Engine Spray Research Articles

Pengaruh Densitas dan Viskositas terhadap Sudut Injeksi Biodiesel Jatropha-Jagung (1:4 dan 4:1)

Biodiesel has attracted attention as an alternative fuel in efforts to reduce emissions and dependence on fossil fuels. Among various potential sources for biodiesel production, jatropha and corn oil have stood out due to their availability and high yield potential. However, each has unique characteristics that affect their performance as fuels. Jatropha oil has relatively high viscosity, while corn oil is generally used as a food ingredient. This study aimed to explore the potential of combining jatropha and corn biodiesel in different proportions and its impact on fuel characteristics and diesel engine spray injection. Both types of oil were processed into biodiesel through esterification and transesterification processes. Subsequently, biodiesel mixtures were created in ratios of 1:4 and 4:1. Each mixture was then varied with diesel to produce B5, B10, B15, B20, B25, B30, B35, and B40. Each sample was tested for its physical properties such as density and viscosity, and injection spray angle. The results of this study indicated that the density and viscosity values of the 1:4 jatropha-corn biodiesel mixture were lower than those of the 4:1 jatropha-corn biodiesel mixture. There was a significant relationship between viscosity and density with the injection angle. The higher the density and viscosity, the narrower the injection angle.

Experimental investigation of near-field spray characteristics of RP3 aviation fuel based on multivariable sensitivity and uncertainty analysis

The utilization of aviation kerosene RP3 in diesel engines and ground vehicles has attracted more attention due to the implementation of the army's Single Fuel Concept. To explore the characteristics of the RP3 near-field spray primary breakup, experimental studies were carried out via the diffuser back-illumination imaging (DBI) method under single-hole injectors accommodated to varied engine spray circumstance. The critical factors of the variability in RP3 spray characteristics response were figured out by constructing a one-dimensional active subspace to perform multivariable synergistic effects via sensitivity analysis. Moreover, the uncertainties associated with unstable cavitation within nozzle were quantified with a varied array of operating conditions. In comparison to diesel, it is indicated that, there is a range of critical cavitation, in where greater uncertainties in spray cone angles are exhibited, especially for RP3. RP3 tends to form a ‘mushroom’ spray structure, with a smaller spray cone angle compared to diesel, but the disparity gradually diminishes as the fuel injection pressure increases. The gradual transition from ‘needle’ to ‘mushroom’ shape in RP3's near-field spray structure is revealed with increased fuel injection pressure, and the appearance time of the ‘mushroom’ structure advances with higher ambient pressures. Based on the active space construction, the sensitivity analysis discovers that the spray cone angle is dominantly influenced by ambient pressure and cavitation within the nozzle, thus providing a new perspective on analyzing test data without the expense of single variable statistical work.

Ethanol Blend Effects on The Spray Properties of a Biodiesel Fuel by Ambient Pressure Variation

Diesel engine spray nozzles are crucial to pollutant generation and engine efficiency. Nozzle performance can be enhanced by adjusting the nozzle's internals. A successful demonstration of the nozzle would be one in which the spray's outcome was uniformly dispersed throughout a wide area, with the grains scattered similarly. The purpose of this research was to examine how a diesel-ethanol characteristic under normal atmospheric pressure (spray tip penetration, the velocity of spray, and spray angle) and, in general, to assess the performance of biodiesel fuel on diesel engines, a substantial amount of biodiesel and operational expenses for the engine are necessary. It was an experimental approach to the study. The research involved recording spray fuel at the nozzle. Using a 480 fps high-speed camera, we tested BD20, BD20E5, and BD20E10 fuel at three different ambient pressures (1 bar, 2 bar, and 3 bar). The injection pressure was 15 MPa, and the fuel temperature was 28.2 degrees Celsius. Spray tip penetration and spray velocity decreased and spray angle increased after ethanol was added to the mixture, consistent with the studies' findings. Lowered spray tip penetration, slower spray speeds, and a complete spray angle result from the increased ambient pressure.

Radiative Heat Transfer in Turbulent Combustion 2021 Max Jakob Memorial Award Paper

Abstract In many important combustion applications, heat transfer is dominated by thermal radiation from combustion gases and soot. Thermal radiation from combustion gases is extremely complicated, and accurate and efficient predictions are only now becoming possible with the use of accurate global methods, such as full-spectrum k-distributions, and with state-of-the-art line-by-line accurate Monte Carlo methods. The coupling between turbulence and radiation can more than double the radiative loss from a flame, while making theoretical predictions vastly more complicated. This paper is an embellished version of the 2021 Max Jakob Award lecture: Radiative properties and computational methods will be briefly discussed, and several examples of turbulent reacting flows, an oxy-fuel furnace, and high-pressure fuel sprays in combustion engines will be presented. Thermal radiation can also be used as an optical diagnostic tool to determine temperature and concentration distributions, which will be briefly discussed.

Schlieren and mie-scattering visualization of an evaporating spray under marine diesel engine conditions

Due to the critical influence on combustion, extensive research has been carried out to deepen the understanding of diesel spray evolution. However, for the greater share of land-based diesel engines, most of the studies have focused on the injectors with small nozzle diameter and rare studies can be found on marine diesel engines, which has a larger mass flow rate and longer injection duration with large nozzle diameter. In this study, the influence of injection pressure, ambient temperature, ambient density and nozzle diameter on spray morphology for medium speed marine diesel engine injectors (with nozzle diameter up to 0.53 mm) were investigated under various non-reacting but evaporative conditions. The experiments were performed via a highly enhanced constant volume chamber (highest temperature of 900 K and highest pressure of 8 MPa) with an optical window diameter of 205 mm. Liquid and vapor penetration of sprays were recorded by Mie-scattering and schlieren optical configurations respectively. Results show that the vapor penetration velocity is mainly affected by injection pressure. Ambient temperature has the most significant effect on liquid penetration length, but less effect can be found on the vapor penetration velocity. Given the obvious deviation from heavy duty engine sprays, the empirical correlations for liquid penetration length and vapor spray evolution are updated to fit the spray characteristics of medium speed marine diesel engine injectors, which is helpful to understand the spray behavior for large nozzle diameter injector under marine diesel engine conditions.

Artificial neural network models for phase equilibrium predictions under engine trans/supercritical spray conditions

Engine spray models based on phase equilibrium have made great progress in simulating trans/supercritical engine spray processes, but there are inherent weaknesses in terms of efficiency and stability for the conventional phase equilibrium algorithm due to the iterative schemes for solving complex nonlinear equations. The low efficiency of the conventional algorithm limits the amount of detail that can be considered in the simulation, while the instability may lead to unphysical results or even simulation divergence. In this work, a method based on artificial neural networks (ANNs) was developed as a potential alternative to the conventional algorithm applied in the engine spray models to achieve fast and robust phase equilibrium calculations. Three ANNs were constructed, including isothermal-isobaric-ANN (TPn-ANN), isenthalpic-isobaric-ANN (HPn-ANN) and adiabatic-mixing-temperature-ANN (AMT-ANN). The latter two models combined with TPN-ANN can be applied to heat and mass transfer flow and adiabatic mixing problems, respectively, to achieve the prediction of phase equilibrium temperature, phase stability and phase splitting. The current work shows that the ANN method leads to significant efficiency improvements while maintaining almost the same accuracy as the conventional algorithm. Analysis of execution time for a high-fidelity n-dodecane spray simulation shows that the conventional phase equilibrium calculation can take up to 70% of total computational time, which can be reduced to negligible levels with the current proposed ANN approach.

Vortex shedding controlled combustion of the wake flame of an n-heptane wetted porous sphere

Aiming at the combustion characteristics of the microscopic flying fuel drops in fuel sprays in engines, an n-heptane wetted porous sphere (d0 = 6 mm) was employed to simulate the combustion of the fuel drops according to the flow similarity indicated by the Reynolds number (Re). The hot airflow provided by a wind tunnel with an inner diameter of 40 mm varied in flow velocity from U = 0.6 to 7.1 m/s and from temperature T = 423 to 723 K, with Re ∈ [0, 800]. Experimental results show that flow velocity plays a dominant role in determining the morphologies and fluctuation frequencies of the wake flame. The flame length and suspension height have a trade-off relationship and approach a linear relationship with the increase in air temperature. With increasing Re, the yellow flame gradually vanishes, and the blue flame ratio in the total flame increases following a hyperbolic tangent function. In addition, the length of the flame outline increases linearly with Re. The fluctuations in the flames under both natural and forced convective conditions and various air temperatures are proved to be determined by the vortex shedding behind the sphere, which helps one understand the underlying physics of spray combustion better.

Denoising and fuel spray droplet detection from light-scattered images using deep learning

A deep learning-based method for denoising and detecting the gas turbine engine spray droplets in the light-scattered image (Mie scattering) is proposed for the first time. A modified U-Net architecture is employed in the proposed method to denoise and regenerate the droplets. We have compared and validated the performance of the modified U-Net architecture with standard conventional neural networks (CNN) and modified ResNet architectures for denoising spray images from the Mie scattering experiment. The modified U-Net architecture performed better than the other two networks with significantly lower Mean Squared Error (MSE) on the validation dataset. The modified U-Net architecture also produced images with the highest Power Signal to Noise Ratio (PSNR) compared to the other two networks. This superior performance of the modified U-Net architecture is attributed to the encoder-decoder structure. During downsampling, as part of the encoder, only the most prominent features of the image are selectively retained by excluding any noise. This reconstruction of the noise-free features has produced a more accurate and better denoised image. The denoised images are then passed through a center predictor CNN to determine the location of the droplets with an average error of 1.4 pixels. The trained deep learning method for denoising and droplet center detection takes about 2.13 s on a single graphics processing unit (GPU). This study shows the promise for real-time processing of the experimental data using the well-optimized network.

A reduced-order model for turbulent reactive sprays in compression ignition engines

In this work, we present a reduced-order model for transient turbulent reactive sprays in compression ignition engines. The model is an extension of the previously developed cross-sectionally averaged spray model (CAS) (Deshmukh et al., 2021). A transient turbulence model is derived for the gas phase that allows to model the transient scalar dissipation rate, which is a key parameter in non-premixed combustion. Representative chemistry is solved in mixture fraction space interactively with the flow. The turbulent CAS model combined with the combustion model is termed the cross-sectionally averaged reactive turbulent spray (CARTS) model and can represent unsteady non-premixed combustion behavior. The CARTS model is validated against experimental data as well as three-dimensional (3D) numerical simulations. The model is able to reasonably predict the trends of ignition delay time, flame lift-off length, and soot emissions. The computational cost of the CARTS model is orders of magnitude lower than the 3D simulation methods. This low computational cost enables various applications, including but not limited to the rapid screening of novel fuel candidates as well as off-line training of models to be eventually used in closed-loop control.

Thermodynamic modeling of trans/supercritical fuel sprays in internal combustion engines based on a generalized cubic equation of state

Redlich-Kwong-Peng-Robinson (RK-PR) was developed in recent years as a promising generalized cubic equation of state (EoS) to allow for a good representation of fluids with different critical compressibility factors (Zc), but it cannot be mathematically applied to high Zc fluid such as H2 and CO, thus limiting its application on engine problems. In this work, the Zc ratio was modeled as a function of Zc to extend the calculable range of RK-PR and to achieve higher accuracy for various n-alkanes, liquid oxygen and nitrogen. The thermodynamic and transport properties framework based on RK-PR show superiority over those of SRK and PR for typical IC engine fuels and spray mixtures. In addition, the high-fidelity simulations of n-dodecane spray were performed to investigate qualitatively and quantitatively the effects of EoS and thermodynamic conditions on trans/supercritical spray behavior and characteristics, emphasizing the necessity of applying an accurate EoS for high fidelity spray simulations.

Experimental Research on the Disruptive Evaporation and the Motion Characteristics of Secondary Droplets for Emulsified Biodiesel with a Suspended Droplet Configuration.

The secondary atomization of droplets is one of the means to improve the efficiency of diesel fuel injection atomization. As a promising biomass fuel, emulsified biodiesel showed a good prospect in improving the atomization effect of diesel engines. In this study, a high-temperature and pressure-resistant evaporator was designed to simulate diesel-like conditions, and the evaporation and combustion experiments of emulsified biodiesel droplets were carried out. The morphological changes in the droplets were dynamically captured using a high-speed camera. According to the collected images, the evaporation characteristic parameters, the dynamic parameters of droplet motion, and the correlation between the original and secondary droplets were quantitatively analyzed. The gain effect of secondary atomization for droplets on the diesel engine spray was evaluated. The results showed that the emulsified biodiesel underwent nucleation, agglomeration, puffing, and explosion during the evaporation process, while the classic d2 law only meets a few cases of this fuel. The effect of high temperature was reflected in reducing the normalization time of droplet agglomeration and explosion, while the higher pressure inhibited the expansion of the droplets, thus slowing down the expansion rate and restricting the droplet volume. Driven by the water content, the time of droplet explosion was closer to the droplet lifetime. The evaporation process of the secondary droplet was similar to that of the original droplet over a reduced scale of 1–2 orders of magnitude. (Dd/Dd0)2 ≈ 1 was a necessary condition for the secondary droplets to be produced in large quantities. The average equivalent diameter of the droplets was distributed in the range of 80–140 μm, and the secondary atomization caused expansion of the spray range by 20–40%. Expansion of the range of secondary droplets was beneficial to shortening the ignition delay and increasing the combustion rate.

Development and validation of an improved atomization model for GDI spray simulations: Coupling effects of nozzle-generated turbulence and aerodynamic force

By coupling the Wu-Faeth (WF) turbulent primary breakup theory with the classical Kelvin-Helmholtz (KH) and Rayleigh-Taylor (RT) aerodynamic instability theories, the influences of nozzle-generated turbulence and aerodynamic force on the GDI spray atomization were both modeled in this study. The developed WF-KH-RT model was applied to the spray simulation of a six-hole GDI injector. The model calibration showed that with a simple tuning of a few model parameters, the WF-KH-RT model could predict the spray morphology, spray tip penetration (STP) and Sauter Mean Diameter (SMD) under various injection pressure and ambient pressure conditions with a high fidelity. The influences of specific WF-KH-RT model parameters on the spray simulation were also studied. The results revealed that increasing the KH characteristic time constant B1, WF characteristic length constant Csx and RT characteristic length constant CRT will lead to the increase of STP and SMD under most conditions. As the ratio of fuel density to ambient density ρf/ρg decreases, the aerodynamic effect is enhanced while the turbulent effect is weakened in the primary breakup, as a result the sensitivity of STP and SMD to B1 increases, while that to Csx declines. In summary, the results of this study can provide an insight into the relationship between different mechanisms affecting the fuel spray atomization, and an instruction of calibrating the proposed novel atomization model in GDI engine spray simulations.

Characterization of fuel drop impact on wall films using SPH simulation

The ability to accurately predict the outcome of the drop/wall interaction is essential to engine spray combustion modeling. In this paper, the process of fuel drop impact on a wet wall was simulated using a numerical method based on smoothed particle hydrodynamics (SPH). The present numerical method was first validated using experimental data on the crown height and crown diameter resulting from water drop impact on a liquid film. Then, the impact process of iso-octane drops on wet walls under engine relevant conditions were studied. The presence of a wall film will affect not only the splash threshold but also the crown evolution and the secondary droplets ejected from the rim of the crown. Numerical results show that the splash threshold increases with the film thickness; the splashed mass ratio increases as the kinetic energy of the incident drop increases. The effect of film thickness on the splashed mass ratio is determined by two competing mechanisms. On the one hand, as the film thickness increases, more incident energy will be absorbed and transferred into the crown, thus producing more secondary droplets. On the other hand, more impinging energy will be dissipated during the spreading as the film thickness increases, thus generating fewer secondary droplets. The properties of the secondary droplets are very different as the film thickness increases. Instead of moving outward, the secondary droplets will move upward and even congregate to the center when the film becomes thicker. The impact angle will affect not only the distributions of the secondary droplets but also the splashed mass. The locations and velocities of the secondary droplets were analyzed. These outcomes were incorporated into formulas that can be further developed into a model for simulating engine spray/wall interactions.

Simultaneous Measurement of Vapor and Liquid Phase Concentration Distributions in Engine Spray by 2-Wavelentgh LAS (Laser Absorption Scattering) Technique

Simultaneous Measurement of Vapor and Liquid Phase Concentration Distributions in Engine Spray by 2-Wavelentgh LAS (Laser Absorption Scattering) Technique

IMPROVING THE CALCULATION OF EVAPORATING SPRAYS FOR MEDIUM-SPEED MARINE-ENGINE-LIKE CONDITIONS

In order to reduce maritime transportation's greenhouse gas and pollutant emissions, marine engine manufacturers need to deepen the fundamental understanding of the injection and spray process. But little knowledge is openly available on marine engine fuel sprays, and their numerical simulation. In this paper, two-dimensional unsteady-state Reynolds-averaged Navier-Stokes simulations were performed to study evaporating high-pressure marine engine sprays, in which an injector with a nozzle diameter of 0.44 mm was used. The proposed approach was first validated using measurement data of Spray A and Spray D from the Engine Combustion Network. A satisfactory agreement with the Engine Combustion Network data demonstrated that the simulation can correctly capture the spray processes. However, a discrepancy was found when simulating the marine engine sprays. After summarizing and analyzing the values of the turbulence model constant (C1 of the standard k-ε model) used from the published literature, a lower value of C1 was adopted, and good agreement under a wide range of ambient conditions (density varying from 7.6 to 22.5 kg/m3, and temperature varying from 700 to 950 K) was achieved. Also, the disagreement that was noted for the liquid penetration for a low-temperature case could be explained by the ligament detachment phenomenon which was captured by the computational fluid dynamics simulation.

Image-Based Feedback Control for a Coaxial Spray

Abstract Optimization of jet engine sprays has the potential to improve efficiency and reduce environmental impact. Sprays can be continually optimized in multivariate scenarios using real-time feedback control, but a method of controlling the sprays based on physical properties must first be established. In this study, a spray controller was developed to optimize the spray angle obtained from shadowgraphs, with the assumption that the largest angle is desired. The spray angle was used as an example, as it is a physically important parameter which is easily found through shadowgraph imaging. Varying ratios of swirled air to straight air, determined by the image-based feedback controller were introduced into the air portion of a coaxial airblast nozzle while keeping the total air flow rate constant. A golden section search converged on the swirled air ratio that provided the largest angle and was validated from the distribution of spray angle versus swirled air ratio. The ratio that produced a spray with the greatest angle of 25.8 ± 2 deg was found at a swirled air ratio of 0.66 ± 0.03 for a spray with a momentum ratio of 6. The successful design and implementation of this image-based feedback controller is intended to provide a foundation for developing real-time active feedback controllers for sprays.

Large-eddy spray simulation under direct-injection spark-ignition engine-like conditions with an integrated atomization/breakup model

In this work, a hybrid breakup model tailored for direct-injection spark-ignition engine sprays is developed and implemented in the OpenFOAM CFD code. The model uses the Lagrangian–Eulerian approach whereby parcels of liquid fuel are injected into the computational domain. Atomization and breakup of the liquid parcels are described by two sub-models based on the breakup mechanisms reported in the literature. Evaluation of the model has been carried out by comparing large-eddy simulation results with experimental measurements under multiple direct-injection spark-ignition engine-like conditions. Spray characteristics including liquid and vapor penetration curves, droplet velocities, and Sauter mean diameter distributions are examined in detail. The model has been found to perform well for the spray conditions considered in this work. Results also show that after the end of injection, most of the residual droplets that are still in the breakup process are driven by the bag and bag–stamen breakup mechanisms. Finally, an effort to unify the breakup length parameter is made, and the given value is tested under various ambient density and temperature conditions. The predicted trends follow the measured data closely for the penetration rates, even though the model is not specifically tuned for individual cases.

Large eddy simulation of high pressure spray with the focus on injection pressure

This paper presents a detailed numerical analysis of diesel engine spray structure induced by the Engine Combustion Network (ECN) Spray A at different injection pressures. The non-reacting simulations are performed using OpenFOAM where an Eulerian–Lagrangian model is adopted in the large eddy simulation (LES) framework. Effects of the LES mesh resolution as well as the spray model parameters are investigated with the focus on their impact on spray structure as the injection pressure varies. The predicted liquid and vapour penetration lengths agree well with the measurements at different injection pressures. The mixture fraction is well captured for the injection pressure of 100 and 150 MPa while a slight deviation from the measurements is observed for the injection pressure of 50 MPa near the nozzle. The parametric analysis confirms that the LES mesh resolution has significant effects on the results. A coarser mesh leads to higher liquid and vapour penetration lengths where the deviation from the measurements is larger, resulting in the highest error at the lowest injection pressure. As the mesh size increases, the droplet size distribution becomes narrower, its pick moves to the smaller droplet size and the probability of droplets with higher temperature increases. On the other hand, with increasing the mesh size, the carrier gas velocity decays slower and its radial dispersion decreases. It is found that the droplet characteristics are more affected by the mesh resolution when the injection pressure is the lowest while the opposite is true for the carrier phase. The number of Lagrangian particles also affects the droplet characteristics and the fuel-air mixing but their effects are not as significant as the mesh size. The results become less sensitive to the number of Lagrangian particles as the pressure injection decreases. Finally, the importance of the initial droplet size distribution is investigated, confirming its impact is marginal, particularly on the liquid length. It is observed that the initial droplet size is only important at very close to the nozzle and its impact on the spray structure becomes quickly insignificant due to the high rates of breakup and evaporation. This trend is consistent at different injection pressures.

Scaling liquid penetration in evaporating sprays for different size diesel engines

Scaled model experiments can greatly reduce the cost, time and energy consumption in diesel engine development, and the similarity of spray characteristics has a primary effect on the overall scaling results of engine performance and pollutant emissions. However, although so far the similarity of spray characteristics under the non-evaporating condition has been studied to some extent, researches on scaling the evaporating sprays are still absent. The maximum liquid penetration length has a close relationship with the spray evaporation processes and is a key parameter in the design of diesel engine spray combustion system. In this article, the similarity of maximum liquid penetration length is theoretically derived based on the hypotheses that the spray evaporation processes in modern high-pressure common rail diesel engines are fuel–air mixing controlled and local interphase transport controlled, respectively. After verifying that the fuel injection rates are perfectly scaled, the similarity of maximum liquid penetration length in evaporating sprays is studied for three scaling laws using two nozzles with hole diameter of 0.11 and 0.14 mm through the high-speed diffused back-illumination method. Under the test conditions of different fuel injection pressures, ambient temperatures and densities, the lift-off law and speed law lead to a slightly increased maximum liquid penetration length, while the pressure law can well scale the maximum liquid penetration length. The experimental results are consistent with the theoretical analyses based on the hypothesis that the spray evaporation processes are fuel–air mixing controlled, indicating that the local interphase transports of energy, momentum and mass on droplet surface are not rate-controlled steps with respect to spray evaporation processes.

Large-Eddy Simulation of Turbulent Dispersion Effects in Direct Injection Diesel and Gasoline Sprays

<div class="section abstract"><div class="htmlview paragraph">In most large-eddy simulation (LES) applications to two-phase engine flows, the liquid-air interactions need to be accounted for as source terms in the respective governing equations. Accurate calculation of these source terms requires the relative velocity “seen” by liquid droplets as they move across the flow, which generally needs to be estimated using a turbulent dispersion model. Turbulent dispersion modeling in LES is very scarce in the literature. In most studies on engine spray flows, sub-grid scale (SGS) models for the turbulent dispersion still follow the same stochastic approach originally proposed for Reynolds-averaged Navier-Stokes (RANS). In this study, an SGS dispersion model is formulated in which the instantaneous gas velocity is decomposed into a deterministic part and a stochastic part. The deterministic part is reconstructed using the approximate deconvolution method (ADM), in which the large-scale flow can be readily calculated. The stochastic part, which represents the impact of the SGS flow field, is assumed to be locally homogeneous and isotropic and, therefore, governed by a Langevin-type equation. The model is applied to the spray G and spray H conditions defined by the engine combustion network (ECN) group. Simulation results are compared with the available experimental data for spray characteristics such as penetration rates, mixture fraction profile, and droplet velocity and Sauter mean diameter (SMD) distributions. Simulations with no dispersion and the commonly used RANS-type stochastic model are also performed for comparison purposes. Results show that the turbulent dispersion has a considerable impact on quantitative spray characteristics such as projected liquid volume (PLV) fraction, droplet SMD and velocity, and fuel vapor mixture fractions. On the other hand, the macroscopic spray characteristics such as liquid- and vapor-phase penetrations are not significantly affected by the dispersion modeling. The proposed SGS model also improves the prediction of spray and ignition characteristics at the spray conditions studied in this work.</div></div>