the flash boiling spray was solely governed by Rp regardless of injection pressure while that of the subcooled sprays was altered by the injection pressure. Based on the results, the initial formation mechanism of the flash boiling sprays and the associated bubble dynamics were thoroughly discussed.

Single-Hole Asymmetric GDI Injector: Influence of the Drill Angle and the Counter-Bore under Flash-Boiling and Non-Flash-Boiling Conditions

Single-Hole Asymmetric GDI Injector: Influence of the Drill Angle and the Counter-Bore under Flash-Boiling and Non-Flash-Boiling Conditions

Ambient density effects on initial flow breakup and droplet size distribution of hollow-cone sprays from outwardly-opening GDI injector

Outwardly-opening injectors for gasoline direct-injection engines generate hollow-cone sprays which have better atomization performance than conventional hole-type nozzle sprays. The ambient density alters the initial flow breakup and the downstream vortex structure of the hollow-cone sprays which in turn rearrange the local droplet size distribution. However, the ambient density effects on those spray properties have not been thoroughly characterized in the previous studies despite their crucial effects on engine combustion. The current study investigates the ambient density effects on the initial liquid-sheet breakup and local droplet size distribution of hollow-cone sprays from an outwardly-opening gasoline-direct-injection injector using X-ray and visible light imaging techniques. The ambient density effects were investigated in varied needle lift conditions which altered the initial flow conditions such as liquid-sheet thickness and turbulence. In general, an increase in the ambient density decreased the breakup length of the liquid-sheet but the effects became insignificant as the initial flow turbulence increased in high needle lift conditions. The spray droplet size in the near-nozzle region decreased with the increase in ambient density but a reverse trend was observed at downstream because the spray atomization was terminated faster at high ambient densities. Particularly large droplets were observed near the spray head due to the coalescence of liquid droplets accelerated by the vortex flow. The increase in ambient density brought this large droplet regime closer to the nozzle with the further increase in the droplet sizes.

Effects of Cavitation and Hydraulic Flip in 3-Hole GDI Injectors

Effects of Cavitation and Hydraulic Flip in 3-Hole GDI Injectors

RETRACTED: Mechanism of flash boiling and spray analysis with gasoline, iso-octane, n-pentane and ethanol from a novel heated tip GDI injector

The effects of thermal and fuel properties on the spray characteristics of a novel heated tip GDI injector have been investigated. The novel heated tip injector with an inner heater has been designed and manufactured to study the macroscopic spray characteristics under different conditions. To reveal the effects of injector heated tip temperature on spray characteristics, a six holes novel heated tip injector with different temperature has been studied. Moreover, a model refer to the velocity of a droplet of the flash boiling spray is established to predict the spray angle. A high-speed backlit imaging technique combined with cross-sectional spray patterns based on Mie scattering technique is used to obtain images of transient spray formation. The macroscopic spray formations of gasoline, iso-octane, n-pentane and ethanol were measured and compared under different experimental conditions. Experimental methods were used to validate how temperature effects on macroscopic spray characteristics. The results show that there are two key factors that affect the spray characteristics under the same condition, one is the physical properties and the other is fuel temperature. The spray characteristics is the key factor which has a high sensitive effect on the engine performances.

Investigation of deposit effect on multi-hole injector spray characteristics and air/fuel mixing process

An optical-based experimental study of the injector deposit effect on a multi-hole GDI injector was performed first. After carefully calibrating the spray model with the experiment data, a three-dimensional computational fluid dynamics (CFD) simulation was then carried out to study the deposit effect on the air/fuel mixture preparation process in an optical research GDI engine. Six different injection timings were used for full-cycle simulations. The numerical engine condition was at stoichiometric ratio, 1200rpm and 150bar injection pressure. The experimental results showed that injector deposit would lead to lower fuel mass flow rate, with 5.4%, 5.7% and 6.1% loss at 50, 100 and 150bar respectively. Injector deposit resulted in longer penetration length and the effect displayed hole to hole difference. The maximum increment was observed for the ignition jets with 11.6% at 150bar. Injector deposit led to higher droplet velocity and larger droplet size and the difference increased with injection pressure. For the air/fuel mixing simulation, the injector deposit led to more fuel impingement on the piston and cylinder walls, as well as a lower mean equivalence ratio during late injection events. The distorted spray pattern led to higher fuel stratification level. In very late injection cases, the injector deposit led to a very lean mixture near the spark plug which could result in unstable engine performance; while the rich regions at the cylinder sides could result in higher emissions. Comparison of computed results with PLIF (planar laser induced fluorescence) images provided a satisfactory validation for the model.

A comprehensive study on the factors affecting near-nozzle spray dynamics of multi-hole GDI injectors

In order to improve the engine thermal efficiency with reduced emissions, substantial studies have been carried out to investigate the factors affecting the fuel spray characteristics such as nozzle geometry, fuel property, and injection and ambient conditions. However, most of the previous studies have focused on the macroscopic structures of the fuel sprays, but detailed structures of internal spray dynamics have not been thoroughly investigated, especially in the near-nozzle region. In this study, the effects of critical injection parameters such as injection pressure, ambient density, fuel, nozzle hole diameter and length on the near-nozzle spray dynamics of multi-hole gasoline-direct-injection injectors were investigated using X-ray phase-contrast imaging and visible light imaging. Then, the scaling potential of the near-nozzle spray dynamic structure under various injection parameters was surveyed based on the gas jet theory. The results showed that the density ratio of the fuel and surrounding gas and spray angle are the governing factors of the near-nozzle spray dynamic structure. By introducing the governing factors as the scaling variables, the near-nozzle spray dynamic structure under various injection parameters can be scaled with near 90% correlation performance. However, the scaled dynamic path in the near-nozzle region is different with that of the gas jets that requires modifications of conventional gas-jet-based dynamics models for application to the near-nozzle region.

Transient needle motion of an outwardly opening GDI injector and its effects on initial spray formation

Outwardly opening injectors for gasoline direct-injection engines form thin-sheet hollow-cone sprays. The spray formation of the outwardly opening injectors is governed by the transient needle motion that alters the initial flow conditions such as liquid sheet thickness, emerging flow velocity and turbulence strength. However, the transient needle motion and its effects on the initial spray formation have been difficult to be studied by conventional lasers due to severe absorption and scattering of the laser lights from dense liquid features in the near-field. The current study investigates the transient needle motion of an outwardly opening injector and discusses its effects on initial spray formation using an X-ray phase-contrast imaging technique. An X-ray pulse with 80ps duration in FWHM was used to visualize the transient needle motion and near-nozzle flow morphology. On the other hand, three X-ray pulses with 165.2ns period were used to analyze the dynamics of near-nozzle flow by tracking the movement of the liquid features. An obvious needle vibration was observed through the injection process and the amplitude of the vibration damped down with time. This needle vibration accelerated and decelerated the near-nozzle flow in turn that altered the undisturbed liquid length and flow breakup with time. The temporal variation of the initial flow characteristics caused an irregular droplet size distribution with the distance from the nozzle tip other than monotonous decrease.

분사율을 이용한 직접 분사식 다공 가솔린 인젝터의 분사특성 연구

This paper presents an experimental study on the GDI injector with Bosch method. The injection characteristics, such as the injection quantity, the injection rate, the maximum velocity of the nozzle exit and the injection delay were studied through the change of the injection pressure, the tube pressure and energizing duration in injection rate measurement device using nheptane. The injection quantity is increased by increasing injection pressure, decreasing tube pressure or increasing energizing duration. As the difference of the injection quantity changed, the shape of injection rate was moved with a constant form. The maximum velocity of the nozzle exit showed a tendency to increase as the injection pressure is increased. However, tube pressure did not affect. Overall, it was confirmed that the closing delay is longer than the opening delay in all conditions. As the injection pressure increased, the result has a tendency to decrease the closing delay, it did not affect the opening delay. Reduction of the closing delay showed the reduction of the injection duration. the tube pressure and energizing duration did not affect the injection delay (opening delay, closing delay).