Fuel Injection Nozzle Research Articles

String cavitation formation inside fuel injectors

The formation of vortex or ‘string’ cavitation has been visualised at pressures up to 2000 bar in an automotive-sized optical diesel fuel injector nozzle. The multi-hole nozzle geometry studied allowed observation of the hole-to-hole vortex interaction and, in particular, that of a bridging vortex in the sac region between the holes. Above a threshold Reynolds number, their formation and appearance during a 2 ms injection event was repeatable and independent of upstream pressure and cavitation number. In addition, two different hole layouts and threedimensional flow simulations have been employed to describe how, the relative positions of adjacent holes influenced the formation and hole-to-hole interaction of the observed string cavitation vortices, with good agreement between the experimental and simulation results being achieved.

A review of design considerations for light-duty diesel combustion systems

Practical aspects of light-duty diesel combustion system design are reviewed, with an emphasis on design considerations reported by manufacturers and engine design consultancies. The factors driving the selection of compression ratio, stroke-to-bore ratio, and various aspects of combustion chamber geometry are examined, along with the trends observed in these parameters in recently released engines. The interactions among geometric characteristics, swirl ratio, and the fuel injection nozzle parameters are also reviewed.

Morphology, composition, and structure of carbon deposits from diesel and biomass oil/diesel blends on a pintle-type fuel injector nozzle

A biomass oil/diesel blend was prepared using an emulsion method and combusted in a diesel engine. An injector was then removed and the morphology, composition, and structure of the carbonaceous deposits on the pintle-type nozzle were characterized using a combination of HRTEM, SEM/EDAX, Raman and XRD. Results showed that the carbon deposition of the emulsified fuel with high crystallinity was greater than that of diesel. The agglomerated particulate diameters of the deposited carbon from diesel and emulsified fuel were approximately 10–30μm and 50μm, respectively. The carbon deposition mechanism from the emulsified fuel was attributed to the high oxygen content of the groups leading to increased polymerization and subsequent condensation on the nozzle surfaces that was then carbonised.

Designing the microturbine engine for waste-derived fuels

Presented paper deals with adaptation procedure of a microturbine (MGT) for exploitation of refuse derived fuels (RDF). RDF often possess significantly different properties than conventional fuels and usually require at least some adaptations of internal combustion systems to obtain full functionality. With the methodology, developed in the paper it is possible to evaluate the extent of required adaptations by performing a thorough analysis of fuel combustion properties in a dedicated experimental rig suitable for testing of wide-variety of waste and biomass derived fuels. In the first part key turbine components are analyzed followed by cause and effect analysis of interaction between different fuel properties and design parameters of the components. The data are then used to build a dedicated test system where two fuels with diametric physical and chemical properties are tested – liquefied biomass waste (LW) and waste tire pyrolysis oil (TPO). The analysis suggests that exploitation of LW requires higher complexity of target MGT system as stable combustion can be achieved only with regenerative thermodynamic cycle, high fuel preheat temperatures and optimized fuel injection nozzle. Contrary, TPO requires less complex MGT design and sufficient operational stability is achieved already with simple cycle MGT and conventional fuel system. The presented approach of testing can significantly reduce the extent and cost of required adaptations of commercial system as pre-selection procedure of suitable MGT is done in developed test system. The obtained data can at the same time serve as an input for fine-tuning the processes for RDF production.

A review of accuracy enhancement in microdrilling operations

Micromachining, which is a manufacturing technique to produce miniature parts, carries with it the major factor of precision in machining. The various processes of micromachining, be it contact or non contact methods, have their own merits and demerits. However, producing microstructures such as micro-holes which find widespread application in highly sensitive products such as automotive fuel injection nozzles, watches, medical electronics, and camera parts requires a high degree of accuracy in its profile parameters. Microdrilling, the most ideal micromachining process to generate micro-holes, can generate deeper holes with better straightness, better roundness, and smoother surfaces. This paper focuses on all existing microdrilling techniques that have been used in producing micro-holes along with the various strategies that have been adapted to improve the accuracy in hole dimensioning and its shape. The review of the various accuracy-related microdrilling operations will enable one to understand better the need for accuracy in micro-hole production, the various microdrilling techniques, and most essentially how the accuracy has been improved with technology advancement and better research. It also provides an overview which will help further propagation and implementation of more techniques to further enhance the accuracy of microdrilling operations, bringing about precise components of micromachining.

Ultrafast X-ray study of multi-hole GDI injector sprays: Effects of nozzle hole length and number on initial spray formation

Nozzle hole design factors, such as length, diameter, position and number of nozzle holes, significantly alter the near-field jet flow and following spray formation of fuel injection nozzles. This study investigates the effects of various nozzle hole design factors on near-field jet flow and spray formation of the multi-hole injectors for gasoline direct-injection (GDI) engines. The novelty of this study lies in intensive analysis in the near-field jet breakup, dynamics and droplet formation process that have rarely been characterized from previous studies by exploiting the potentials of synchrotron X-ray for near-field spray analysis. Among several nozzle hole design factors, the effects of the length and number of nozzle holes are investigated in the current paper as the first part. Four prototype injection nozzles, which have different lengths and numbers of nozzle holes with a substantially low needle lift of 35μm, were used for this fundamental study. Single- and multi-exposed X-ray phase-contrast images were used to characterize the jet breakup, dynamics and droplet formation process from the nozzle exit to 30mm downstream. The emerging jet flows from the multi-hole GDI injectors were highly turbulent and perturbed immediately from the nozzle exit. The decrease in nozzle hole length increased the axial and radial flow velocity of the emerging jet flow with an increased void fraction inside the nozzle hole at the nozzle exit. It promoted the jet breakup with formation of smaller and more circular liquid ligaments/droplets in the near-field when the nozzle hole length decreased, which accompanied the higher velocity decrease rate and turbulence strength along the spray axis. On the other hand, the increase in the number of nozzle holes decreased the axial and radial flow velocity of the emerging jet flow. It led to a slower breakup of the jet flow with a lower velocity decrease rate along the spray axis at larger number of nozzle holes.

Anode Shape Prediction in Through-Mask-Ecmm using Fem

Recent technological developments require advanced manufacturing technologies for miniaturized and micro-scale components in various types of industrial products, e.g., fuel injection nozzle for automobiles, miniaturized medical tools, microprobes used to measure surface properties, integrated micro-channels used for drug delivery systems, micro-gears, and various aeronautical components. Through-mask electrochemical micromachining (TM-ECMM) is a feasible process for such products. In the present work, the finite elements method (FEM) is used for solving 2-D Laplace equation in the inter electrode gap to determine the potential and flux distribution for the anode shape prediction in TM-ECMM. Algorithm has been developed and implemented in MATLAB to estimate surface erosion of anode for finite time steps. Anode shape and undercut are predicted using FEM and compared with the experimental results. The shape evolution through finite element simulation is approximately complying with the experimental anode profile. This work would later help in tool (cathode) design for TM-ECMM.

Evaluation of cavitation in injector nozzle and correlation with liquid atomization

Present paper describes the correlation between occurrence of cavitation inside injector nozzle and progress of atomization in discharged liquid jet flow. A transparent two-dimensional shape nozzle was designed and it was used for flow visualization. The visualized images both of cavitation and atomization were obtained simultaneously. The cavitation was evaluated by applying image analysis. The quantitative analysis on length, thickness and their fluctuations of cavitation was made, and the correlation with atomization was examined. The authors proposed an evaluation method of atomization in the previous study, and it was combined with evaluation method of cavitation developed in this study. It is found that the change of cavitation and progress of atomization are synchronized, and that a strong correlation between them exists. The best performance of atomization may be obtained by controlling the cavitation inside nozzle, and obtained aspects with this study will be utilized for the design of fuel injection nozzle of internal combustion engines.

Shear-force microscopy investigation of roughness and shape of micro-fabricated holes

The paper reports the analysis of roughness and shape of micro-machined workpieces carried out with a specifically conceived scanning probe microscope using the shear-force established between a vibrating tungsten tip and the surface under investigation. Samples, fuel injector nozzles, were prepared by different drilling techniques using either electro-discharge or laser-based machining techniques. Owing to its operation in true non-contact mode and the ability to analyse recessed surfaces, the microscope enables comparing the performance of the drilling processes through the determination of roughness parameters of the hole inner surface and the reconstruction of the shape at its edge. Both finishing and morphological details, expected to be involved in determining the fluid dynamics occurring inside the nozzle, can be captured by the developed diagnostics. The findings reveal that the use of ultrafast laser machining can lead to significantly improve the quality of fuel injector nozzles with respect to the present technology standard.

EFFECTS OF NONCONDENSABLE GAS ON CAVITATING NOZZLES

This paper focuses on the analysis of low-pressure regions inside fuel injector nozzles, where fuel vapor formation (strictly referred to as cavitation, or vaporous cavitation) and expansion of noncondensable gas (also referred to as pseudo cavitation, or gaseous cavitation) can simultaneously occur. Recently, X-ray radiography experiments of a 500 µm diameter cavitating nozzle showed that the presence of dissolved gas in the fuel can cause significant changes in the apparent distribution of projected void fraction. In this article, the effect of dissolved gas on cavitation measurements is investigated in further detail through experimentation and numerical simulations. Test conditions have been selected to have highly cavitating conditions. Tests with a standard gasoline calibration fluid and equivalent degassed fluid are compared and discussed. Numerical simulations have been conducted under the same conditions as the radiography experiments. The primary goal of the study is a quantification of the separate contributions of gas expansion as opposed to actual cavitation to the measurement of total void fraction. The multiphase flow is represented using a mixture model. Phase change is modeled via the homogeneous relaxation model. Particular attention is paid to quantifying the effective amount of noncondensable gas included in the mixture, in order to predict the response of regular and degassed fuels. The presence of dissolved gas in the multiphase flow is taken into account using a compressible fluid model with three distinct components (liquid, vapor, and gas). Issues surrounding estimation of the effective amount of noncondensable gas are discussed. Numerical simulation results match well with the experiments and indicate that when a sufficient quantity of gas is dissolved in the fuel, a void is evident in the central region of the channel that can be attributed to local expansion of noncondensed gas. Conversely, degassed fuel shows only intense cavitation at the nozzle wall, with very little contribution from noncondensed gas.

Development of an Inspection System for Micro Level Void Detection

In this paper we discussed a method to carry out a roughness inspection on the surface of fuel injection nozzle of ship engines. The nozzles are manufactured using hot isostatic pressing (HIP) technology. Microscopic blowholes are likely to be created during the process of manufacturing the nozzles, which causes the roughness on the surface even after fine machining. The objective of this research is to develop a technique to detect these microscopic blowholes. Digital image processing and a computational system are used to measure the roughness level. Length and breadth of the blowhole is measured using edge detection technique associated with a Gaussian filter and then edge drawing algorithm is used to draw fine edges along the detected edges. Based on the difference of intensity gradient along x-and y-direction, the edges of the blowholes are drawn. These detected edges are used to measure the size of blowhole.

Numerical study of flame structure in the mild combustion regime

In this paper, turbulent non-premixed CH4+H2 jet flame issuing into a hot and diluted co-flow air is studied numerically. This flame is under condition of the moderate or intense low-oxygen dilution (MILD) combustion regime and related to published experimental data. The modelling is carried out using the EDC model to describe turbulence-chemistry interaction. The DRM-22 reduced mechanism and the GRI2.11 full mechanism are used to represent the chemical reactions of H2/methane jet flame. The flame structure for various O2 levels and jet Reynolds numbers are investigated. The results show that the flame entrainment increases by a decrease in O2 concentration at air side or jet Reynolds number. Local extinction is seen in the upstream and close to the fuel injection nozzle at the shear layer. It leads to the higher flame entertainment in MILD regime. The turbulence kinetic energy decay at centre line of jet decreases by an increase in O2 concentration at hot Co-flow. Also, increase in jet Reynolds or O2 level increases the mixing rate and rate of reactions.

Development of a double fiber probe with a single fiber Bragg grating for dimensional measurement of microholes with high aspect ratios.

A fiber Bragg grating (FBG)-based probe is developed by designing a novel double fiber structure to make the probe sensitive to both axial and radial contact displacements. A matched FBG pair interrogation system for the probe is modeled, and the best matched initial condition is found to make the probing system work in the linear and most sensitive mode. Actual measurements of ring gauges and fuel injection nozzles indicate that, for a microhole with an aspect ratio of greater than 14∶1, an axial resolution of 8nm and a radial resolution of 30nm can be achieved with the developed probe. It is therefore concluded that the double fiber probe with a single FBG developed can be used to measure high aspect ratio microholes.

On the formation of string cavitation inside fuel injectors

The formation of vortex or ‘string’ cavitation has been visualised in the flow upstream of the injection hole inlet of an automotive-sized optical diesel fuel injector nozzle operating at pressures up to 2,000 bar. Three different nozzle geometries and three-dimensional flow simulations have been employed to describe how, for two adjacent nozzle holes, their relative positions influenced the formation and hole-to-hole interaction of the observed string cavitation vortices. Each hole was shown to contain two counter-rotating vortices: the first extending upstream on axis with the nozzle hole into the nozzle sac volume and the second forming a single ‘bridging’ string linked to the adjacent hole. Steady-state and transient fuel injection conditions were shown to produce significantly different nozzle-flow characteristics with regard to the formation and interaction of these vortices in the geometries tested, with good agreement between the experimental and simulation results being achieved. The study further confirms that the visualised vortices do not cavitate themselves but act as carriers of gas-phase components within the injector flow.

Water jet guided laser as an alternative to EDM for micro-drilling of fuel injector nozzles: A comparison of machined surfaces

To characterize the inner surface of the fuel injector nozzle holes drilled by EDM and water jet guided laser drilling (Laser Micro-Jet) a specifically conceived scanning probe microscopy technique with true non-contact operating mode was used. A difference in morphology of the drilled surfaces is evident from the acquired surface topography along the hole axis for the two compared drilling techniques. Results showed that the surface texture can be characterized by (i) maximum peak-to-valley distance and (ii) periodicity. Acquired maps confirm that electro-eroded surfaces are an envelope of craters randomly distributed with total excursion up to 1.7μm with a crater size of 15μm. While, the efficient melt expulsion and immediate cooling of water jet guided laser generates a peak to valley distance of 800nm with a periodicity of 18μm. Average Rq derived from the measured cylindrical surfaces was 450nm and 150nm for EDM and Laser Micro-Jet, respectively. Water jet guided laser drilling has proved to be a reliable alternative to EDM from the point of view of repeatability of the results and surface quality to facilitate the atomization of the fuel jet.

Instantaneous and ensemble average cavitation structures in Diesel micro-channel flow orifices

Cavitation developing upstream and inside the micro-channel orifices of transparent multi-hole fuel injector nozzles has been characterised using a high speed visualisation system. Images have been obtained with short exposure time and sufficiently high spatial and temporal resolution, freezing the formation of cavitation bubbles and their further development during every single injection cycle. Post processing of statistically large number of images collected from many successive injection events and numerous identical nozzles has allowed for the first time estimation of the ensemble average cavitation image and its standard deviation. The instantaneous images reveal the formation of a variety of complex and interacting two-phase flow regimes. Vapour bubbles have been found to exist inside the nozzle prior to start of injection. These bubbles originate from the previous injection cycle as they have not been evacuated from the nozzle and hence, they remain trapped, altering the flow of the subsequent injection event. During the opening and closing stages of the needle valve that controls the fuel flow through the nozzle, cavitation is found to form in the valve’s seat area. Subsequently, vortex or ‘string’ cavitation has been recorded to take place in a rather chaotic manner; its life time and most probable location of appearance have been estimated. The ensemble average images reveal the probability of cavitation appearance at a specific location within the nozzle and the micro-channel flow orifice. The standard deviation from the mean reveals locations with significant cycle-to-cycle variations of the flow. These are linked to significant deviations from the mean of the fuel spray dispersion angle forming downstream of the nozzle exit.

High-speed imaging of transient diesel spray behavior during high pressure injection of a multi-hole fuel injector

Reliable prediction of spray penetration and spray break-up is required to achieve increases in fuel efficiency and reduction of emissions in diesel engines. Of particular interest is the early transient-flow regime. In the current work, diesel fuel spray development was studied using high-speed imaging of a high-pressure diesel common-rail fuel injector mounted in a spherical constant volume combustion chamber. The fuel injector nozzle had four holes aligned on a radial plane with diameters of 90, 110, 130, and 150μm. Fuel was injected into a room temperature T=298K (±1.5%), nitrogen environment at chamber densities of 17.5, 24.2, and 32.7kg/m3 (±3%) and for fuel-rail pressures of 1000, 1500, and 2000bar (±1.5%). High-speed images of the backlit fuel injection were captured at 100,000 frames per second. Image processing algorithms were used to determine fuel spray penetration distance and maximum penetration rate as a function of time. The early time history of the spray penetration was not sensitive to orifice size, orifice location or chamber density at the conditions studied. However, fuel injection pressure significantly affected the spray-tip penetration and time to spray break-up. The experimental results for maximum penetration rate and transition time were compared with various quasi-one-dimensional fuel-spray models. The experimental data indicated a power law relationship for the spray-tip penetration at early times in the spray development, which is consistent with recent recommendations. However, the experimental results for time to spray break up departed from the model predictions at most of the conditions studied, with the model significantly under-predicting the time for spray transition. Furthermore, the spray penetration data showed significant fluctuations in the spray geometry at early times. A fuel spray-tip tracking algorithm was developed and the results showed the maximum penetration distance did not occur along the spray center-line during the transient period of injection and the results quantified the angular location of the maximum penetration distance. These data provide valuable new insights into transient fuel spray behavior and will guide the development of the next generation of spray theory and models.

Experimental characterization of the inner surface in micro-drilling of spray holes: A comparison between ultrashort pulsed laser and EDM

Abstract In this research, the inner surface characteristics of micro-drilled holes of fuel injector nozzles were analyzed by Shear Force Microscopy (SHFM). The surface texture was characterized by maximum peak-to-valley distance and periodicity whose dimensions were related to the adopted energy. 180 µm diameter holes were drilled using ultrashort pulsed laser process using pulse energies within the range of 10–50 µJ. Laser ablated surfaces in the tested energy range offer a smooth texture with a peculiar periodic structure with a variation in height between 60 and 90 nm and almost constant periodicity. The Scanning Electron Microscopy (SEM) photograph of the Laser Induced Periodic Surface Structure (LIPSS) showed the co-existence of Low Spatial Frequency LIPSS (LSFL) and High Spatial Frequency LIPSS (HSFL). A comparative analysis was carried out between the highest laser pulse energy in the tested range energy laser drilling which enables the shortest machining time and micro-Electrical Discharge Machining (µ-EDM). On the contrary, results showed that surfaces obtained by electro-erosion are characterized by a random distribution of craters with a total excursion up to 1.5 µm with a periodicity of 10 µm. The mean-squared surface roughness ( R q ) derived from the scanned maps ranges between 220 and 560 nm for µ-EDM, and between 50 and 100 nm for fs-pulses laser drilling.

Studies on a diesel engine fuelled with used transformer oil at different fuel injection nozzle opening pressures

After prolonged use of transformer oils they become waste and utilised in minor applications. Used transformer oil (UTO) possess physical properties similar to diesel fuel. Earlier investigation reveals that the UTO fuelled in a single cylinder, four stoke, direct injection diesel engine developing 4.4 kW at a rated speed of 1500 rpm at 200 bar standard nozzle opening pressure, gave lower brake thermal efficiency and nitric oxide emission and higher smoke compared to diesel fuel operation. In this investigation, the fuel injector in the same engine was subjected to five different injection nozzle opening pressures (200, 210, 220, 230, 240 and 250). The effect on the performance and emissions of a compression ignition engine were evaluated, compared with standard diesel fuel operation and presented in this paper. Results indicated that UTO at 230 bar fuel nozzle opening pressure gave a better performance with lower emissions than UTO at 200 bar.

Experimental study of the Effect of Fuel Injector nozzle holes on Direct Injection Diesel Engine

Fuel injection parameters play an important role in diesel engine performance for obtaining proper combustion. The performance and emission characteristics of diesel engine depend on many parameters. The important parameters which influence the performance and emission of diesel engine are fuel injection pressure, fuel nozzle holes and its size. An experimental study was performed on a light duty direct injection diesel engine at 200 bar, 220 bar and 240 bar injection pressure to study its effect on performance and emission. The injection pressure was changed by adjusting the fuel injector spring tension. Future emission legislation will require substantial reductions of NO x and Smoke emissions from diesel engines. The combustion and formation in a diesel engine is governed mainly by spray formation and mixing. Important parameters governing these are droplet size, distribution concentration and injection velocity. Smaller orifices are believed to give smaller droplet size, even with reduce injection pressure, which leads to better fuel atomization, faster evaporation and better mixing. The performance and emission characteristics were presented graphically to conclude that they were found better with 5 hole nozzle of O = 0.2 mm at the fuel injection pressure 220 bar for the light duty engine. Keywords: Diesel engines, performance, fuel injection parameters, BSFC, NOx emission.