X. Margot

To comply with the very strict emissions regulation the automotive industry is succeeding in developing ever more efficient engines, and there is scope for more improvements. In this regard, some investigations have suggested that insulating the combustion chamber walls of an internal combustion engine (ICE) yield low thermal losses. Most of the literature available on this topic presents simplified models that do not allow studying in detail the coating impact on engine efficiency. A more precise approach that consists in the combination of Computational Fluid Dynamics (CFD) and Conjugate Heat Transfer (CHT) simulations is used in this paper to predict the heat losses through the combustion chamber walls of a spark ignition (SI) engine. Two configurations are considered for the single cylinder engine: the metallic case and the same engine with coated piston and cylinder head. The insulation material has a low thermal conductivity ( k[Formula: see text]1.0 W/( mK)). The numerical re...

The 11th edition of the THIESEL Conference on Thermo-and Fluid Dynamic Processes in Direct Injection Engines, THIESEL 2020, was celebrated online due to the COVID pandemic. Despite this, it gathered over 500 participants, thus proving once more that it is consolidated as a meeting point between industry, research institutions, and academia involved in R&D for automotive engines. All in all, 9 papers out of the 36 presented at the conference have been chosen to make this issue, based on a double peer-review, the first one by two referees for the Conference selection itself, and a second review by two peers for the IJER special issue. These papers reflect the high-quality standards of all the papers presented at the conference. With this selection, it is clear that there has been a shift in the main research focus of internal combustion engine developers. While in the special edition dedicated to the THIESEL 2018 conference, the papers reflected that improving Diesel and gasoline injection and combustion were still important issues to comply with emission regulations, the trend initiated already a few years back to bring new ways of controlling these has been consolidated in THIESEL 2020. Research has turned toward alternative fuels, such as biofuels (CalleAsensio et al.), ethanol (Giramondi et al.), and natural gas (Winter et al.). Studies presented in the THIESEL 2020 papers comprise the evaluation of advanced biofuels on the performance and regulated emissions of a Euro6 light-duty Diesel vehicle, to injection strategies to enhance auto-ignition and combustion of ethanol fuel in CI heavy duty engines and injection strategies optimization for dual gas-fuel. The importance of reducing CO2 emissions has led to studies about improving engine efficiency in a significant manner. Splitter et al. analyze the effect on soot production of using EGR and late intake valve closing in a single-cylinder SI high compression ratio engine and conclude that depending on the fuel characteristics (gasoline or LPG), combustion efficiency may be significantly improved when compared to a conventional Diesel engine. Keskinen et al. measured heat fluxes in an engine-relevant environment to determine if the use of thermo-swing coating materials helps significantly reduce heat transfer losses. However, they concluded that it is rather difficult to improve the thermal efficiency of the engine by these means. Doulgeris et al., on the other hand, centered their study on the definition of specific real-world driving cycles to evaluate the overall energy efficiency of electrified powertrains. Naturally, the reduction of NOx emissions has also been one of the topics at the heart of the conference. Lee et al. developed and validated a real-time prediction model based on in-cylinder pressure to estimate NO and NO2 separately in real time. The idea is to use this model to manage NOX aftertreatment systems and minimize tail-pipe emissions. Esposito et al. also developed a model to predict gaseous pollutants from a SI direct injection engine. And Galindo et al. presented a study of the impact of using high-pressure EGR during particulate filter (DPF) regeneration mode to reduce NOx emissions and clean soot emissions during cold operation mode. The success of research lies in the close cooperation between different organizations, and particularly between academia and stakeholders. In this sense, the THIESEL conference has always favored papers where the industrial implication is high. Four of the abovementioned papers are collaborative papers, either between a research center and a university, or between an industrial company and a university. To conclude, the papers selected from the THIESEL 2020 Conference for this special issue are a good sample of all relevant topics investigated nowadays to further improve engines efficiency and reduce emissions and fuel consumption The editor wishes to thank the authors for improving their papers and the reviewers for their time and effort.

The 3D Conjugate Heat transfer (CHT) calculation of the heat transfer from the gas to the walls of a combustion chamber requires very fine meshing, particularly so when the walls are coated with a very thin insulation layer. It is practically impossible to mesh such thin layers for numerical as well as computational cost reasons. In this paper a solution to this problem is presented: an equivalent material layer with a reasonable meshing thickness is defined in such a way that its thermal behavior matches that of the real very thin coating layer. The methodology used to define the thermodynamic properties of the equivalent coating material is based on a combination of a 1D heat transfer model and a multi-factorial sweep of material properties. This equivalent material layer can then be introduced in the 3D CHT calculation instead of the real coating thin layer, and can be adequately meshed to predict with accuracy the heat losses. The approach is illustrated for a real case and a pa...

In this article, a numerical methodology for assessing combustion noise in compression ignition engines is described with the specific purpose of analysing the unsteady pressure field inside the combustion chamber. The numerical results show consistent agreement with experimental measurements in both the time and frequency domains. Nonetheless, an exhaustive analysis of the calculation convergence is needed to guarantee an independent solution. These results contribute to the understanding of in-cylinder unsteady processes, especially of those related to combustion chamber resonances, and their effects on the radiated noise levels. The method was applied to different combustion system configurations by modifying the spray angle of the injector, evidencing that controlling the ignition location through this design parameter, it is possible to decrease the combustion noise by minimizing the resonance contribution. Important efficiency losses were, however, observed due to the injector...

... Journals Books Begell Digital Library Submission. ISSN: 1044-5110 Print. ... The Delay Phenomena in Thermal Explosion of Polydisperse Fuel Spray: Asymptotic Analysis OPhir Nawe, Vladimir Gol'dshtein, Eitan Dan DOI: 10.1615/AtomizSpr.v21.i1.50 pages 69-85. ...

... Journals Books Begell Digital Library Submission. ISSN: 1044-5110 Print. ... The Delay Phenomena in Thermal Explosion of Polydisperse Fuel Spray: Asymptotic Analysis OPhir Nawe, Vladimir Gol'dshtein, Eitan Dan DOI: 10.1615/AtomizSpr.v21.i1.50 pages 69-85. ...

Cold startability of automotive direct injection (DI) Diesel engines is frequently one of the negative features when these are compared to their closest competitor, the gasoline engine. This situation worsens with the current design trends (engine downsizing) and the emerging new Diesel combustion concepts, such as HCCI, PCCI, etc., which require low compression ratio engines. To mitigate this difficulty, pre-heating systems (glow plugs, air heating, etc.) are frequently used and their technologies have been continuously developed. For the optimum design of these systems, the determination of the threshold temperature that the gas should have in the cylinder in order to provoke the self-ignition of the fuel injected during cold starting is crucial. In this paper, a novel methodology for estimating the threshold temperature is presented. In this methodology, experimental and computational procedures are adequately combined to get a good compromise between accuracy and effort. The measurements have been used as input data and boundary conditions in 3D and 0D calculations in order to obtain the thermodynamic conditions of the gas in the cylinder during cold starting. The results obtained from the study of two engine configurations -low and high compression ratio- indicate that the threshold in-cylinder temperature is a single temperature of about 415 °C.

In order to analyze the influence of nozzle geometry on the internal flow characteristics of a Diesel injector, a CFD analysis of the flow through various nozzle geometries has been carried out with a commercial code. This program includes a numerical model simulating the effect of cavitation. For the flow simulation, cylindrical and conical nozzles with different grades of hydro-grinding were used in order to observe the individual effects of these geometrical parameters. The model predicts accurately the onset of cavitation, but is very limited for strongly cavitating flow, so that the analysis of the solution may only be qualitatively assessed. However, the simulations confirm the tendency observed in experiments, that the nozzle geometry significantly influences the inner flow characteristics. In particular, by increasing the hydro-grinding radius of the orifice inlet, the mean outlet velocity near the wall and the discharge coefficient are increased, while the zone of cavitating flow is reduced. In addition, it was found that conical nozzles do not produce cavitation.

ABSTRACT The combustion process in direct injection (DI) Diesel engines is an important source of noise, and it is thus the main reason why end-users could be reluctant to drive vehicles powered with this type of engine. This means that the great potential of Diesel engines for environment preservation—due to their lower consumption and the subsequent reduction of CO2 emissions—may be lost. Moreover, the advanced combustion concepts—e.g. the HCCI (homogeneous charge compression ignition)—developed to comply with forthcoming emissions legislation, while maintaining the efficiency of current engines, are expected to be noisier because they are characterized by a higher amount of premixed combustion. For this reason many efforts have been dedicated by car manufacturers in recent years to reduce the overall level and improve the sound quality of engine noise. Evaluation procedures are required, both for noise levels and sound quality, that may be integrated in the global engine development process in a timely and cost-effective manner. In previous published work, the authors proposed a novel method for the assessment of engine noise level. A similar procedure is applied in this paper to demonstrate the suitability of combustion indicators for the evaluation of engine noise quality. These indicators, which are representative of the peak velocity of fuel burning and the resonance in the combustion chamber, are well correlated with the combustion noise mark obtained from jury testing. Quite good accuracy in the prediction of the engine noise quality has been obtained with the definition of a two-component regression, which also permits the identification of the combustion process features related to the resulting noise quality, so that corrective actions may be proposed.

The study of the three-dimensional acoustic field inside an exhaust muffler is usually performed through the numerical solution of the linearized equations. In this paper, an alternative procedure is proposed, in which the full equations are solved in the time domain. The procedure is based on the CFD simulation of an impulsive test, so that the transmission loss may be computed and compared with measurements and other numerical approaches. Also, the details of the flow inside the muffler may be studied, both in the time and the frequency domains. The results obtained compare favorably with a conventional FEM calculation, mostly in the ability of the procedure to account for dissipative processes inside the muffler.

ABSTRACT The resonant oscillation of burned gases in the combustion chamber of direct injection (DI) diesel engines appears to be the main excitation source of the engine block during combustion. This has led to the application of different techniques in order to study its generation mechanisms and to determine its relationship with combustion parameters such as bowl geometry, type of injector, injection parameters, etc. In this paper, a numerical methodology for the analysis of combustion chamber resonances is proposed. The numerical approach is validated by comparison with results from modal theory in a simple case. Then, this technique has been applied to the analysis of three different bowls, indicating their potential for the control of combustion chamber resonances.

ABSTRACT A combined analysis of computational fluid dynamics (CFD) and phenomenological model is proposed in this work to improve the liquid length predictions of diesel sprays under evaporative conditions. The stable diameter of droplets was evaluated using a trade-off mechanism between a standard CFD model and a phenomenological correlation, and this allowed a better prediction of the measured maximum liquid length than by using the collision models. The standard drop drag coefficient calculation was corrected with empirical correlations that introduce different effects, such as drop deformation, void fraction effects, and the influence of the mass transfer from liquid to vapor phase during the evaporation of droplets. Moreover, the heat and mass transfer between the droplets and gas were also corrected considering a larger surface area of the droplets caused by their deformation during the break-up process. Experimental data available in literature has been used to validate the model for single components and diesel fuels, and encouraging results have been obtained contributing to a better simulation of the atomization, breakup, and evaporative processes in sprays.

... (José) Christian Donayre, CMT-Motores Termicos, Universidad Politecnica de Valencia, Valencia, Spain. Abstract. ... A first approach to analyse this phenomenon was made in the work by Torregrosa et al. (2004), where they used the modal theory. ...