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3 results on '"Dimitris Assanis"'

1. Fuel temperature and injection pressure influence on the cold start GDI sprays

Author

Kyungwon Lee, Dario Lopez Pintor, Dimitris Assanis, Seokwon Cho, and Joonsik Hwang

Subjects
Cold start, Computed tomography (CT), Gasoline direct injection (GDI), Schlieren, Spray, Fuel, TP315-360, Energy industries. Energy policy. Fuel trade, HD9502-9502.5
Abstract

Cold start in gasoline direct injection engines (GDI) is a critical issue that significantly impacts fuel consumption and emissions. Therefore, it is essential to investigate and improve the spray and air-fuel mixing processes during cold starts. This study employed a complimentary set of optical diagnostic techniques, including line-of-sight(extinction, Schlieren, and long-distance microscopy) and 3D computed tomography (CT), to characterize and understand the cold-start spray dynamics under various fuel temperature and injection pressure conditions. The experiments were conducted in a constant volume spray vessel and the fuel temperature was varied using a coolant circulator, with temperatures reaching as low as -7 °C to simulate cold-start conditions. The cold fuel exhibited longer liquid/vapor penetration lengths compared to hot fuel under low injection pressure conditions. This deterioration in spray characteristics was attributed to the attenuated fuel evaporation and reduced entrainment of ambient air. The 3D spray visualization obtained through the CT algorithm, particularly the cut plane images, revealed that plumes with low fuel temperatures had narrower individual plume widths, resulting in minimized plume-to-plume interaction. Microscopic imaging further confirmed this observation which showed separate plumes in the near-nozzle region for cold fuel conditions. Meanwhile, hot fuel under high injection pressure conditions exhibited complete plume collapsing, leading to a significant amount of liquid fuel remaining in the spray core. The liquid penetration reached 70 mm during the injection period, potentially can cause wall wetting on the piston top or cylinder wall. Based on the experimental findings, this study suggests the application of multiple injections with a moderate level of injection pressure for optimized engine performance and reduced emissions during cold starts.

Published
2023
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2. Wood Stove Combustion Modeling and Simulation: Technical Review and Recommendations

Author

Dimitris Assanis and Mahmoud Koraïem

Subjects
Computer science, business.industry, General Chemical Engineering, FOS: Physical sciences, Numerical modeling, Applied Physics (physics.app-ph), Physics - Applied Physics, Surface reaction, Condensed Matter Physics, Combustion, Atomic and Molecular Physics, and Optics, Experimental research, Modeling and simulation, Stove, Wood stove, Road map, Process engineering, business
Abstract

With the rise in wood stove use in recent years, a number of experimental research efforts have been undertaken with the objective of developing cleaner, and more efficient stove designs. However, numerical modeling of stoves is still in its nascent years, thus making it imperative to start adapting more mature computational techniques, established in other combustion-based applications (e.g., combustion engines), to wood stoves. This study focuses on a critical review of the state-of-the-art in wood combustion modeling techniques and on providing recommendations for needed enhancements. In order to develop an optimum conceptual numerical model for wood stoves, the basic processes inside the stove are broken down and isolated into generic computational domains: surface reactions, gas reactions, and the fluid domain. Then state-of-the-art numerical efforts for wood stove and similar applications are broken down in a similar manner to highlight points of strength and possible improvements. Finally, based on the comparison between the different models, an improved modeling approach is proposed as a road map for future research efforts to achieve a higher fidelity wood stove numerical model., 14 pages, 10 figures, 1 table

Published
2021

3. Energy-Optimal Coordination of Connected and Automated Vehicles at Multiple Intersections

Author

Dimitris Assanis, Andreas A. Malikopoulos, Liuhui Zhao, and A M Ishtiaque Mahbub

Subjects
050210 logistics & transportation, 0209 industrial biotechnology, Computer science, 05 social sciences, Real-time computing, 02 engineering and technology, Energy consumption, Optimal control, 020901 industrial engineering & automation, Traffic congestion, Optimization and Control (math.OC), 0502 economics and business, Fuel efficiency, FOS: Mathematics, Boundary value problem, Baseline (configuration management), Mathematics - Optimization and Control, Energy (signal processing)
Abstract

Urban intersections, merging roadways, roundabouts, and speed reduction zones along with the driver responses to various disturbances are the primary sources of bottlenecks in corridors that contribute to traffic congestion. The implementation of connected and automated technologies can enable a novel computational framework for real-time control aimed at optimizing energy consumption and travel time. In this paper, we propose a decentralized energy-efficient optimal control framework for two adjacent intersections. We derive a closed-form analytical solution that includes interior boundary conditions and evaluate the effectiveness of the solution through simulation. Fuel consumption and travel time are significantly reduced compared to the baseline scenario designed with conventional fixed time signalized intersections.

Published
2019

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