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Journal Article

Enhanced Low-Order Model with Radiation for Total Temperature Probe Analysis and Design

2018-05-16
Abstract Analysis and design of total temperature probes for accurate measurements in hot, high-speed flows remains a topic of great interest in aerospace propulsion and a number of other engineering areas. One can apply detailed computational methods for simultaneous convection, conduction and radiation heat transfer, but such approaches are not suitable for rapid, routine analysis and design studies. For these studies, there is still a place for low-order approximate methods, and that is the subject of this paper. Here, an enhanced, low-order model is presented that includes conduction with variable thermal conductivity, convection with varying convection coefficient, varying diameter (and thus area) along the length of the sensor and radiation, all implemented in a convenient MATLAB code.
Journal Article

Modeling of Ducted-Fan and Motor in an Electric Aircraft and a Preliminary Integrated Design

2018-10-04
Abstract Electric ducted-fans with high power density are widely used in hybrid aircraft, electric aircraft, and VTOL vehicles. For the state-of-the-art electric ducted-fan, motor cooling restricts the power density increase. A motor design model based on the fan hub-to-tip ratio proposed in this article reveals that the thermal coupling effect between fan aerodynamic design and motor cooling design has great potential to increase the power density of the motor in an electric propulsion system. A smaller hub-to-tip ratio is preferred as long as the power balance and cooling balance are satisfied. Parametric study on a current 6 kW electric ducted-fan system shows that the highest motor power density could be increased by 246% based on the current technology. Finally, a preliminary design was obtained and experiments were conducted to prove the feasibility of the model.
Journal Article

Design and Experiment on Aircraft Electromechanical Actuator Fan at Different Altitudes and Rotational Speeds

2019-06-07
Abstract For electromechanical actuators (EMAs) and electronic devices cooling on aircraft, there is a need to study cooling fan performance at various altitudes from sea level to 12,000 m where the ambient pressure varies from 1 to 0.2 atm. As fan static pressure head is proportional to air density, the fan’s rotational speed has to be increased significantly to compensate for the low ambient pressure of 0.2 atm at the altitude of 12,000 m. To evaluate fan performance for EMA cooling, a high-rotational-speed, commercially available fan made by Ametek with a diameter of ~82 mm and ~3 m3/min zero-load open cooling flow rate when operating at 20,000 rpm was chosen as the baseline. According to fan scaling laws, this fan was expected to meet the cooling needs for an EMA when operating at 0.2 atm. Using a closed flow loop, the performance of the fan operating in the above ambient pressure range and at a rotational speed between 15,000 and 30,000 rpm was evaluated.
Journal Article

Mathematical Model of Heat-Controlled Accumulator (HCA) for Microgravity Conditions

2020-01-20
Abstract It is reasonable to use a two-phase heat transfer loop (TPL) in a thermal control system (TCS) of spacecraft with large heat dissipation. One of the key elements of TPL is a heat-controlled accumulator (HCA). The HCA represents a volume which is filled with vapor and liquid of a single working fluid without bellows. The pressure in a HCA is controlled by the heater. The heat and mass transfer processes in the HCA can proceed with a significant nonequilibrium. This has implications on the regulation of TPL. This article presents a mathematical model of nonequilibrium heat and mass transfer processes in an HCA for microgravity conditions. The model uses the equations of mass and energy conservation separately for the vapor and liquid phases. Interfacial heat and mass transfer is also taken into account. It proposes to use the convective component k for the level of nonequilibrium evaluation.
Journal Article

Microturbine Blade Cooling

2020-05-20
Abstract The main technical barrier to commercial use of microturbines is its low efficiency, not exceeding 15%. Efficiency and specific power are as high as the Turbine Inlet Temperature (TIT), generally limited to 950°C in microturbines, as its tiny rotors make internal blade cooling impossible. This work uses Computational Fluid Dynamics (CFD) to develop an external cooling system of the blades of a microturbine by incorporating a compressor into the disk to blow air over the blades’ walls. The engine used as the basis of the work is the FD-3/64. The work was divided into two steps. In the first, Step 1, the reactive flow in the combustor was simulated to obtain the boundary conditions for Step 2. In Step 2, the flow through the turbine wheel during rotation is simulated. Four rotor models were simulated.
Journal Article

Two-Way Coupled CFD Approach for Predicting Gear Temperature of Oil Jet Lubricated Transmissions

2018-07-24
Abstract This article focuses on the development of a two-way coupled methodology to predict gear temperature of oil jet lubricated transmissions using commercial software for computational fluid dynamics simulation. The proposed methodology applies an overset mesh technique to model the gear interlocking motion, multiphase of air-oil mixture, and heat transfer. Two gear pairs were used to develop and validate the methodology, an overdrive helical gear pair of a commercial vehicle transmission and a standard spur gear pair. Different oil jet lubrication methods were investigated using the proposed methodology, such as oil jet directed at the into-mesh position and at the out-of-mesh position. This investigation showed that out of mesh lubrication direction shows better cooling performance which is in well agreement with previous studies of literature.
Journal Article

Implementation and Optimization of a Variable-Speed Coolant Pump in a Powertrain Cooling System

2020-02-07
Abstract This study investigates methods to precisely control a coolant pump in an internal combustion engine. The goal of this research is to minimize power consumption while still meeting optimal performance, reliability and durability requirements for an engine at all engine-operating conditions. This investigation achieves reduced fuel consumption, reduced emissions, and improved powertrain performance. Secondary impacts include cleaner air for the earth, reduced operating costs for the owner, and compliance with US regulatory requirements. The study utilizes mathematical modeling of the cooling system using heat transfer, pump laws, and boiling analysis to set limits to the cooling system and predict performance changes.
Journal Article

Investigations on Drive Axle Thermal Behaviour: Power Loss and Heat-Transfer Estimations

2018-03-08
Abstract In the present study, a truck drive axle and its gear set are analysed. As the gear set is a hypoid or a spiral bevel one, sliding and so tooth friction are an important source of dissipation. Other losses are mainly due to rolling element bearings and oil churning. The power losses are first calculated according to relationships given in ISO technical report. As comparison with test results shows great discrepancies, some modifications of the previous formulae are proposed. The thermal exchanges are also reviewed. Finally, two methods to obtain the bulk temperatures of the gear set are compared: a classical approach which focuses on the gear set only and a global approach which considers the complete axle using the thermal-network method.
Journal Article

Complete Engine Thermal Model, a Comprehensive Approach

2018-04-18
Abstract Upcoming engine generations are characterized by both a general trend of increased specific-power and higher efficiency. This leads to increased thermal loads, compromising reliability, and simultaneously to a limited amount of heat under ordinary engine use. Heat is a valuable resource in providing passenger comfort and emission control. For these reasons the subject of engine thermal management is receiving increasing attention. This work presents a comprehensive study of the complete engine thermal behavior at relevant running conditions: rated-power, peak-torque and ordinary use. The work is further extended to the engine warm-up period. The result is a high-resolution complete engine thermal model, capable of simultaneously reporting the local temperature of any engine part, and the global engine heat balance at any engine load.
Journal Article

ERRATUM

2019-10-07
The paper was originally published with the authors in the incorrect order. The correct author order should be as follows: Charlotte Fossier, Université de Lyon Dennis Barday, Volvo Group Christophe Changenet, Université de Lyon Fabrice Ville, Université de Lyon Vincent Berier, Volvo Group
Journal Article

A Novel Approach towards Stable and Low Emission Stratified Lean Combustion Employing Two Solenoid Multi-Hole Direct Injectors

2018-04-18
Abstract Stratified lean combustion has proven to be a promising approach for further increasing the thermal efficiency of gasoline direct injection engines in low load conditions. In this work, a new injection strategy for stratified operation mode is introduced. A side and a central-mounted solenoid multi-hole injector are simultaneously operated in a single-cylinder engine. Thermodynamic investigations show that this concept leads to improved stability, faster combustion, reduced particle number emissions, and lower fuel consumption levels compared to using only one injector. Experiments at an optical engine and three-dimensional computational fluid dynamics (CFD) simulations explain the improvements by a more compact mixture and reduced piston wetting with two injectors. Finally, the application of external EGR in combination with the above concept allows NOx emissions to be effectively kept at a low level while maintaining a stable operation.
Journal Article

Fast-Running Autoignition Model for Diesel Combustion Modeling and Control, Based on Detailed Reaction Kinetics Simulation

2018-06-25
Abstract Detailed and reduced kinetic mechanisms have been proposed for description of the complex chemistry of autoignition processes of n-heptane, as a representative diesel fuel. These kinetic models are attractive for a detailed 3-D CFD or multi-zone simulation, however the simulation time is normally not affordable for phenomenological engine process modeling. For phenomenological combustion models, typically single-to multiple-step Arrhenius equations are used to model the autoignition processes. Based on the number of Arrhenius equations and model structure the low-temperature, high-temperature and the negative temperature coefficient (NTC) behavior can be modeled. For diesel engine simulation modeling the ignition delay using Arrhenius equation(s) and a Livengood-Wu integration can deliver fairly good results, depending on the number of equations and calibration of constant parameters.
Journal Article

Partial Transparency of Advanced Compression Ignition Combustion Chamber Deposits, Its Impact on Combustion Chamber Wall Temperatures and Application to Thermal Barrier Coating Design

2018-04-18
Abstract The proven impact of combustion chamber deposits, CCD, on advanced compression ignition, ACI, combustion strategies has spurred researchers to develop thermal barrier coatings, TBC, which can mimic CCD benefits on combustion efficiency and operational range expansion. However, application of TBCs within multi-mode engines exposes them to non-negligible soot radiation. In the present paper, the impact of radiation heat transfer on combustion chamber deposits is studied. The morphological construction of the combustion chamber deposit layer is shown to be partially transparent to radiation heat transfer, drawing corollaries with ceramic-based TBCs. Additional experimentation eliminates the optical transparency of CCD to reveal an “effective radiation penetration depth” facilitated by open surface porosity. The effective radiation penetration depth is then utilized to establish the relative communicating porosity of CCD and a magnesium zirconate TBC.
Journal Article

A Method for Turbocharging Single-Cylinder, Four-Stroke Engines

2018-07-24
Abstract Turbocharging can provide a low cost means for increasing the power output and fuel economy of an internal combustion engine. Currently, turbocharging is common in multi-cylinder engines, but due to the inconsistent nature of intake air flow, it is not commonly used in single-cylinder engines. In this article, we propose a novel method for turbocharging single-cylinder, four-stroke engines. Our method adds an air capacitor-an additional volume in series with the intake manifold, between the turbocharger compressor and the engine intake-to buffer the output from the turbocharger compressor and deliver pressurized air during the intake stroke. We analyzed the theoretical feasibility of air capacitor-based turbocharging for a single-cylinder engine, focusing on fill time, optimal volume, density gain, and thermal effects due to adiabatic compression of the intake air.
Journal Article

Analysis of Temperature Swing Thermal Insulation for Performance Improvement of Diesel Engines

2019-01-23
Abstract Insulating combustion chamber surfaces with thermal barrier coatings (TBCs) provides thermal efficiency improvement when done appropriately. This article reports on insulation heat transfer, engine performance characteristics, and damage modelling of “temperature swing” TBCs. “Temperature swing” insulation refers to the insulation material applied on surfaces of combustion chamber walls that enables selective manipulation of its surface temperature profile over the four strokes of an engine cycle. A combined GT Suite-ANSYS Fluent simulation methodology is developed to investigate the impact of thermal properties and insulation thickness for a variety of TBC materials for its “temperature swing” characteristics. This one-dimensional transient heat conduction analyses and engine cycle simulations are performed using scaled-down thermal properties of yttria-stabilized zirconia.
Journal Article

A Distributed Parameter Approach for the Modeling of Thermoelectric Devices

2018-12-04
Abstract Thermoelectric devices (TEDs) allow direct electric and thermal energy mutual conversion. Because of the absence of working fluids and moving components, they can be used where it is not possible to refer to conventional technologies. In automotive applications, TEDs can give support in air conditioning and internal combustion engine (ICE) thermal heat recovery, contributing to increase the overall vehicle efficiency. Phenomena taking place in these devices are of a different nature and involve electric, thermal, and thermoelectric aspects, being highly influenced by materials’ characteristics and by system geometry. With the aim to offer a design tool, a TED mathematical model is presented in this article. The proposed model is based on a distributed parameter approach and has been conceived to consider heat transfer actual conditions. It accurately describes thermal energy production and removal terms due to Peltier and Joule effects.
Journal Article

Optimizing Cooling Fan Power Consumption for Improving Diesel Engine Fuel Efficiency Using CFD Technique

2019-06-11
Abstract Fan cooling system of an air-cooled diesel engine is optimized using 3D CFD numerical simulation approach. The main objective of this article is to increase engine fuel efficiency by reducing fan power consumption. It is achieved by optimizing airflow rates and flow distribution over the engine surfaces to keep the maximum temperature of engine oil and engine surfaces well within the lubrication and material limit, respectively, at the expense of lower fan power. Based on basic fan laws, a bigger fan consumes lesser power for the same airflow rate as compared to a smaller fan, provided both fans have similar efficiency. Flow analysis is also conducted with the engine head and block modeled as solid medium and fan cooling system as fluid domain. Reynolds-averaged Navier-Stokes turbulence (RANS) equations were solved to get the flow field inside the cooling system and on the engine liner fins. The Moving Reference Frame approach was used for simulating the rotation of a fan.
Journal Article

A Guide to Uncertainty Quantification for Experimental Engine Research and Heat Release Analysis

2019-08-22
Abstract Performing an uncertainty analysis for complex measurement tasks, such as those found in engine research, presents unique challenges. Also, because of the excessive computational costs, modeling-based approaches, such as a Monte Carlo approach, may not be practical. This work provides a traditional statistical approach to uncertainty analysis that incorporates the uncertainty tree, which is a graphical tool for complex uncertainty analysis. Approaches to calculate the required sensitivities are discussed, including issues associated with numerical differentiation, numerical integration, and post-processing. Trimming of the uncertainty tree to remove insignificant contributions is discussed. The article concludes with a best practices guide in the Appendix to uncertainty propagation in experimental engine combustion post-processing, which includes suggested post-processing techniques and down-selected functional relationships for uncertainty propagation.
Journal Article

Numerical Aspects Affecting Heat Transfer in ICE Applications and Definition of a Temperature Wall Function Accounting for the Boundary Layer Compressibility

2019-08-22
Abstract The heat transfer phenomena in Internal Combustion Engines (ICEs) are one of the main research topics that need to be addressed to enhance the performance in terms of power, efficiency, emissions and reliability. The present study is focused on the evaluation of the in-cylinder heat fluxes through the use of Computational Fluid Dynamic (CFD) simulations, with a wall function approach. In particular, the aim of this work is to present a new fully non-isothermal wall function obtained from the one-dimensional (1-D) energy balance equation for turbulent flows in the boundary layers, specifying all the steps and assumptions which have carried to the final fully compressible formulation. The new proposed wall function has been validated against experimental data of the General Motors (GM) Pancake Engine, representative of low Brake Mean Effective Pressure (bmep) operating point, comparing the results with other existing wall functions.
Journal Article

Exhaust Manifold Thermal Assessment with Ambient Heat Transfer Coefficient Optimization

2018-06-04
Abstract Exhaust manifolds are one of the most important components on the engine assembly, which is mounted on engine cylinder head. Exhaust manifolds connect exhaust ports of cylinders to the turbine for turbocharged diesel engine therefore they play a significant role in the performance of engine system. Exhaust manifolds are subjected to very harsh thermal loads; extreme heating under very high temperatures and cooling under low temperatures. Therefore designing a durable exhaust manifold is a challenging task. Computer aided engineering (CAE) is an effective tool to drive an exhaust manifold design at the early stage of engine development. Thus advanced CAE methodologies are required for the accurate prediction of temperature distribution. However, at the end of the development process, for the design verification purposes, various tests have to be carried out in engine dynamometer cells under severe operating conditions.
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