Nozzle Flow Simulations Research Articles

Realistic fuel spray modeling for gasoline direct injection engine applications

Fuel spray modeling plays a critical role during modern gasoline direct injection (GDI) engine development due to fuel injection’s dominant impact on engine performance and emissions as well as the complex physical processes involved. In engineering three-dimensional (3D) computational fluid dynamics (CFD) simulations, the liquid-phase fuel atomization, evaporation, and mixing are usually modeled with the discrete droplet model (DDM) adopting a Lagrangian approach for multiphase CFD simulations. To this end, general practices heavily depend on the reduced order characterization of the injector nozzle flow. However, such simplified injector modeling may lead to insufficient representations of the complex spray dynamics. To tackle this problem, this study proposes a novel workflow to numerically evaluate GDI sub-cooled and flash-boiling sprays under engine-relevant conditions using a side-mounted GDI injector together with real gasoline fuel properties. The workflow introduces a one-way coupling (OWC) method leveraging high-fidelity nozzle flow simulations to provide realistic boundary conditions to the Lagrangian injector model. The proposed workflow was first verified in a constant volume chamber (CVC) environment and then implemented in a practical GDI engine setup to study spray morphology, fuel-air mixing, and wall-wetting propensity. In addition, detailed comparison was performed between the OWC method and the conventional rate of injection (ROI) routine. Quantitative analysis of spray characteristics was conducted to highlight possible source of discrepancies of the conventional ROI method.

Complete Workflow of Internal Nozzle Flow and Engine Simulation Using Multi-Component Fuel at Flash Boiling Conditions

Article Complete Workflow of Internal Nozzle Flow and Engine Simulation Using Multi-Component Fuel at Flash Boiling Conditions Bejoy Mandumpala Devassy 1, Yidan Zhang 2, * , Enyuan Zhang 2, and Long Zhou 2 1 AVL LIST GmbH, Hans-List-Platz 1, Graz 8020, Austria 2 AVL List Technical Center (Shanghai) Co., LTD. Shanghai 201206, China * Correspondence: yidan.zhang@avl.com Received: 17 May 2023 Accepted: 1 September 2023 Published: 14 September 2023 Abstract: At present 3D CFD simulation tools are getting more and more importance for addressing complex physical problems. This article presents a complete virtual analysis of the in-cylinder workflow in gasoline engine at flash boiling condition. Using the standard gasoline surrogate fuel PACE-20, properties of different fuel components was considered both the nozzle and in-cylinder flow. The flow, evaporation, spray jet interaction and spray collapse under flash boiling condition was studied. Molar density fraction was used to describe fuel component distribution for both gas phase and liquid phase. Based on nozzle flow simulation result, in-cylinder simulation has been done, the distribution of different fuel components and the influence on wall film, flame propagation, emission distribution has been studied. It shows that the simulation results have good agreement with testing data, and it proves the model validation for gasoline engine virtual development method under flash boiling conditions.

Two Dimensional CFD Analysis on Different Rocket Nozzles

The reduction of Earth-to-orbit launch costs in conjunction with an increase in launcher reliability and operational Efficiency is the key demands on future space transportation systems, like single-stage-to-orbit vehicles (SSTO). The realization of these vehicles strongly depends on the performance of the engines, which should deliver high performance with low system complexity. Performance data for rocket engines are practically always lower than the theoretically attainable values because of imperfections in the mixing, combustion, and expansion of the propellants. The main part of the project addresses different nozzle concepts with improvements in performance as compared to conventional nozzles achieved by Different Mach numbers, thus, by minimizing losses caused by over- or under expansion. The design of different nozzle shapes and flow simulation is done in gambit and fluent software’s respectively for various parameters

ECN Spray G: Coupled Eulerian internal nozzle flow and Lagrangian spray simulation in flash boiling conditions

Flash-boiling of fuel sprays occurs when a super-heated fuel is discharged into an environment whose pressure is lower than the saturation pressure of the fuel and can dramatically alter spray formation due to complex two-phase flow effects and rapid droplet vaporization. In gasoline direct injection (GDI) engines, typically, it occurs during the injection process when high fuel temperatures make its saturation pressures higher than the in-cylinder one. Flash boiling significantly affects the spray structure and fuel-air mixture formation, with, potentially, if spray collapse is avoided, positive consequences for the engine performance and pollutant emissions. Hence, this paper developed a modelling approach based on the coupling of Eulerian multi-phase and Eulerian-Lagrangian simulations to reproduce flash boiling sprays physics. It allows a comprehensive description of the flash-boiling phenomena that begins within the injector’s ducts and continues outside, where a particular mechanism for primary breakup occurs. Experimental data of the Engine Combustion Network (ECN) Spray G injector, covering various operating conditions, were exploited to assess the reliability of the numerical technique adopted. The validation was performed taking into account various parameters such as axial liquid and vapour penetrations, droplet size and images regarding the near-nozzle zone. The numerical model achieves a pretty good level of agreement with the experimental data and, in particular, it is sensitive to the spray behaviour in the different operating conditions.

Investigation of the Performances of a Diesel Engine Operating on Blended and Emulsified Biofuels from Rapeseed Oil

The article discusses the possibility of using blended biofuels from rapeseed oil (RO) as fuel for a diesel engine. RO blended diesel fuel (DF) and emulsified multicomponent biofuels have been investigated. Fuel physicochemical properties have been analyzed. Experimental tests of a diesel engine D-245 in the operating conditions of the external characteristic curve and the 13-mode test cycle have been conducted to investigate the effect of these fuels on engine performances. CFD simulations of the nozzle inner flow were performed for DF and ethanol-emulsified RO. The possibility of a significant improvement in brake thermal efficiency of the engine has been noted. The efficiency of using blended biofuels from RO as a motor fuel for diesel engines has been evaluated based on the experimental test results. It was shown that in comparison with the presence of RO in emulsified multicomponent biofuel, the presence of water has a more significant effect on NOx emission reduction. The content of RO and the content of water in the investigated emulsified fuels have a comparable influence on exhaust smoke reduction. Nozzle inner flow simulations show that the emulsification of RO changes its flow behaviors and cavitation regime.

Nozzle Flow Simulation by Small Disturbance Approximation and Euler Method

The nozzle is a kind of equipment with a wide range of usage in the aerospace industry, of which its performance is vital for rocket engines by changing the geometry of the inner wall of the pipe section to accelerate the airflow. There are two types of nozzles commonly used: one is a tapered nozzle, and the other is a Laval nozzle. To analyze the flow phenomenon in nozzle is vital before transferring prototype design into industrial production, whether by laboratory experiment or computational simulation. In this paper, two different numerical methods are adopted to simulate gas behavior inside a simplified nozzle with upper and bottom symmetrical bumps. The first is to solve one dimensional Euler equations, and the other is to solve a scalar variable named velocity potential with small disturbance equations (SDE). The solutions under various inlet Mach numbers are compared by analysing the velocity fields and Mach number contours obtained by these two approaches. Similarities and differences between the Euler method and the potential SDE method for subsonic flow and supersonic flow are the key emphases in this work. For either subsonic or supersonic flow, the Mach number distribution along the nozzle’s center line shows a consistent trend for both methods. In contrast, the values of maximum or minimum Mach number have corresponding differences. Moreover, by using potential SDE simulation, several types of shock waves are successfully captured. All results show that the incoming airflow decelerates at the leading edge of the nozzle then accelerates when passing through the bumps, and finally decelerates back to the speed of inlet flow. The difference is that flows with varied Mach numbers has distinct velocity distributions in the nozzle.

Simulation of nozzle flow based on Euler equations

The nozzle is a widely used device in daily life, such as water fountains to rocket engines. It is important to find out the influence of the position of the nozzle throat for the application or the design of the nozzle. To that end, the finite difference method was employed to solve the 1D Euler equations to obtain the flow inside the nozzle. To implement the method, an in-house python code was developed. The relationship among the velocity, pressure and density in the convergent-divergent nozzle flow was found. It is observed that: the velocity rose quickly along with the nozzle and reached the top before a rapid decrease; pressure remained constant initially, which eventually began to drop; density dropped steadily and had a turning point. Moreover, the influence of the nozzle throat position is investigated thoroughly. It is observed that the position of the nozzle throat influences the velocities at the nozzle exit. The faster the flow reaches the throat, the higher the velocity or Mach number at the exit boundary.

Numerical simulation of nozzle flow based on Euler equation

In this paper, the Euler-based numerical simulation method is employed to investigate the flow characteristics inside the Laval nozzle. In detail, the central difference method is used to discretize the flow field of the nozzle. And two kinds of flow conditions are simulated numerically: the isentropic flow from subsonic to supersonic, and the isentropic flow at full subsonic speed. The results show that the velocity increases and then decreases slowly, reaching the peak point near the nozzle throat. The pressure decreases non-linearly, and the density increases at first and then drops, following by a sharp rise later. The shock wave oscillation also appears in the flow from subsonic to supersonic, and this is because the artificial viscous term is not enough in discrete solution. Then we analyze the law of change of physical quantity by changing the shape of the nozzle. The results demonstrate that the larger the nozzle’s curvature, the faster the change rate of a physical quantity is. And the velocity at the nozzle inlet approaches zero when the area at the inlet and outlet approaches infinity.

Euler and Small Disturbance Equation-based Simulation of a Nozzle Flow

The de Laval nozzle has been widely studied and used in many industries ranging from the aerospace to the dairy industry. This study investigated two numerical methods used to simulate nozzle flow, namely one-dimensional Euler equations and the small disturbance equations (SDE) based simulation. The simulation results reveal that the SDE method accurately captured the shock bubbles in the nozzle flow. However, the one-dimensional Euler method is not sufficient to handle two-dimensional nozzle flow simulation because at any particular nozzle location, a mix of subsonic and supersonic flow can occur. This research allows an informed choice between Euler and SDE method.

Numerical Analysis of Side-loads Reduction in a Sub-scale Dual-bell Rocket Nozzle

A calibrated delayed detached eddy simulation of a sub-scale cold-gas dual-bell nozzle flow at high Reynolds number and in sea-level mode is carried out at nozzle pressure ratio NPR = 45.7. In this regime the over-expanded flow exhibits a symmetric and controlled flow separation at the inflection point, that is the junction between the two bells, leading to the generation of a low content of aerodynamic side loads with respect to conventional bell nozzles. The nozzle wall-pressure signature is analyzed in the frequency domain and compared with the experimental data available in the literature for the same geometry and flow conditions. The Fourier spectra in time and space (azimuthal wavenumber) show the presence of a persistent tone associated to the symmetric shock movement. Asymmetric modes are only slightly excited by the shock and the turbulent structures. The low mean value of the side-loads magnitude is in good agreement with the experiments and confirms that the inflection point dampens the aero-acoustic interaction between the separation-shock and the detached shear layer.

Numerical investigation of the effect of multi-walled carbon nanotube additive on nozzle flow and spray behaviors of diesel fuel

The thermal-physical properties of multi-walled carbon nanotubes (MCNTs) and MCNT blended diesel fuel were analyzed. Internal flow in injector Spray A of Engine Combustion Network and spray in a constant-volume chamber with considering the effect of the turbulence-induced breakup were modeled for pure diesel fuel and MCNT blended diesel fuel. Nozzle flow simulation showed that the addition of MCNTs into diesel fuel increased the flow turbulence at the nozzle hole outlet. Spray simulation statistically coupled with nozzle flow modeling showed that during stable spray development, there were a positive linear relationship between the liquid penetration length and the MCNT content in diesel fuel and a negative linear relationship between the Sauter mean diameter of the droplets and the MCNT content; the addition of MCNTs reduced the liquid cone angle and had an insignificant influence on the vapor penetration length.

Internal Nozzle Flow Simulations of the ECN Spray C Injector under Realistic Operating Conditions

<div class="section abstract"><div class="htmlview paragraph">In this study, three-dimensional large eddy simulations were performed to study the internal nozzle flow of the ECN Spray C diesel injector. Realistic nozzle geometry, full needle motion, and internal flow imaging data obtained from X-ray measurements were employed to initialize and validate the CFD model. The influence of injection pressure and fuel properties were investigated, and the effect of mesh size was discussed. The results agreed well with the experimental data of mass flow rate and correctly captured the flow structures inside the orifice. Simulations showed that the pressure drop near the sharp orifice inlet triggered flow separation, resulting in the ingestion of ambient gas into the orifice via a phenomenon known as hydraulic flip. At higher injection pressure, the pressure drop was more significant as the liquid momentum increased and the stream inertia was less prone to change its direction. Two fuels were tested in both experiments and simulations, namely iso-octane and n-dodecane. With the former, the gas species in the low-pressure region consisted of both fuel vapor and non-condensable gas. With n-dodecane, due to its low saturation pressure, fuel vapor was practically absent. Furthermore, it was found that fuel cavitation might not be the only phenomenon able to trigger flow separation, as “pseudo-cavitation” caused by non-condensable gas expansion played a similar role in promoting the conditions that led the flow to detach from the wall. Finally, it was found that a minimum mesh size of 10 μm within the orifice was sufficient to ensure the main flow features were captured. However, it was shown that finer meshes allowed for better resolution of the near-wall gas layer, resulting in more flow features to be resolved.</div></div>

StanShock: a gas-dynamic model for shock tube simulations with non-ideal effects and chemical kinetics

A high-order, quasi-one-dimensional, reacting, compressible flow solver is developed to simulate non-ideal effects and chemical kinetics in shock tube systems. To this end, physical models for the thermoviscous boundary-layer development, area variation, gas interfaces, and reaction chemistry are considered. The model is first verified through simulations of steady isentropic nozzle flow, multi-species Sod’s problem, laminar premixed flame, and ZND detonation test cases. Comparisons with experiments are made by examining end-wall pressure traces that are gathered from shock tube experiments designed to test the code’s capabilities. Subsequently, the solver is utilized for uncertainty quantification and design optimization of a driver insert. Both applications prove to be highly efficient, indicating the utility of the solver for the design of experiments in consideration of non-ideal gas-dynamic effects.

Nozzle Flow Characteristics and Simulation of Pesticide Spraying Drone

Nozzle Flow Characteristics and Simulation of Pesticide Spraying Drone

Impact of the Primary Break-Up Strategy on the Morphology of GDI Sprays in 3D-CFD Simulations of Multi-Hole Injectors

The scientific literature focusing on the numerical simulation of fuel sprays is rich in atomization and secondary break-up models. However, it is well known that the predictive capability of even the most diffused models is affected by the combination of injection parameters and operating conditions, especially backpressure. In this paper, an alternative atomization strategy is proposed for the 3D-Computational Fluid Dynamics (CFD) simulation of Gasoline Direct Injection (GDI) sprays, aiming at extending simulation predictive capabilities over a wider range of operating conditions. In particular, attention is focused on the effects of back pressure, which has a remarkable impact on both the morphology and the sizing of GDI sprays. 3D-CFD Lagrangian simulations of two different multi-hole injectors are presented. The first injector is a 5-hole GDI prototype unit operated at ambient conditions. The second one is the well-known Spray G, characterized by a higher back pressure (up to 0.6 MPa). Numerical results are compared against experiments in terms of liquid penetration and Phase Doppler Anemometry (PDA) data of droplet sizing/velocity and imaging. CFD results are demonstrated to be highly sensitive to spray vessel pressure, mainly because of the atomization strategy. The proposed alternative approach proves to strongly reduce such dependency. Moreover, in order to further validate the alternative primary break-up strategy adopted for the initialization of the droplets, an internal nozzle flow simulation is carried out on the Spray G injector, able to provide information on the characteristic diameter of the liquid column exiting from the nozzle.

Numerical Analysis of Nozzle Flow and Spray Characteristics from Different Nozzles Using Diesel and Biofuel Blends

In this paper, the discrete phase model (DPM) was introduced to study the fuel injector cavitations process and the macro spray characteristic of three different types of nozzle spray shape with diesel and hybrid biofuel blend for several injection pressures and backpressures. The three types of nozzle spray shapes used were circle, elliptical A type, and elliptical B type. The cavitations’ flows inside the injector nozzles were simulated with Computer Fluid Dynamics (CFD) simulations using the cavitations mixture approach. The effect of nozzle spray shape towards the spray characteristic of hybrid biofuel blends is analyzed and compared with the standard diesel. Furthermore, a verification and validation from both the experimental results and numerical results are also presented. The nozzle flow simulation results indicated that the fuel type did not affect the cavitation area vastly, but were more dependent on the nozzle spray shape. In addition, the spray width of the elliptical nozzle shape was higher as compared to the circular spray. Moreover, as the backpressure increased, the spray width downstream increased as well. The spray tip penetration for the elliptical nozzle shape was shorter than the circular nozzle shape due to circular nozzles having smaller nozzle widths and lesser spray cone angles. Thus, this resulted in smaller aerodynamic drag.

Numerical simulation of nozzle flow for design of the devices using supersonic nozzle

Numerical simulation of nozzle flow for design of the devices using supersonic nozzle

Numerical Model for Nozzle Flow Application Under Liquid Oxygen/Methane Hot-Flow Conditions

A numerical study is conducted to investigate the impact of different chemical reaction mechanisms on the behavior of reactive nozzle flow. Therefore, a 66-step chemical reaction mechanism for oxygen/methane combustion is implemented into German Aerospace Center’s flow solver TAU. Ignition delay simulations are conducted and compared to experimental data to demonstrate the validity of this implementation. The implemented 66-step baseline chemistry model is applied for generic nozzle flow simulations, and the results are compared to frozen nozzle flow and nozzle flow in chemical equilibrium in order to investigate the impact of the finite-rate approach. The 66-step baseline reaction mechanism is reduced to a seven-step basic configuration, which is applied to the generic nozzle flow. A good agreement of the 66-step and the seven-step model is observed. Both approaches are applied for Reynolds-averaged Navier–Stokes simulations of a dual-bell nozzle hot-gas flow. Almost no deviation between the 66-step baseline model and the reduced chemical seven-step approach is observed. The dual-bell transition behavior at different values of combustion chamber mixture ratio is investigated, applying Reynolds-averaged Navier–Stokes simulations with a reduced chemistry model. Validation data for the simulations are obtained during a hot-flow test campaign. The experimentally observed impact of the combustion chamber mixture ratio on the dual-bell transition nozzle pressure ratio is clearly reproduced by the numerical approach. A good agreement with the experimentally obtained, transition nozzle pressure ratio values is reached by the numerical simulations. A reduction of 93% of the computational cost is observed due to the reduction of the chemical reaction mechanism.

Numerical simulation of needle movement nozzle flow coupled with spray for a diesel injector using an Eulerian spray atomization model

This research was performed in the frame of the project Estudio de la interaccion chorro-pared en condiciones realistas de motor (SPRAY WALL) reference TRA2015-67679-c2-1-R from Ministerio de Economia y Competitividad (Spanish Ministry of Economy).

Numerical analysis of deposit effect on nozzle flow and spray characteristics of GDI injectors

Injector deposit is a common phenomenon for gasoline direct ignition (GDI) engines that greatly affects the spray behavior and consequently the combustion performance and emissions. In this study, the effect of deposit on both the in-nozzle flow dynamics and downstream spray behaviors was numerically investigated. High-resolution X-ray microtomographic scans were performed first to obtain nozzle and deposit morphologies and topology. In-nozzle simulation was then carried out in the Euler-Euler framework with cavitation taken into account by a homogeneous relaxation model (HRM). Finally, the effect of deposit on spray behaviors was evaluated in the Euler-Lagrangian framework, coupled with the in-nozzle simulation results. Results of the nozzle flow simulations highlight that the rough surface of the deposits leads to additional cavitation inception and restricts the flow area, causing mass flow rate losses. Deposits inside the counterbore act as an extension to the inner orifice and constrain the air recirculation. Turbulent levels at the exit of the counterbore are lower for the coked injector due to the reduced air/fuel interaction. Spray simulations have shown that deposits would lead to longer spray penetration, a smaller spray cone angle and larger droplets diameters. Simulation results agree reasonably well with the available experimental data.