The effects of crevices on the engine-out hydrocarbon emissions in spark ignition engines

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1994.Includes bibliographical references (p. 141-144).by Kyoungdoug Min.Ph.D

Analysis of surface and interior degradation of gas diffusion layer with accelerated stress tests for polymer electrolyte membrane fuel cell

© 2022 Hydrogen Energy Publications LLCThe effects of surface and interior degradation of the gas diffusion layer (GDL) on the performance and durability of polymer electrolyte membrane fuel cells (PEMFCs) have been investigated using three freeze-thaw accelerated stress tests (ASTs). Three ASTs (ex-situ, in-situ, and new methods) are designed from freezing −30 °C to thawing 80 °C by immersing, supplying, and bubbling, respectively. The ex-situ method is designed for surface degradation of the GDL. Change of surface morphology from hydrophobic to hydrophilic by surface degradation of GDL causes low capillary pressure which decreased PEMFC performance. The in-situ method is designed for the interior degradation of the GDL. A decrease in the ratio of the porosity to tortuosity by interior degradation of the GDL deteriorates PEMFC performance. Moreover, the new method showed combined effects for both surface and interior degradation of the GDL. It was identified that the main factor that deteriorated the fuel cell performance was the increase in mass transport resistance by interior degradation of GDL. In conclusion, this study aims to investigate the causes of degraded GDL on the PEMFC performance into the surface and interior degradation and provide the design guideline of high-durability GDL for the PEMFC.N

Dynamic simulation of a fuel cell hybrid vehicle during the federal test procedure-75 driving cycle

The dynamic behavior of a proton exchange membrane fuel cell (PEMFC) system is a crucial factor to ensure the safe and effective operation of fuel cell hybrid vehicles (FCHVs). Specifically, water and thermal management are critical to stabilize the performance of the PEMFC during severe load changes. In the present study, the FCHV dynamic model is developed. The dynamic model of the PEMFC system developed by Matlab-Simulink (R) is integrated into the electric vehicle model embedded in the Amesim (R). The dynamic model of the PEMFC system is composed of a PEMFC stack, an air feeding system, and a thermal management system (TMS). The component models of PEMFC, a shell-and-tube gas-to-gas membrane humidifier, and a heat exchanger are validated via a comparison with the experimental data. The FCHV model is simulated during a federal test procedure (FTP)-75 driving cycle. One system configuration and control strategy is adopted to attain optimal water and thermal management in the PEMFC system. The vehicle speed obtained from the FCHV model aptly tracks the target velocity profile of the FTP-75 cycle within an error of +/- 0.5%. The dynamic behavior and correlation of each component in the PEMFC system is investigated. The mass and heat transfer in the PEMFC, a humidifier, and a heat exchanger are resolved to determine the species concentration and the temperature more accurately with discretization in the flow's perpendicular direction. Discretization in the flow parallel direction of humidifier and heat exchanger model makes it possible to capture the distribution of the characteristics. The present model can be used to attain the optimization of the system and control design for the PEMFC system in FCHVs. (C) 2015 Elsevier Ltd. All rights reserved.N

Understanding the effect of turbulent flow on the combustion cyclic variation in a spark ignition engine using Large-Eddy simulation

© 2022 Elsevier LtdAt the present, emission regulations have been tightened around the world in an effort to reduce emissions from internal combustion engine (ICE) vehicles. The one of the issues in the development of eco-friendly spark ignition (SI) internal combustion engines is a cycle-to-cycle variation (CCV) of combustion. Therefore, research on the CCV is also being actively carried out. Because the causes that affect the cycle deviation are various and complex, it is difficult to conduct detailed research on the source of the CCV through experimental studies. Therefore, the 3D simulation, especially large-eddy simulation (LES) approach is actively carried out. In the present study, the Lagrangian ignition model developed for LES is introduced. The Lagrangian particles were employed to realize the ignition channel and the secondary electric circuit model was implemented to predict the spark energy and the end of ignition time. And 30 LES cycles were performed to identify the cause of the CCV and validated against the experimental data. The vortex produced by wall flow on the secondary tumble plane was identified as an important factor. A new piston shape was designed to strengthen the vortex formation by wall flow. The result of new piston case showed the reduced combustion CCV than the base case. This research provides the guide how to investigate the sources of the combustion CCV and how to reduce the combustion CCV for the future engine development.N

Dynamic modeling of a proton exchange membrane fuel cell system with a shell-and-tube gas-to-gas membrane humidifier

The proton exchange membrane fuel cell (PEMFC) system with a shell-and-tube gas-to-gas membrane humidifier is considered to be a promising PEMFC system because of its energy-efficient operation. However, because the relative humidity of the dry air flowing into the stack depends on the stack exhaust air, this system can be unstable during transients. To investigate the dynamic behavior of the PEMFC system, a system model composed of a lumped dynamic model of an air blower, a two-dimensional dynamic model of a shell-and-tube gas-to-gas membrane humidifier, and a one-dimensional dynamic model of a PEMFC system is developed. Because the water management during transient of the PEMFC system is one of the key challenges, the system model is simulated at the step change of current. The variations in the PEMFC system characteristics are captured. To confirm the superiority of the system model, it is compared with the PEMFC component model during transients.N

Two dimensional dynamic modeling of a shell-and-tube water-to-gas membrane humidifier for proton exchange membrane fuel cell

Water management is a crucial factor in determining the performance of proton exchange membrane fuel cell (PEMFC) for automotive application. The shell-and-tube water-to-gas membrane humidifier is useful for humidifying the PEMFC due to its good performance. Shell-and-tube water-to-gas membrane humidifiers have liquid water on one side of the tube wall and a dry gas on the other. In order to investigate humidifier performance, a two-dimensional dynamic model of a shell-and-tube water-to-gas membrane humidifier is developed. The model is discretized into three control volumes - shell, tube and membrane - in the cross-sectional direction to resolve the temperature and species concentration of the humidifier. For validation, the dew point temperature of the simulation result is compared with that of experimental data and shows good agreement with only a slight difference. The distribution of humidification characteristics can be captured using the discretization along the air-flow direction. The humidification performance of two different flow configurations, counter and parallel, are compared under various operating conditions and geometric parameters. Finally, the dynamic response of the humidifier at the step-change of various air flow rates is investigated. These results suggest that the model can be used to optimize the inlet flow humidity of a PEMFC. Crown Copyright (C) 2009 Published by Elsevier Ltd on behalf of Professor T Nelat Veziroglu. All rights reserved.N

Transient response of a unit PEM fuel cell under various operating conditions

The transient response of proton-exchange membrane fuel cells (PEMFCs) is an important criterion in their application to automotive systems. Nevertheless, few papers have attempted to study experimentally this dynamic behaviour and its causes. Using a large-effective-area (330 cm2) unit PEMFC and a transparent unit PEMFC (25 cm2), systematic transient response and cathode flooding during load changes are investigated. The cell voltage is acquired according to the current density change under a variety of stoichiometry, temperature and humidity conditions, as well as different flooding intensities. In the case of the transparent fuel cell, the cathode gas channel images are obtained simultaneously with a CCD imaging system. The different levels of undershoot occur at the moment of load change under different cathode stoichiometry, both cathode and anode side humidity and flooding intensity conditions. It is shown that undershoot behaviour consists of two stages with different time delays: one is of the order of 1 s and the other is of the order of 10 s. It takes about 1 s for the product water to come up on to the flow channel surface so that oxygen supply is temporarily blocked, which causes voltage loss in that undershoot. The correlation of dynamic behaviour with stoichiometry and cathode flooding is analyzed from the results of these experiments.This research was supported by Brain Korea 21 (BK21) and KOSEF/SNU-IAMD

Effects of Piston Bowl Geometries On Diesel and Gasoline Dual-Fuel Combustion under Low Load Conditions

This study investigated the combustion characteristics by changing the operating parameters and piston bowl geometries in diesel/gasoline dual-fuel combustion. The experiment was conducted in a light-duty single cylinder diesel engine satisfying the EURO-6 regulation adapted for dual-fuel operation. The engine was operated under a low load condition, which was 1,500 rpm and gross IMEP 5.2 bar, with compression ratio of 14. The effects of the operating parameters, namely, the fuel ratio, diesel injection timing, and pilot duration, were analyzed for three different piston bowl geometries. Based on each result, the optimization experiments were conducted to satisfy the various constraints. The gross indicated specific NOx (gISNOx) was restricted below 0.21 g/kWh, the soot emission was limited to below 0.2 FSN, and the maximum pressure rise rate (mPRR) was confined to below 5 bar/deg. Simultaneously, the gross indicated efficiency (GIE) was controlled over 40 %. As a result, these constraints were completely satisfied in all pistons.N

Numerical Analysis of the Combustion and Emission Characteristics of Diesel Engines with Multiple Injection Strategies Using a Modified 2-D Flamelet Model

The multiple injection strategy has been widely used in diesel engines to reduce engine noise, NOx and soot formation. Fuel injection developments such as the common-rail and piezo-actuator system provide more precise control of the injection quantity and time under higher injection pressures. As various injection strategies become accessible, it is important to understand the interaction of each fuel stream and following combustion process under the multiple injection strategy. To investigate these complex processes quantitatively, numerical analysis using CFD is a good alternative to overcome the limitation of experiments. A modified 2-D flamelet model is further developed from previous work to model multi-fuel streams with higher accuracy. The model was validated under various engine operating conditions and captures the combustion and emissions characteristics as well as several parametric variations. The model is expected to be used to suggest advanced injection strategies in engine development processes