Effective Injection Velocity Research Articles

Investigation on spray combustion modeling for performance analysis of future low- and zero-carbon DI engine

Global warming issues and fossil fuel depletion crisis have forced transportation industry to seek clean engine fuels both liquid and gaseous. Dual-fuel mode with high-pressure direct injection (HPDI) has been recognized as mainstream method in developing flexible-fuel internal combustion engines (ICEs). But flexible-fuels’ physicochemical properties and spray combustion characteristics under HPDI have changed a lot. Unfortunately, there is currently no universal model for predicting spray combustion behaviors and analyzing performance of flexible-fuel ICEs. Therefore, this paper aims to develop a novel spray combustion model and provide optimal injection and combustion strategies for performance improvement of low- and zero-carbon HPDI ICEs. Based on balance of momentum change and vortex ring drag force, the jet spray effective injection velocity is obtained. Then the jet spray penetration under varying injection rate is solved. Finally, the developed model is established and validated experimentally, with the spray combustion characteristics of various fuels investigated. The results show that the developed model has a good accuracy and robustness for flexible-fuels’ characteristic analysis. Meanwhile, multiple-injection could increase the combustion efficiency (CE) over 10.27 % than single-injection, and CE increases with dwell time. Moreover, CE of H2 in nitrogen-oxygen (N2–O2) atmosphere is 10.15 % higher than that in argon-oxygen (Ar–O2) atmosphere.

A flexible diesel spray model for advanced injection strategy

Diesel engine has witnessed an increasingly stringent emission regulation due to its concomitant serious environmental pollution problems. Various advanced injection strategies have been proposed to cope with the emissions issues of diesel engine, but also increase the difficulty for evaluating spray tip penetration (Stip). Meanwhile the time dependence characteristics of Stip in multiple-injection is still unknown so far. Gaining a thorough understanding of Stip is extremely important to assess the spray mixing process and further adjust injection and combustion strategy to maximize the efficiency of diesel engines. Therefore, this paper aims to develop a flexible spray model for the quick and robust prediction of Stip under various advanced injection strategies and study the time dependence characteristics of Stip in multiple-injection. First a reduced analytical expression of effective injection velocity is derived based on the assumption of transient quasi-steady jet. Then a variable Stokes number (St) depending upon the change of injection velocity is formulated. Next a single injection spray model is developed by embedding the effective injection velocity in an existing analytical spray model. Meanwhile, the multiple-injection spray model is established with a penetrating enhancement coefficient (EC) introduced to correct its time dependence characteristics of Stip. Finally, the newly developed Stip models are validated experimentally under varied injection strategies. The results show that the newly developed Stip models could flexibly apply to various advanced injection strategies, and for the multiple-injection strategy, the first injection quantity and the dwell time are two major impact factors to the second injection.

Influence of Cavitation in Common-Rail Diesel Nozzles on the Soot Formation Process through Measuring Soot Emissions

The influence of cavitation in common-rail diesel nozzles on the soot formation process has been analysed experimentally. The soot formation process was characterized by measuring soot emissions in a single-cylinder engine, which was mounted on a test bench equipped with an opacimeter. In order to do this, operating conditions where the soot oxidation process was equivalent were chosen, whereby differences in the soot formation process were possible to be analysed. The results achieved confirm that cavitation provokes a soot formation process reduction. This reduction can be attributed by combining results of three effects: a reduction of the effective diameter, an increase in effective injection velocity, and an increase in turbulence level inside the nozzle orifice leading to a longer lift-off length. The three effects lead to a decrease in relative fuel/air ratio at the lift-off, therefore explaining the soot formation reduction.

Phenomenological modeling of diesel spray with varying injection profile

Accurate and quick prediction of spray characteristics such as spray penetration is paramount for the understanding and quantitative analysis of the combustion process in diesel engines, in order to perform parametric study on advanced combustion process in diesel engines, zero-dimensional diesel spray model is often used for the prediction of the spray evolution. In this study, a previous zero-dimensional diesel spray model applied for the spray penetration prediction including the part after the end of injection with a constant injection rate was extended to the cases with varying injection rate. The effective injection velocity was introduced into the previous spray model, which is defined as the ratio of the momentum flux and fuel mass flow rate over the spray tip cross-sectional area. Combined with this definition, the analysis of effective injection rate and its response time was performed during and after the end of injection. After that, the fuel mass flow rate and momentum flux over the spray tip cross-sectional area were derived for varying injection rate even after the end of injection based on the momentum and fuel mass conservation along the spray axis, and further the spray penetration. Finally, the developed model was validated by comparing with the experimental data.

Effects of cavitation in common-rail diesel nozzles on the mixing process

A study to experimentally analyze the effect of cavitation on the mixing process in diesel nozzles was carried out. The mixing process was studied through the spray cone angle. It was characterized in two different scenarios: with the liquid length (nearly realistic conditions, that is, evaporative but non-reactive spray) and the heat release fraction (fully realistic conditions, that is, evaporative and reactive spray). In both studied scenarios, the increase in spray cone angle caused by the cavitation phenomenon, which leads to a better mixing process, has been confirmed. Nevertheless, when the variations of the effective injection velocity and the spray cone angle obtained by comparing a cylindrical nozzle (i.e. a nozzle that promotes the cavitation phenomenon) with a conical nozzle (i.e. a nozzle that inhibits this phenomenon) were analyzed together, it was found that, for the cases studied here, the mixing process worsens with the cylindrical nozzle.

Using a homogeneous equilibrium model for the study of the inner nozzle flow and cavitation pattern in convergent–divergent nozzles of diesel injectors

In this paper, the behaviour of the internal nozzle flow and cavitation phenomenon are numerically studied for non-conventional Diesel convergent–divergent nozzles in order to assess their potential in terms of flow characteristics. The used nozzles differ each other in the convergence–divergence level of the orifices but all of them keep the same diameter at the middle of the nozzle orifice. The calculations have been performed using a code previously validated and able to simulate cavitation phenomenon using a homogeneous equilibrium model for the biphasic fluid and using a RANS method (RNG k-ε) as a turbulence modelling approach. For the simulations, one injection pressure and different discharge pressures were used in order to assess the characteristics of nozzles for different Reynolds conditions involving cavitating and non-cavitating conditions.The comparison of the nozzles has been carried out in terms of flow characteristics such as mass flow, momentum flux, effective velocity and other important dimensionless parameters which help to describe the behaviour of the inner flow: discharge coefficient (Cd), area coefficient (Ca) and velocity coefficient (Cv). Additionally, the nozzles have been compared in terms of cavitation inception conditions and cavitation development.The study has shown a high influence on the results of the level of convergence–divergence used in the nozzles. In these nozzles, the vapour originated from cavitation phenomenon came from the throttle of the orifice at the midpoint, and it extended along the whole wall of the divergent nozzle part towards the outlet of the orifice. The main results of the investigation have shown how the different geometries modify the cavitation conditions as well as the discharge coefficient and effective velocity. In particular, the nozzle with highest convergence–divergence level showed cavitation for all the tested conditions while for the nozzle with lowest convergence–divergence level, the cavitation phenomenon could be avoided for high discharge pressures. Additionally, the nozzle with highest convergence–divergence level showed the lowest discharge coefficient values but similar effective injection velocity than the nozzle with lowest level of convergence–divergence level despite of its higher orifice outlet area.

Analysis of the combined effect of hydrogrinding process and inclination angle on hydraulic performance of diesel injection nozzles

A computational study to investigate the influence of the orifices inclination and the rounding radius at the orifice inlet (consequence of the hydro-erosive grinding process applied after the orifices machining) over the internal nozzle flow is performed in this paper. The study starts with the analysis of experimental results where the mass flow and momentum flux of two nozzles with very different values of these two variables are compared. This analysis shows relatively small differences in terms of mass flow and momentum flux, since the higher losses associated to the higher deflection of the streamlines with a higher inclination of the orifices are counteracted by the higher rounding radius, which favours the flow entrance to the orifice.To explain this experimental outcome, an extensive computational study involving nine geometries that combine different inclination angles and rounding radius is conducted, in order to quantify the influence of both parameters on the flow separately, as well as to assess the potential of their combination. These geometries are compared in terms of discharge coefficient, critical cavitation conditions and effective injection velocity, among others. Results show differences up to 15% in terms of mass flow rate and 8% for the effective injection velocity among the two extreme cases (lowest inclination and highest hydro-erosion level versus the nozzle with the highest inclination and lowest hydro-erosion level). Given the importance of these phenomena on the subsequent mixing and combustion processes, the results hereby presented are of interest for diesel engines injectors and combustion chambers designers.

Impact of Varying Indium(x) Concentration and Quantum Confinement on PBTI Reliability in InxGa1-xAs FinFET

In this letter, we present a comparative study of positive bias temperature instability (PBTI) reliability in InxGa1-xAs FinFET with varying Indium ( $x=0.53$ , 0.70) percentage and quantization [bulk, quantum well (QW)]. Due to lower effective transport mass and higher injection velocity, In0.7Ga0.3As QW FinFET provides better performance than In0.53Ga0.47As bulk FinFET. However, stronger quantization lowers the effective barrier height between the carriers and defect density in the oxide causing degraded PBTI reliability in the former. Our preliminary PBTI stress study shows that In0.7Ga0.3As QW FinFETs may need to operate at a gate overdrive of 0.1 V (i.e., near threshold operation) to meet 10 years of reliability specifications at 85 °C.

Comparative analysis of hole transport in compressively strained InSb and Ge quantum well heterostructures

Compressively strained InSb (s-InSb) and Ge (s-Ge) quantum well heterostructures are experimentally studied, with emphasis on understanding and comparing hole transport in these two-dimensional confined heterostructures. Magnetotransport measurements and bandstructure calculations indicate 2.5× lower effective mass for s-InSb compared to s-Ge quantum well at 1.9 × 1012 cm–2. Advantage of strain-induced m* reduction is negated by higher phonon scattering, degrading hole transport at room temperature in s-InSb quantum well compared to s-Ge heterostructure. Consequently, effective injection velocity is superior in s-Ge compared to s-InSb. These results suggest s-Ge quantum well heterostructure is more favorable and promising p-channel candidate compared to s-InSb for future technology node.

A comprehensive study on the effect of cavitation on injection velocity in diesel nozzles

Results when testing cavitating injection nozzles show a strong reduction in mass flow rate when cavitation appears (the flow is choked), while the momentum flux is reduced to a lesser extent, resulting in an increase in effective injection velocity. So as to better understand the origin of this increase in effective injection velocity, the basic equations for mass and momentum conservation were applied to an injection nozzle in simplified conditions.The study demonstrated that the increase in injection velocity provoked by cavitation is not a direct effect of the latter, but an indirect effect. In fact, the vapor appearance inside the injection hole produces a decrease in the viscosity of the fluid near the wall. This leads to lower momentum flux losses and to a change in the velocity profile, transforming it into a more “top hat” profile type. This change in the profile shape allows explaining why the momentum flux reduction is not so important compared to that of the mass flow rate, thus explaining why the effective injection velocity increases.

가스제트 분무 모델을 이용한 다양한 분사 패턴의 디젤 분무에 대한 CFD 및 0-D 시뮬레이션 비교 연구

The CFD simulation of diesel spray tip penetrations were compared with 0-D simulation for experimental data obtained with common rail injection system. The simulated four injection patterns include single, pilot and split injections. The CFD simulation of the spray penetration over these injection patterns was performed using the KIVA-3V code, which was implemented with both the standard KIVA spray and original gas jet sub-models. 0-D simulation of the spray tip penetration with time-varying injection profiles was formulated based on the effective injection velocity concept as an extension of steady gas jet theory. Both the CFD simulation of the spray tip penetration with the standard KIVA spray model and 0-D simulation matched better with the experimental data than the results of the gas jet model for the entire fuel injection patterns.

A contribution to the understanding of cavitation effects in Diesel injector nozzles through a combined experimental and computational investigation

In this paper a combined experimental and computational study was carried out in order to assess the ability of a homogeneous equilibrium model in predicting the experimental behaviour observed from the hydraulical characterization of a nozzle. The nozzle used was a six-orifice microsac nozzle, with cylindrical holes, and therefore inclined to cavitate. The experimental results available for the validation purpose comprised measurements of mass flow rate and spray momentum flux, which correctly combined provide also fundamental information such as discharge coefficient, nozzle exit effective velocity and area contraction. The model was proved to be able of reproducing the experimental results with high degree of confidence and, through the exploration of the internal flow, allowed the explanation of widely reported experimental findings related to cavitation phenomena: the mass flow choking induced by cavitation and the increment of effective injection velocity.

Investigation of scalability of In 0.7Ga 0.3As quantum well field effect transistor (QWFET) architecture for logic applications

In this paper, the scalability of In 0.7Ga 0.3As QWFET is investigated using two-dimensional numerical drift–diffusion simulation. Numerical drift–diffusion simulations were calibrated using experimental results on short-channel In 0.7Ga 0.3As QWFETs [7] to include the effects of velocity overshoot. Logic figures of merit (sub-threshold slope, saturated threshold voltage, drain induced barrier lowering, I ON/ I OFF ratio over a specified gate swing, effective injection velocity and intrinsic switching delay) extracted from the numerical simulations are in excellent agreement with the experimental data. Three alternate QWFET device architectures are proposed and thoroughly investigated for 15 nm node and beyond logic applications. Amongst them, double-gate In 0.7Ga 0.3As QWFET shows the best scalability in terms of logic figures of merit, thus making it an ideal candidate for the design and demonstration of the ultimate scaled transistor.

Numerical simulation and extended validation of two-phase compressible flow in diesel injector nozzles

In this paper, the ability of a computational fluid dynamics code to reproduce cavitation phenomena accurately is checked by comparing data acquired by numerical simulations against those obtained from different experiments involving the mass flow, the momentum flux, and the effective injection velocity. Cavitation is modelled using a single-phase cavitation model based on a barotropic equation of state together with a homogeneous equilibrium assumption. In the research reported in this paper, the ability to use the code for actual diesel injector nozzle geometries and conditions has been checked and validated. The main contribution of the present investigation and what makes it different from previous work in the literature is the consideration of extended experimental data for validation purposes: the mass flow, the momentum flux at the nozzle exit, and the effective injection velocity. These are unique features in contrast with other publications, which normally take into account at the most, if at all, the cavitation morphology or the mass flow. The results obtained and their comparison with available experimental data show how the model is able to predict the behaviour of the fluid in such conditions with a high level of confidence.

Validation of a code for modeling cavitation phenomena in Diesel injector nozzles

In this paper, the validity of a code implemented for OpenFOAM ® for modeling cavitation phenomena has been checked by comparing data acquired by numerical simulations against data obtained for a simple contraction nozzle and for a real diesel injector nozzle. The comparison of numerical and experimental data has been performed, for the simple nozzle, in terms of mass flow rate, velocity at the exit and pressure and cavitation distributions. The numerical results for the real diesel nozzle geometry have been validated with experimental measurements of mass flow rate, momentum flux and effective injection velocity. The results obtained in both cases and their comparison with available experimental data showed that the model is able to predict with a high level of confidence the behavior of the fluid in such conditions.

Nozzle flow and atomization characteristics of ethanol blended biodiesel fuel

This study was conducted to investigate the injection and atomization characteristics of biodiesel–ethanol blended fuel. The injection performance of biodiesel–ethanol blended fuel was analyzed from the injection rate characteristics using the injection rate measuring system, and the effective injection velocity and effective spray diameter using the nozzle flow model. Moreover, the atomization characteristics, such as local and overall SMD distributions, overall axial velocity and droplet arrival time were analyzed and compared with these from diesel and biodiesel fuels to obtain the atomization characteristics of biodiesel–ethanol blended fuel. It was revealed that ethanol fuel affects the decrease of the peak injection rate and the shortening of the injection delay due to the decrease of fuel properties, such as fuel density and dynamic viscosity. In addition, the ethanol addition improved the atomization performance of biodiesel fuel, because the ethanol blended fuel has a low kinematic viscosity and surface tension, then that has more active interaction with the ambient gas, compared to BD100.

Unsteady turbulent round jets and vortex motion

A new model to predict the velocity distribution in round jets with time-varying injection profiles has been formulated as an extension of steady jet theory. The approach introduces an effective injection velocity within the jet based on a representative response time. It is assumed that the instantaneous injection velocity affects the velocity within the jet with an exponential response function and that the response time is related to the fluid particle’s residence time within the jet, consistent with the theory of translation of jet vortex rings from Helmholtz’s vortex motion analysis [P. G. Tait, London Edinburgh Dublin Philos. Mag. J. Sci. 33, 485 (1867)]. The Helmholtz theory is also shown to reduce to the well-known velocity decay rate in the case of steady turbulent gas jets. A Duhamel superposition integral is used to determine the effective injection velocity for time-varying injection rates. The model is tested with different injection profiles and different ambient densities. The results are also compared with numerical results from a computational fluid dynamics code. The comparisons agree very well and the new model is shown to offer an efficient method to predict jet tip penetrations for unsteady jets.

Novel designs for the DECADE coaxial plasma gun

New designs for the coaxial plasma injector (cablegun) used in the plasma opening switch (POS) of the DECADE pulsed-power facility were tested experimentally. A two-beam Mach-Zehnder interferometer operating in heterodyne mode was used to acquire, in addition to time-varying path-integrated electron number density and effective injection velocity, transverse radial scans for the ejected plasma. Abel inversion of this projected data yielded electron number density at a given downstream position as a function of radial position and time. Modifications to the baseline DECADE cablegun (a copper-core copper-sheath coaxial arrangement, with a Teflon insulator and a 60-degree muzzle cone) were investigated. Replacement of the copper center conductor with tungsten reduced radiative ablation of copper into the plasma and produced higher effective injection velocity with somewhat lower number density and similar radial divergence properties to that of the baseline cablegun. Substitution of the Teflon insulator with polyethylene continued that trend. The effect of cone angle was investigated by means of a simple flat-face arrangement whose plasma exhibited similar divergence to that of the baseline cablegun, although with lower number density, higher velocity, and more pronounced modulation in response to the driver current. The addition of a boron-nitride auxiliary nozzle proved effective at controlling the plasma divergence and concentrating the free electrons on axis while reducing the effects of driver current modulation.

New insights into carrier transport in n-MOSFETs

This paper discusses recent experimental investigations of the relation between low-field effective mobility and effective injection velocity of electrons from the source into the channel, as manifested in current drive, of deeply scaled n-MOSFETs. It is first established that the effective velocity in electrostatically sound, “well-tempered” scaled devices, for example with drain-induced barrier lowering (DIBL) limited to 120 mV/V, is well below the theoretical fully ballistic injection velocity. This is consistent with the fact that, as the channel length is scaled and the longitudinal field increases, preservation of electrostatic integrity requires increasing transverse field, which leads to increased surface scattering and therefore decreased mobility. In addition, evidence is presented that the effective channel mobility in modern short-channel devices is further decreased, probably due to increased ionized dopant scattering in the heavily doped channel halos. Then a correlation range of 45–60% between effective injection velocity and low-field mobility is established experimentally in sub-50-nm-channel MOSFETs. All of these factors point to the possibility of increasing the performance of deeply scaled n-MOSFETs by pursuing enhanced channel-mobility device structures such as double-gate MOSFET, or materials such as strained Si on relaxed SiGe.