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Technical Paper

Internal Flow and Cavitation in a Multi-Hole Injector for Gasoline Direct-Injection Engines

2007-04-16
2007-01-1405
A transparent enlarged model of a six-hole injector used in the development of emerging gasoline direct-injection engines was manufactured with full optical access. The working fluid was water circulating through the injector nozzle under steady-state flow conditions at different flow rates, pressures and needle positions. Simultaneous matching of the Reynolds and cavitation numbers has allowed direct comparison between the cavitation regimes present in real-size and enlarged nozzles. The experimental results from the model injector, as part of a research programme into second-generation direct-injection spark-ignition engines, are presented and discussed. The main objective of this investigation was to characterise the cavitation process in the sac volume and nozzle holes under different operating conditions. This has been achieved by visualizing the nozzle cavitation structures in two planes simultaneously using two synchronised high-speed cameras.
Technical Paper

Internal Flow and Spray Characteristics of Pintle-Type Outwards Opening Piezo Injectors for Gasoline Direct-Injection Engines

2007-04-16
2007-01-1406
The near nozzle exit flow and spray structure generated by an enlarged model of a second generation pintle type outwards opening injector have been investigated under steady flow conditions as a function of flow-rate and needle lift. A high resolution CCD camera and high-speed video camera have been employed in this study to obtain high-magnification images of the internal nozzle exit flow in order to identify the origin of string ligaments/droplets formation at the nozzle exit. The images of the flow around the nozzle seat area showed clearly that air was entrained from outside into the nozzle seat area under certain flow operating conditions (low cavitation number, CN); the formed air pockets inside the annular nozzle proved to be the main cause of the breaking of the fuel liquid film into strings as it emerged from the nozzle with a structure consisting of alternating thin and thick liquid filaments.
Technical Paper

Structure of high-pressure diesel sprays

2001-09-23
2001-24-0009
A comprehensive set of computational and experimental results for high- pressure diesel sprays are presented and discussed. The test cases investigated include injection of diesel into air under both atmospheric and high pressure/temperature chamber conditions, injection against pressurized and cross-flowing CF6 simulating respectively the density and flow conditions of a diesel engine at the time of injection, as well as injection into the piston bowl of both research and production turbocharged high-speed DI diesel engines. A variety of high-pressure injection systems and injector nozzles have been used including mechanical and electronic high-pressure pumps as well as common-rail systems connected to nozzles incorporating a varying number of holes with diameters ranging from conventional to micro-size.
Technical Paper

Cavitation Initiation, Its Development and Link with Flow Turbulence in Diesel Injector Nozzles

2002-03-04
2002-01-0214
The initiation and development of cavitation in enlarged transparent acrylic models of six-hole nozzles for direct injection Diesel engines has been visualised by a high-speed digital video camera in a purpose-built refractive index matching test rig. The obtained high temporal resolution images have allowed improved understanding of the origin of the cavitation structures in Diesel injector nozzles and clarification of the effect of sac geometry (conical mini-sac vs. VCO) on cavitation initiation and development in the nozzle holes. The link between cavitation and flow turbulence in the sac volume and, more importantly, in the injection holes has been quantified through measurements of the flow by laser Doppler velocimetry (LDV) at a number of planes as a function of the Reynolds and cavitation numbers.
Technical Paper

Flow, Combustion and Emissions in a Five-Valve Research Gasoline Engine

2001-09-24
2001-01-3556
The in-cylinder flow, mixture distribution, combustion and exhaust emissions in a research, five-valve purpose-built gasoline engine are discussed on the basis of measurements obtained using laser Doppler velocimetry (LDV), fast spark-plug hydrocarbon sampling, flame imaging and NOx/HC emissions using fast chemiluminescent and flame ionisation detectors/analysers. These measurements have been complemented by steady flow testing of various cylinder head configurations, involving single- and three-valve operation, in terms of flow capacity and in-cylinder tumble strength.
Technical Paper

Prediction of Liquid and Vapor Penetration of High Pressure Diesel Sprays

2006-04-03
2006-01-0242
A dense-particle Eulerian-Lagrangian stochastic methodology, able to resolve the dense spray formed at the nozzle exit has been applied to the simulation of evaporating diesel sprays. Local grid refinement at the area where the spray evolves allows use of cells having sizes from 0.6 down to 0.075mm. Mass, momentum and energy source terms between the two phases are spatially distributed to cells found within a distance from the droplet centre; this has allowed for grid-independent interaction between the Eulerian and the Lagrangian phases to be reached. Additionally, various models simulating the physical processes taking place during the development of sprays are considered. The cavitating nozzle flow is used to estimate the injection velocity of the liquid while its effect on the spray formation is considered through an atomisation model predicting the initial droplet size.
Technical Paper

Flow and Spray Investigation in Direct Injection Gasoline Engines

2002-03-04
2002-01-0832
An investigation into the spray structure generated by two swirl pressure atomisers under various operating conditions in a constant-volume chamber and the in-cylinder flow pattern in an optical research direct-injection gasoline engine has been performed using CCD camera and laser Doppler velocimetry, respectively. The results provided detailed information about the effect of back pressure on the spray structure generated by the two injectors and the in-cylinder flow field which the sprays encounter following fuel injection into the cylinder during the induction and compression strokes.
Technical Paper

Effect of Multi-Injection Strategy on Cavitation Development in Diesel Injector Nozzle Holes

2005-04-11
2005-01-1237
The effect of multiple-injection strategy on nozzle hole cavitation has been investigated both experimentally and numerically. A common-rail Diesel injection system, used by Toyota in passenger car engines, has been employed together with a double-shutter CCD camera in order to visualise cavitation inside a submerged and optically accessible (in one out of the six holes) real-size VCO nozzle. Initially the cavitation development was investigated in single injection events followed by flow images obtained during multiple injections consisting of a pilot and a main injection pulse. In order to identify the effect of pilot injection on cavitation development during the main injection, the dwell time between the injection events was varied between 1.5-5ms for different pilot injection quantities. The extensive test matrix included injection pressures of 400 and 800bar and back pressures ranging from 2.4 up to 41bar.
Technical Paper

Evaluation of the Predictive Capability of Diesel Nozzle Cavitation Models

2007-04-16
2007-01-0245
The predictive capability of Lagrangian and Eulerian multi-dimensional computational fluid dynamics models accounting for the onset and development of cavitation inside Diesel nozzle holes is assessed against experimental data. These include cavitation images available from a real-size six-hole mini-sac nozzle incorporating a transparent window as well as high-speed/CCD images and LDV measurements of the liquid velocity inside an identical large-scale fully transparent nozzle replica. Results are available for different cavitation numbers, which correspond to different cavitation regimes forming inside the injection hole. Discharge coefficient measurements for various real-size nozzles operating under realistic injection pressures are also compared and match well with models' predictions.
Technical Paper

Modeling of Advanced High-Pressure Fuel Injection Systems for Passenger Car Diesel Engines

1999-03-01
1999-01-0910
A one-dimensional, transient and compressible flow model was used in order to simulate the flow and pressure distribution in advanced high-pressure fuel injection systems; these include electronic distributor-type pumps with either axial or radial plungers and a common-rail system. Experimental data for the line pressure, needle lift, injection rate and total fuel injection quantity obtained over a wide range of operating conditions (from idle to high speed/full load) were used to validate the model. The FIE system used for validation comprised an electronic high-pressure pump connected to two-stage injectors of different type including 6-hole vertical and 5-hole inclined conical-sac and VCO nozzles.
Technical Paper

Modeling of Pressure-Swirl Atomizers for GDI Engines

1999-03-01
1999-01-0500
A new simulation approach to the modeling of the whole fuel injection process within a common-rail fuel injection system for direct-injection gasoline engines, including the pressure-swirl atomizer and the conical hollow-cone spray formed at the nozzle exit, is presented. The flow development in the common-rail fuel injection system is simulated using an 1-D model which accounts for the wave dynamics within the system and predicts the actual injection pressure and injection rate throughout the nozzle. The details of the flow inside its various flow passages and the discharge hole of the pressure-swirl atomizer are investigated using a two-phase CFD model which calculates the location of the liquid-gas interface using the VOF method and estimates the transient formation of the liquid film developing on the walls of the discharge hole due to the centrifugal forces acting on the swirling fluid.
Technical Paper

Investigation of Cavitation in a Vertical Multi-Hole Injector

1999-03-01
1999-01-0524
An enlarged transparent model of a six-hole vertical diesel injector has been used to allow visualization of the flow at Reynolds and cavitation numbers matching those of real size injectors operating under normal Diesel engine conditions. The visualization system comprised a CCD camera, high-magnification lenses and a spark light source which allowed high-resolution images to be obtained. The flow conditions examined in terms of flow rates and pressures covered the range from low to full load of the real size injector while the needle lift position corresponded to that of full lift of the first- and second- stage in two-stage injectors. In addition, different values of needle eccentricity were tested in order to examine its effect on the cavitation structures within the injection holes.
Technical Paper

Cavitation in Real-Size Multi-Hole Diesel Injector Nozzles

2000-03-06
2000-01-1249
A production six-hole conical sac-type nozzle incorporating a quartz window in one of the injection holes has been used in order to visualize the flow under cavitating flow conditions. Simultaneous variation of both the injection and the back chamber pressures allowed images to be obtained at various cavitation and Reynolds numbers for two different fixed needle lifts corresponding to the first- and the second-stage lift of two-stage injectors. The flow visualization system was based on a fast and high resolution CCD camera equipped with high magnification lenses which allowed details of the various flow regimes formed inside the injection hole to be identified. From the obtained images both hole cavitation initiated at the top inlet corner of the hole as well as string cavitation formed inside the sac volume and entering into the hole from the bottom corner, were identified to occur at different cavitation and Reynolds numbers.
Technical Paper

Spray and Combustion Development in a Four-Valve Optical DI Diesel Engine

2000-03-06
2000-01-1183
An optical single-cylinder four-valve high speed DI Diesel engine equipped with a high-pressure electronic fuel injection system has been used to obtain information about the spray development, combustion and exhaust emissions (NOx and smoke levels) for a range of operating conditions corresponding to engine speeds between 600 and 1800 rpm, injection pressures up to 1200 bars and fuel injection quantities from idle to full load. Two six-hole vertical mini-sac type injection nozzles with different hole sizes have been employed in order to investigate the effect of nozzle hole diameter on spray formation, combustion and exhaust emissions. Parallel to the experimental programme, a computational investigation of the fuel flow distribution inside the injection system and of the subsequent spray characteristics has been performed in order to assist in the interpretation of the results.
Technical Paper

Pressure-Swirl Atomizers for DISI Engines: Further Modeling and Experiments

2000-03-06
2000-01-1044
A combined two-phase CFD nozzle model and 1-D fuel injection system model is used to predict the flow development inside the discharge hole of a pressure-swirl atomizer connected to a common-rail based fuel injection system for DISI engines. The fuel injection model accounts for the transient pressure pulses developing inside the common-rail and the injector upstream of the nozzle tip and predicts the fuel injection rate through the nozzle. This is then used as input to a 3-D single-phase CFD model estimating the transient development of the swirl velocity inside the pressure-swirl atomizer, as a function of the geometric characteristics of nozzle.
Technical Paper

Mixture Formation and Combustion in the Dl Diesel Engine

1997-08-06
972681
The diesel engine is the most efficient user of fossil fuels for vehicle propulsion and seems to best fulfill the requirements of the future. It is for this reason that Volkswagen has initiated a very broad research programme for diesels. The purpose of this paper is to build a bridge between fundamental research and technical developments which could allow evaluation of the prospects of direct- injection diesels as powerplants of choice for passenger cars in the turn of the century. The current knowledge on mixture formation, combustion and pollutant formation in diesel engines is presented and discussed with special emphasis given to the concept of the direct-injection diesel engine.
Technical Paper

Measurements and Calculations of the Flow in a Research Diesel Engine

1986-10-01
861563
Multidimensional calculations and laser Doppler anemometry measurements are presented of the air flow in a research diesel engine motored at 900 rpm with a compression ratio of ∼8.5. The engine comprised the cylinder head of a Ford 2.5L high speed direct-injection diesel mounted on a single cylinder Fetter engine modified to provide optical access for LDA measurements in a toroidal piston-bowl. The accuracy of the predictions is assessed against ensemble-averaged velocity data and found to be sufficient to allow better understanding of the flow in production engine geometries under realistic operating conditions.
Technical Paper

Effect of Fuel Injection Processes on the Structure of Diesel Sprays

1997-02-24
970799
A diesel spray model has been developed and validated against experimental data obtained for different injection and surrounding gas conditions to allow investigation of the relative importance of the different physical processes occurring during the spray development. The model is based on the Eulerian-Lagrangian approximation and the Navier-Stokes equations, simulating the gas motion, are numerically solved on a collocated non-uniform curvilinear non-orthogonal grid, while the spray equation is solved numerically using a Lagrangian particle tracking method. The injection conditions are determined by another recently developed model calculating the flow in the fuel injection system, the sac volume and injection holes area which accounts for the details of the injection velocity, the fuel injection rate per injection hole and occurrence of hole cavitation. Thus, differences between the sprays from inclined multihole injectors can be simulated and analysed.
Technical Paper

Swirl Generation by Helical Ports

1989-02-01
890790
The effect of inlet port design on swirl generation has been investigated for four helical ports from production, prototype and research Dl diesel engines by analyzing experimentally measured steady flow velocity distributions at the inlet valve curtain area and comparing their swirl characteristics in terms of the calculated in-cylinder angular momentum components and swirl ratio under operating conditions.
Technical Paper

Gaseous Simulation of Diesel-Type Sprays in a Motored Engine

1989-02-01
890793
The effect of fuel injection on the flow and the spray/swirl and spray/piston interactions in direct-injection diesel engines have been investigated by simulating diesel sprays with gaseous jet(s) injected through centrally located, single- and multi-hole nozzles into the quiescent and swirling air of a motored engine running at 200rpm and incorporating a flat piston and a re-entrant piston-bowl. The axisymmetric velocity field with and without ‘fuel’ injection was characterised by laser velocimetry near TDC of compression in terms of spatially-resolved ensemble-averaged axial and swirl velocities, the ‘fuel’ concentration field was quantified by laser Rayleigh scattering and the two-dimensional flow was visualised by gated still photography using hollow microballoons as light scatterers.
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