scholarly journals Numerical Investigation of Spray Collapse in GDI with OpenFOAM

Fluids ◽  
2021 ◽  
Vol 6 (3) ◽  
pp. 104
Author(s):  
Jan Wilhelm Gärtner ◽  
Ye Feng ◽  
Andreas Kronenburg ◽  
Oliver T. Stein
Keyword(s):  
Experimental Data ◽  
Direct Injection ◽  
Operating Conditions ◽  
Test Case ◽  
Direct Injection Engines ◽  
Shock Interactions ◽  
Single Hole ◽  
First Case ◽  
Collapse Behavior

During certain operating conditions in spark-ignited direct injection engines (GDI), the injected fuel will be superheated and begin to rapidly vaporize. Fast vaporization can be beneficial for fuel–oxidizer mixing and subsequent combustion, but it poses the risk of spray collapse. In this work, spray collapse is numerically investigated for a single hole and the spray G eight-hole injector of an engine combustion network (ECN). Results from a new OpenFOAM solver are first compared against results of the commercial CONVERGE software for single-hole injectors and validated. The results corroborate the perception that the superheat ratio Rp, which is typically used for the classification of flashing regimes, cannot describe spray collapse behavior. Three cases using the eight-hole spray G injector geometry are compared with experimental data. The first case is the standard G2 test case, with iso-octane as an injected fluid, which is only slightly superheated, whereas the two other cases use propane and show spray collapse behavior in the experiment. The numerical results support the assumption that the interaction of shocks due to the underexpanded vapor jet causes spray collapse. Further, the spray structures match well with experimental data, and shock interactions that provide an explanation for the observed phenomenon are discussed.

Parallel Multi-Cycle LES of an Optical Pent-Roof DISI Engine Under Motored Operating Conditions

2017 ◽  
Author(s):  
Noah Van Dam ◽  
Wei Zeng ◽  
Magnus Sjöberg ◽  
Sibendu Som
Keyword(s):  
Experimental Data ◽  
Direct Injection ◽  
Operating Conditions ◽  
New Strategy ◽  
Long Time ◽  
Order Of Magnitude ◽  
Structure Index ◽  
Number Of Cycles ◽  
The Many ◽  
Direct Injection Spark Ignition

The use of Large-eddy Simulations (LES) has increased due to their ability to resolve the turbulent fluctuations of engine flows and capture the resulting cycle-to-cycle variability. One drawback of LES, however, is the requirement to run multiple engine cycles to obtain the necessary cycle statistics for full validation. The standard method to obtain the cycles by running a single simulation through many engine cycles sequentially can take a long time to complete. Recently, a new strategy has been proposed by our research group to reduce the amount of time necessary to simulate the many engine cycles by running individual engine cycle simulations in parallel. With modern large computing systems this has the potential to reduce the amount of time necessary for a full set of simulated engine cycles to finish by up to an order of magnitude. In this paper, the Parallel Perturbation Methodology (PPM) is used to simulate up to 35 engine cycles of an optically accessible, pent-roof Direct-injection Spark-ignition (DISI) engine at two different motored engine operating conditions, one throttled and one un-throttled. Comparisons are made against corresponding sequential-cycle simulations to verify the similarity of results using either methodology. Mean results from the PPM approach are very similar to sequential-cycle results with less than 0.5% difference in pressure and a magnitude structure index (MSI) of 0.95. Differences in cycle-to-cycle variability (CCV) predictions are larger, but close to the statistical uncertainty in the measurement for the number of cycles simulated. PPM LES results were also compared against experimental data. Mean quantities such as pressure or mean velocities were typically matched to within 5–10%. Pressure CCVs were under-predicted, mostly due to the lack of any perturbations in the pressure boundary conditions between cycles. Velocity CCVs for the simulations had the same average magnitude as experiments, but the experimental data showed greater spatial variation in the root-mean-square (RMS). Conversely, circular standard deviation results showed greater repeatability of the flow directionality and swirl vortex positioning than the simulations.

Assessment of CFD Approaches for Next-Generation Combustor Design

2014 ◽  
Author(s):  
Kumud Ajmani ◽  
Hukam C. Mongia ◽  
Phil Lee
Keyword(s):  
Experimental Data ◽  
Direct Injection ◽  
Operating Conditions ◽  
Reacting Flow ◽  
Cfd Analysis ◽  
Next Generation ◽  
Lean Direct Injection ◽  
Liquid Spray ◽  
Exit Temperature ◽  
Computational Predictions

An effort was undertaken to perform CFD analysis of fluid flow in Lean-Direct Injection (LDI) combustors with axial swirl-venturi elements for next-generation LDI-2 design. The National Combustion Code (NCC) developed at NASA Glenn Research Center was used to perform reacting flow computations on an LDI-2 combustor configuration with thirteen injector elements arranged in four fuel stages. Reacting computations were performed with a consistent approach for mesh-optimization, liquid spray modeling and kinetics modeling. Computational predictions of Emissions Index (EINOx) and combustor exit temperature were compared with two sets of experimental data at medium and high-power operating conditions, for two different pressure-drop conditions in the combustor. The NCC simulations predicted the combustor exit temperature to within 1–2% of experimental data. The accuracy of the EINOx predictions from the NCC simulations was within 10% to 30% of experimental data.

Impact of Turbine Center Frame Wakes on Downstream Rows in Heavy-Duty Low-Pressure Turbine

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Sara Biagiotti ◽  
Juri Bellucci ◽  
Michele Marconcini ◽  
Andrea Arnone ◽  
Gino Baldi ◽  
...  
Keyword(s):  
Experimental Data ◽  
Low Pressure ◽  
Numerical Approach ◽  
Forced Response ◽  
Operating Conditions ◽  
Response Analysis ◽  
Test Case ◽  
Low Pressure Turbine ◽  
Harmonic Content ◽  
The Impact

Abstract In this work, the effects of turbine center frame (TCF) wakes on the aeromechanical behavior of the downstream low-pressure turbine (LPT) blades are numerically investigated and compared with the experimental data. A small industrial gas turbine has been selected as a test case, composed of a TCF followed by the two low-pressure stages and a turbine rear frame (TRF) before the exhaust plenum. Full annulus unsteady computations of the whole low-pressure module have been performed. Two operating conditions, full (100%) and partial (50%) load, have been investigated with the aim of highlighting the impact of TCF wakes convection and diffusion through the downstream rows. Attention was paid to the harmonic content of rotors’ blades. The results show a slower decay of the wakes through the downstream rows in off-design conditions compared with the design point. The analysis of the rotors’ frequency spectrum reveals that moving from design to off-design conditions, the effect of the TCF does not change significantly. The harmonic contribution of all turbine components has been extracted, highlighting the effect of statoric parts on the last LPT blade. The TCF harmonic content remains the most relevant from an aeromechanic point of view as per experimental evidence, and it is considered for an forced response analysis (FRA) on the last LPT blade itself. Finally, aerodynamic and aeromechanic predictions have been compared with the experimental data to validate the numerical approach. Some general design solutions aimed at mitigating the TCF wakes impact are discussed.

Numerical and experimental study on knocking combustion in turbocharged direct-injection engines for a wide range of operating conditions

2021 ◽  
pp. 146808742110601
Author(s):  
Magnus Kircher ◽  
Emmeram Meindl ◽  
Christian Hasse
Keyword(s):  
Experimental Data ◽  
Experimental Study ◽  
Numerical Study ◽  
Direct Injection ◽  
Operating Conditions ◽  
Auto Ignition ◽  
Spark Timing ◽  
Crank Angle ◽  
Wide Range ◽  
The Mean

A combined experimental and numerical study is conducted on knocking combustion in turbocharged direct-injection spark-ignition engines. The experimental study is based on parameter variations in the intake-manifold temperature and pressure, as well as the air-fuel equivalence ratio. The transition between knocking and non-knocking operating conditions is studied by conducting a spark timing sweep for each operating parameter. By correlating combustion and global knock quantities, the global knock trends of the mean cycles are identified. Further insight is gained by a detailed analysis based on single cycles. The extensive experimental data is then used as an input to support numerical investigations. Based on 0D knock modeling, the global knock trends are investigated for all operation points. Taking into consideration the influence of nitric oxide on auto-ignition significantly improves the knock model prediction. Additionally, the origin of the observed cyclic variability of knock is investigated. The crank angle at knock onset in 1000 consecutive single cycles is determined using a multi-cycle 0D knock simulation based on detailed single-cycle experimental data. The overall trend is captured well by the simulation, while fluctuations are underpredicted. As one potential reason for the remaining differences of the 0D model predictions local phenomena are investigated. Therefore, 3D CFD simulations of selected operating points are performed to explore local inhomogeneities in the mixture fraction and temperature. The previously developed generalized Knock Integral Method (gKIM), which considers the detailed kinetics and turbulence-chemistry interaction of an ignition progress variable, is improved and applied. The determined influence of spark timing on the mean crank angle at knock onset agrees well with experimental data. In addition, spatially resolved information on the expected position of auto-ignition is analyzed to investigate causes of knocking combustion.

Comparison of Theoretical and Experimental Data for an Oscillating Transonic Compressor Cascade

1999 ◽  
Author(s):  
Volker Carstens ◽  
Stefan Schmitt
Keyword(s):  
Experimental Data ◽  
Transonic Flow ◽  
Operating Conditions ◽  
Experimental Investigations ◽  
Test Case ◽  
Flow Conditions ◽  
Compressor Cascade ◽  
Blade Passage ◽  
Aerodynamic Damping ◽  
Transonic Compressor

Numerical and experimental results are compared for a compressor cascade performing harmonic oscillations in transonic flow. The flow field was calculated by a Q3D Navier Stokes code, the basic features of which are the use of an upwind flux difference scheme for the convective terms, the implementation of an effective one-equation turbulence model and the use of deforming multi-block grids. The experimental investigations were performed in an annular cascade windtunnel where unsteady blade pressures were measured for two different operating conditions of the cascade. The present data were all obtained for tuned torsional modes where the blades performed pitching oscillations with the same frequency and amplitude, but with a constant interblade phase angle. In the first test case the steady flow around the blades was purely subsonic. For the second test case the compressor cascade was run under transonic flow conditions where a normal shock in the front part of the blades’ suction side is followed by a blade passage shock. It becomes apparent that under subsonic flow conditions the predicted aerodynamic damping coefficients are in resonable agreement with the experimental data, although the numerical pressure amplitudes are much higher than the measured ones. In transonic flow significant discrepancies between computed and experimentally determined pressure amplitudes are observed, whereas the accuracy of the pressure phase prediction is comparable to the subsonic test case. Another important result of these investigations is that oscillations of the blade passage shock lead to strong variations of the local aerodynamic damping of the blades, but do not significantly change the global damping coefficient of the tested compressor cascade.

Analytical model for liquid film evaporation on fuel injector tip for the mitigation of injector tip wetting and the resulting particulate emissions in gasoline direct-injection engines

2020 ◽  
pp. 146808742097389
Author(s):  
Fahad M Alzahrani ◽  
Mohammad Fatouraie ◽  
Volker Sick
Keyword(s):  
Liquid Film ◽  
Analytical Model ◽  
Time Constant ◽  
Direct Injection ◽  
Operating Conditions ◽  
Gasoline Direct Injection ◽  
Particulate Emissions ◽  
Fuel Injector ◽  
Direct Injection Engines ◽  
Film Evaporation

Unevaporated fuel films forming on the fuel injector tip of gasoline direct-injection engines burn in a diffusion flame at the time of spark, producing particulates and at some operating conditions, these films have been identified as the dominating source of particulate emissions. This work developed an analytical model for liquid film evaporation on the injector tip, that is, injector tip drying, for the mitigation of injector tip wetting and the resulting particulate emissions. The model explains theoretically how fuel films on the injector tip evaporate with time from the end of injection to the spark. The model takes into consideration engine operating conditions, including engine load and speed, tip and fuel temperatures, gas temperature and pressure, and fuel properties. The model explains the observed trends in particulate number (PN) emissions due to injector tip wetting. Engine experiments were used to validate the model by correlating the predicted film mass at the time of spark to measurements of PN emissions at different conditions. A tip drying time constant was also defined and was found to correlate well with the measured PN for all conditions tested. This time constant is a deterministic factor for mitigating tip wetting. In general, the results indicate that the liquid film evaporation on the injector tip follows a first order, asymptotic behavior. Furthermore, the tip drying physics causes the observed increasing and decreasing non-linear trends in PN emissions with the engine load and the available time for tip drying, respectively. Additionally, the liquid film evaporation on the injector tip is highly sensitive to most of the injector initial and boundary conditions, including the initial film mass after the end of injection, the wetted surface area, the available time for tip drying and the injector tip temperature. The initial film temperature has the least effect on film mass evaporation.

Mechanisms of fuel injector tip wetting and tip drying based on experimental measurements of engine-out particulate emissions from gasoline direct-injection engines

2020 ◽  
pp. 146808742091605 ◽  
Author(s):  
M Medina ◽  
FM Alzahrani ◽  
M Fatouraie ◽  
MS Wooldridge ◽  
V Sick
Keyword(s):  
Conceptual Understanding ◽  
Direct Injection ◽  
Operating Conditions ◽  
Gasoline Direct Injection ◽  
Coolant Temperature ◽  
Particulate Emissions ◽  
Fuel Injector ◽  
Wetting And Drying ◽  
Direct Injection Engines ◽  
Particulate Number

Gasoline fuel deposited on the fuel injector tip has been identified as a significant source of particulate emissions at some operating conditions of gasoline direct-injection engines. This work proposes simplified conceptual understanding for mechanisms controlling injector tip wetting and tip drying in gasoline direct-injection engines. The objective of the work was to identify which physical mechanisms of tip wetting and drying were most important for the operating conditions and hardware considered and to relate the mechanisms to measurements of particulate number emissions. Trends for each of the physical processes were evaluated as a function of engine operating conditions such as engine speed, start of injection timing, engine load, fuel rail pressure, and coolant temperature. The effects of fuel injector geometries on the tip wetting and drying mechanisms were also considered. Several mechanisms of injector tip wetting were represented with the conceptual understanding including wide plume wetting, vortex droplet wetting, fuel dribble wetting, and fuel condensation wetting. The main tip drying mechanism considered was single-phase evaporation. Using the conceptual understanding for tip wetting and drying mechanisms that were created in this work, the effects of engine operating conditions and fuel injector geometries on the mechanisms were compared with experimental results for particulate number. The results indicate that measured particulate number was increased by increasing injected fuel mass. Increasing injected fuel mass was suspected to increase tip wetting via wide plume wetting and vortex droplet wetting mechanisms. Particulate number was also observed to increase with hole length. Longer hole length was suspected to result in higher tip wetting via vortex droplet and fuel dribble wetting mechanisms. Longer timescale was found to decrease particulate number emissions. Lower speeds and early injection timings increased the timescale. Similarly, higher coolant temperature decreased particulate number. The coolant temperature influenced tip temperature resulting in higher tip drying.

Validation of a comprehensive computational fluid dynamics methodology to predict the direct injection process of gasoline sprays using Spray G experimental data

2019 ◽  
Vol 21 (1) ◽  
pp. 199-216 ◽  
Author(s):  
Davide Paredi ◽  
Tommaso Lucchini ◽  
Gianluca D’Errico ◽  
Angelo Onorati ◽  
Lyle Pickett ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Experimental Data ◽  
Computational Fluid Dynamics ◽  
Liquid Velocity ◽  
Direct Injection ◽  
Combustion Process ◽  
Operating Conditions ◽  
Gasoline Direct Injection ◽  
Injection Process ◽  
Dynamics Simulations

A detailed prediction of injection and air–fuel mixing is fundamental in modern direct injection, spark-ignition engines to guarantee a stable and efficient combustion process and to minimize pollutant formation. Within this context, computational fluid dynamics simulations nowadays represent a powerful tool to understand the in-cylinder evolution of spray and air–fuel charge. To guarantee the accuracy of the adopted multidimensional spray sub-models, it is mandatory to validate the computed results against available experimental data under well-defined operating conditions. To this end, in this work, the authors proposed the calibration and validation of a comprehensive set of spray sub-models by means of the simulation of the Spray G experiment, available in the context of the engine combustion network. For a suitable validation of the proposed numerical setup in addition to the baseline condition, gasoline direct injection operating points typical of early injection with homogeneous operation, late injection with high ambient density and flash boiling with enhanced fuel evaporation were also simulated. Numerical computations were validated against a wide set of available experimental data by means of an accurate post-processing analysis taking into account axial liquid and vapor penetrations, gas-phase velocity between spray plumes, droplet size, plume liquid velocity, direction and mass distribution. Satisfactory results were achieved with the proposed setup, which is able to predict gasoline spray evolution under different operating conditions.

Sign in / Sign up

Export Citation Format

Share Document