A Numerical Investigation of a Spark Ignition Opposed Piston Linear Engine Fueled by Hydrogen

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\u27s 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\u27s 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\u27s 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\u27 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\u27s 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\u27s 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\u27s potential superiorities in engine dynamics, performance, and emission patterns

Modeling and Control of Hydraulic Linear and Free-Piston Engines.

The EPA has developed a free-piston engine (FPE) and a hydraulic linear engine (HLE) for application as hydraulic power plants in a hydraulic hybrid vehicle. Both engines extract power from the piston motion using a linear hydraulic pump. This dissertation's objective is to compare HLE and FPE performance trends through modeling while developing the control tools necessary to enable reliable engine operation. A physics-based engine model combines dynamics, thermodynamics, and hydraulics correlations to evaluate performance trends and assist with control development. Preliminary simulations show that asymmetric piston behavior causes variations in cylinder-to-cylinder HLE efficiency that necessitate cylinder balancing. An adaptive control scheme estimates and adjusts for HLE cylinder performance discrepancies. A control-oriented model captures HLE behavior using an estimate of rotational kinetic energy sampled at the turnaround points. State feedback control ensures that the HLE tracks a set point and a recursive least squares algorithm estimates periodic differences in HLE response. An extremum seeking algorithm exploits the adaptive scheme to optimize injection timing of each cylinder individually. Precise control of piston turnaround location is paramount to reliable FPE operation. Combining an energy balance and the Otto cycle, a control-oriented model implicitly describes FPE clearance height evolution. A linearization of the control-oriented model suggests open-loop unstable operating conditions at high load. State feedback using dynamic inversion stabilizes the FPE system. In order to constrain piston motion, a reference governor manages load changes. When implemented on the physics-based model with the feedback control law, the reference governor successfully enforces a position constraint of 0.5 mm. Using the proposed control and modeling methods, a series of physics-based simulations explore HLE, FPE, and conventional engine performance. The primary difference in engine behavior is friction. While the FPE exhibits low frictional losses and the highest relative hydraulic conversion efficiency, it also suffers from a restricted power range compared to the HLE and the conventional engine due to engine speed limitations. The HLE has lower friction than the conventional engine at most operating conditions. However, inertial forces resulting from a large piston assembly mass increase HLE bearing loads and friction at high speeds.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/102345/1/kzaseck_1.pd

Techniques for improving the hydraulic automatic simulation package (HASP)

SIGLEAvailable from British Library Document Supply Centre- DSC:DX84320 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

The Case for Distributed Engine Control in Turbo-Shaft Engine Systems

The turbo-shaft engine is an important propulsion system used to power vehicles on land, sea, and in the air. As the power plant for many high performance helicopters, the characteristics of the engine and control are critical to proper vehicle operation as well as being the main determinant to overall vehicle performance. When applied to vertical flight, important distinctions exist in the turbo-shaft engine control system due to the high degree of dynamic coupling between the engine and airframe and the affect on vehicle handling characteristics. In this study, the impact of engine control system architecture is explored relative to engine performance, weight, reliability, safety, and overall cost. Comparison of the impact of architecture on these metrics is investigated as the control system is modified from a legacy centralized structure to a more distributed configuration. A composite strawman system which is typical of turbo-shaft engines in the 1000 to 2000 hp class is described and used for comparison. The overall benefits of these changes to control system architecture are assessed. The availability of supporting technologies to achieve this evolution is also discussed

Analysis and Design of a Linear Tubular Electric Machine for Free-piston Stirling Micro-cogeneration Systems

The UE investments for the renewable source development, in order to achieve the set goals (Kyoto protocol and “20-20-20” targets), push to investigate in new technologies and to develop the existing. In this context, the cogeneration (CHP) plays a fundamental role, and in particular, the micro-CHP has wide development margins. Among the different cogeneration process, the systems driven by a free-piston Stirling engine are one of the most significant challenges in the research area. In such systems, the thermal energy, coming from primary energy source (for example renewable energy), is converted into mechanical energy through a Stirling engine, and then a linear generator converts the mechanical energy into electrical energy, finally, the generator is connected to the electric grid or to the load by means of an electric converter. The use of the linear generator, instead of the traditional systems of linear to alternating motion conversion (rod-crank system), allows achieving several advantages, including: improving the system reliability, noise and cost reduction. Finally, this kind of system, if well-designed, allows improving the system efficiency. In this thesis a linear generator, directly coupled to a free-piston Stirling engine in a CHP system, was developed and analysed. It was found, after a first phase of the study and literature review, that the most convenient choice, from the technical and economic point of view, is a single-phase tubular permanent magnet linear generator. In particular, the magnets are made of plasto-neodymium, while, for the realization of the stator magnetic circuit, due to the geometrical complexity, soft magnetic composites (SMC) materials have been considered. In order to determine the generator performance, an analysis method based on FEAs was developed. This simplified method (HFEA) allows the study and the comparison of different magnetization patterns and current supply strategies. The proposed methodology exploits the representation of the magnetization spatial harmonics through an analytical processing that allows taking into account different magnetization profile of the permanent magnets. Thus, it was possible to reconstruct the most important quantities, such as the flux density and the flux linkage, superposing the effect of each harmonic obtained through the Fourier analysis. Furthermore, a procedure, able to reproduce the effects of magnetic saturation of the mover, generally not negligible in such kind of machines, was developed. For this purpose, an appropriate surface current distribution on the yoke of the mover was introduced, in order to reproduce the demagnetizing effect due to the saturation. By means of the air gap flux density, the force provided by linear generator was calculated, while, by means of the flux density sampled on suitable points on the stator and mover yokes, the iron losses were estimated and then the machine efficiency. By means of the flux linkage the emf provided by linear generator was determined. The results show a very good agreement with corresponding FEAs. The proposed analysis method allows carrying out a parametric analysis with a lower computational effort. Thanks to this feature, different magnetization patterns, supply strategies and SMC materials can be compared in order to optimize the machine design. A prototype based on the design guidelines was built; then, a procedure based on experimental measurement was developed to characterize the electromagnetic parameters. To determine the magnetization profile of the magnets, the flux density on the mover surface was carried out by means of a Gaussmeter. As regards the SMC materials that compose the stator core, a calculation method was developed from suitable experimental elaborations, in order to determine the most important magnetic properties, such as the BH curve and core loss coefficients. From experimental results, it can be noted that the actual characteristics are poorer than those provided by the manufactured datasheets, likely due to the manufacturing processes and spurious air gaps between the SMC modules. The update electromagnetic parameters are used to determine the actual performance of the machine, particularly to estimate the efficiency, the emf and the force. Finally, a simplified model of the cogeneration system was developed in order to predict the dynamic behaviour and particularly, the actual values of the speed, output power and efficiency. This model allows developing the control strategy of the linear generator acting on the electric converter

Should we have a new engine? An automobile power systems evaluation. Volume 2: Technical reports

Alternative automotive powerplants were examined for possible introduction during the 1980-1990 time period. Technical analyses were made of the Stratified-Charge Otto, Diesel, Rankine (steam), Brayton (gas turbine), Stirling, Electric, and Hybrid powerplants as alternatives to the conventional Otto-cycle engine with its likely improvements. These alternatives were evaluated from a societal point of view in terms of energy consumption, urban air quality, cost to the consumer, materials availability, safety, and industry impact. The results show that goals for emission reduction and energy conservation for the automobile over the next 5-10 years can be met by improvements to the Otto-cycle engine and to the vehicle. This provides time for the necessary development work on the Brayton and Stirling engines, which offer the promise of eliminating the automobile as a significant source of urban air pollution, dramatically reducing fuel consumption, and being saleable at a price differential which can be recovered in fuel savings by the first owner. Specifically, the Brayton and Stirling engines require intensive component, system, and manufacturing process development at a funding level considerably higher than at present

Bibliography of Lewis Research Center technical publications announced in 1986

This compilation of abstracts describes and indexes the technical reporting that resulted from the scientific and engineering work performed and managed by the Lewis Research Center in 1986. All the publications were announced in the 1986 issues of Scientific and Technical Aerospace Reports (STAR) and/or International Aerospace Abstracts (IAA). Included are research reports, journal articles, conference presentations, patents and patent applications, and theses

Aeronautical engineering: A continuing bibliography with indexes (supplement 225)

This bibliography lists 429 reports, articles, and other documents introduced into the NASA scientific and technical information system in March, 1988

Digital displacement hydrostatic transmission systems

Digital Displacement pumps and motors are a new type of hydraulic machine, in which fluid commutation and displacement control are achieved by solenoid actuated valves under the command of a microprocessor, rather than mechanical means. The thesis is that radial piston machines, built according to this principle, offer energy efficiency and control advantages over variable stroke axial piston pumps, when applied to hydrostatic vehicle transmissions.Experimental results on the efficiency of prototypes are analysed and compared to published results from swashplate machines, showing an improvement in energy efficiency. Loss models are proposed and compared with experiment.A Digital Displacement motor suitable for propelling a vehicle is described and the design and development of the mechanics, electro-magnetics and embedded software are described. Experimental results are also presented, illustrating the performance of a demonstrator vehicle driven by the motor, in particular demonstrating the closed-loop regulation of vehicle speed using motor displacement control.A demonstrator vehicle is described which features a hydrostatic transmission using both a Digital Displacement pump and an axial piston motor. Experimental results of pump performance are presented with specific focus on vehicle propel. A control technique is described which increases the sensitivity of the pump at low speeds. Results are presented of tests on the prototype transmission system, focussing on the time-domain system dynamics. A computer simulation model of the vehicle is presented and results compared to experiment