Swirl Injector Research Articles

Spray propagation and mixture formation in an air guided direct injection gasoline engine

Numerical analysis is used to gain information on the spray propagation and mixture formation in tumble guided gasoline direct injection (DI) engines. In order to achieve reliable predictions an atomization model for high-pressure swirl injectors is described and verified by comparison to experimental data. The approach is capable of adequately predicting the most important effects, such as nozzle orifice diameter, cone angle or injection pressure on spray development. Furthermore, it is found that the pre-jet generated at the beginning of the injection strongly affects the overall spray development. The temporal development of the pre-jet is described empirically. The in-cylinder computational fluid dynamics (CFD) analysis reveals that the tumble charge motion strongly affects spray propagation and mixture formation in the stratified operation mode, as it transports the fuel vapour cloud towards the spark plug. The CFD simulation improves understanding of the interaction between the flow field, spray propagation and evaporation and enables guidance of the optimization of the flow control and of the injection parameters for tumble guided gasoline DI engines.

2205 VOF モデルを用いたスワールインジェクタの内部流れ解析

A two-phase analysis of air and fuel flow through a swirl injector was performed by using a volume of fluid (VOF) model. This model makes it possible to calculate the cavity that is formed at the exit of the nozzle, thereby facilitating calculation of the liquid film thickness which strongly influences fuel atomization. The calculated results were compared with experimental data for fully developed spray characteristics, including the flow coefficient, cone angle and cavity factor. Moreover, the initial spray development process was also calculated. The calculated results were compared with visualizations of the initial spray development process. They showed relatively good agreement with the experimental data.

714 PIVを用いたスワールインジェクタの噴霧解析と設計への適用(オーガナイズドセッション7 流れの可視化応用解析)

714 PIVを用いたスワールインジェクタの噴霧解析と設計への適用(オーガナイズドセッション7 流れの可視化応用解析)

LDA/PDA measurements of instantaneous characteristics in high pressure fuel injection and swirl spray

Transient dynamics of two injection flows, upstream and downstream a swirl injector, are investigated. Capillary n-heptane pipe flow is measured using laser Doppler anemometer to obtain instantaneous time series of centerline velocity and to reconstruct series of instantaneous and integrated flow rates and pressure gradient. A collimated laser sheet and a high-speed video camera visualize injected spray flow. Finally, the phase Doppler anemometer measurements are introduced to analyze instantaneous patterns of droplets velocity-size and number density into fuel spray. All measurements are employed at similar temporal resolution close to 30 μs. Results indicate that both flows are strongly time-dependent and well correlated in time-phases. Initial transitions are completed by 100 μs. Opening or closing of the injector valve affects both flows as strong delta oscillation causes spray penetration dynamics and a post injection effect. A combination of intrusive laser-based techniques allows indication of the basic injection and spraying characteristics need to optimize high-pressure fuel injectors and combustion late injection mode at a high speed.

Recent Developments in Simulations of Internal Flows in High Pressure Swirl Injectors

As far as design of direct injection spark ignited engine is concerned, the fuel injector is a key component for success. Internal flow simulation is the best adapted tool for the design of the internal geometry of the injector. First, simulations of the internal flow will be discussed, especially transient stages of an injection event as well as the prediction of the fuel characteristics at the nozzle exit. Second, a coupling between internal flow calculations and instability model in order to predict initial spray characteristics will be suggested.

A study on fuel spray of spark-ignited direct injection engine using laser image technology

One of the important research for developing a spark-ignited direct injection engine is optimization of the fuel spray distribution and air flow field in the cylinder. Therefore, spray pattern and mean fuel droplet size of swirl injector were investigated using Laser Light Sheet Photography and PDPA' respectively. And, for the formation of stratified mixture with adequate strength near a spark plug at injection mode in compression stroke, spray distribution after impingement on flat piston or bowl piston in a transparent motoring engine was visualized for the three different injector positions.

Visualization and Measurements of Sub-Millisecond Transient Spray Dynamics Applicable to Direct Injection Gasoline Engine. Part 3: Measurements of Instantaneous and Integrated Flow Rates in High Pressure Injection System Using LDA-Based Meter.

Time-dependent centerline velocity is measured using LDA-flow meter. Swirl injector at frequencies of 22 and 46 Hz generates oscillated flow under high-pressure from 4 up to 7 MPa. The encoded time-series of velocity is used to reconstruct the time-variable series of instantaneous flow rate and pressure gradient. Transient injection dynamics are analyzed to obtain basec characteristics of an injection system that will be able to be used for real time monitoring or active controlling of high-pressure gasoline injectors. The results obtained through analyzing the integrated mass rates within a cycle, indicate that a certain injection system is characterized by the flow rate constant γ which independent on injection duration and can be obtained from only accurate measurement of centerline velocity in the fuel transport pipeline. The present technique allows us to simplify the injection model and can be effectively adopted for practical employment on active and passive control with respect to gasoline direct injection engines.

TRANSIENT 3D ANALYSIS OF A Dl GASOLINE INJECTOR SPRAY

A cycle-resolved, phase Doppler anemometry (PDA) methodology is appraised for the collection and analysis of data from a gasoline fuel injector. A high-pressure swirl injector is utilized, spraying unleaded gasoline into air at ambient pressure and temperature. Results are presented in terms of Sauter mean diameter (SMD) of droplets, three components of velocity, and semiquantitative mass flow rate for the entire flow field. Spray development is analyzed using time increments of between 0.25 ms and 1 ms over the first 12 ms after injection. High-speed photography confirms the validity of some of the global trends identified, including vortex development, spray penetration, and needle bounce. PDA measurements indicate that larger droplets are produced in the early stages of the injection. These populate the and periphery of the spray cone, which becomes essentially hollow for a period between 0.75 and 2 ms. Smaller droplets in the center of the cone attain velocities in excess of 50 m/s, while those on the edge are entrained by the recirculating vortex. During the early injection period, the majority of the liquid mass resides within the head and an annular section of the spray, which indicates the hollow cone design. After 3 ms, the spray becomes more homogenous, with little mass flow rate variation across the cone identifiable after 4.5 ms. The data are finally compared with a standard time-averaged correlation usually utilized for this type of injector. This emphasizes the need for continued effort on transient predictive spray modeling in future direct-injection (DI) gasoline investigations.

Hysteretic interaction of conical liquid sheets from coaxial atomizers: Influence on the spray characteristics

In the context of coaxial swirl injectors used in liquid bipropellant rockets, a detailed experimental study has been made on the mutual interaction between thin coaxial, conical liquid sheets. As the flow rates are increased, the sheets move close to each other and merge at a definite flow condition. The presence of the inner jet influences the behavior of the outer jet, even before merging. The merging and separation processes exhibit hysteresis. This leads to drastic variations in spray characteristics depending on the approach to the hysteresis regime. Many of these features as well as those on the movement of the contact point can be traced to changes occurring in the static pressure in the cavity between the two sheets.

Development of in-cylinder gasoline direct injection engine

An in-cylinder gasoline direct injection (GDI) engine, incorporating novel combustion technologies, has been developed. Such innovative technologies consist of the upright straight ports to generate tumble motion, the electro magnetic swirl injector to realize optimized spray dispersion and atomization and the compact piston cavity to maintain charge stratification, and in addition other highly advanced technologies to achieve desirable engine management. This new GDI engine is thus available with ultra lean stratified combustion for higher thermal efficiency under partial loads as well as homogenous combustion to realize higher performance under full load.

An experimental study of combustion dynamics of a premixed swirl injector

A comprehensive experimental study has been conducted on combustion instabilities in a premixed swirler injector system at various equivalence ratios, chamber pressures, and inlet air temperatures. A stability map has been determined to indicate the range of operating conditions conductive to the occurrence of instabilities. The amplitude of instabilities was found to be a strong function of the equivalence ratio, with pressure oscillations as high as 20% of the mean chamber pressure and unsteady velocities comparable to the mean flow values observed for equivalence ratios around 0.6. On the other hand, beyond an initial threshold value of inlet air temperature at which instability suddenly initiated, variations in inlet air temperature had minimal effect on the strength of instabilities. Measurements of steady and unsteady flame structures carried out using CH chemiluminescence and photographic imaging techniques indicate that the onset of instabilities can potentially cause significant alterations in flame structure, sometimes even causing near extinction of the flame during certain periods of the oscillation cycle. Coupled longitudinal oscillations were observed in the combustion chamber and upstream duct. Instability characteristics such as frequency, mode shape, and phase obtained through pressure measurements were found to be in excellent agreement with predictions from a linear acoustic analysis. A strong correlation was found between the heat release and pressure fluctuations near the dump plane, indicating a possible mechanism for creating and sustaining instabilities.

The effect of fuel volatility on sprays from high-pressure swirl injectors

The effect of fuel volatility on the spray distribution of a pressure-swirl atomizer of the type used in direct-injection gasoline engines was investigated in a firing optical engine. Planar laser-induced fluorescence (PLIF) and planar Mie scattering were used to visualize the fuel spray. Experiments were performed at three loads (0.3, 0.6, and 0.9 bar intake pressure) and two head temperatures (30 °C and 90 °C). Fuel mixtures consisted of doped and undoped isooctane and indolene. Dopants were ketones of varied volatility: acetone ( T b =56°C), 2-butanone ( T b =80°C), and 3-pentanone ( T b =102°C). At high head temperature and low pressure with volatile, fuel species, the spray characteristics changed from the hollow-cone structure observed under cold conditions to a solid-cone distribution. This transition was observed with both the PLIF and Mie-scattering images, suggesting that not only vapor was being drawn to the interior of the cone, but droplets as well. The observed solid-cone structure can be explained by flash boiling of the highly volatile species, followed by entrainment of the smaller droplets into the cone center by the airflow induced by the spray. The observed transition temperatures and pressures agree well with bubble-point calculations and suggest that a superheat of about 20 K is necessary for flash boiling to be vigorous enough to noticeably affect the spray structure. Similar results were obtained with a full-boiling-range gasoline.

Computation of the hollow-cone sprays of a high-pressure swirl injector for a gasoline direct-injection SI engine Toyosei Yamauchi (Subaru Research Center Co., Ltd.), Tomoyuki Wakisaka (Kyoto University)

Computation of the hollow-cone sprays of a high-pressure swirl injector for a gasoline direct-injection SI engine Toyosei Yamauchi (Subaru Research Center Co., Ltd.), Tomoyuki Wakisaka (Kyoto University)

Jet Interaction in Liquid-Liquid Coaxial Injectors

Interaction between two conical sheets of liquid formed by a coaxial swirl injector has been studied using water in the annular orifice and potassium permanganate solution in the inner orifice. Experiments using photographic techniques have been conducted to study the influence of the inner jet on outer conical sheet spray characteristics such as spray cone angle and break-up length. The core spray has a strong influence on the outer sheet when the pressure drop in the latter is low. This is attributed to the pressure variations caused by ejector effects. This paper also discusses the merging and separation behavior of the liquid sheets which exhibits hysteresis effect while injector pressure drop is varied.

Experimental study of liquid sheets formed in coaxial swirl injectors

The shape and disintegration characteristics of swirled annular liquid sheets formed in coaxial injectors are investigated. The effects of ambient pressure and gas flows over the outer and inner surfaces of the liquid sheet are determined. Two general regimes of annular sheets, comprised of a tulip shape and a conical diverging shape, are shown to be formed depending on injector pressure drop, swirl, and orifice size. The transition from the tulip shape to the diverging conical shape occurs when the centrifugal forces at the injector orifice exit exceeds the surface tension forces by about two orders of magnitude. A conical sheet is not formed in annular orifice when the radial clearance of the orifice is of the same order of magnitude as the thickness of the liquid film. The tulip-shaped sheet is very sensitive to small changes in environmental and injection conditions, unlike the diverging conical liquid sheet.

Visualization of the Evaporating Process of Fuel Spray in the Cylinder of a Diesel Engine

A single cylinder engine with the combustion chamber mounted on the piston was designed to allow visualization in the direction of the cylinder axis. By using this engine, the evaporating process of the fuel injected into the combustion chamber was observed. High-speed Schlieren, shadowgraph, and back-illuminated photographs were taken for detailed observation of the combustion chambers with a single hole injector and a swirl injector which have different atomization characteristics. The chamber with a single hole injector showed strong collision of the spray with the bottom of the chamber and fast evaporation. That with a swirl injector showed no evidence of such collision and relatively slow evaporation.

Visualization of the evaporating process of fuel spray in the cylinder of a diesel engine.

A single cylinder engine with the combustion chamber mounted on the piston was designed to allow visualization in the direction of the cylinder axis. By using this engine, the evaporating process of the fuel injected into the combustion chamber was observed. High speed Schlieren, shadowgraph, and back-illuminated movies were taken for detailed observation of the combustion chambers with a single hole injector and a swirl injector which have different injection characteristics. The one with a single hole injector shows strong collision of the spray with the bottom of the chamber and fast evaporation. Another with a swirl injector shows no trace of such collision and relatively slow evaporation.

Atomizing Characteristics of Swirl Injection Nozzle : 3rd Report, The Effect of the Physical Properties of Liquid on the Coefficient of Discharge

The all characteristics of the swirl nozzle are affected by the viscosity of liquid, but the effect upon the discharge coefficient among these is considerably complicated. In this paper, the effects of the surface tension and the viscosity on the discharge coefficient were investigated. The discharge coefficients are fairly arranged by introducing a Reynolds' number Re of the swirl chamber, and in the range of Re=1 600-2 800, all swirl injection nozzles have a transition from the laminar flow to the turbulent. The changes of discharge coefficients by the transition are rather gradual, including the extreme case of no change. A general empirical formula of discharge coefficient was made from the results.

Atomizing Characteristics of Swirl Injection Nozzle : Supplement of 2nd Report, The Effect of the Dimensions of the Swirl Chamber on the Coefficient of Discharge, the Spray Angle and the Size of Drop

In the 2nd Report, the effect of the dimensions of swirl chamber on the size of drop was investigated and an attempt was made to search for the condition of the optimum form of nozzle. Besides the size of drop, the characters of the swirl nozzle can be represented by the discharge coefficient and the spray angle. These two can be obtained from the potential flow theory but they agree with the experiments only in the narrow range. In the present paper, the auther made the empirical formulas of the discharge coefficient and the spray angle which were applicable to wide range of the dimensions of swirl chamber for the non-viscous liquids, and obtained the more accurate empirical formula than that of the second report for the mean diameter of drop taking into accout the effect of ratio between the length and diameter of orifice.

On the Theory of Viscous Swirl

To analyse the flow in the swirl injection nozzles used for the gas turbines, we have attempted to calculate the properties of the viscous swirling flow solving the Navier-Stokes' equation. The integration constants appeared in the solutions are obtained from the consideration of the energy loss between two consecutive layers of viscous fluid, thus enabling the determination of the size of the cavity or the core, which rotates like a solid cylindrical column. The effects of viscosities of the fuels on the discharge coefficients and spray angles are also calculated with various actual examples. As a special case, the mathematical conditions for the generation of 'the eye of the swirl' is also explained, where the cavity or the core ceases its rotation and forms a cylindrical column of fluid at rest similar to that happens in the swirling wind such as in the Typhoon, the Cyclone or the Hurricane.