Graduate Theses, Dissertations, and Problem Reports 2016 Modeling and Simulation of a Free-Piston Engine with Electrical Generator Using HCCI Combustion Mohammad Alrbai Follow this and additional works at: https://researchrepository.wvu.edu/etd Recommended Citation Alrbai, Mohammad, "Modeling and Simulation of a Free-Piston Engine with Electrical Generator Using HCCI Combustion" (2016). Graduate Theses, Dissertations, and Problem Reports. 5086. https://researchrepository.wvu.edu/etd/5086 This Dissertation is protected by copyright and/or related rights. It has been brought to you by the The Research Repository @ WVU with permission from the rights-holder(s). You are free to use this Dissertation in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you must obtain permission from the rights-holder(s) directly, unless additional rights are indicated by a Creative Commons license in the record and/ or on the work itself. This Dissertation has been accepted for inclusion in WVU Graduate Theses, Dissertations, and Problem Reports collection by an authorized administrator of The Research Repository @ WVU. For more information, please contact [email protected]. Modeling and Simulation of a Free-Piston Engine with Electrical Generator Using HCCI Combustion ____________________________________________ Mohammad Alrbai Dissertation Submitted to the Benjamin M. Statler College of Engineering and Mineral Resources at West Virginia University in partial fulfillment of the requirements for the degree of Doctorate of Philosophy in Mechanical Engineering Nigel Clark, Ph.D., Chair Hailin Li, Ph.D. Cosmin Dumitrescu, Ph.D. Terence Musho, Ph.D. Fernando V. Lima, Ph.D. Department of Mechanical and Aerospace Engineering Morgantown, West Virginia 2016 Keywords: Free Piston Engine, Electrical Generator, Chemical kinetics, HCCI Combustion, Model Control, EGR, Equivalence Ratio. Copyright 2016 Mohammad Alrbai ABSTRACT Modeling and Simulation of a Free-Piston Engine with Electrical Generator using HCCI Combustion Mohammad Alrbai Free-piston engines have the potential to challenge the conventional crankshaft engines by their design simplicity and higher operational efficiency. Many studies have been performed to overcome the limitations of the free-piston devices especially the stability and control issues The investigations within the presented dissertation aim to satisfy many objectives by employing the approach of chemical kinetics to present the combustion process in the free-piston engine. This approach in addition to its advanced accuracy over the empirical methods, it has many other features like the ability to analyze the engine emissions. The effect of the heat release rate (HRR) on the engine performance is considered as the main objective. Understanding the relation between the HRR and the piston dynamics helps in enhancing the system efficiency and identifying the parameters that affect the overall performance. The dissertation covers some other objectives that belongs to the combustion phasing. Exhaust gas recirculation (EGR), equivalence ratio and the intake temperature represent the main combustion parameters, which have been discussed in this dissertation. To obtain the stability in system performance, the model requires a proper controller to simulate the operation and manage the different system parameters; for this purpose, different controlling techniques have been employed. In addition, the dissertation considers some other topics like engine emissions, fuels and fuels mechanisms. The model of the study describes the processes within a single cylinder, two stroke engine, which includes springs to support higher frequencies, reduce cyclic variations and sustain the engine compression ratio. An electrical generator presents the engine load; the generator supports different load profiles and play the key role in controlling the system. The 1st law of thermodynamics and Newton`s 2nd law are applied to couple the piston dynamics with the engine thermodynamics. The model governing equations represent a single zone perfectly stirred reactor (PSR) which contain a perfect mixing ideal gas mixture. The chemical kinetics approach is applied using Cantera/ MATLAB® toolbox, which presents the combustion process. In this research, a homogenous charge compression ignition (HCCI) at different operational conditions is used. HCCI engines have high efficiencies and low emissions and can work within a wide range of fuels. The results have been presented in a multi-cycle simulation and a parametric study forms. In the case of the multi-cycle simulation, a 100 cycles of the engine operation have been simulated. The overall work that is delivered to the electrical generator presents 47% of the total fuel energy. The model indicates an average frequency of 125 Hz along the operational cycles. In order to eliminate the cyclic variations and ensure a continuous operation, a proportional derivative (PD) controller has been employed. The controller adjusts the generator load in order to minimize the difference between the bottom dead center (BDC) locations along the operation cycles. The PD controller shows weakness in achieving the full steady state operation, for this purpose; a proportional integral (PI) controller has been implemented. The PI controller seeks to achieve a specific compression ratio. The results show that; the PI controller indicates unique behavior after 15 cycles of operation where the model ended to fluctuate between two compression ratios only. The complex relation between the thermodynamics and the dynamics of the engine is the greatest challenge in examining the effectiveness of the PI controller. In the parametric investigations, EGR examinations show that NOx emission is reduced to less than the half, as 30 % of EGR is used; this occurs due to the EGR thermal and dilution effects, which cause significant drop in the peak bulk temperature and CO emissions as well. Under the applied conditions, EGR has the ability to raise the work output ratio by increasing the engine compression ratio. The examination of the EGR temperature on the engine performance indicates that cooled EGR charges have the advantage over the hot EGR mixtures on enhancing the work output ratio. At the same time, EGR temperature affects the NOx formation by speeding its instantaneous reactions rate. The dissertation includes a study of the effect of the intake temperature and the equivalence ratio (φ) as well. The increasing in the intake temperature reduce the time needed for ignition, but leads to a reduction in the work output ratio at the same time. Such results can help in studying high knock resistance fuels where ignition delay is a matter. In the case of the equivalence ratio, lean mixtures show efficiencies that exceed 50% compared to those at the stoichiometric conditions. In the case of the ultra-lean (φ<0.5) combustion, the results show that the NOx emission is with the minimal levels as well as the CO and the unburned hydrocarbons (UHC) emissions. Sensitivity analysis to the chemical kinetic mechanism for the fuel combustion has been presented also in the dissertation. Many mechanisms for different fuels have been investigated, for example; a modified mechanism for Methane that includes 36 species and 222 reactions has been compared with the full GRI 3.0 mechanism (53 species and 325 reactions). The results of this comparison indicate that the modified mechanism has the potential to replace the full one in some cases like in demonstrating the engine operation, but not in the engine emissions analysis. I. Dedication I dedicate this work to my parents and to all of my family members. iv II. Acknowledgments First, I would like to thank Allah for his guidance and care during my whole life. I could not have met the challenges of this research without him. All of the appreciations and thanks go to my advisor Dr. Nigel Clark and my Co. Advisor Dr. Hailin Li. In addition, I want to thank all of the other committee members, Dr. Terence Musho, Dr. Cosmin Dumitrescu, and Dr. Fernando V. Lima. Their help and Advices were the motivators of my work. Special thanks goes to Dr. Hany Ammar for his continuous support along my study. At the same time, many thanks go to George Berry Chair for the financial support during this research. Finally, thanks to all of those friends, colleagues, instructors, and mentors who gave some of their time to make this work successful. v III. Table of Contents Dedication………………………………………………………………………………………………………………………………………………iv Acknowledgments…………………………………………………………………………………………………………………………………..v Table of Contents……………………………………………………………………………………………………………………………..…...vi List of Figures……………….…………………………………………………………………………………………………………….….……...ix List of Tables....................................................................................................................................….........xi List of Nomenclature…………………………………………………………………………………………………………………….….……xii Chapter 1. Introduction ................................................................................................................1 1.1 Linear engine ................................................................................................................................. 1 1.2 Homogeneous charge compression ignition engines ................................................................... 1 1.3 Review of literature .....................................................................................................................