Exploration of Combustion Strategies for High-efficiency, Extreme-compression Engines PDF Download

Author: Mr. Matthew Neil Svrcek
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Increasing the compression ratio of an internal combustion engine to 100:1 or greater could potentially enable efficiencies greater than 60%. Understanding and managing the combustion process is a critical component to achieving this in practice. This thesis explores strategies for combustion at extreme compression ratios. First, the setup of a free-piston device capable of operating at 100:1 compression ratio is described. Initial performance results are reported for air-only experiments. Diesel-style combustion was the first approach taken, as it provides facile ignition phasing. Results are reported from initial lean Diesel combustion experiments at compression ratios ranging from 30 to 100:1. Indicated efficiency peaked at 60% for these experiments. To further understand Diesel-style combustion at extreme compression ratios, a study of Diesel sprays in the extreme compression apparatus was performed. The setup of a combined schlieren and direct luminosity imaging system with full-bore optical access is described. Spray penetration, dispersion, liquid length, and ignition delay are reported for combusting and non-combusting sprays. Compression ratios for these experiments ranged from 30 to 100:1. Spray behavior followed expected trends as a function of primary variables such as gas density. However, rapidly varying gas density from the free-piston profile impacts the spray penetration. Furthermore, at the highest compression ratios in-cylinder fluid motion dramatically affects the spray behavior, enabled by the low ratio of fuel to gas density. Systems added to the extreme compression apparatus to measure gaseous and particulate emissions are described. Emissions measurements from Diesel-style combustion of isooctane at 35:1 compression ratio are reported, to provide a reference case at conditions similar to conventional engines. Emissions were similar to those from production Diesel engines, with the exception that soot, HC, and CO increased more rapidly with equivalence ratio in the present study. Results from experiments with Diesel combustion up to 100:1 compression ratio are also reported. The combustion efficiency was 99% up to 100:1 compression ratio, and HC, CO and soot emissions were low. Emissions of NOx were 5 times higher at 100:1 than at 35:1, and would require aftertreatment. Stoichiometric, premixed-charge combustion enables the use of a three-way catalyst and produces low soot levels. Using this approach at extreme compression ratios requires delaying autoignition until the minimum volume is reached. Options for control of autoignition are discussed, and gas cooling is identified as the most effective. Pre-refrigeration, intercooling, and evaporation of a liquid are modeled and shown to effectively achieve the desired ignition timing at 100:1 compression ratio, without impacting the overall engine efficiency. Experimental results are reported for premixed methane-air combustion with intercooling control of autoignition, for 0.96 to 1.04 equivalence ratio and 35 to 90:1 effective compression ratio. The gas cooling requirement for autoignition control was higher than predicted by the models, but still within practical reach. The indicated efficiency peaked at 57%. Emissions levels from these experiments were similar to stoichiometric spark-ignited natural gas engines reported in the literature, and indicate that a three-way catalyst could be successfully used even at extreme compression ratios. Results are also reported for water injection control of autoignition. Autoignition was successfully controlled up to 60:1 effective compression ratio, but the mass of water required was an order of magnitude higher than predicted. This is shown to result from practical limitations of the current water injector setup.

Author: Gautam Kalghatgi
Publisher: Springer Nature
ISBN: 9811687358
Category : Technology & Engineering
Languages : en
Pages : 339

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This book focuses on gasoline compression ignition (GCI) which offers the prospect of engines with high efficiency and low exhaust emissions at a lower cost. A GCI engine is a compression ignition (CI) engine which is run on gasoline-like fuels (even on low-octane gasoline), making it significantly easier to control particulates and NOx but with high efficiency. The state of the art development to make GCI combustion feasible on practical vehicles is highlighted, e.g., on overcoming problems on cold start, high-pressure rise rates at high loads, transients, and HC and CO emissions. This book will be a useful guide to those in academia and industry.

Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 21

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Many research studies have shown that low temperature combustion in compression ignition engines has the ability to yield ultra-low NOx and soot emissions while maintaining high thermal efficiency. To achieve low temperature combustion, sufficient mixing time between the fuel and air in a globally dilute environment is required, thereby avoiding fuel-rich regions and reducing peak combustion temperatures, which significantly reduces soot and NOx formation, respectively. It has been demonstrated that achieving low temperature combustion with diesel fuel over a wide range of conditions is difficult because of its properties, namely, low volatility and high chemical reactivity. On the contrary, gasoline has a high volatility and low chemical reactivity, meaning it is easier to achieve the amount of premixing time required prior to autoignition to achieve low temperature combustion. In order to achieve low temperature combustion while meeting other constraints, such as low pressure rise rates and maintaining control over the timing of combustion, in-cylinder fuel stratification has been widely investigated for gasoline low temperature combustion engines. The level of fuel stratification is, in reality, a continuum ranging from fully premixed (i.e. homogeneous charge of fuel and air) to heavily stratified, heterogeneous operation, such as diesel combustion. However, to illustrate the impact of fuel stratification on gasoline compression ignition, the authors have identified three representative operating strategies: partial, moderate, and heavy fuel stratification. Thus, this article provides an overview and perspective of the current research efforts to develop engine operating strategies for achieving gasoline low temperature combustion in a compression ignition engine via fuel stratification. In this paper, computational fluid dynamics modeling of the in-cylinder processes during the closed valve portion of the cycle was used to illustrate the opportunities and challenges associated with the various fuel stratification levels.

Author: Hongsheng Guo
Publisher: Frontiers Media SA
ISBN: 2889666212
Category : Technology & Engineering
Languages : en
Pages : 125

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Author: Jun Han
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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Piston-engine-powered ground vehicles account for a large fraction of the U.S. consumption of petroleum-based fuels, and are major sources of pollutant emissions including oxides of nitrogen, particulate matter, and greenhouse gases. With uncertainties in crude oil supplies and increasingly stringent emissions regulations, advanced-concept engines and alternative (non-petroleum-derived) fuels have become active research areas. Of particular interest are low-temperature combustion strategies for compression-ignition engines that have the potential for high efficiency with low in-cylinder emissions formation. To make progress, predictive computational fluid dynamics (CFD) tools are needed that can provide insight into in-cylinder processes in hostile aero-thermo-chemical environments with unconventional fuels. Challenges include: dealing with multiphase turbulent flow in complex geometric configurations with moving boundaries; accounting for unresolved turbulent fluctuations in velocity, composition, and temperature; and availability of gas-phase reaction mechanisms and soot models that capture autoignition, combustion, and emissions formation under relatively unexplored conditions. This thesis focuses on two topics related to CFD modeling for advanced compression-ignition engines: the ignition behavior of gasoline-like fuels under homogeneous low-temperature-combustion conditions, and the ignition and sooting characteristics of a class of molecules that is representative of those in algae-derived fuels under conditions that are representative of a direct-injection diesel engine. In both cases, an unsteady Reynolds-averaged (URANS) modeling approach is used, and model results are compared with available experimental data. For the first part, a CFD model of a Cooperative Fuel Research (CFR) engine was developed and exercised to explore the ignition behavior of low-reactivity (gasoline-like) two- and three-component fuel blends under extremely fuel-lean conditions. The principal metric of interest was the critical compression ratio (CCR), which is defined as the minimum compression ratio for which complete ignition is achieved, as determined by computed or measured CO levels. The ability of several chemical mechanisms from the literature to capture the experimentally measured CCRs over a range of conditions was evaluated. No single mechanism performed best for all fuel blends and all conditions. Furthermore, even in cases where CCRs were computed accurately, significant differences were found between measured and computed apparent-heat-release rates, suggesting that the reaction mechanisms do not accurately represent the kinetics of the ignition process. An initial reaction pathways analysis provided some insight into the reasons for the observed discrepancies between model and experiment. For the second part, a CFD model of a constant-volume high-pressure combustion chamber was exercised to explore the ignition and sooting behavior of two large n-alkane molecules (n-dodecane and n-hexadecane) under diesel-engine-relevant conditions. The extent to which unresolved turbulent fluctuations influence the results was determined by comparing results from a model that accounts for turbulent fluctuations (a transported probability density function-- tPDF-- method) with one that ignores them (a locally well-stirred-reactor-- WSR-- model). The largest influence of turbulent fluctuations was found to be in the soot predictions, which were in better agreement with the experiment for the tPDF model. Differences between n-dodecane and n-hexadecane results were found to be small. There is some evidence from the literature that it may be possible to take advantage of differences between the physical and chemical properties of these two molecules in an engine to realize nonnegligible differences in efficiency and soot levels. However, more sophisticated gas-phase chemistry and soot models may be needed to capture the subtle differences in CFD modeling.

Author: Hua Zhao
Publisher: CRC Press
ISBN:
Category : Technology & Engineering
Languages : en
Pages : 562

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Homogeneous charge compression ignition (HCCI)/controlled auto-ignition (CAI) has emerged as one of the most promising engine technologies with the potential to combine fuel efficiency and improved emissions performance, offering reduced nitrous oxides and particulate matter alongside efficiency comparable with modern diesel engines. Despite the considerable advantages, its operational range is rather limited and controlling the combustion (timing of ignition and rate of energy release) is still an area of on-going research. Commercial applications are, however, close to reality. HCCI a.

Author: M.J. Pilling
Publisher: Elsevier
ISBN: 0080535658
Category : Science
Languages : en
Pages : 823

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Combustion has played a central role in the development of our civilization which it maintains today as its predominant source of energy. The aim of this book is to provide an understanding of both fundamental and applied aspects of low-temperature combustion chemistry and autoignition. The topic is rooted in classical observational science and has grown, through an increasing understanding of the linkage of the phenomenology to coupled chemical reactions, to quite profound advances in the chemical kinetics of both complex and elementary reactions. The driving force has been both the intrinsic interest of an old and intriguing phenomenon and the centrality of its applications to our economic prosperity. The volume provides a coherent view of the subject while, at the same time, each chapter is self-contained.

Author: Flavio Dal Forno Chuahy
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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Dual fuel reactivity controlled compression ignition (RCCI) combustion is a promising method to achieve high efficiency with near zero NOx and soot emissions; however, the requirement to carry two fuels on-board has limited practical applications. Advancements in catalytic reforming have demonstrated the ability to generate syngas (a mixture of CO and hydrogen) from a single hydrocarbon stream. The reformed fuel mixture can then be used as a low reactivity fuel stream to enable RCCI out of a single parent fuel. Beyond enabling dual-fuel combustion strategies out of a single parent fuel, fuel reforming can be endothermic and allow recovery of exhaust heat to drive the reforming reactions, potentially improving overall efficiency of the system. Previous works have focused on using reformed fuel to extend the lean limit of spark ignited engines, and enhancing the control of HCCI type combustion. The strategy pairs naturally with advanced dual-fuel combustion strategies, and the use of dual-fuel strategies in the context of on-board reforming and energy recovery has not been explored. Accordingly, the work presented in this dissertation attempts to fill in the gaps in the current literature and provide a pathway to "single" fuel RCCI combustion through a combination of experiments and computational fluid dynamics modeling. Initially, a system level analysis focusing on three common reforming techniques (i.e., partial oxidation, steam reforming and auto-thermal reforming) was conducted to evaluate the potential of reformed fuel. A system layout was proposed for each reforming technique and a detailed thermodynamic analysis using first- and second-law approaches were used to identify the sources of efficiency improvements. The results showed that reformed fuel combustion with a near TDC injection of diesel fuel can increase engine-only efficiency by 4% absolute when compared to a conventional diesel baseline. The efficiency improvements were a result of reduced heat transfer and shorter, more thermodynamically efficient, combustion process. For exothermic reforming processes, losses in the reformer outweigh the improvements to engine efficiency, while for endothermic processes the recovery of exhaust energy was able to allow the system efficiency to retain a large portion of the benefits to the engine combustion. Energy flow analysis showed that the reformer temperature and availability of high grade exhaust heat were the main limiting factors preventing higher efficiencies. RCCI combustion was explored experimentally for its potential to expand on the optimization results and achieve low soot and NOx emissions. The results showed that reformed fuel can be used with diesel to enable RCCI combustion and resulted in low NOx and soot emissions while achieving efficiencies similar to conventional diesel combustion. Experiments showed that the ratio H2/(H2+CO) is an important parameter for optimal engine operation. Under part-load conditions, fractions of H2/(H2+CO) higher than 60% led to pressure oscillations inside the cylinder that substantially increased heat transfer and negated any efficiency benefits. The system analysis approach was applied to the experimental results and showed that chemical equilibrium limited operation of the engine to sub-optimal operating conditions. RCCI combustion was able to achieve "diesel like" system level efficiencies without optimization of either the engine operating conditions or the combustion system. Reformed fuel RCCI was able to provide a pathway to meeting current and future emission targets with a reduction or complete elimination of aftertreatment costs. Particle size distribution experiments showed that addition of reformed fuel had a significant impact on the shape of the particle size distribution. Addition of reformed fuel reduced accumulation-mode particle concentration while increasing nucleation-mode particles. When considering the full range of particle sizes there was a significant increase in total particle concentration. However, when considering currently regulated (Dm>23nm) particles, total concentration was comparable. To address limitations identified in the system analysis of the RCCI experiments a solid oxide fuel cell was combined with the engine into a hybrid electrochemical combustion system. The addition of the fuel cell addresses the limitations by providing sufficient high grade heat to fully drive the reforming reactions. From a system level perspective, the impact of the high frequency oscillations observed in the experiments are reduced, as the system efficiency is less dependent on the engine efficiency. From an engine perspective, the high operating pressures and low reactivity of the anode gas allow reduction of the likelihood of such events. A 0-D system level code was developed and used to find representative conditions for experimental engine validation. The results showed that the system can achieve system electrical efficiencies higher than 70% at 1 MWe power level. Experimental validation showed that the engine was able to operate under both RCCI and HCCI combustion modes and resulted in low emissions and stable combustion. The potential of a hybrid electrochemical combustion system was demonstrated for high efficiency power generation

Author: Akhilendra Pratap Singh
Publisher: Springer Nature
ISBN: 9811504180
Category : Technology & Engineering
Languages : en
Pages : 329

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This book covers alternative fuels and their utilization strategies in internal combustion engines. The main objective of this book is to provide a comprehensive overview of the recent advances in the production and utilization aspects of different types of liquid and gaseous alternative fuels. In the last few years, methanol and DME have gained significant attention of the energy sector, because of their capability to be utilized in different types of engines. This book will be a valuable resource for researchers and practicing engineers alike.

Author: Yidnekachew Messele Ayele
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 0

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Gasoline fuel is the most convenient energy source for light-duty vehicles in energy density and refueling time. However, the emission regulations for internal combustion engines force the industry to exploit innovative combustion technologies. The spark-ignition engine was forced to be cleaner and more efficient, changing from regular combustion engines to a more advanced internal combustion engine and electrification. The current scenario shows that automotive companies and researchers are exploring hybrid powertrains with advanced internal combustion engine technologies with electrification or pure electric vehicles. The Dual Mode, Turbulent Jet Ignition (DM-TJI) system is one of the promising advanced combustion systems, powered by active air/fuel scavenging pre-chamber ignition systems. The distributed ignition sites created by the pre-chamber flames improve the combustion engine's efficiency, simultaneously mitigating combustion knock at a high engine compression ratio and enabling lean-burn or high level of external EGR dilution operation. This study analyzes the performance of a single-cylinder DM-TJI metal engine with gasoline and alternative fuels. The first part of the study presents the experimental investigations on three pre-chamber nozzle orifice diameters at various engine speeds and 10 bar engine load. The combustion parameters for each tested orifice diameter are presented for the incremental engine speeds. A numerical analysis was conducted using the GT-Power model simulation tool to support the experimental result. The DM-TJI engine's maximum gross indicated efficiency was examined and found to be 44.56%, with a higher EGR dilution rate of 45%. This orifice diameter study reported on the first published results of the desertion. Additional experimental data were collected for the selected orifice diameter at a wide range of engine operating test matrices. A predictive engine model was introduced with experimental data validation. The experimental data and predictive model generated the engine performance and fuel map for a real-world fuel economy study. Conventional and hybrid powertrain vehicles were developed with GT-Suite commercial software. Each powertrain model was calibrated in terms of components (battery, electric motors) capacity, internal combustion engine operative points, energy management strategy, and gear ratios with chassis dynamometer measured data of the vehicle drive cycle. A selected U.S. Environmental Protection Agency (EPA) driving schedule was implemented on the GT-Suite powertrain. The DM-TJI engine drive cycle fuel economy is compared to an industry-based conventional vehicle with the same powertrain except for the engine map. The results show the DM-TJI engine fuel economy improvement between 10.5%-17.29% and CO2 emissions reductions between 9.51%-14.75% for the selected driving schedule. Mild and parallel hybrid powertrain further improve the fuel economy by 9.23% and 29.88%, respectively, compared to the conventional powertrain of the DM-TJI engine. The CO2 emission was reduced by 23%. Finally, the single-cylinder DM-TJI metal engine performance under different alternative fuels was studied. An experimental test was carried out at stoichiometric conditions with different fuels, engine speed, engine load, and EGR dilution rates. Compared to gasoline fuel, E80 ethanol blend fuel produces 4.47% less CO2 and 25.75% less CO emission, and methane fuel produces 27.91% less CO2 and 57.85% less CO emission. E80 ethanol blend has the highest indicated efficiency of 45.61% with 45% EGR dilution. Methane fuel has a maximum indicated efficiency of 45.03% with 38.5% EGR dilution.