Injection Nozzle Research Articles

Cavitation in Diesel Fuel Injector Nozzles and its Influence on Atomization and Spray

AbstractIn combustors, high‐pressure fuel injector nozzles are employed for liquid atomization and spray generation. The internal flow within nozzles, especially cavitation, plays an important role in promoting the breakup of liquid jets. The formation mechanism and evolvement of cavitation are reviewed and described. Different cavitation regimes were characterized experimentally and the positive effect of cavitation on liquid atomization was confirmed. Different empirical formulas correlating the discharge coefficient with fluid‐dynamical parameters are summarized. The applicability, advantages, and disadvantages of two popular computational models for flow modeling, i.e., the interface tracking model and the homogeneous equilibrium model, are reviewed. The effects of cavitation on the generated spray are discussed.

Two-Hundred-Newton Laboratory-Scale Hybrid Rocket Testing for Paraffin Fuel-Performance Characterization

A series of firing tests have been performed on a laboratory-scale hybrid rocket engine of 200 N class, fed with gaseous oxygen through a converging nozzle injector, to assess the mechanical feasibility and regression rate of a newly developed paraffin-based fuel. Such an injector configuration, by producing recirculation at the motor head hand, has been already demonstrated to influence the standard fuels regression rate, which yields an increase with the port diameter at given mass flux. In this study, paraffin-fuel regression rate dependence on the mass flux and grain port diameter in the form of a power function is determined to be similar to that established with polymeric fuels, despite the different mechanism of consumption that involves the fuel surface liquid-layer instability other than the vaporization typical of classical polymers. Comparison with some data in the literature is presented. Data retrieved from the testing campaign are compared with numerical results obtained by adopting a simple but efficient modeling strategy and a commercial solver. The numerical solution gives evidence of the recirculating flow at the injector exit, which is also responsible for the paraffin contamination observed in the motor prechamber. A good agreement is found with chamber pressure experimentally measured.

Comparison of the Optical Connectivity Method to X-Ray spray measurements in the near field of a diesel injector

For diesel sprays, the primary breakup processes are only rarely understood due to the high optical density and the resulting difficulties to measure them with extremely high spatial and sufficient temporal resolution. The Optical Connectivity Method (OCM) has been proposed in the last years to allow the determination of the breakup length of the connected liquid core, thus giving a measurement quantity of the primary breakup. In this work, an improved optical setup of the OCM is applied to a three-hole test injector nozzle where several measurement techniques are compared currently under well-defined conditions up to 100 MPa injection pressure. In this work, the direct comparison with X-Ray measurements done at the Advanced Photon Source of the Argonne National Laboratory will be described. This allows an evaluation of the OCM technique and a comparison of the different measurement quantities in the first 500 µm range of the spray. The structure of the spray is measured by X-Ray phase contrast imaging and the fuel mass distribution is measured by X-Ray absorption imaging. A detailed comparison of the two X-Ray techniques and the OCM technique has been possible for the first time. It is found that the measurement data of the spray near field are very congruent with all three methods. Due to this comparison, the measurement of the non-perturbed length, which describes the distance from the nozzle orifice up to the point where the formation of surface disturbances is starting, by the OCM is validated for the first time. Within this non-perturbed length of the spray, the OCM signal is weak before it starts to illuminate from the scattering of the perturbed surface. Thus, the OCM technique can deliver two characteristic length scales, the non-perturbed length and the breakup length, characterizing the primary spray breakup.

The Investigation of Geometric Parameters on the Injection Characteristic of the High Pressure Common-Rail Injector

According the actual structure and working principle of a fuel injector to build a model of the common-rail injector, including the control valve, the solenoid valve, and the needle valve of the injector. The model includes the leakage model for the control piston and needle valve that takes into account increasing leakage at high pressure. The performance of the fuel injector is investigated using a one-dimensional numerical model. Analyzing the effect of the system and structure parameters including common-rail pressure, injection pulse width, inlet and outlet hole diameter, and the injection nozzle on the injection characteristics of the fuel injector. Results show that the geometric parameter is the main property affecting the flow characteristic of the injector, which includes the flow rate of inlet and outlet hole, pressure waves in the control chamber and injection rate. The common-rail pressure, injection pulse width and the geometric parameters mainly affect the injection performance, such as the injection rate and injected volume. The investigation result can provide some useful information to improve the injection characteristic in follow-up studies.

The evolution of soot morphology and nanostructure along axial direction in diesel spray jet flames

This study aims at providing new insights into the soot formation and oxidation processes in diesel spray jet flames under the diesel-like conditions. Soot particles are sampled within a reacting diesel jet spray flame in a constant-volume combustion chamber under diesel-like high-temperature and pressure ambient conditions. The experiments are conducted with an injector hole of 0.28 mm and injection mass of 30 mg per shot. Soot particles at different locations along the axis of the diesel jet flame are sampled by a thermophoretic probe, and the variation of soot morphology and nanostructure of the sampled soot particles along the axial location in the flame is analyzed by using the transmission electron microscopy (TEM). At upstream of the jet flame, large “liquid-like” particles are observed in the TEM images. As these particles are delivered to the downstream, (1) there are many immature primary particles formed on the surface of large “liquid-like” particles, and (2) they are carbonized into the larger soot aggregates with the matured structure, and then at last, (3) the larger soot aggregates gradually break up into the smaller particles with relatively compact structure. Both the diameter of primary particles and radius of gyration of the soot aggregates decrease as the distance between the injector nozzle tip and the center of TEM grid is increased, while the opposite trend is found in the behavior of the fractal dimensions of soot aggregates. The high resolution TEM images show that the soot primary particles exhibit the turbostratic state at the upstream of the jet flame, while more matured structures with the graphitic crystallite in outer shell and several fine particles in the inner core are observed as the sampling distance from orifice is increased. The average fringe length increases while the average tortuosity and separation decrease with the distance from the nozzle. These results suggest that the mechanism of mature soot aggregates generated directly from the large “liquid-like” particles should be one of the ways of soot particle formation along the axis of diesel jet flames.

The effect of cavitation on the estimation of fuel injection rates based on momentum flux measurements

A study was conducted to determine how geometry-induced cavitation affects the reliability of injection rate estimates based on momentum flux measurements. Experiments were performed with two hydro-grinding diesel injector nozzles (Do = 190 µm), one having a cylindrical nozzle orifice that has a strong tendency to induce cavitation, and the other having a convergent nozzle orifice that tends to suppress cavitation. In addition, near-field microscopic images were captured to investigate the influence of cavitation on the liquid jet at the nozzle exit. The momentum flux measurements and near-field imaging were conducted at ambient pressure, using injection pressures of up to 2500 bar. When estimating the injection rate based on momentum flux measurements, failure to account for cavitation caused the integrated injection rate to be overestimated around 9% for the cavitating (cylindrical) nozzle but not for the non-cavitating (convergent) nozzle. We therefore recommend that cavitation should be accounted for when estimating injection rates for cavitating nozzles but not for non-cavitating nozzles. Further, we show that the tendency of a given nozzle orifice to induce cavitation can be evaluated by measuring the nozzle’s momentum flux under the assumption of zero cavitation and then comparing the estimated mass of injected fuel to the weighed mass.

Binary Biodiesel Blend Endurance Characteristics in a Compression Ignition Engine

The results obtained on wear assessment from a compression ignition (CI) engine fueled with a blend of 70% amla seed biodiesel (AB) and 30% eucalyptus oil (EU) on volume basis (called AB70EU30). The results showed stable engine operation and good operability of the engine-fuel system with the binary biodiesel fuel blend. The feasibility of this blend over a long-term endurance tests was explored. The specific assessment examination included the fate of cylinder head, pump plunger, injector nozzle, and piston crown, which affects the engine performance and engine life. The experimental results revealed better tribological performance characteristics with the binary fuel blend as compared to contemporary diesel fuel. No specific problem was encountered during the long-term endurance tests with the binary fuel blend using the modified engine parameters. The results show that the binary fuel mixture offers good potential for use as diesel fuel in CI engines while maintaining good performance and endurance.

Effects of a Diverging Cup on Swirl Number, Flow Pattern, and Topology of Premixed Flames

Impact of the diverging cup angle of a swirling injector on the flow pattern and stabilization of technically premixed flames is investigated both theoretically and experimentally with the help of OH* chemiluminescence, OH laser-induced fluorescence and particle image velocimetry (PIV) measurements. Recirculation enhancement with a lower position of the internal recirculation zone (IRZ) and a flame leading edge protruding further upstream in the swirled flow are observed as the injector nozzle cup angle is increased. A theoretical analysis is carried out to examine whether this could be explained by changes of the swirl level as the diffuser cup angle is varied. It is shown that pressure effects need in this case to be taken into account in the swirl number definition and expressions for changes of the swirl level through a diffuser are derived. It is demonstrated that changes of the swirl level including or not the pressure contribution to the axial momentum flux are not at the origin of the changes observed of the flow and flame patterns in the experiments. The swirl number without the pressure term, designated as pressure-less swirl, is then determined experimentally with laser Doppler velocimetry (LDV) measurements at the injector outlet for a set of diffusers with increasing quarl angles under nonreacting conditions and the values found corroborate the predictions. It is finally shown that the decline of axial velocity and the rise of adverse axial pressure gradient, both due to the cross section area change through the diffuser cup, are the dominant effects that control the leading edge position of the IRZ of the swirled flow. This is used to develop a model for the displacement of the recirculation bubble as the quarl angle varies that shows very good agreement with experiments.

Engine characteristics analysis of chaulmoogra oil blends and corrosion analysis of injector nozzle using scanning electron microscopy/energy dispersive spectroscopy

This work describes the performance, combustion and emission behavior of chaulmoogra oil blend and neat diesel in the variable compression ratio, variable speed compression ignition engine with exhaust gas recirculation (EGR). Exergy analysis was employed to investigate availability shares involved in the research engine. Artificial neural network (ANN) modeling and particle swarm optimization (PSO) are adopted with response surface methodology (RSM) in order to investigate the engine performance fuelled with ternary blend (65% diesel+25% chaulmoogra oil+10% diethyl ether) and neat diesel. In this work, compression ratio (CR) is varied from 14.5 to 20.6, engine speed varied from 1500 to 2400 revolution per minute (rpm) and EGR varied from 0 to 30%. The optimized condition was observed as 10% EGR, 18.1CR and 1672 rpm with respect to lesser exhaust emissions and enhanced thermal efficiency. Maximum brake thermal efficiency of 29.12% was observed 10% EGR rate and maximum exergy efficiency of 52.64% was observed for the ternary blend at the optimized engine condition. The results conclude that the RSM-ANN-PSO provide better the engine performance modeling with acceptable accuracy. The corrosion and wear analyses were done on the fuel injector nozzle and cylinder gaskets using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS).

CFD optimization of injection nozzles geometric dimensions of RHVT-machines in order to enhance the cooling capability

CFD optimization of injection nozzles geometric dimensions of RHVT-machines in order to enhance the cooling capability

Experimental mitigation of NO x emission in exhaust gases of CI engine fuelled with methyl ester of cottonseed oil blend

ABSTRACT This paper discusses the development of a B20 cottonseed oil blend for passenger vehicle with vanadium-based Selective Catalytic Reduction (SCR) technology addition on exhaust system. SCR is a progressive emissions governor technology organism that injects a liquid-Urea (also called aqueous urea, Ad Blue or Diesel Exhaust Fluid) through an injector nozzle into the exhaust manifold of diesel engine. The methyl ester of cottonseed oil blend was analysed in a single cylinder, 4-stroke, computerised water-cooled, diesel engine of 5.2 kW rated power for performance and emission characteristics with SCR. The results indicate that the emissions of the CI engine running on B20 blend with the catalytic convertor reduced NO x emission up to 76% with different quantity of dosing. However, it is noted that the brake thermal efficiency is reduced slightly by 2% for SCR due to the back pressure created by the SCR system.

Microscopic study on diesel spray under cavitating conditions by injecting fuel into water

Cavitation is a phenomenon which can significantly enhance spray breakup and affect the mixture preparation by introducing air or vapour bubbles. Attempts were made to capture the bubbles due to cavitation by injecting fuel into water based on the difference of density and refraction between water and vapour bubbles apart from the attempts to directly visualize vapour bubbles in an enlarged transparent nozzle. Tests were carried out with the employment of highly resolved microscope and ultra-high speed camera. The spray morphology and primary breakup characteristics in the near field were also investigated. It was found that irregularly shaped bubbles due to cavitation under low pressure can be observed in the nozzle. The increase of injection pressure (thereby increase of velocity) could significantly prolong the bubbles. At the nozzle outlet, the significant variation of pressure prolonged air bubbles into “thread” before collapsing. Vapour bubbles after exiting the injector nozzle were very small and the resolution of 3 µm/pixel was insufficient to capture the bubbles through direct visualization. A tree-shaped spray tip with significant radial propagation was observed. The sucking-in of water when the needle started to lift, the flow regime and the strong water resistance were closely related to the formation of tree-shaped spray tip. In addition, although the increase of fuel temperature generally enhanced the atomization of spray, the primary breakup of spray during the initial stage and end stage when the spray velocity was low surprisingly deteriorated for hot fuel.

Impact of swirl and bluff-body on the transfer function of premixed flames

The frequency response of three lean methane/air flames submitted to flowrate perturbations is analyzed for flames featuring the same equivalence ratio and thermal power, but a different stabilization mechanism. The first flame is stabilized by a central bluff body without swirl, the second one by the same bluff body with the addition of swirl and the last one only by swirl without central insert. In the two last cases, the swirl level is roughly the same. These three flames feature different shapes and heat release distributions, but their Flame Transfer Function (FTF) feature about the same phase lag at low frequencies. The gain of the FTF also shows the same behavior for the flame stabilized by the central insert without swirl and the one fully aerodynamically stabilized by swirl. Shedding of vortical structures from the injector nozzle that grow and rollup the flame tip controls the FTF of these flames. The flame stabilized by the swirler-plus-bluff-body system features a peculiar response with a large drop of the FTF gain around a frequency at which large swirl number oscillations are observed. Velocity measurements in cold flow conditions reveal a strong reduction of the size of the vortical structures shed from the injector lip at this forcing condition. The flame stabilized aerodynamically only by swirl and the one stabilized by the bluff body without swirl do not exhibit any FTF gain drop at low frequencies. In the former case, large swirl number oscillations are still identified, but large vortical structures shed from the nozzle also persist at the same forcing frequency in the cold flow response. These different flame responses are found to be intimately related to the dynamics of the internal recirculation region, which response strongly differs depending upon the injector used to stabilize the flame.

Evaluation of the cavitation effect on liquid fuel atomization by numerical simulation

Heavy duty diesel vehicles deteriorate urban air quality by discharging a large volume of air pollutants such as soot and nitrogen oxides. In this study, a newly introduced auxiliary device a fuel activation device (FAD) to improve the combustion efficiency of internal engines by utilizing the cavitation effect was closely investigated by the fluid flow mechanism via a numerical analysis method. As a result, the FAD contributed to fuel atomization from the injection nozzle at lower inlet pressure by reducing the pressure energy. The improved cavitation effect facilitated fuel atomization, and ultimately reduced pollutant emission due to the decrease in fuel consumption. The axial velocity along the flow channel was increased 8.7 times with the aid of FAD, which improved the primary break-up of bubbles. The FAD cavitation effect produced 1.09-times larger turbulent bubbles under the same pressure and fuel injection amount than without FAD.

Fault detection of injectors in diesel engines using vibration time-frequency analysis

In CI engines, injector spraying into the combustion chamber has extreme importance in fuel atomization and knocking control in the CI engines. Knocking and malfunction of engines due to faulty injectors can lead to efficiency reduction, damages, and acoustic noise. Much research is developing methods of engine knock detection. Hence, injector fault detection has not been addressed specifically, this research is focused on the subject and corresponding vibration amplitudes and frequencies, likely to cause the knock phenomenon. Welch test, Short-Term Fourier Transform (STFT), Wigner-Ville Distribution (WVD), and Choi-Williams Distribution (CWD) were employed for detailed scrutiny of vibrations generated by an under-load engine. For an ideal combustion, the acceleration peak values should be placed in the range of 0–10 kHz in time-frequency (TFR) diagram. While a faulty injection unit can cause components at higher frequency, between 10 and 25 kHz, in TFR diagram for each cylinder, and this can effects on the engine performance. Regarding the results which are presented in this research it infers that, in real-time performance monitoring of an engine, the STFT technique is more efficient for fault diagnosis of fuel injection nozzles and knock detection. By comparing vibration response of healthy and faulty injectors, the RMS and kurtosis of the faulty injectors showed an increase of 12.9% and 20.6% respectively.

Effect of oil-injection on twin screw compressor performance

Oil-injection improves twin-screw compressor performance significantly and its overall effect depends on the working fluid mass flow rate, the shaft speed, the injection position and the injected oil temperature. However, the individual contribution of each of these variables to the machine performance is yet not fully researched. Therefore, tests have been carried out on an air compressor with a male rotor diameter of 98mm, with injection nozzle sizes of 2, 3 and 4mm and with a nozzle of multiple holes. Tests were carried out with discharge pressures of 6.5, 8.5, 10.5 and 12.5 bar and rotor shaft speeds of 3000, 4000 and 5000 RPM. The results from the tests were compared with performance estimates at the same operating conditions as measurements against the standard injection nozzle of 5mm diameter. It was found that there is an optimum quantity of oil injected to obtain the best performance.

Experimental and modeling study of liquid fuel injection and combustion in diesel engines with a common rail injection system

Fuel injection is one of the most important processes in compression-ignition internal combustion engines owing to its significant impact on the exhaust emissions and thermal efficiency. In this study, experiments were carried out to investigate the influence of injection pressure and injection timing on the temporal evolution of the injection rate and injection duration in a specially designed experiment rig equipped with a common rail injection system. It is well known that the injection signal from the electronic control unit (ECU) of the injection system, which is often the only injection information available in engine operation and experiments, gives little information about the actual injection rate profile. It is shown in the present experiments that the actual injection duration is usually longer than the energizing time (ET). The time delay between the actual injection of the fuel and the ECU signal is about 0.3–0.4 ms, and the time delay appears to be insensitive to the injector geometry and injection pressure condition. The injection process can be characterized as five stages, a fast injector valve opening stage, a slow valve opening stage, a valve fully open stage, followed by a slow valve closing stage, and finally a rapid valve closing stage. It is found that the first stage, the fast valve opening stage, is insensitive to the injection pressure and injector nozzle diameter; however, the peak injection rate is a strong function of these parameters. The second and the third stage may not appear with a short injection duration. A new injection model was developed for the common rail injection system, which was capable of simulating the instantaneous fuel injection rate and injection duration for a range of injection pressure and injection duration. The model was shown to be able to replicate the experimental injection rate profile of the present experiments and experiments found in the literature for common rail injection system. The new injection model was applied to predict the effect of injection pressure and injection duration on the performance of a diesel engine under various engine speed and load conditions. The new injection model was shown to be able to describe the injection mass flow rate, which eventually leads to a reasonably good prediction of the variations of the spray development, in-cylinder pressure, heat release rate, and emissions.

Development and characterization of a high-sensitivity fiber Bragg grating-based vibrating nano-probe for 3D measurement

PurposeThere is an increasing demand for higher-accuracy dimensional measurements of nano- and micro-structures. Recently, the authors presented a fiber Bragg grating (FBG) sensor-based dynamic nano-coordinate-measuring machine (CMM) probe for true three-dimensional coordinate measurement, in which a specific mechanical structure with several FBG sensors was developed to provide the probe with sensitivity to loading in all directions.Design/methodology/approachThe study presents a three-dimensional sensing and demodulation system based on an improved matched filter design and the time division multiplexing technique that helps solve the problem of multiplex FBG-signals conflicts. In addition, the application of the dynamic mode of the probe system effectively solves the problem presented by the surface interaction forces.FindingsConsequently, this FBG-based vibrating probe system has increased sensitivity to strain, while maintaining smaller contact force. The experiments for testing probe performance show that the prototype yielded a measurement resolution of 13 nm, a repeatability of 50 nm and a vertical measurement force of less than1.5 mN.Research limitations/implicationsThe force tests in the horizontal directions are difficult to conduct because both the probe and the dynamometer are only adaptable to vertical use.Practical implicationsDevelopment of the FBG-based dynamic nano-coordinate-measuring machine probe will achieve a new and inexpensive method for higher-accuracy dimensional measurements of nano- and micro-structures, such as micro-electromechanical systems, micro-fluidic chips, inkjet and diesel engine injector nozzles that are in overall dimensions within the micrometer scale.Originality/valueThe study presents a three-dimensional sensing and demodulation system for the vibrating nano-coordinate-measuring machine probe based on FBG sensors. The prototype yielded a measurement resolution of 13 nm, a repeatability of 50 nm and a vertical measurement force of less than1.5 mN.

Experimental Study on the Effects of Nozzle Temperature on Internal Deposits of a Gasoline Direct Injector

Internal deposit formation in the injector nozzle can both restrict the fuel flow and alter the spray characteristics of the injectors, which will lead to a loss in power and fuel economy, as well ...

Analysis of the turbulent flow structure in a jet stirred reactor using proper orthogonal decomposition

The accuracy of the experimental measurement of gas phase chemical kinetics related quantities using Jet Stirred Reactors (JSR) depends to a large degree on the homogeneity of the mixture inside the reactor. It is well-established that the mixing process in fluids is dominated by turbulent motions. Coherent turbulent structures are identified by applying the technique of Proper Orthogonal Decomposition (POD) based on previously performed highly-resolved large-eddy simulations. The structures of the highest energies are generated by the jets which inject fresh gases and in the wakes of the pipes leading to the injection nozzles. Furthermore, lower energetic regions were observed in the proximity of the impingement areas of the inlet jets on the surface of the spherical reactor chamber. The data provided herein contributes to the understanding of the flow dynamics in JSRs and aims to guide their future development in order to increase measurement accuracy.