Research Interests and Accomplishments
Internal combustion (IC) engines have been widely used in various sizes in many different applications because of their low specific cost, high power density, reliability and versatility. However, as the concerns on the global warming, environmental issues and limited fossil fuel grow IC engines are now facing the most formidable challenges. With various but no clearly standing-out technical options for cleaner, more efficient and sustainable energy conversion systems, exploring newly emerging technologies and improving matured technologies in every possible aspect is critical to find globally-optimized energy conversion solutions in transportation. My research interest has been focused on thermal-fluid sciences and their applications to automotive energy conversion systems such as IC engines, hybrid powertrains, PEM fuel cell systems, vehicle thermal and energy management, and system integration.
During my academic career I have developed 33 funded grants and contracts as the principal or co-principal investigator. The accumulated amount of grants and contracts is over $3.8 million including $1.9 million for the programs that I have developed as the principal investigator. Sponsors include automotive industry, heavy-duty industry, U.S. government, and nonprofit foundation (BorgWarner Inc., Ford, General Dynamics Land Systems, Hyundai-Kia, DOE, NSF, US Army TARDEC, DENSO North America Foundation). I have ewceied Distinguished Research Award from the University of Michigan-Dearborn in 2012. I have published 33 peer-reviewed journal papers, 22 conference papers, 1 book chapter, and 10 articles in professional magazine . I am a member of SAE Advanced Power Sources Committee since 2007 and have served as an editorial member of Auto Journal published by KSAE since 2010.
Research Areas
IC Engine Processes and Systems
One of my major contributions is developing models and simulation of IC engine processes and systems, and conducting experimental validation of the models for engine heat transfer, combustion, and pollutant formation. I have developed simulation models of direct injection (DI) Diesel engines at different levels of fidelity tailored for individual research purposes. The engine models were developed based on a multi-zone fuel spray combustion model with a quasi-dimensional modeling approach to predict the engine performance, fuel economy and pollutant emissions. The models were extensively validated with experimental data measured at the University of Michigan (UM) as well as published data. In diesel engines, spatial information within the diesel spray such as local temperature, fuel-air mixture ratio, and composition of combustion products is essential for the accurate prediction of pollutant formation. However, it is very challenging to predict the spatial variations due to heterogeneous combustion characteristics of diesel spray. The unique feature of the quasi-dimensional combustion modeling approach is that it can provide spatial information at much lower computational cost compared to multi-dimensional models. Thanks to superior computational efficiency and emission prediction capability, they have been implemented into multi-cylinder engine system models as well as transient engine system models and used for engine design optimization study and engine-in-vehicle system integration that require enormous amount of engine cycle computations.
In additional to the quasi-dimensional models I also have developed a physics based, engine control oriented mean value model that predicts engine combustion, heat transfer, gas exchange, and friction loss. The model is developed starting from the thermodynamic principles of an ideal gas standard limited pressure cycle concept. The idealized assumptions that are typically used in a limited pressure cycle concept are relieved to enhance the fidelity of the model by introducing variables that account for the in-cylinder heat transfer and the combustion characteristics that change under varying exhaust gas recirculation rate as well as the engine speed and load. The model is a flexible simulation tool that provides excellent computational efficiency without sacrificing critical physical details of the Diesel combustion process required by the engine control development.
Heat transfer is one of the major factors affecting performance, efficiency and emissions of IC engines. As convection heat transfer is dominant in engine heat transfer, accurate modeling of the boundary layer heat transfer is required. In engine computational fluid dynamics (CFD) simulations, the wall function approach has been widely used to model the near-wall flow and temperature field. A modified wall function correlation is developed to model the heat transfer in IC engines. Special emphasis has been placed on introducing the effect of variable density and variable viscosity in the model formulation. The suggested model is applied in a CFD program and is validated against experimental data from spark ignition and homogeneous charged compression ignition engines.
The engine efficiency can be improved by increasing the compression ratio. In conventional engines the compression ratio is constrained by fuel properties and operating conditions and it is geometrically fixed. Fuel economy improvement with a variable compression ratio concept of spark ignition engines was investigated with a pressure reactive piston (PRP). The PRP is composed of two pieces of pistons and a specially designed spring in-between. The spring deforms in response to cylinder pressure and changes the effective engine compression ratio. The piston design was optimized by using an engine simulation and the experimental investigation demonstrated that the fuel consumption of the engine at light load conditions can be improved up to 18 % by using this novel technology compared to the conventional engine.
As a collaborative study with researchers in manufacturing area, I lead a study on the effects of manufacturing variations in DI Diesel fuel injector nozzle on the engine performance and emissions. We developed nozzle geometry characterization techniques with real Diesel injectors, measured the geometric changes due to the manufacturing process, and assessed the resulting influence of the geometric changes on the engine performance and emissions experimentally and numerically over a wide range of manufacturing process variables.
Dual-stage boosting is an advanced technology recently implemented into the Diesel engine system to improve the rated output while simultaneously improving the steady-state torque at low engine speeds and the transient response of the engine by rapidly building up the boost pressure. I have studied steady-state and transient performance characteristics and fuel economy improvements of the engines with various types of the dual-stage boosting system.
Vehicle System Integration and Alternative Powertrains
I have played a major role in pioneering the integration of high fidelity engine models with driveline and vehicle models and used these tools for assessment and design optimization of conventional and alternative powertrains. I have been collaborating with researchers in dynamics, control, and optimization areas to develop various integrated powertrain-in-vehicle system models including spark ignition engine, Diesel engine, hybrid, and fuel cell propulsion systems.
An integrated vehicle system simulation has been developed to take advantage of advances in physical process and component models, flexibility of graphical programming environments (such as MATLAB/SIMULINK). A comprehensive, transient model of the multi-cylinder engine is linked with models of the torque converter, transmission, transfer case and differentials. The integrated simulation was used for predictions of dynamic response and performance of engine and driveline systems for the assessment of alternative system configurations. I also have developed an automotive powertrain System model for the systematic development and seamless integration of modular powertrain component and system models for the matching of a gasoline engine with a dual clutch transmission.
Hybrid powertrain systems are currently employed in many light duty vehicles and expected to be adopted in heavy duty vehicles. I have worked on the concept development and design of hybrid powertrain systems for heavy duty applications. I participated in the project to setup a test cell for concurrent running of a real engine and a vehicle system simulation, and its use for evaluating engine performance when integrated with a conventional and a hybrid electric driveline/vehicle. This engine-in-the-loop (EIL) system uses fast instruments and emissions analyzers to investigate how critical in-vehicle transients affect engine system response, fuel economy and transient emissions. Another relevant work is the modeling of a series hybrid electric vehicle (SHEV) for the military application. The SHEV has many advantages compared to conventional propulsion systems such as improved fuel economy, better acceleration performance, low acoustic signature, and exportable electric power for advanced weapon systems. However, it also has unique challenges. I directed projects to develop a SHEV simulation including vehicle thermal management system as a vehicle design and development tool to cope with the challenges in developing a SHEV.
Fuel cell is one of the promising alternative energy conversion devices with near zero-emissions. I have been working on Proton Exchange Membrane (PEM) Fuel Cell system for the application of ground vehicle power plant and auxiliary power unit. The performance of the PEM fuel cell is very sensitive to its operating temperature and humidity conditions. To maximize the power output of the fuel cell it is important to properly control those conditions. Therefore, I have developed a comprehensive fuel cell system models based on mass and thermal transport sub-models that enable to predict the effects of humidity control and temperature distribution on the fuel cell performance and proposed a thermal management strategy for better performance, reduced parasitic power loss and optimal temperature control.
Vehicle Thermal Management and Waste Energy Recovery
Thermal management system design and optimization of conventional and hybrid powertrains has been another area of my research interests since I worked at Daewoo Motor Co. My research experiences on the engine thermal management at Daewoo became a critical background of my researches that I conducted at UM such as low heat rejection (adiabatic) engines for improved thermal efficiency [J29] and electrified cooling components for engine and vehicle thermal management for on-demand control and reduced parasitic power consumption.
The thermal management of a hybrid electric vehicle is much challenging than conventional vehicle cases because additional cooling circuits for electric components are required due to considerable heat rejections and different cooling requirements of the components. The previously developed hybrid powertrain system model is integrated with a comprehensive vehicle cooling system model and use to develop guidelines and a methodology for the cooling system architecture design with the constraints of cooling performance requirements, parasitic power consumption, fuel economy, temperature stability, packaging, and driving conditions. In electric vehicles or plug-in hybrid electric vehicles with larger capacity battery pack battery thermal management is extremely important for maximized performance, durability, and safety. Efficient battery package design and configuration optimization using numerical simulation was demonstrated.
About two thirds of the fuel energy is wasted either through a cooling system or as high temperature exhaust gas in IC engines. There is a huge potential in improving the efficiency of conventional powertrain systems by developing ways to convert wasted energy to usable energy. Because of the complex and intimate heat and energy transfer paths between powertrain, vehicle, thermal management systems integrated vehicle energy analysis model is very efficient and effect tool for the evaluation of various novel energy recovery concepts.
Industrial Experiences
I started my professional career as a research engineer (1991-1996) at Daewoo Motor Co. in Korea. I was in charge of system development and component design of vehicle cooling and climate control systems for passenger cars. I established an engine heat rejection test procedure and a technique to measure the temperatures of the engine piston and components using telemetry linkage system for the thermal analysis of engines.
Prof. Dewey Dohoy Jung, PhD
