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Technical Paper

Spray Structure Generated by Multi-Hole Injectors for Gasoline Direct-Injection Engines

The performance of multi-hole injectors designed for use in second-generation direct-injection gasoline engines has been characterised in a constant-volume chamber. Two types of multi-hole injector have been used: the first has 11 holes, with one hole on the axis of the injector and the rest around the axis at 30 degrees apart, and the second has 6 asymmetric holes located around the nozzle axis. Measurements of droplet axial and radial velocity components and their diameter were obtained using a 2-D phase Doppler anemometer (PDA) at injection pressures up to 120 bar, chamber pressures from atmospheric to 8 bar, and ambient temperatures. Complementary spray visualisation made use of a pulsed light and a CCD camera synchronised with the injection process.
Technical Paper

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

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

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

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

Experimental Evaluation of a Wall-Flow Filter for Gasoline Engine Particulate Emission Control

Motivated by the possibility of future emission regulations based on particle number as well as mass, after-treatment of ultrafine particles by a cordierite wallflow filter has been investigated. In a laboratory simulation, synthetic carbon particles of known size and concentration in air were captured with number-based efficiency exceeding 70% in the 20–100 nm size range. Effects of temperature, up to 400°C, filter loading time and ambient-temperature sample dilution have been quantified. Steady-speed and European drive cycle results for the same filter fitted to a passenger car with gasoline direct-injection engine have shown promising reductions in emissions, except at the highest speed of the cycle.
Technical Paper

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Swirl Generation by Helical Ports

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.
Journal Article

Fuel Film Behavior Analysis Using Simulated Intake Port

Transient behavior of the engine is one of the most crucial factors for motorcycle features. Characterization of the fuel film with port fuel injection (PFI) is necessary to enhance this feature with keeping others, such as high output, low emissions and good fuel consumption. In order to resolve the complicated phenomena in real engine condition into simple physical issues, a simulated intake port was used in our research with Laser Induced Fluorescence (LIF) technique to allow accurate measurement of the fuel film thickness, complemented by visualization of the film development and spray behavior using high-speed video imaging. Useful results have been conducted from the parametric studies with various sets of conditions, such as injection quantity, air velocity and port backpressure.
Technical Paper

An Approach to Charge Stratification in Lean-Burn, Spark- Ignition Engines

A constant-volume combustion chamber was used to examine injection of a small quantity of slightly rich fuel/air mixture towards the spark plug around the time of ignition, in an overall very lean mixture rotating at velocities representative of modern spark-ignition engines. The results show that it is possible to achieve 100% ignitability with overall air-fuel ratios in excess of 50 and much faster burn rates than those with initially homogenous mixtures of the same equivalence ratio with high swirl and turbulence. The advantages of this method of local charge stratification have been demonstrated in terms of both pressure measurements and shadowgraphs of the early flame development while the transient characteristics of the injected rich mixture at the spark plug gap were monitored by a fast flame ionization detector.