13 research outputs found

    Development and Assessment of Large Eddy Simulation Methodology for Internal Combustion Engines

    Get PDF
    Large Eddy Simulation (LES) represents nowadays one of the most promising techniques for the evaluation of the dynamics and evolution of turbulent structures characterizing Internal Combustion Engines (ICE). The demand for a high level of resolution accuracy as well as the need to evaluate different scenarios and system configurations lead to considerable computational and economic costs for both the hardware infrastructure and the licensing fees of commercial codes. In such context, the present Doctoral project has the objective to define the most suitable numerical methodology to perform LES analysis of ICE flows and to implement such methodology in an efficient, accurate and robust CFD code, based on open-source components. An evaluation of freely available CFD codes has led to the choice of the open-source CFD package OpenFOAM as the most suited code for the project’s objective. The LES modeling of interest for ICE applications has been then studied and three Sub-grid scale models particularly suited for such flows have been implemented and assessed into OpenFOAM. Moreover, Python scripts have been developed in order to automate and speed-up both pre-processing and post-processing phases. The CFD methodology has been then applied to a real world ICE systems such as a stationary flow bench, for which prior RANS simulations had shown some predictive deficiencies. The quality of the analyses has been assessed through specific LES quality estimators and the computational results have been validated against measurements, showing pretty good agreement. Finally, LES simulations have allowed the accurate investigation of the flow bench fluid-dynamic behavior and, thanks to the insights gained, an alternative RANS approach based on the Reynolds Stress Tensor Modeling has been proposed and tested in order to alleviate the aforementioned predictive deficiencies

    Assessment of the Cavitation Models Implemented in OpenFOAM® Under DI-like Conditions

    Get PDF
    Abstract Direct injection engine performance is strictly correlated to the fluid dynamic characteristics of the injection system. Actual DI engines, both Diesel and gasoline, employ injector characterized by high injection pressure that, associated to micro-orifice design, result in cavitation flow conditions inside injector holes. The cavitation has a beneficial effect on the atomization process and a negative one on the physical erosion generated by the vapor bubble collapse. In order to quantify both effects with a numerical approach, the reduced dimension and the complex flow structures reduce the efficacy of an experimental approach, thus the cavitation model used is of primary importance. The present work addresses the validation of the mixture model-based cavitation models that are implemented in OpenFOAM®, with particular focus on the Schnerr and Sauer model, using the experimental results, available in literature, for a two-phase flow in an optically accessible nozzle under diesel-like conditions

    Large Eddy Simulation of a Steady Flow Test Bench Using OpenFOAM®

    Get PDF
    Abstract Stationary flow bench testing is a standard experimental methodology used by the automotive industry to characterize a cylinder head. In order to reduce the development time, the use of a CFD-based virtual test bench is nowadays a standard practice too. The use of a conventional \RANS\ methodology for the simulation of the flow through the ducts of an engine head allows to get only the mean flow variables distributions because the time average of the generic flow variable fluctuation is zero by definition, but the fluid-dynamics of a stationary flow bench is not really stationary due to the flow instability induced by the duct design and the interaction between valve jets in a multi-duct head. In order to obtain an in-depth knowledge of the fluid-dynamics of a stationary flow bench test rig a \LES\ simulation of a heavy duty \DI\ diesel engine head with two intake ducts, for which experimental data was available, has been carried out using OpenFOAM®. The comparison between LES, experimental and conventional \RANS\ results widened the understanding of the test-bench fluid-dynamics and of the swirl generation process. Due to the high computational cost of the \LES\ approach, the outcomes of this latter have been also used to evaluate potential accuracy improvements of the \RANS\ simulation, namely using a model sensible to flow anisotropies and curvatures such as a \RSTM\ model. The simulation with the new turbulence model has been carried out and compared with the previous results demonstrating predictive improvements with an affordable computational cost for industrial routine usage

    numerical evaluation of the applicability of steady test bench swirl ratios to diesel engine dynamic conditions

    Get PDF
    Engine coherent flow structures such as swirl and tumble motions are key factors for the combustion process due to their capability to rise turbulence levels and enhance mixing which, in turns, severely influence both fuel efficiency and pollutant emissions. Automotive industry has therefore put great efforts over the last decades in evaluating air flow during induction stroke and air flow within the cylinder. Nowadays swirl and tumble motion characterizing a specific cylinder head are evaluated experimentally at design stage mainly using stationary flow benches. Such tests allow characterizing each head prototype using non-dimensional parameters like swirl and tumble ratios and, finally, to compare the different designs. In the present work the authors focused their attention on the swirl ratio characterization, firstly reviewing the two main methodologies for evaluating such parameter and more precisely the AVL and the Ricardo ones. A numerical method is then proposed in order to reproduce the stationary test bench with the final goal to develop a fast and accurate virtual test bench for cylinder head design. Simulations have been carried out on different VM Motori engine heads for which experimental data were available. The comparison between computational and experimental swirl ratios allowed to evaluate the suitability of using a virtual test bench as alternative or complementary to experiments. These results widened the understanding of the swirl fluid-dynamics and suggested that care must be taken when comparing duct designs having no geometrical similarity. Finally dynamic simulations have been performed for the head prototypes in order to compute the engine swirl in realistic conditions and to compare it with the steady bench results. This allowed evaluating the capability of the two different "static" swirl ratio definition (AVL/Ricardo) in correctly estimating real engine swirl. © 2015 The Authors. Published by Elsevier Ltd

    The Effect of the Throttle Valve Rotational Direction on the Tumble Motion at Different Partial Load Conditions

    No full text
    In PFI and GDI engines the tumble motion is the most important charge motion for enhancing the in-cylinder turbulence level at ignition time close to the spark plug position. In the open literature different studies were reported on the tumble motion, experimental and not. In the present paper the research activity on the tumble generation at partial load and very partial load conditions was presented. The added value of the analysis was the study of the effect of the throttle valve rotational direction on the tumble motion and the final level of turbulence at the ignition time close to the spark plug location. The focus was to determine if the throttle rotational direction was crucial for the tumble ratio and the turbulence level. The analyzed engine was a PFI 4-valves motorcycle engine. The engine geometry was formed by the intake duct and the cylinder. The CFD code was FIRE AVL code 2013.1. The intake and the compression phases till TDC were simulated: inlet boundary conditions from 1D simulations were imposed. The modelled fluid was only air because the next step, now in progress, is the analysis of the mixture formation at the same partial load conditions modelling the injection. Once assessed the influence of the throttle valve on both the tumble motion and the turbulence, the authors' focus is the analysis of the mixture formation process and the evaluation of the final mixture index value. Copyright \ua9 2015 SAE International

    Large Eddy Simulation of a Steady Flow Test Bench Using OpenFOAM®

    Get PDF
    Abstract Stationary flow bench testing is a standard experimental methodology used by the automotive industry to characterize a cylinder head. In order to reduce the development time, the use of a CFD-based virtual test bench is nowadays a standard practice too. The use of a conventional \RANS\ methodology for the simulation of the flow through the ducts of an engine head allows to get only the mean flow variables distributions because the time average of the generic flow variable fluctuation is zero by definition, but the fluid-dynamics of a stationary flow bench is not really stationary due to the flow instability induced by the duct design and the interaction between valve jets in a multi-duct head. In order to obtain an in-depth knowledge of the fluid-dynamics of a stationary flow bench test rig a \LES\ simulation of a heavy duty \DI\ diesel engine head with two intake ducts, for which experimental data was available, has been carried out using OpenFOAM®. The comparison between LES, experimental and conventional \RANS\ results widened the understanding of the test-bench fluid-dynamics and of the swirl generation process. Due to the high computational cost of the \LES\ approach, the outcomes of this latter have been also used to evaluate potential accuracy improvements of the \RANS\ simulation, namely using a model sensible to flow anisotropies and curvatures such as a \RSTM\ model. The simulation with the new turbulence model has been carried out and compared with the previous results demonstrating predictive improvements with an affordable computational cost for industrial routine usage

    Analysis of the mixture formation at partial load operating condition: The effect of the throttle valve rotational direction

    No full text
    In the next incoming future the necessity of reducing the raw emissions leads to the challenge of an increment of the thermal engine efficiency. In particular it is necessary to increase the engine efficiency not only at full load but also at partial load condit ions. In the open literature very few technical papers are available on the partial load conditions analysis. In the present paper the analysis of the effect of the throttle valve rotational direction on the mixture formation is analyzed. The engine was a PFI 4-valves motorcycle engine. The throttle valve opening angle was 17.2', which lays between the very partial load and the partial load condition. The CFD code adopted for the analysis was the FIRE AVL code v. 2013.2. The exhaust, intake and compression phases till TDC were simulated: inlet/outlet boundary conditions from 1D simulations were imposed. The injection system operation was experimentally investigated in terms of spray shape and drop sizing and veloci ty for a proper tuning of the numerical model. The injection process was modelled and the final results in terms of mixture compositi on and turbulence level at the ignition time were investigated. The aim of the paper was to deeply analyze the dynamic effect of the throttle valve position on the engine behavior. The wallfilm effect on the effective mixture formation process was considered by means a new methodological approach. The wallfilm thickness and its dynamics affect the final mixture formation process and the level of the mixture index at the ignition time close to the spark plug. It is also necessary to consider that, even though the CFD simulations were RANS simulations, it could take some days for reaching the converged wallfilm thickness, even 20 or more engine cycles at full load conditions could be necessary. The research group proposed a new methodological approach for facing this problem within a computational time compatible with industrial applications too. \ua9 2015 SAE International

    Machine Learning Algorithms Highlight tRNA Information Content and Chargaff’s Second Parity Rule Score as Important Features in Discriminating Probiotics from Non-Probiotics

    No full text
    Probiotic bacteria are microorganisms with beneficial effects on human health and are currently used in numerous food supplements. However, no selection process is able to effectively distinguish probiotics from non-probiotic organisms on the basis of their genomic characteristics. In the current study, four Machine Learning algorithms were employed to accurately identify probiotic bacteria based on their DNA characteristics. Although the prediction accuracies of all algorithms were excellent, the Neural Network returned the highest scores in all the evaluation metrics, managing to discriminate probiotics from non-probiotics with an accuracy greater than 90%. Interestingly, our analysis also highlighted the information content of the tRNA sequences as the most important feature in distinguishing the two groups of organisms probably because tRNAs have regulatory functions and might have allowed probiotics to evolve faster in the human gut environment. Through the methodology presented here, it was also possible to identify seven promising new probiotics that have a higher information content in their tRNA sequences compared to non-probiotics. In conclusion, we prove for the first time that Machine Learning methods can discriminate human probiotic from non-probiotic organisms underlining information within tRNA sequences as the most important genomic feature in distinguishing them

    Potential of Full-Fat Silkworm-Based Diets for Laying Quails: Performance and Egg Physical Quality

    Get PDF
    The present research was conducted to determine the optimal inclusion level of full-fat silkworm chrysalis meal (SWM) into laying quails’ diets, focusing on performance traits and egg physical quality. A total of 240 31-day-old female Japanese quails were randomly assigned to four dietary groups (12 replicates/treatment; 5 quails/replicate); quails were initially fed a standard commercial diet for pullets until 63 days of age. When oviposition started, the experimental groups received the following diets: a conventional corn and soybean-based diet (control diet—C) and three other diets, including 4%, 8%, or 12% of full-fat SWM (SWM4, SWM8, SWM12, respectively). Experimental diets were provided until quails reached 119 days of age. Birds displayed satisfactory productive performance throughout the trial. SWM12 and SWM8 had higher (p p p 8%) require special attention because SWM also contains anti-nutritional factors
    corecore