Characteristics of Knock in Hydrogen-Oxygen-Argon SI Engine

A promising approach for improving the efficiency of internal combustion engines is to employ a working fluid with a high specific heat ratio such as the noble gas argon. Moreover, all harmful emissions are eliminated when the intake charge is composed of oxygen, nonreactive argon, and hydrogen fuel. Previous research demonstrated indicated thermal efficiencies greater than 45% at 5.5 compression ratio in engines operating with hydrogen, oxygen, and argon. However, knock limits spark advance and increasing the efficiency further. Conditions under which knock occurs in such engines differs from typical gasoline fueled engines. In-cylinder temperatures using hydrogen-oxygen-argon are higher due to the high specific heat ratio and pressures are lower because of the low compression ratio. Better understanding of knock under these conditions can lead to operating strategies that inhibit knock and allow operation closer to the knock limit. In this work we compare knock with a hydrogen, oxygen, and argon mixture to that of air-gasoline mixtures in a variable compression ratio cooperative fuels research (CFR) engine. The focus is on stability of knocking phenomena, as well as, amplitude and frequency of the resulting pressure waves

Dynamical Mean-Field Theory

The dynamical mean-field theory (DMFT) is a widely applicable approximation scheme for the investigation of correlated quantum many-particle systems on a lattice, e.g., electrons in solids and cold atoms in optical lattices. In particular, the combination of the DMFT with conventional methods for the calculation of electronic band structures has led to a powerful numerical approach which allows one to explore the properties of correlated materials. In this introductory article we discuss the foundations of the DMFT, derive the underlying self-consistency equations, and present several applications which have provided important insights into the properties of correlated matter.Comment: Chapter in "Theoretical Methods for Strongly Correlated Systems", edited by A. Avella and F. Mancini, Springer (2011), 31 pages, 5 figure

Investigation of Alternative Fuels and Advanced Engine Technology: Improving Engine Efficiency and Reducing Emissions

The internal combustion engine has vastly improved over the past 100 years. With global warming and pollution being a rising concern, engineers are working towards improving efficiency and emissions of engines. The spark-ignited engine (or gasoline engine) offers improvement in emissions with a sacrifice in thermal efficiency. The compression ignition engine (Diesel engine) increases the thermal efficiency, due to operation at higher compression ratios, but emits high amounts of particulate matter and oxides of nitrogen (NOx). Although improvements in fuel refinement have decreased the amount of engine pollutants, the output of pollutants for both spark-ignited and Diesel engines is still too great.This dissertation explores two advanced engine concepts with alternative fuels for improving thermal efficiency and reducing emissions in automobiles. The first concept investigated is a spark-ignited internal combustion engine operating using hydrogen, oxygen, and argon. Basic engine theory predicts such an engine will see a considerable improvement in engine efficiency (theoretically ~75%, and in practice ~50% including heat transfer and friction losses) over standard engines. These gains in thermal efficiency are due to argon's monatomic structure, which yields a high specific heat ratio (γ = 1.67 compared to γ < 1.4 for air). The water produced by the combustion of hydrogen can be extracted in the exhaust by a condenser, allowing the recycling of nearly pure argon in a closed loop system. Therefore, argon re-fueling is not required.Achieving efficiencies above 50% with a hydrogen-oxygen-argon engine, however, is difficult due to engine knock limiting spark advance. In an effort to obtain the highest efficiency of this engine concept, experiments were conducted using single and dual spark-ignition for high argon concentrations. Results showed dual spark-ignition slightly increased indicated thermal efficiency, but was still limited by engine-knock. A three-zone model showed that argon as a working fluid increases in-cylinder temperatures, unburned gas temperatures, and laminar flame speed. The model suggests that specific heat ratio affects end gas temperatures more than increasing flame speed.The second engine concept investigates variables and fuel trends for predicting ignition in homogenous charge compression ignition (HCCI) engines. Octane number, a metric for fuel performance in gasoline engines, and cetane number, a metric for fuel performance in Diesel engines, do not accurately predict fuel performance in HCCI engines. To develop a metric for predicting fuel performance in HCCI engines, correlations between ignition of fuels in an HCCI engine and varying engine parameters are investigated. A relationship between fuel chemistry and ignition in HCCI engines is also explored. Results show that previous methods for predicting ignition do not correlate well with experimental data and auto-ignition is highly sensitive to fuel chemistry.A single-zone well-mixed-reactor model is used to investigate three different mechanisms for predicting auto-ignition in the HCCI engine. All three mechanisms accurately predicted the auto-ignition order of fuels containing isooctane and n-heptane, but did not predict auto-ignition of blends containing toluene and ethanol. Blends of toluene and n-heptane were further investigated using the model to identify potential problems with the toluene mechanisms. The model results showed increasing the amount of toluene linearly by volume did not result in a linear advance in auto-ignition

Investigation of Alternative Fuels and Advanced Engine Technology: Improving Engine Efficiency and Reducing Emissions

The internal combustion engine has vastly improved over the past 100 years. With global warming and pollution being a rising concern, engineers are working towards improving efficiency and emissions of engines. The spark-ignited engine (or gasoline engine) offers improvement in emissions with a sacrifice in thermal efficiency. The compression ignition engine (Diesel engine) increases the thermal efficiency, due to operation at higher compression ratios, but emits high amounts of particulate matter and oxides of nitrogen (NOx). Although improvements in fuel refinement have decreased the amount of engine pollutants, the output of pollutants for both spark-ignited and Diesel engines is still too great.This dissertation explores two advanced engine concepts with alternative fuels for improving thermal efficiency and reducing emissions in automobiles. The first concept investigated is a spark-ignited internal combustion engine operating using hydrogen, oxygen, and argon. Basic engine theory predicts such an engine will see a considerable improvement in engine efficiency (theoretically ~75%, and in practice ~50% including heat transfer and friction losses) over standard engines. These gains in thermal efficiency are due to argon's monatomic structure, which yields a high specific heat ratio (γ = 1.67 compared to γ < 1.4 for air). The water produced by the combustion of hydrogen can be extracted in the exhaust by a condenser, allowing the recycling of nearly pure argon in a closed loop system. Therefore, argon re-fueling is not required.Achieving efficiencies above 50% with a hydrogen-oxygen-argon engine, however, is difficult due to engine knock limiting spark advance. In an effort to obtain the highest efficiency of this engine concept, experiments were conducted using single and dual spark-ignition for high argon concentrations. Results showed dual spark-ignition slightly increased indicated thermal efficiency, but was still limited by engine-knock. A three-zone model showed that argon as a working fluid increases in-cylinder temperatures, unburned gas temperatures, and laminar flame speed. The model suggests that specific heat ratio affects end gas temperatures more than increasing flame speed.The second engine concept investigates variables and fuel trends for predicting ignition in homogenous charge compression ignition (HCCI) engines. Octane number, a metric for fuel performance in gasoline engines, and cetane number, a metric for fuel performance in Diesel engines, do not accurately predict fuel performance in HCCI engines. To develop a metric for predicting fuel performance in HCCI engines, correlations between ignition of fuels in an HCCI engine and varying engine parameters are investigated. A relationship between fuel chemistry and ignition in HCCI engines is also explored. Results show that previous methods for predicting ignition do not correlate well with experimental data and auto-ignition is highly sensitive to fuel chemistry.A single-zone well-mixed-reactor model is used to investigate three different mechanisms for predicting auto-ignition in the HCCI engine. All three mechanisms accurately predicted the auto-ignition order of fuels containing isooctane and n-heptane, but did not predict auto-ignition of blends containing toluene and ethanol. Blends of toluene and n-heptane were further investigated using the model to identify potential problems with the toluene mechanisms. The model results showed increasing the amount of toluene linearly by volume did not result in a linear advance in auto-ignition

A high turndown, ultra low emission low swirl burner for natural gas, on-demand water heaters:

Previous research has shown that on-demand water heaters are, on average, approximately 37% more efficient than storage water heaters. However, approximately 98% of water heaters in the U.S. use storage water heaters while the remaining 2% are on-demand. A major market barrier to deployment of on-demand water heaters is their high retail cost, which is due in part to their reliance on multi-stage burner banks that require complex electronic controls. This project aims to research and develop a cost-effective, efficient, ultra-low emission burner for next generation natural gas on-demand water heaters in residential and commercial buildings. To meet these requirements, researchers at the Lawrence Berkeley National Laboratory (LBNL) are adapting and testing the low-swirl burner (LSB) technology for commercially available on-demand water heaters. In this report, a low-swirl burner is researched, developed, and evaluated to meet targeted on-demand water heater performance metrics. Performance metrics for a new LSB design are identified by characterizing performance of current on-demand water heaters using published literature and technical specifications, and through experimental evaluations that measure fuel consumption and emissions output over a range of operating conditions. Next, target metrics and design criteria for the LSB are used to create six 3D printed prototypes for preliminary investigations. Prototype designs that proved the most promising were fabricated out of metal and tested further to evaluate the LSB’s full performance potential. After conducting a full performance evaluation on two designs, we found that one LSB design is capable of meeting or exceeding almost all the target performance metrics for on-demand water heaters. Specifically, this LSB demonstrated flame stability when operating from 4.07 kBTU/hr up to 204 kBTU/hr (50:1 turndown), compliance with SCAQMD Rule 1146.2 (14 ng/J or 20 ppm NOX @ 3% O2), and lower CO emissions than state-of-the art water heaters. Overall, the results from this research show that the LSB could provide a simple, low cost burner solution for significantly extending operating range of on-demand water heaters while providing low NOX and CO emissions

Matching diverse feedstocks to conversion processes for the future bioeconomy

A wide variety of wasted or underutilized organic feedstocks can be leveraged to build a sustainable bioeconomy, ranging from crop residues to food processor residues and municipal wastes. Leveraging these feedstocks is both high-risk and high-reward. Converting mixed, variable, and/or highly contaminated feedstocks can pose engineering and economic challenges. However, converting these materials to fuels and chemicals can divert waste from landfills, reduce fugitive methane emissions, and enable more responsible forest management to reduce the frequency and severity of wildfires. Historically, low-value components, including ash and lignin, are poised to become valuable coproducts capable of supplementing cement and valuable chemicals. Here, we evaluate the challenges and opportunities associated with converting a range of feedstocks to renewable fuels and chemicals