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Feasibility of Multiple Piston Motion Control Approaches in a Free Piston Engine Generator

West Virginia University-Mehar Bade, Nigel Clark, Parviz Famouri, PriyaankaDevi Guggilapu
  • Technical Paper
  • 2019-01-2599
To be published on 2019-10-22 by SAE International in United States
The control and design optimization of a Free Piston Engine Generator (FPEG) has been found to be difficult as each independent variable changes the piston dynamics with respect to time. These dynamics, in turn, alter the generator and engine response to other governing variables. As a result, the FPEG system requires an energy balance control algorithm such that the cumulative energy delivered by the engine is equal to the cumulative energy taken by the generator for stable operation. The main objective of this control algorithm is to match the power generated by the engine to the power demanded by the generator. In a conventional crankshaft engine, this energy balance control is similar to the use of a governor and a flywheel to control the rotational speed. In general, if the generator consumes more energy in a cycle than the engine provides, the system moves towards a stall. If the generator consumes less energy, then the effective stroke, compression ratio and maximum translator velocity must rise steadily from cycle-to-cycle until the heat transfer losses stop the…
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Experimental Investigation of Combustion Characteristics in a Heavy-Duty Compression-Ignition Engine Retrofitted to Natural-Gas Spark-Ignition Operation

West Virginia University-Jinlong Liu, Cosmin Dumitrescu
Published 2019-09-09 by SAE International in United States
Recent development in hydraulic fracking made natural gas (NG) to be a promising alternative gaseous fuel for heavy-duty diesel engines. The existing compression ignition (CI) engine can be retrofitted to NG spark ignition (SI) operation by replacing the diesel injector with a spark plug and fumigating NG into the intake manifold. However, the original diesel piston geometry (flat head and bowl-in-piston chamber) was usually retained to reduce modification cost. The goal of this study was to increase the understanding of the NG lean-burn characteristics in a diesel-like, fast-burn SI combustion chamber. The experimental platform can operate in conventional (i.e., all engine parts are metal) or in optical configuration (i.e., the stock piston and cylinder block are replaced with a see-through piston and an extended cylinder block). The optical data indicated a fast-propagated flame inside the piston bowl. However, this rapid-burning process did not shorten the combustion duration, which can be explained by an important fuel mass trapped in the squish that burned slowly during the expansion stroke. Steady-state experiments that operated at the metal engine…
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Heavy-Duty Aerodynamic Testing for CO2 Certification: A Methodology Comparison

West Virginia University-Berk Demirgok, Cem Baki, Marc Besch, Arvind Thiruvengadam
Intl. Council on Clean Transportation-J. Felipe Rodriguez, Oscar Delgado
Published 2019-04-02 by SAE International in United States
Aerodynamic drag testing is a key component of the CO2 certification schemes for heavy-duty vehicles around the world. This paper presents and compares the regulatory approaches for measuring the drag coefficient of heavy-duty vehicles in Europe, which uses a constant-speed test, and in the United States and Canada, which use a coastdown test. Two European trucks and one North American truck were tested using the constant-speed and coastdown methods. When corrected to zero yaw angle, a difference of up to 12% was observed in the measured drag coefficients from the US coastdown procedure and the EU constant-speed test. The differences in the measured drag coefficient can be attributed, among others, to the assumptions in the speed-dependence of the tire rolling resistance and axle spin losses, the data post-processing required by each methodology, unaccounted frictional losses in the transmission, the behavior of the automated manual transmission during the coastdown run, and the yaw angle correction.
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Experimental Investigation of a Natural Gas Lean-Burn Spark Ignition Engine with Bowl-in-Piston Combustion Chamber

West Virginia University-Jinlong Liu, Cosmin Dumitrescu
Published 2019-04-02 by SAE International in United States
On- and off-road heavy-duty diesel engines modified to spark-ignition natural gas operation can reduce U.S. dependence on imported oil and enhance national energy security. Engine conversion can be achieved through the addition of a gas injector in the intake manifold and of a spark plug in place of the diesel injector. This paper investigated combustion characteristics and engine performance at several lean-burn operating conditions that changed spark timing, mixture equivalence ratio, and engine speed, using methane as NG surrogate. The results show that the bowl-in-piston geometry separated the combustion process into two distinct events: an inside-the-bowl burning (due to the squish effect) that had a short duration and consumed a high fraction of fuel, and a slower inside-the-squish burning process, most probably due to the large surface/volume ratio (that increased the heat transfer to the boundaries) and to the lower in-cylinder pressure and temperature during the expansion stroke. While the operating conditions affected the overlapping of these two combustion stages, conditions that increased their phasing separation produced a second peak in the rate of heat…
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Quantification of Windage and Vibrational Losses in Flexure Springs of a One kW Two-Stroke Free Piston Linear Engine Alternator

West Virginia University-Nima Zamani Meymian, Nigel Clark, Jayaram Subramanian, Gregory Heiskell, Derek Johnson, Fereshteh Mahmudzadeh, Mahdi Darzi, Terence Musho, Parviz Famouri
Published 2019-04-02 by SAE International in United States
Methods to quantify the energy losses within linear motion devices that included flexural springs as the main suspension component were investigated. The methods were applied to a two-stroke free-piston linear engine alternator (LEA) as a case study that incorporated flexure springs to add stiffness to the mass-spring system. Use of flexure springs is an enabling mechanism for improving the efficiency and lifespan in linear applications e.g. linear engines and generators, cryocoolers, and linear Stirling engines. The energy loss due to vibrations and windage effects of flexure springs in a free piston LEA was investigated to quantify possible energy losses. A transient finite element solver was used to determine the effects of higher modes of vibration frequencies of the flexure arms at an operational frequency of 65 Hz. Also, a computational fluid dynamics (CFD) solver was used to determine the effects of drag force on the moving surfaces of flexures at high frequencies. A parametric study was performed to understand the effects of geometrical and operational parameters including the diameter of flexures, gap width between flexure…
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Gaseous Fuels Variation Effects on Combustion and Emissions of a Small Direct Injection Natural Gas Engine

West Virginia University-Mahdi Darzi, Derek Johnson, Mehar Bade, Parviz Famouri
Published 2019-04-02 by SAE International in United States
Our research focused on the assessment of fuel variation effects on performance of a 34 cc two-stroke, natural gas combustion engine designed for use as the prime mover in either slider-crank or novel linear generator applications. Nearly two-thirds of US homes have either natural gas or liquefied petroleum gas available at low pressures. We tested the engine with three different natural gas blends, pure methane, and pure propane. In order to reduce fuel compression power, we modified the engine to use low-pressure direct injection (LPDI) of gaseous fuels. We examined regulated gaseous emissions, greenhouse gas emissions, and combustion trends over a range of delivered air fuel ratios. Start of Injection (SOI) occurred at either 180 or 190 CA BTDC and efficiency improved by reducing fuel slip. However, for natural gas blends, the predominant emissions were methane - a potent greenhouse gas. We showed that while propane had the highest CO2 emissions, it also produced the lowest CO2 equivalent emissions. However, propane also tended to have the highest NOx, NMHC+NOx, and CO emissions. As expected, propane…
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Sensitivity Analysis and Control Methodology for Linear Engine Alternator

SAE International Journal of Advances and Current Practices in Mobility

West Virginia University-Mehar Bade, Nigel Clark, Parviz Famouri, PriyaankaDevi Guggilapu, Mahdi Darzi, Derek Johnson
  • Journal Article
  • 2019-01-0230
Published 2019-04-02 by SAE International in United States
Linear engine alternator (LEA) design optimization traditionally has been difficult because each independent variable alters the motion with respect to time, and therefore alters the engine and alternator response to other governing variables. An analogy is drawn to a conventional engine with a very light flywheel, where the rotational speed effectively is not constant. However, when springs are used in conjunction with an LEA, the motion becomes more consistent and more sinusoidal with increasing spring stiffness. This avoids some attractive features, such as variable compression ratio HCCI operation, but aids in reducing cycle-to-cycle variation for conventional combustion modes. To understand the cycle-to-cycle variations, we have developed a comprehensive model of an LEA with a 1kW target power in MATLAB®/Simulink, and an LEA corresponding to that model has been operated in the laboratory. This MATLAB®/Simulink numerical model has been used to examine the sensitivity of the LEA dynamics and performance parameters to changes in the design and operating inputs. The sensitivity analysis provides insight into the pathway for improving and optimizing the design, as well as…
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CFD Simulation of Metal and Optical Configuration of a Heavy-Duty CI Engine Converted to SI Natural Gas. Part 2: In-Cylinder Flow and Emissions

West Virginia University-Jinlong Liu, Cosmin Dumitrescu
Published 2019-01-15 by SAE International in United States
Internal combustion diesel engines with optical access (a.k.a. optical engines) increase the fundamental understanding of combustion phenomena. However, optical access requirements result in most optical engines having a different in-cylinder geometry compared with the conventional diesel engine, such as a flat bowl-in-piston combustion chamber. This study investigated the effect of the bowl geometry on the flow motion and emissions inside a conventional heavy-duty direct-injection diesel engine that can operate in both metal and optical-access configurations. This engine was converted to natural-gas spark-ignition operation by replacing the fuel injector with a spark plug and adding a low-pressure gas injector in the intake manifold for fuel delivery, then operated at steady-state lean-burn conditions. A 3D CFD model based on the experimental data predicted that the different bowl geometry did not significantly affect in-cylinder emissions distribution. In addition, while in-cylinder flow motion was similar for both engine configurations, the different combustion chamber geometry affected the combustion-induced flow motion. Similar turbulence-generating mechanisms for engines with or without optical access show promise for optical investigations of cold-flow turbulence measurements representative…
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CFD Simulation of Metal and Optical Configuration of a Heavy-Duty CI Engine Converted to SI Natural Gas. Part 1: Combustion Behavior

West Virginia University-Jinlong Liu, Cosmin Dumitrescu
Published 2019-01-15 by SAE International in United States
Internal combustion engines with optical access (a.k.a. optical engines) provide additional information in the quest for understanding the fundamental in-cylinder combustion phenomena. However, most optical engines have flat bowl-in-piston combustion chamber to optimize the visualization process, which is different, for example, from the traditional re-entrant bowl in compression ignition engines. A conventional heavy-duty direct-injection compression ignition engine was converted to spark ignition operation by replacing the fuel injector with a spark plug in both optical and metal setups to investigate the effect of the bowl geometry on flame propagation. Experimental data from steady-state lean-burn conditions was used to develop and validate a 3D CFD model of the engine. Numerical simulation results show that flame propagation in the radial direction was similar for both combustion chambers despite their different geometries. However, there were differences in the late combustion behavior. As a result, the similar flame propagation inside the optical engine suggests that such engines are best used to investigate flame inception and early flame propagation inside heavy-duty CI engines converted to natural gas spark ignition operation.
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Design, Manufacturing, Testing, and Analysis of a Highly-Constrained Single-Use UAV Wing

West Virginia University-Patrick H. Browning, Levi S. Hubbard, Philip Pennock
Published 2018-10-30 by SAE International in United States
Unmanned aerial vehicle (UAV) design aspects are as broad as the missions they are used to support. In some cases, the UAV mission scope can impose design constraints that can be difficult to achieve. This paper describes recent work performed at West Virginia University (WVU) to support repeated flight testing of a single-use UAV platform with emphasis on the highly specialized wings required to help meet the overall airframe mass properties constrained by the project sponsor. The wings were fabricated using a molded polyurethane (PU) foam as the base material which was supported by several different types of rigid and flexible substructures, skins, and matrix-infused fiber elements. Different ratios of infused fiber mass to PU foam were tested and additional tungsten masses were added to the wings to achieve the correct total mass and mass distribution of the wings. Expected accelerations were applied to the wing designs analytically and numerically to establish appropriate test limits and explore potential structural loading aspects, and static and dynamic experimental tests were employed to determine the suitability of the…
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