• Energy Research

[EN] Several investigations related to increasing engine thermal efficiency focusing on the engine hydraulic circuits (oil and coolant) were performed over the last years. According to literature, more than 20% of the fuel energy is rejected to the coolant in steady state conditions. Thus, better use of that energy, especially during warm up of the engine, would lead to an improvement of engine performance and fuel consumption. In the present work, a complete engine and its subsystems were modeled and validated in a 0D/1D in-house software. After, several case studies based on modifying the volume of the engine hydraulic circuits were simulated and analyzed. The simulations were performed for steady state and transient conditions. On one hand, the impact of the present thermal management strategy was practically negligible in steady state conditions. On the other hand, for transient conditions and ambient boundary conditions, the results showed that by reducing the coolant volume by 45% the reduction in warm up time and fuel consumption compared with the base case were 7% and 0.4% respectively. Additionally, for cold conditions, the impact was even higher, obtaining a reduction of warm up time and fuel consumption of 13% and 0.5% respectively. Acknowledgment Authors would like to sincerely acknowledge the founding sup-port provided by Conselleria de Innovacion, Universidades, Ciencia y Sociedad Digital in the framework of the Ayuda Predoctoral GVA. (ACIF/2020/234) .

Most of hydrocarbon (HC) and carbon monoxide (CO) emissions from automotive DI Diesel engines are produced during the engine warm-up period and are primarily caused by difficulties in obtaining stable and efficient combustion under these conditions. Furthermore, the contribution of engine starting to these emissions is not negligible; since this operating condition is highly unfavorable for the combustion progress. Additionally, the catalytic converter is ineffective due to the low engine temperature. In conjunction with adequate engine settings (fuel injection and fresh air control), either the glow plugs or the intake air heater are activated during a portion of the engine warm-up period, so that a nominal engine temperatures is reached faster, and the impact of these difficulties is minimized. Measurement of gaseous pollutants during engine warm-up is currently possible with detectors used in standard exhaust gas analyzers (EGA), which have response times well-suited for sampling at such transient conditions. However, these devices are not suitable for the measurement of exhaust emissions produced during extremely short time intervals, such as engine starting. Herein, we present a methodology for the measurement of the cumulative pollutant emissions during the starting phase of passenger car DI Diesel engines, with the goal of overcoming this limitation by taking advantage of standard detectors. In the proposed method, a warm canister is filled with an exhaust gas sample at constant volumetric flow, during a time period that depends on the engine starting time; the gas concentration in the canister is later evaluated with a standard EGA. When compared with direct pollutant measurements performed with a state-of-art EGA, the proposed procedure was found to be more sensitive to combustion changes and provided more reliable data.

This article presents an electro-thermal model of a prismatic lithium-ion cell, integrating physics-based models for capacity and resistance estimation. A 100 Ah prismatic cell with LFP-based chemistry was selected for analysis. A comprehensive experimental campaign was conducted to determine electrical parameters and assess their dependencies on temperature and C-rate. Capacity tests were conducted to characterize the cell’s capacity, while an OCV test was used to evaluate its open circuit voltage. Additionally, Hybrid Pulse Power Characterization tests were performed to determine the cell’s internal resistive-capacitive parameters. To describe the temperature dependence of the cell’s capacity, a physics-based Galushkin model is proposed. An Arrhenius model is used to represent the temperature dependence of resistances. The integration of physics-based models significantly reduces the required test matrix for model calibration, as temperature-dependent behavior is effectively predicted. The electrical response is represented using a first-order equivalent circuit model, while thermal behavior is described through a nodal network thermal model. Model validation was conducted under real driving emissions cycles at various temperatures, achieving a root mean square error below 1% in all cases. Furthermore, a comparative study of different cell cooling strategies is presented to identify the most effective approach for temperature control during ultra-fast charging. The results show that side cooling achieves a 36% lower temperature at the end of the charging process compared to base cooling.

[EN] Thermal management is a major challenge for new generation turbofan aero-engines. One of the most promising heat exchangers are the so-called surface air-cooled oil coolers (SACOCs). In this study, an experimental methodology is proposed and implemented in order to characterize SACOCs mounted in turbofan bypass ducts. Three different SACOC geometries have been characterized under the same nominal operating point, while the actual velocity profile in the bypass was reproduced by means of a distortion screen upstream the test section. The heat exchangers were mounted in counterflow configuration and feature the same fin geometry in the oil side. The three prototypes varied only in the air side, being the first a baseline flat plate, the second a SACOC with standard trapezoidal fins and the third featuring optimized fins designed to reduce the pressure drop. Aerothermal results demonstrated that the effect of the SACOC on the bypass flow was confined to a region about the same height and width of the finned area, avoiding the need of reproducing the whole bypass duct. However, for this reduced-height experimental approach to be valid, we show that the velocity profile needs to be rearranged to match the specific section of the whole bypass. We also demonstrate how the optimized fin geometry achieved a 10% lower friction factor than the standard one at nominal flow conditions while increasing the overall heat transfer coefficient by 5.2%. This project has received funding from the Clean Sky 2 Joint Undertaking under the European Union's Horizon 2020 research and innovation programme under grant agreement n° 831977: Aerodynamic upgrade of Surface Air-Cooled Oil Coolers (SACOC). A. Felgueroso is supported through the Programa de Apoyo para la Investigación y Desarrollo of the Universitat Politècnica de València under grant PAID-01-20 n° 21589. The authors also wish to thank Safran Aircraft Engines for their kind permission to share the data presented in this publication. Special thanks are also given to Mr. Adolfo Guzmán for his inestimable support during the experimental campaign.

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.

[EN] In modeling an Internal Combustion Engine, the combustion sub-model plays a critical role in the overall simulation of the engine as it provides the Mass Fraction Burned (MFB). Analytically, the Heat Release Rate (HRR) can be obtained using the Wiebe function, which is nothing more than a mathematical formulation of the MFB. The mentioned function depends on the following four parameters: efficiency parameter, shape factor, crankshaft angle, and duration of the combustion. In this way, the Wiebe function can be adjusted to experimentally measured values of the mass fraction burned at various operating points using a least-squares regression, and thus obtaining specific values for the unknown parameters. Nevertheless, the main drawback of this approach is the requirement of testing the engine at a given engine load/speed condition. Furthermore, the main objective of this study is to propose a predictive model of the Wiebe parameters for any operating point of the tested SI engine. For this purpose, an Artificial Neural Network (ANN) is developed from the experimental data. A criterion was defined to choose the best-trained network. Finally, the Wiebe parameters are estimated with the neural networks for different operating conditions. Moreover, the mass fractions burned generated from the Wiebe functions are compared with the respective experimental values from several operating points measured in the engine test bench. Small differences were found between the estimated and experimental mass fractions burned. Therefore, the effectiveness of the developed ANN model as a prediction tool for the engine MFB is verified.

[EN] A surface air-cooled oil cooler (SACOC) is a passive heat exchanger used to evacuate a large quantity of heat from the oil circuit of a turbofan engine to its secondary flow with minimal perturbation. Using the secondary flow as a heat sink has the advantage of the evacuated enthalpy being available in the nozzle. The performance of a SACOC is therefore measured in terms of maximum heat release capacity with minimal pressure loss and flow perturbations. These heat exchangers are typically composed of parallel fins and are usually tested in bespoke wind tunnels where the interaction between the three-dimensional high velocity flow and the heat exchangers is evaluated. Modern numerical computations that include the solution of the fluid equations in the flow field and a conjugate thermal problem can be also performed. This numerical approach, once validated, allows a complete and computationally affordable analysis of the aero-thermodynamic performance of the SACOC. In this work, a first comparison between both experimental and computational perspectives is presented in terms of pressure and temperature profiles to achieve a complete characterization of the device. This double experimental numerical perspective allows comparing the behaviour of the different fins of the SACOC depending on their relative position but also to trust the numerical conclusions with experimental robust data. This project has received funding from the Clean Sky 2 Joint Undertaking under the European Union¿s Horizon 2020 research and innovation programme under grant agreement No 831977 Aerodynamic upgrade of Surface AirCooled Oil Coolers (SACOC). Leo M. González acknowledges the financial support from the Spanish Ministry for Science, Innovation and Universities (MCIU) under grant RTI2018-096791-B-C21 Hidrodinámica de elementos de amortiguamiento del movimiento de aerogeneradores flotantes. The authors also wish to thank Safran Aircraft Engines for their kind permission to share the data presented in this publication