Multi-hole Spray Research Articles

Spray formation and spray-wall-flow interaction in a gasoline direct-injection (GDI) engine under early-injection conditions: A flow bench study

The work presented in this study aims to understand the spray-wall-flow interaction within a gasoline direct-injection (GDI) engine flow bench under simulated early-injection conditions. The Engine Combustion Network (ECN) Spray G injector is installed in the Darmstadt optically accessible engine flow bench. Under simulated early-injection conditions, the formation of a multi-hole spray and the interaction with characteristic intake flows, such as the intake jet and central tumble flow, are extensively discussed. By reducing the complexity in the number of variables inherent in engine flow and whole-engine simulation, an engine flow bench operating under various mass flow rates is applied in this study. The numerical simulation is carried out using Large Eddy Simulation (LES) under the Eulerian-Lagrangian framework for spray simulation. Experimental data, acquired through particle image velocimetry (PIV) measurements, provides 2-D flow fields on both the central tumble and valve planes, facilitating the validation of in-cylinder flow fields. Furthermore, experimental data obtained through Mie scattering is utilized to investigate spray formation and evolution within the GDI engine, providing the liquid penetration length and liquid spray angle. Comparison between the numerical and experimental data demonstrates several agreements. Moreover, the variation of different spray plumes under different mass flow rates is observed in the case of both experimental and numerical data. Increasing the mass flow rate distorts the overall plume shape and shifts it away from the intake port. This phenomenon is examined by extracting the liquid volume fraction and vapor fields of each plume. Spray plumes encounter different convective disturbances and evaporation due to their local characteristic in-cylinder flow. Furthermore, spray-wall-flow interaction and wall film deposits are observed during the injection. Lastly, the influence of the spray-induced turbulence is analyzed under different mass flow rates.

Characteristics and mechanism of spray deviation of ethanol and its blended fuel in multi-hole spray

Research on renewable fuels is crucial to render engines compliant with energy and environmental efficiency, and alcohol fuels have become hotspots in the field of modern gasoline direct injection engines. This study aims to elucidate the effects of ethanol addition on spray deviation under non-flash and flashing conditions. Macroscopic characteristics and microscopic characteristics can be obtained from Diffused Back Illumination and Phase Doppler Anemometry. The influential factors accounting for the spray deviation were examined, and internal flow simulations were also performed to obtain in-nozzle flow information. The angled momentum induced by the short L/D ratio leaves space for ambient gas ingestion into the counterbore under non-flash conditions. The entrained gas was affected by cavitation intensities, leading to the spray deviation, which was tracked by the Lagrangian particle trajectory method. The spray deviation is also affected by the formation of the low-pressure zone and droplets' migration. The higher surface tension and lower molecular weight of ethanol facilitate the spray expansion, forming the liquid barrier to draw the spray moving toward the injector center. Ethanol's high latent heat of evaporation inhibits the further reduction in droplets' radius, resulting in a persistent decrease in the relative span factor. On the other hand, the high latent heat of evaporation leads to a larger pressure drop induced by the vapor condensation, accounting for the “more powerful” abilities in drawing droplets into the jet center. The trade-off between the droplets' size and migration ability should be achieved to efficiently modulate spray deviation.

Primary break-up characterisation and droplet statistics of multi-hole sprays using a probabilistic surface density methodology

The work provides novel physical insight into the complex near-field flow dynamics and the primary break-up characteristics of sprays injected through multi-hole injectors (gasoline ECN Spray G). We use a stochastic fields transported-PDF method ( Σ-Y-PDF ) that allows for more accurate modelling of the sub-grid dynamics. Within this framework, the joint sub-grid probability density function of the liquid volume and surface density is solved using stochastic methods. Initially, the predicted spray dynamics resulting from the primary atomisation are simulated in terms of droplet size, velocity and spray angle. The spray from each hole is then investigated individually. The distribution of liquid near the nozzles agrees very well to the available experimental measurements. It is found that the spray break-up process in these gasoline sprays produces a quasi-log-normal droplet distribution. Such normalised distributions can be used to feed Eulerian–Lagrangian approach, showing a great potential to represent the full spray combustion process coupling the two approaches. Moreover, comparing the statistical and radial distributions of the droplets, we observe that the core of the plumes are characterised by larger droplets (≥10μm), although the overall spray is represented by lower size droplets surrounding the plume centre (≤10μm). Finally, the paper shows that the geometry asymmetry has a considerable effect on the flow field, which in turn affects the droplet behaviour. Even if the average droplet size was not affected by the asymmetry, the droplet velocity presented significant variation ( ≈50% ) for some of the holes.

Effect of Conical Spray and Multi-Hole Spray on Gasoline Engine Mixture Formation and Combustion Performance Based on Different Injection Strategies

Abstract This article presents a numerical investigation carried out to determine the effects of second and third injection timing on combustion characteristics and mixture formation of a gasoline direct injection (GDI) engine by comparing conical spray against multihole spray. The results showed that at the engine 80% full load of 2000 r/min, the difference in mixture distribution between the two sprays was obvious with double and triple injection strategies. With the second injection timing from 140 deg CA delay to 170 deg CA, the in-cylinder pressure, the in-cylinder temperature, and the heat release rate of the conical spray increased by 20.8%, 9.8%, and 30.7% and that of the multihole spray decreased by 30.7%, 13.6%, and 37.8%. The delay of the injection time reduced the performance of the engine with the multihole spray, and the performance of the multihole spray was obviously in the simulation of the triple injection strategy. However, for the conical spray, the application of the triple injection strategy increased the temperature and the pressure compared with the double injection strategy.

The spray vaporization characteristics of gasoline/diethyl ether blends at sub-and super-critical conditions

The multi-hole spray vaporization characteristics of gasoline, diethyl ether (DEE) and their blends were investigated at two pressures and elevated temperatures by using high speed schlieren photography and laser sheet patternation. Results show that the effects of DEE addition on spray behaviors depend on the ambient conditions that may lead to sub- and supercritical vapor generation mechanisms: (a) for 0.5 MPa ambient pressure at sub-critical state, spray plumes from different nozzle holes are separated. DEE addition results in higher vapor tip penetration, higher spray angle and decreased liquid cross-sectional area, indicating that DEE addition enhances vaporization. However, this effect becomes weaker at higher temperature due to accelerated gasoline vaporization. (b) for 3.8 MPa ambient pressure, spray plumes coalesce as a single plume-like structure due to stronger aerodynamic resistance to the axial penetration of each plume. In addition, opposite from the 0.5 MPa ambient pressure case, DEE addition results in an inhibited vaporization because the fuel blends are more easily heated to supercritical state with the addition of DEE. The thickened interface and reduced mean free path at supercritical state lead to restricted vapor phase generation. This phenomenon is also evidenced by the absence of large liquid blob on the patternation images.

Experimental study of flash boiling spray vaporization through quantitative vapor concentration and liquid temperature measurements

Flash boiling sprays of liquid injection under superheated conditions provide the novel solutions of fast vaporization and better air–fuel mixture formation for internal combustion engines. However, the physical mechanisms of flash boiling spray vaporization are more complicated than the droplet surface vaporization due to the unique bubble generation and boiling process inside a superheated bulk liquid, which are not well understood. In this study, the vaporization of flash boiling sprays was investigated experimentally through the quantitative measurements of vapor concentration and liquid temperature. Specifically, the laser-induced exciplex fluorescence technique was applied to distinguish the liquid and vapor distributions. Quantitative vapor concentration was obtained by correlating the intensity of vapor-phase fluorescence with vapor concentration through systematic corrections and calibrations. The intensities of two wavelengths were captured simultaneously from the liquid-phase fluorescence spectra, and their intensity ratios were correlated with liquid temperature. The results show that both liquid and vapor phase of multi-hole sprays collapse toward the centerline of the spray with different mass distributions under the flash boiling conditions. Large amount of vapor aggregates along the centerline of the spray to form a “gas jet” structure, whereas the liquid distributes more uniformly with large vortexes formed in the vicinity of the spray tip. The vaporization process under the flash boiling condition is greatly enhanced due to the intense bubble generation and burst. The liquid temperature measurements show strong temperature variations inside the flash boiling sprays with hot zones present in the “gas jet” structure and vortex region. In addition, high vapor concentration and closed vortex motion seem to have inhibited the heat and mass transfer in these regions. In summary, the vapor concentration and liquid temperature provide detailed information concerning the heat and mass transfer inside flash boiling sprays, which is important for the understanding of its unique vaporization process.

Macroscopic characteristics for direct-injection multi-hole sprays using dimensionless analysis

The macroscopic spray characteristics were quantified using dimensionless analysis by examining the role of the dominating forces associated with liquid-jet breakup. The Weber number, Reynolds number, and air-to-liquid density ratio dimensionless numbers were used to capture the primary forces including the inertia, viscous, surface tension, and aerodynamic drag forces. Planar Mie-scattering technique was applied to generate spray images over a broad range of conditions found in today’s spark-ignition-direct-injection (SIDI) engines, providing a relatively large range of dimensionless numbers. The effect of fuel properties were examined using gasoline, methanol and ethanol fluids. Six regions described on a Weber number versus Reynolds number domain were selected to identify the relative importance of the inertia force, surface tension force, and viscous force on macroscopic spray structure. The effect of aerodynamic drag was individually determined by characterizing the spray over a range of ambient air-to-liquid density ratios. As a result, for the non-flash-boiling multi-hole sprays in this study, the Weber number and air-to-liquid density ratio have much more profound effect on the spray penetration and spray–plume angle compared to the Reynolds number contribution. The inertia force and air drag force are more important factors compared to the viscous force and surface tension force. This analysis yielded dimensionless correlations for spray penetration and spray–plume angle that provided important insight into the spray breakup and atomization processes.

FLOW-FIELD INVESTIGATION OF MULTI-HOLE SUPERHEATED SPRAYS USING HIGH-SPEED PIV. PART I.CROSS-SECTIONAL DIRECTION

Superheated sprays are expected to improve the spray atomization and evaporation processes owing to the flash-boiling effects. However, the breakup mechanism and evaporation processes of superheated sprays have not been fully understood. In this study, a multi-hole spray flow-field on three cross-sectional planes was investigated by using high-speed particle image velocimetry (PIV) in a well-controlled high-pressure constant-volume chamber. Firstly, the spray structure under various superheated degrees was examined: As the superheat degree (SD) starts to increase, the eight individual circular plumes expand; then the expanded plumes gradually move towards the spray axis, connect with adjacent plumes, and form a donut-shaped spray pattern. With further increase of the superheat degree, the spray becomes a pancake-shaped pattern; as the fuel spray enters the fully flashing zone, an octopus-arms spray pattern can be observed. To elucidate the mechanism driving such dramatic change of the spray pattern with superheated degree, the interactions among spray plumes under various superheated conditions were investigated based on PIV data. A mixing zone is formed in between spray plumes when spray plumes approach each other. The dynamic variation of this mixing zone was analyzed through the flow-field measurement results. It is shown that the magnitude of the velocity vector in the mixing zone increases with the superheat degree, and this magnitude can be higher than that in the spray plumes' main stream, as can be observed under fully flashing conditions. The results provide insight into the spray-collapse processes and the interaction between the spray plumes. It is proven that the superheat degree is the predominant factor influencing the structure and the flow-field of the spray.

SI2-3 Development of Non-dimensional Drop Size Correlations of SIDI Multi-hole Sprays Using Phase Doppler Interferometry and High Speed Imaging(SI: Spark-Ignition Engine Combustion,General Session Papers)

SI2-3 Development of Non-dimensional Drop Size Correlations of SIDI Multi-hole Sprays Using Phase Doppler Interferometry and High Speed Imaging(SI: Spark-Ignition Engine Combustion,General Session Papers)

Atomization and vaporization for flash-boiling multi-hole sprays with alcohol fuels

The spray structural changes and vaporization processes for flash-boiling multi-hole sprays over a broad range of superheated conditions were investigated using Mie-scattering and Laser-induced-exciplex-fluorescence (LIEF) optical techniques. The fuel property effects were examined by characterizing n-hexane, methanol and ethanol fluids over a wide range of conditions consistent with that found in today’s spark-ignition-direct-injection (SIDI) engines. The macroscopic spray structure was quantified using spray penetration, spray-plume width and normalized distance between spray plumes. These structural parameters were correlated to the ratio of the ambient pressure to saturation pressure (Pa/Ps) that represents the superheated degree. Three continuous regions were identified by quantifying the spray transformation with increasing superheated degree; namely the non-flash-boiling, transitional flash-boiling and flare flash-boiling regions. Two critical values of Pa/Ps were identified, where the flash-boiling and spray collapsing transitions occurred at Pa/Ps values of 1.0 and 0.3, respectively. The evaporation process was examined using the LIEF optical technique for n-hexane, providing the relative vapor quantity throughout the spray transformation process. The correlations of the spray structural change and extent of vaporization with increasing superheated degree provided good insight into the mechanisms responsible for the observed behaviors during flash-boiling conditions.

Experimental Study on the Stratified and Homogeneous Charge of a Direct-Injection Spark Ignition Methanol Engine

Based on the gasoline direct-injection spark ignition (DISI) engine technologies and methanol fuel characteristics, a complex-guided multi-hole spray coupled with induction swirl and chamber-wall-guided stratified-charge combustion system for a DISI methanol engine was developed. It was retrofitted from a four-cylinder diesel engine with a compression ratio of 14. It was developed to run on methanol in stratified-charge and homogeneous-charge combustion modes; under part-load operating conditions, stratified-charge combustion is adopted to improve fuel economy while, under high- and full-load conditions, the homogeneous-charge combustion mode is adopted for the purpose of a higher power output. Under both combustion modes, the key parameters of the combustion system were matched and optimized respectively. The operating map for both combustion modes was obtained. Then, the engine power performance, emissions, and combustion characteristics were studied. The power output of the developed methanol engine is higher than that of the original diesel engine. By using the stratified combustion mode under low-load conditions, the engine fuel economy (the brake thermal efficiency) is improved; the stratified-charge combustion of methanol performed relatively well with acceptable values of the coefficient of the cyclic variation in the indicated mean effective pressure. The smoke and nitrogen oxide emissions from the DISI methanol engine are both reduced simultaneously and significantly.

Spray stability of outwards opening pintle injectors for stratified direct injection spark ignition engine operation

The spray characteristics and spray stability from three prototype piezoelectric pintle-type injectors were investigated under different operating conditions in an optical direct injection engine designed for stratified combustion. The pintle-type outwards opening injector has the potential to address and overcome many of the typical problems related to close-spacing, spray-guided configurations owing to its hollow cone spray, exhibiting better air utilization than multihole sprays, with good penetration during early injection, and a spray angle almost independent of cylinder backpressure. The three prototype injectors have different nozzle exit geometries for optimization of spray stability under all engine operating conditions. The emerging fuel sprays for both single- and double-injection operation were visualized using Mie scattering and a high-speed CCD camera. The performance of the injectors was assessed by constructing mean and RMS images at different operating conditions of injection pressure, backpressure, injector needle lift, and engine speed. From these images, a spray angle analysis was performed by comparing the mean, standard deviation, maximum, and minimum cone angle under different operating conditions; the spray stability was quantified by analysing the mean and RMS images and the mean and RMS spray cone angles. Evaluation of the three prototypes has revealed that the positive-step inward seal band design produces the most robust spray angle ideally suited for stratified fuel/air mixture formation and combustion in spray-guided direct injection spark ignition (DISI) gasoline engines.

A Study on Multi-hole Spray Interference and Mixture Formation in Diesel Combustion

A Study on Multi-hole Spray Interference and Mixture Formation in Diesel Combustion

Delphi’s new Flex Metal Catalyst cuts precious metal content while substantially reducing emissions

Performance of internal combustion engines is well known being greatly affected by the air-fuel mixture formation process. In spark ignition engines, in particular, the gasoline direct injection (GDI) technology is currently preferred, as it allows obtaining the desired air-to-fuel ratio distribution at each regime of operation, either by creating stoichiometric mixtures under high power demands, or through charge stratification around the spark plug at intermediate or lower loads. The impact of the gasoline spray on the piston or cylinder walls is a key factor, especially under the so-called wall-guided mixture formation mode. The impact causes droplets rebound and/or the deposition of a liquid film (wallfilm). After being rebounded, droplets undergo what is called secondary atomization. The wallfilm, on the other hand, may remain of no negligible size and evaporate slowly, leading to increased unburned hydrocarbons and particulate matter emissions.Optimization of the heterogeneous mixture behavior in GDI engines is fundamental for guaranteeing high energetic and environmental performance over the whole working map. Computational fluid dynamics (CFD) can be useful in this perspective to effect proper choices of control strategies. Assessment of predictive engine models, able to describe the complex phenomena underlying energy conversion in modern engines, is therefore mandatory to the scope.In the present paper, a basic study is performed on gasoline sprays issuing from high pressure injectors under controlled conditions: the experimental characterization of multi-hole and single-hole GDI sprays in their impact over a plate is carried out with the aim of creating a set of data to be used for the validation of a properly developed simulation model. The multi-hole spray allows accounting for the jet-to-jet interaction and represents a condition closer to the actual gasoline supply mode in present GDI engines. The single-hole injector configuration is instead preferred for a more detailed study, as it allows capturing effects related to the role that diverse parameters characterizing the liquid droplet dynamics play during and after their impingement on heated solid surfaces. The CFD model is conceived with the scope of its future application within numerical calculations of entire engine working cycles. A highly portable free spray sub-model allows correctly reproducing the injection dynamics under different conditions in a confined vessel, while the spray-wall impingement sub-model is shown being able to highlight to an acceptable extent the gasoline splashing and deposition phenomena.