Needle Valve Lift Research Articles

Investigation of Needle Motion Profile Effect on Diesel Spray in Near-Nozzle Field.

A variety of needle-motion profiles are used in diesel injectors. However, it is unclear what the underlying mechanism is to determine the needle-motion profiles and how they affect the spray dynamics. It has been of significant interest to examine how the spray dynamics will change if only altering the needle valve opening speed or closing speed while all other parameters are kept the same. The different needle-motion profiles were obtained using a piezo nozzle (Nozzle #P) and a solenoid nozzle (Nozzle #S), which have identical nozzle geometry. By utilizing the X-ray imaging technique, it was observed that the average needle valve speed of Nozzle #P was 51% higher at the opening stage but 17% lower at the closing stage than Nozzle #S. When the needle valve lift is low (approximately 200 μm), the needle valve opening speed has a crucial effect on spray dynamics. The faster needle valve opening of Nozzle #P results in a 42% larger spray spreading angle and 34% lower spray velocity at the downstream field. The spray dynamics may be controllable by properly designing the needle-motion profiles in the scenarios of the low needle lifts. However, when the needle valve is sufficiently open (approximately over 200 μm), almost identical spray characteristics were observed regardless of the needle-motion profiles.

Experimental study into the effects of stability between multiple injections on the internal flow and near field spray dynamics of a diesel nozzle

To improve the control accuracy and injection stability in multiple injection processes, the coupling effects of needle valve wobbling and residual bubbles on the nozzle internal flow and near field in diesel engines were researched. And the high-speed microscopic imaging technology was employed to study the dynamics behaviors of a real-size tapered hole nozzle under different multiple injection strategies. Research results indicated that during the pre-injection and post-injection process, the difference in throttling effect caused by the wobbling of the needle valve is the main reason for the instability of the fuel injection quantities. As the pulse widths increases, the actual injection duration and the maximum needle valve lift increased, so that the throttling position changes from the passage between the needle valve and the needle seat to the nozzle holes, and two kinds of string cavitation are gradually formed. String cavitation starts at the needle valve apex and propagates outward along the nozzle wall in a sinusoidal wave trend. During the main injection stage, the spray cone angle showed a boot-shaped trend, forming a development stage, a transformation stage and a stable stage. When the needle valve rises and falls, there is air suction in the nozzle, and there is a secondary disturbance phenomenon. During the injection, the spray pattern is affected by the combined influences of the axial momentum and radial momentum of the injected fuel, resulting in a difference between the secondary disturbance and the primary breakup. When the secondary disturbance occurs, the subsequent high-speed fuel will hit the spray mass with a slow speed, which forms a vortex at both ends to develop radially, and expands the range of the spray tip.

Study on Influencing Factors and Laws of Fuel Injection Consistency of Common Rail Injector

In order to study the influence of parameters of common rail injector internal components on cycle injection consistency, its simulation model is established by AMESim, and the model is validated by the experimental injection rate data. The effects of solenoid valve spring preload, gag bit lift, fuel discharge hole diameter, fuel inlet hole diameter, needle valve lift, needle valve preload and nozzle diameter on the change of injection quantity under different operating conditions are studied by simulation method, and the impact weight of each parameter on fuel injection consistency is analyzed. The results show that the preload of solenoid valve, fuel discharge hole diameter, oil inlet hole diameter, needle valve lift and nozzle diameter are the main parameters affecting the consistency of cycle injection. The percentages of five parameters influencing on the consistency of cyclic injection are 8.68-16.84%, 11.41-23.68%, 17.2086-37.74%, 12.772-18.34% and 9.69-37.27% respectively.

Experimental investigations into the effects of string cavitation on diesel nozzle internal flow and near field spray dynamics under different injection control strategies

On the test bench of the high-pressure common rail injection system with a high-speed camera, the visualization experiments of real-size tapered hole nozzle of the diesel engine were performed to obtain needle valve lift, string cavitation in the sac chamber and nozzle hole, residual bubbles and near-field spray characteristic. And a high-pressure sensor was utilized to measure the real pressure fluctuation for the nozzle inlet. On the basis, under different control strategies, the comprehensive effects of needle valve throttling and pressure fluctuation for nozzle inlet on the internal flow and near-field spray characteristic under the multiple injections were studied. Research indicated that the spray cone angle and the spray area ratio in the main injection stage shows a boot-shaped increasing trend of slowness and then abruptness. In the development stage, the spray cone angle fluctuates in a little range (20°-30°); In the saturation phase, the spray cone angle fully develops and the fluctuation is relatively stable (40°-50°). As the throttling position shifts, there is an obvious string cavitation process, and the spray cone angle increases suddenly. In the process of pre-injection and post-injection, needle valve and valve seat throttling and lift instability cause fuel pressure fluctuation in the control chamber and sac, which is the main immediate cause of the fluctuation of low fuel injection quantity. Besides, the interval time between multiple injections, on the one hand, affects the state of residual bubbles in the nozzle before the next injection beginning, on the other hand, it also affects the stability of the inlet pressure at this time. The flow transition in the low-lift zone and the cavitation changing in the high-lift stable zone also cause transformation in the form of pressure fluctuation.

Design, modeling, and analysis of giant magnetostrictive injector

In view of the shortcomings of the traditional high-pressure common rail electronically controlled injector in needle valve driving mode and driving components, a direct-drive type giant magnetostrictive injector (GMI) is designed. Based on the working principle of the GMI, the magnetic field model, hysteresis nonlinear model, and magnetostrictive model are established. The magnetic field model and hysteresis nonlinear model are simulated and analyzed, and the GMA magnetostrictive model is solved numerically and verified experimentally. Finally, COMSOL Multiphysics software is used to conduct electro-magnetic-mechanical coupling simulation analysis on the whole GMI output model, and the relationship between the needle valve lift of the injector and the output displacement of the actuator was obtained. The research results show that the displacement curve calculated using the GMA magnetostrictive model is basically consistent with the displacement curve measured by experiment, which proves that the established model can reflect the actual situation and verify the correctness of the model. The magnitude and direction of the GMI needle valve lift are determined by the magnitude and direction of GMA output displacement. The two directions are opposite, and the size ratio is 4, so when the current is 6 A, the GMA output displacement is 0.12 mm, and the needle valve lift is 0.48 mm, which meets the requirements of the injector needle valve lift, verifies the feasibility of GMI structure design, and has good theoretical and practical guiding values.

Experimental Study into the Effects of Stability between Multiple Injections on the Internal Flow and Near Field Spray Dynamics of a Diesel Nozzle

To understand the coupling effects of needle valve wobbling and residual bubbles on the nozzle internal flow and near field in diesel engines, high-speed microscopic imaging technology was employed to study the dynamics behaviors of a real-size tapered hole nozzle. Research results indicated that during the pre-injection and post-injection process, the difference in throttling effect caused by the wobbling of the needle valve is the main reason for the instability of the fuel injection quantities. As the pulse widths increases, the actual injection duration and the maximum needle valve lift increased, so that the throttling position changes from the passage between the needle valve and the needle seat to the nozzle holes, and the cavitation mode changes from geometrically induced cavitation to string cavitation. During the main injection stage, the spray cone angle and spray area ratio showed a boot-shaped trend of firstly low and then high, forming a development stage, a transformation stage and a stable stage. And in the initial stage of injection, the spray pattern is affected by the combined influences of the axial momentum and radial momentum of the injected fuel, resulting in a difference between the second spray disturbance and the primary breakup.

Preferential cavitation and friction-induced heating of multi-component Diesel fuel surrogates up to 450MPa

The present work investigates the formation and development of cavitation of a multicomponent Diesel fuel surrogate discharging from a high-pressure fuel injector operating in the range of injection pressures from 60MPa to 450MPa. The compressible form of the Navier-Stokes equations is numerically solved with a density-based solver employing the homogeneous mixture model for accounting the presence of liquid and vapour phases, while turbulence is resolved using a Large Eddy Simulation approximation. Simulations are performed on a tapered heavy-duty Diesel engine injector at a nominal fully-open needle valve lift of 350μm. To account for the effect of extreme fuel pressurisation, two approaches have been followed: (i) a barotropic evolution of density as function of pressure, where thermal effects are not considered and (ii) the inclusion of wall friction-induced and pressurisation thermal effects by solving the energy conservation equation. The PC-SAFT equation of state is utilised to derive thermodynamic property tables for an eight-component surrogate based on a grade no.2 Diesel emissions-certification fuel as function of pressure, temperature, and fuel vapour volume fraction. Moreover, the preferential cavitation of the fuel components within the injector's hole is predicted by Vapour-Liquid Equilibrium calculations; lighter fuel components are found to cavitate to a greater extent than heavier ones. Results indicate a significant increase of temperature with increasing pressures due to friction-induced heating, leading to a significant increase in the mean vapour pressure of the fuel and an increase of the mass of fuel cavitating, but at the same time to an unprecedented decrease of cavitation volume inside the fuel injector with increasing injection pressure. This has been attributed to the shift of the pressure drop from the feed to the back pressure inside the injection hole orifice as fuel discharges; as injection pressure increases, so does the pressure inside the orifice, confining the location of cavitation formation to a smaller volume attached to the upper part of orifice, thus restricting cavitation growth.

Formation and development of cavitation in a transparent nozzle with double orifices on different planes

ABSTRACT In this paper, the formation and development of cavitation in a transparent nozzle with double orifices on different planes are studied through a visual transparent nozzle experiment. The effect of different injection conditions on the formation and development of cavitation are analyzed. The results demonstrate that with a decrease in needle valve lift and an increase in injection pressure, the amount of cavitation is augmented, which significantly improves the energy utilization efficiency and reduces the emission of harmful substances. The instantaneous and mean images reveal that cavitation in the nozzle presents clear cycle-to-cycle variation and that string cavitation is related to the geometry of nozzle.

Application of X-ray micro-computed tomography on high-speed cavitating diesel fuel flows

The flow inside a purpose built enlarged single-orifice nozzle replica is quantified using time-averaged X-ray micro-computed tomography (micro-CT) and high-speed shadowgraphy. Results have been obtained at Reynolds and cavitation numbers similar to those of real-size injectors. Good agreement for the cavitation extent inside the orifice is found between the micro-CT and the corresponding temporal mean 2D cavitation image, as captured by the high-speed camera. However, the internal 3D structure of the developing cavitation cloud reveals a hollow vapour cloud ring formed at the hole entrance and extending only at the lower part of the hole due to the asymmetric flow entry. Moreover, the cavitation volume fraction exhibits a significant gradient along the orifice volume. The cavitation number and the needle valve lift seem to be the most influential operating parameters, while the Reynolds number seems to have only small effect for the range of values tested. Overall, the study demonstrates that use of micro-CT can be a reliable tool for cavitation in nozzle orifices operating under nominal steady-state conditions.

Numerical analyses of transient flow characteristics within each nozzle hole of an asymmetric diesel injector

In order to simultaneously study the differences in transient flow characteristics within each nozzle hole of an asymmetric multi-hole diesel injector used in off-road machinery, a three-dimensional gas–liquid two-phase flow model of cavitation was developed, which takes the influence of injection conditions and bubble number density into consideration. The computational model was validated by comparing it with the experiment conducted by Winklhofer. The result shows high level of consistency and sensitivity. Following the successful verification of the model, the differences in transient flow characteristics within each nozzle hole based on a P-type asymmetric multi-hole nozzle with sac were analyzed using the model. Results obtained from simulation shows that the cavitation phenomenon, velocity profile and mass flow rate in each nozzle hole of an asymmetric injector differ greatly. The hole with the higher nozzle hole angle (wider angle between nozzle hole axis and needle axis) was more inclined to cavitate, therefore the cavitation effect intensity is directly related to the size of the nozzle hole angle. During the lifting stages of the needle valve, the cavitation effect for each nozzle hole and the fuel flow velocity are gradually enhanced while on the contrary, the fuel flow velocity decreases and cavitation effect slightly increases at the closing stages of the needle valve lift. Also, the cavitation morphology at the same needle valve lift in any nozzle hole differs during opening and closing stages of fuel injection. In addition, the fuel flow velocity profile from the needle valve opening at the sac and into the hole of each nozzle shows that, in the order of increasing nozzle hole angle βi, the velocity effect gradually reduces as a result of dramatic change in flow direction.

小弁開度燃料噴射におけるディーゼル噴霧液滴の分裂特性

A laser 2-focus velocimeter (L2F) was used for measurements of velocity and size of droplets in diesel fuel sprays. Diesel fuel was injected intermittently into the atmosphere using a 8-hole injector nozzle. The diameter of the nozzle orifice was 0.112mm. The rail pressure was set at 40MPa by using a common rail system. The period of injector solenoid energizing was set at 0.8ms to investigate the spray behavior under small valve opening. The L2F had a micro-scale probe which consists of two foci. The focal diameter was about 3μm, and the distance between two foci was 20μm. The data sampling rate of the L2F system was markedly high as 15MHz. L2F measurement was conducted at 10mm downstream from the nozzle exit. Temporal and spatial changes in the velocity and size of droplets inside sprays were investigated near the nozzle orifice and were correlated with the needle valve lift of the injector nozzle. Spray images were taken by using a 180ns spark light source, and temporal changes of the spray width were estimated. The spray was divided into two regions; the inner region and the periphery region. The results showed that temporal changes in droplet velocity at the spray center corresponded with the temporal changes in needle valve lift. The droplets’ Weber number in the inner region was larger than that in the periphery region of the spray. It was found that the turbulence intensity of droplet velocity was strongly correlated to the size of droplet in the inner region of the spray.

Simulation and Measurement of Fuel Injection Quantity Based on TB4P

In order to improve the measurement accuracy of fuel injection quantity based on Test Bench for fuel injection Pump (abbr. TB4P), on the basis of the function between needle valve lift and fuel injection quantity, two-level pressure adjustment module, which combines proportional flow rate valve with pressure sensor and takes advantage of spring of fuel injector, is used to control the outlet pressure of fuel injection pump, which results in the fuel injection pressure stably. Fuel injection pump and fuel injector are modeled by use of HCD of AMESim, and the system model of fuel injection quantity measurement is built. Simulation curve of fuel injection quantity is got by AMESim, which is compared with the curve of standard fuel injection quantity according to relative error. The results show that the relative error from the data of simulation system is smaller, so the methods of measurement and simulation in this paper are effective.

Investigation of the injection process and combustion of a dimethyl ether engine with different nozzle flow areas

Dimethyl ether (DME) is a promising alternative fuel, which can be used as a substitute for fossil diesel fuels, with a smaller lower heating value. When used in diesel engines, the nozzle flow area (i.e. the number of nozzle holes × nozzle hole diameter) of the engine is normally increased to maintain the engine power. In this study, three kinds of nozzle (with nozzle flow areas of 5 × 0.30 mm, 5 × 0.35 mm, and 5 × 0.40 mm respectively) were prepared. With a two-cylinder diesel engine, the effects of the nozzle flow area on the DME injection process and combustion characteristics were investigated. The experimental results indicate that the DME acoustic velocity shows no variation with the change in the nozzle hole diameter and that the DME injection timing is not affected. However, as the nozzle hole diameter increased, the DME line pressure (and, in particular, the second peak of the line pressure on the nozzle side) is greatly decreased. Meanwhile, the fall of the needle valve lift is advanced, resulting in a decrease in the injection duration. Further, the engine ignition delay is slightly increased, the total combustion duration is slightly shortened, and the engine brake thermal efficiency is slightly elevated.

Digital fuel measurement of fuel injection pump test bench based on needle valve lift

Digital fuel measurement of fuel injection pump test bench based on needle valve lift

Injection Rate Measurement of a Gaseous Fuel Injector Using a Beam Cut Method

Injection rate of a gaseous fuel injector was calculated by measuring the needle valve lift history. In our lab, a gaseous fuel injection rate meter using 1-dimensional pipe flow was developed. In the present study, the measurement accuracy of the injection rate meter was examined by comparing the theoretical injection rate estimated from the needle valve lift history. The needle valve lift was measured using an optical method. A small beam cut plate is attached to the needle valve of the gaseous fuel injector. A laser beam passes through the beam cut plate, and the variation of the beam intensity was measured with a photo sensor. From the beam intensity, the needle valve lift history was estimated. One-dimensional, compressible, inviscid, adiabatic flow was assumed, and the instantaneous mass flow rate through the needle valve sheet, the injector sack, and the injection hole was estimated. The estimated injection rate was compared with that obtained with the gaseous fuel injection rate meter. The estimated and measured injection rates agree relatively well even at transient duration. It is shown that the injection rate meter has high reliability and accuracy.

ディーゼル燃料弁のニードルバルブのリフト計測法

This paper describes the new detecting methods of needle valve lift behavior in diesel fuel injector. Authors detected the needle valve lift behavior by using two types of sensors which are the strain gauge type sensor and the piezo-electric sensor in order to verify the fuel injection characteristic for medium speed diesel engine. It was found that these sensors had enough quick response concerning to both opening and closing timing of the needle valve without modification of fuel injector's structure.