Dennis N. Assanis

Development and Use of a Computer Simulation of the Turbocompounded Diesel System for Engine Performance and Component Heat Transfer Studies

Mise au point et utilisation dune simulation sur ordinateur pour letude des performances et des transferts de chaleur dun moteur diesel turbocompound

Transient Heat Conduction in Low-Heat-Rejection Engine Combustion Chambers

Conduction de chaleur transitoire dans la chambre de combustion dun moteur a faibles pertes de chaleur

The effect of inlet flow distribution on catalytic conversion efficiency

Abstract A methodology is developed for analyzing the effect of non-uniform inlet flow distribution on the conversion efficiency of an automotive catalytic converter. The flow through the converter is treated as steady, incompressible, and isothermal. Conversion rates through the monolith passages are assumed to be diffusion-controlled. Under these assumptions, the equation governing one-dimensional laminarized flow with mass transfer through monolith passages simplifies to a form that can be solved analytically. A relation between concentration of reactants and passage length may thus be obtained, with flow velocity as a governing parameter. In order to determine the complex flow field through the diffuser, monolith, and nozzle sections of the converter, for various flow rates and passage diameters, a finite element code is used. The methodology is then utilized to predict the distribution of reactant concentrations across the monoliths outlet based on its inlet velocity distribution. The proposed approach is an effective design tool for optimizing the geometry and performance of an automotive catalytic converter.

A methodology for coupled thermodynamic and heat transfer analysis of a diesel engine

Abstract A methodology for a coupled thermodynamic and heat transfer analysis of diesel engine combustion chambers is presented here. Using one-dimensional (1-D) resistor heat flow models, a thermodynamic diesel engine simulation first predicts instantaneous gas temperatures and convective heat transfer coefficients throughout the engine cycle. These time-dependent boundary conditions are subsequently applied to the gas-exposed surfaces of two-dimensional, transient, finite-element models of heat conduction through the combustion chamber components. Finite-element predictions of instantaneous heat flow rates through each component surface are then used to determine equivalent resistance values for an improved resistor network, accounting for two-dimensional (2-D) heat conduction paths and component geometry effects. Finally, the thermodynamic cycle simulation is performed again with the improved resistor network to update heat rejection predictions. The use of the coupled strategy is illustrated by predicting the performance of an insulated diesel engine. Results show that our methodology can uncover complicated transient heat flow paths in the engine combustion chamber and significantly improve conduction heat flow models for use with diesel engine simulations.

A thin-film thermocouple for transient heat transfer measurements in ceramic-coated combustion chambers

Abstract A chromel-alumel overlapping thin-film thermocouple (TFTC) has been developed for transient heat transfer measurements in ceramic-coated combustion chambers. The TFTC was first evaluated using various metallurgical techniques, and calibrated against a standard thermocouple. Subsequently, the TFTC was tested in a diesel engine combustion chamber operating at 1900 rpm and full load. A mean temperature of 613 K with a cyclic swing of 55 K was measured for a ceramic-coated chamber surface. Calculations showed a dramatic reduction in transient heat flux into the surface with the application of the ceramic coating.

Creating and using models for engineering design: a machine-learning approach

An adaptive and interactive modeling system (AIMS) that integrates simulation, optimization and machine learning to help engineers make design decisions is described. AIMS views engineering decision making as a two-phase process of creating and then using models. The competitive relation learner and the induce-and-select optimizer, AIMSs two main components, and their roles in both phases of decision-making are discussed. AIMSs role in supporting the design of a diesel engine that outputs power within the 440- to 460-kW range and consumes the least amount of fuel is also discussed.<<ETX>>

THREE-DIMENSIONAL INCOMPRESSIBLE FLOW CALCULATIONS WITH ALTERNATIVE DISCRETIZATION SCHEMES

Abstract A finite-volume calculation procedure for steady, incompressible, elliptic flows in complex geometries is presented. The methodology uses generalized body-fitted coordinates to model the shape of the boundary accurately. All variables are stored at the centroids of the elements, thus achieving simplicity and low cost of computations. Turbulence is modeled by using the standard two-equation k-e model. The purpose of this work is to evaluate the performance and accuracy of flow calculations under different discretization schemes in the light of experimental results. The discretization schemes that are incorporated in the code include the classical hybrid scheme, the third-order QUICK scheme, and a fifth-order upwind scheme. Benchmark tests are performed for laminar and turbulent flows in 90° curved ducts of square and circular cross sections. Flow solutions obtained using the classical hybrid scheme are compared with solutions obtained with the higher-order schemes. The results show that accurate s...

Transient Analysis of Piston-Linear Heat Transfer in Low-Heat-Rejeetion Diesel Engines

A two-dimensional finite element program has been developed to analyze the transient heat flow paths in low-heat-rejection engine combustion chambers. This analysis tool is used to study the transient heat transfer performance of a ceramic-coated piston with steel-alloy rings reciprocating within a ceramic-coated liner at a speed of 1900 revolutions per minute. This study can provide realistic guidelines for the successful design of ceramic-insulated components and tribological systems

Multidimensional finite-element code for transient heat transfer calculations

A transient, multidimensional, finite-element code has been developed for predicting the time-dependent thermal field within solid geometries exposed to spatially varying, time-dependent boundary conditions. First, validation of the code is performed using both two- and three-dimensional finite-element meshes exposed to either step change or harmonically varying boundary conditions. Numerical predictions from the simulation are in very good agreement with analytical solutions for all types of elements and boundary conditions considered. Subsequently, the effects of time step, sampling frequency of harmonic boundary conditions, and grid density on solution accuracy and convergence are explored. The results suggest appropriate time stepping strategies for the time derivative of temperature, and optimum sampling rates for harmonic boundary conditions. Guidelines for mesh refinement near boundary surfaces are also furnished.