Author ORCID Identifier

https://orcid.org/0009-0004-9445-5432

Semester

Fall

Date of Graduation

2023

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Hailin Li

Committee Co-Chair

Songgang Qiu

Committee Member

Vyacheslav Akkerman

Committee Member

Scott Wayne

Committee Member

Fernando Lima

Abstract

The traditional Slider-Crank Engine, also known as the Internal Combustion Engine (ICE), has been criticized for its complex structure, friction loss, low efficiency and high maintenance cost. In contrast, the Free-Piston Linear Engine (FPLE) reduces this friction due to its simpler design. With rising concerns about air quality and stricter regulations, there's a renewed interest in hydrogen as a carbon-free fuel for ICEs.

The Opposed Piston Linear Generator (OPLG) system is an integrated arrangement of parts operating harmoniously to generate power efficiently. By leveraging synchronized pistons, accurate fuel distribution, and seamless thermodynamic cycles, it transforms kinetic energy into electrical energy. Dynamic control ensures its operations are both efficient and eco-friendly. However, despite the potential benefits of the OPLG, the intricacies of its operations have posed several challenges, such as misfiring, overfueling, instantaneous transient changes, stalling, and piston control, which can reduce its efficiency and increased emission levels.

This dissertation deployed the nuances of suitable correlational, analytical, numerical and control models to better illustrate the performance of the OPLG as against its limitations. The model introduces a non-dimensional streamlined symmetric analytical solution, succeeded by a broader general analytical resolution, with careful attention to the significant influence of thermodynamic effects at each phase, offering insights into the engine's dynamic performance. The Runge-Kutta technique guarantees swift and dependable computational outcomes, which captures cyclic variation as typical ICE compression ratios are reproduced. The study showed a nearly linear interaction between thermal efficiency and the translator's starting position within specific ranges for OPLE. However, maintaining the engine within a narrow high-efficiency band requires precise control, crucial for harnessing the full potential of the OPLG system without compromising its performance.

Precise control of TDC piston clearance is crucial for optimizing combustion efficiency and load management. The Model Predictive Control (MPC) algorithm forecasts the pistons' future positions by considering current control inputs and system behaviors. Concurrently, the closed-loop bisection method observer refines the piston position estimates by comparing actual and projected outputs. This algorithm is specifically chosen for its dichotomy feature in finding the roots of equations, which is essential for confining the pistons’ locus within the line of symmetry. This method plays a significant role in refining the control strategy, making it more responsive and accurate in adjusting to the engine's dynamic needs and operational changes.

Comparative studies are conducted between the Opposed Piston Linear Engine (OPLE) and the slider-crank engine, fueled by hydrogen. This comparison incorporates hydrogen metering and its interaction with nitrogen oxides. The engine's characteristic includes a volumetric compression ratio of 12 and a fuel equivalence ratio of 0.5, so chosen because hydrogen engines typically require nearly double the air amount for complete combustion. This lean mixture is essential as it leads to combustion temperatures below the threshold for thermal nitric oxide (NOx) formation. Consequently, NOx emissions are virtually non-existent, underscoring a notable environmental benefit of FPLE with its unique combustion characteristics compared to the equivalent slider-crank engines. Simulations highlight OPLE's potential superiorities in engine dynamics, performance, and emission patterns.

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