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Darzi, Mahdi
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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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In-Use Efficiency of Oxidation and Three-Way Catalysts Used in High-Horsepower Dual Fuel and Dedicated Natural Gas Engines

SAE International Journal of Engines

West Virginia University-Derek Johnson, Mahdi Darzi, Nigel Clark, Andrew Nix, Robert Heltzel
  • Journal Article
  • 03-11-03-0026
Published 2018-07-01 by SAE International in United States
Directional drilling rigs and hydraulic stimulation equipment typically use diesel fueled compression ignition (CI) engines. The majority of these engines are compliant with US Environmental Protection Agency (EPA) Tier 2 standards. To reduce fuel costs, industry is investing in dual fuel (DF) and dedicated natural gas (DNG) engines. DF engines use diesel oxidation catalysts (DOCs) to reduce CO and NMHC emissions. DNG engines may be either lean-burn or rich-burn and the latter uses three-way catalysts (TWC) to reduce CO, NMHC, and NOx emissions. This research presents in-use catalyst efficiency data collected pre- and post-catalyst for three DF engines and two DNG engines. One DF engine was converted earlier and did not include a DOC. Data were collected from six Tier 2 engines, two CI drilling engines converted to operate as DF, two CI hydraulic fracturing engines converted to operate as DF, and two SI DNG drilling engines. DF engines with DOCs were able to reduce CO and NMHC during DF operation by >90 and >50%, respectively. The DOCs did not reduce methane and NOx emissions.…
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Continuously Varying Exhaust Outlet Diameter to Improve Efficiency and Emissions of a Small SI Natural Gas Two-Stroke Engine by Internal EGR

West Virginia University-Mahdi Darzi, Derek Johnson, Ramanjaneya Mehar Ba Bade, Christopher Ulishney, Nima Zamani Meymian, Nigel Clark, Gregory Thompson, Parviz Famouri
Published 2018-04-03 by SAE International in United States
With continuously increasing concern for the emissions from two-stroke engines including regulated hydrocarbon (HC) and oxides of nitrogen (NOx) emissions, non-road engines are implementing proven technologies from the on-road market. For example, four stroke diesel generators now include additional internal exhaust gas recirculation (EGR) via an intake/exhaust valve passage. EGR can offer benefits of reduced HC, NOx, and may even improve combustion stability and fuel efficiency. In addition, there is particular interest in use of natural gas as fuel for home power generation. This paper examines exhaust throttling applied to the Helmholtz resonator of a two-stroke, port injected, natural gas engine. The 34 cc engine was air cooled and operated at wide-open throttle (WOT) conditions at an engine speed of 5400 RPM with fueling adjusted to achieve maximum brake torque.Exhaust throttling served as a method to decrease the effective diameter of the outlet of the convergent cone. Throttling balanced energy and exergy flows by acting as a source of internal EGR and lowering combustion temperatures, which yielded lower heat transfer. Though exhaust throttling improved efficiency, it…
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Quantification of Energy Pathways and Gas Exchange of a Small Port Injection SI Two-Stroke Natural Gas Engine Operating on Different Exhaust Configurations

West Virginia University-Mahdi Darzi, Derek Johnson, Christopher Ulishney, Ramanjaneya Mehar Ba Bade, Nima Zamani Meymian, Gregory Thompson, Parviz Famouri
West Virginia University Foundation Inc.-Nigel Clark
Published 2018-04-03 by SAE International in United States
This paper examines the energy pathways of a 29cc air-cooled two-stroke engine operating on natural gas with different exhaust geometries. The engine was operated at wide-open-throttle at a constant speed of 5400 RPM with ignition adjusted to yield maximum brake torque while the fueling was adjusted to examine both rich and lean combustion. The exhaust configurations examined included an off-the-shelf (OTS) model and two other custom models designed on Helmholtz resonance theory. The custom designs included both single and multi-cone features. Out of the three exhaust systems tested, the model with maximum trapping efficiency showed a higher overall efficiency due to lower fuel short-circuiting and heat transfer. The heat transfer rate was shown to be 10% lower on the new designs relative to OTS model. The fuel slip rate was in the range of 20-30% with custom designs showing 15% higher fuel slip rates on average, whereas the exhaust thermal energy was in the range of 12-18% of total input fuel energy and found to be 20% lower on custom designs relative to OTS model.…
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