Chenaniah Langness

Moderate Substitution of Varying Compressed Natural Gas Constituents for Assisted Diesel Combustion

ABSTRACT The recent growth of hydraulic fracking has made compressed natural gas (CNG) a viable option for fueling the United States transportation sector in a dual fuel scenario with ultra low sulfur diesel (ULSD). To clarify literature trends, this effort investigates the influence of CNG speciation (methane, ethane, propane, and isobutane) by employing energy substitution rates (ESR) of 7%, 18%, and 40% (approximately) to prevent significant changes to ignition delay. Results demonstrate that maintaining hydrocarbon (HC) constituents within typical global levels has no noticeable bearing on the findings; however, added CNG does noticeably change the peak rate of heat release. Overall, nitrogen oxides (NOx) and particulate matter emissions remained lower than ULSD values except for the highest load and ESR rate when NOx increased due to a significant growth of the premixed combustion phase. At all ESR values, methane and non-methane hydrocarbons increased subsequently leading to a decrease in combustion efficiency.

Employing Adaptive Mesh Refinement for Simulating the Exhaust Gas Recirculation Mixing Process

One significant emissions issue of compression ignition engines that directly influences human health is the production of nitrogen oxides (NOx). Once produced, these species are difficult to convert catalytically in the exhaust and often require a complex aftertreatment system to mitigate their release into the environment. The common methodology by the internal combustion engine community to reduce the amount of NOx is to employ Exhaust Gas Recirculation (EGR) in order to dilute the intake mixture with inert species (e.g., water). This lowers the combustion temperature lessening the thermal NO production mechanism. Improper mixing of EGR with the intake (species in-homogeneity, low levels of mixing turbulence, etc.) can lead to significant cylinder-to-cylinder variation in combustion temperatures and NOx emissions, making it more difficult to achieve regulatory standards.In this effort, a three-dimensional (3-D), transient, computational fluid dynamics (CFD) analysis was performed in order to more accurately model the mixing of EGR and intake for a single-cylinder test engine. Mixing is achieved for this engine by using a small rectangular box in which clean air and engine exhaust for controlled recirculation are mixed prior to engine intake. A matrix of computational analyses at different engine loads, and simulation types (large eddy and Reynolds-averaged Navier-Stokes) at 25% EGR were performed to check computational time and agreement with experimental measurements. Moreover, this effort employs the use of adaptive mesh techniques in order to understand their usage and validate correct implementation for later endeavors including more complex geometries, such as the manifold of a multi-cylinder engine. The simulation results indicate that mass flow rate and temperature of the mixture as it leaves the mixing box agree to within 3% of experimental values. Furthermore, pressures at the air and EGR inlet boundaries showed agreement to around 1% and 12%, respectively, with the experimental measuring points indicated as the reason for the difference. In addition, species mixing of carbon monoxide was uniform to within 440 ppm. Finally, the use of the models may also account for a prior discrepancy in the output power of the single-cylinder engine test stand.Copyright

Exergy Analysis of Dual-Fuel Operation with Diesel and Moderate Amounts of Compressed Natural Gas in a Single-Cylinder Engine

ABSTRACT An energy-exergy heat release model is used with in-cylinder pressure measurements to analyze dual-fuel combustion in a high compression ratio diesel engine. Compressed natural gas (CNG) addition does not exceed 40% of total fuel energy, in order to avoid significant changes to liquid fuel injection timing needed to maintain efficient engine operation. Increasing CNG usage is observed to enhance exergetic efficiency, as premixed combustion is promoted over diffusion burn. In addition, CNG usage is associated with higher exergy retention by the exhaust gases. However, this comes with decreased combustion efficiency as CNG survives combustion and is lost to the exhaust. Overall, the analysis shows that CNG usage may result in lower absolute exergy consumption by the engine, even alongside the lost exergy from unburned fuel, as the wasted CNG is simultaneously less exergetically useful, and thermal efficiency rises due to increased premixed combustion.

Proof-of-Concept Combined Shrouded Wind Turbine and Compressed Air Energy Storage System

As the push for renewable energy sources continues, one significant drawback over fossil fuels is that they are not reliable. Wind is not guaranteed at all times, and the sun does not always shine. Moreover, the demand for electricity is variable due to daily and seasonal swings in power draw from the grid. Conventional power plants can increase or reduce production to meet seasonal demand, but usually cannot meet daily fluctuations. Therefore, power plants must maintain a relatively high level of electrical generation capacity throughout the day even if the current demand is low. A prime place to focus upon electrical demand fluctuations and the unreliability of the renewable sources is at the location of the changes in demand. Homes often sit vacant throughout the day and draw little power from the grid. When residents return in the late afternoon and evening, a sudden increase in demand occurs. To address this increase in demand at a local level, a small-scale proof-of-concept shrouded wind turbine (SWT) and compressed air energy storage (CAES) system was designed, built, and tested for an undergraduate capstone design project. The concept is that a small SWT charges the CAES system and when the residents return, the energy stored within the CAES system is released lessening the demand on the main electrical grid. The SWT was investigated due to the theorized increase in efficiency that the shroud provides by accelerating the air beyond ambient velocity at the location of the turbine blades. The CAES system consisted of a three-stage compressor that filled a high-pressure scuba tank. This air was then released in a controlled manner in order to operate an air motor coupled to an alternator that generated electricity. Testing of the SWT found that the prototype was too small to power the compressors for the CAES; however, the concept of the SWT was shown to hold true. Experiments using the CAES system demonstrated significant losses, but it did generate electricity. The small-scale prototype did reveal that the idea of focusing on the source of the power fluctuations is a viable option. As a result, by using many small power production and storage devices, the overall daily swings in demand for electricity can be corrected to levels that current power plants can meet.Copyright

Small Scale Prototype Biomass Drying System for Co-Combustion With Coal

Thermoelectric power plants burn thousands of tons of non-renewable resources every day to heat water and create steam, which drives turbines that generate electricity. This causes a significant drain on local resources by diverting water for irrigation and residential usage into the production of energy. Moreover, the use of fossil reserves releases significant amounts of greenhouse and hazardous gases into the atmosphere. As electricity consumption continues to grow and populations rise, there is a need to find other avenues of energy production while conserving water resources. Co-combusting biomass with coal is one potential route that promotes renewable energy while reducing emissions from thermoelectric power plants. In order to move in this direction, there is a need for a low-energy and low-cost system capable of drying materials to a combustion appropriate level in order to replace a significant fraction of the fossil fuel used. Biomass drying is an ancient process often involving the preservation of foods using passive means, which is economically efficient but slow and impractical for large-scale fuel production. This effort, accomplished as an undergraduate capstone design project, instead implements an active drying system for poplar wood using theorized waste heat from the power plant and potentially solar energy. The use of small-scale prototypes demonstrate the principles of the system at a significantly reduced cost while allowing for calculation of mass and energy balances in the analysis of drying time, Coefficient of Performance, and the economics of the process. Experimental tests illustrate the need to distribute air and heat evenly amongst the biomass for consistent drying. Furthermore, the rotation of biomass is critical in order to address the footprint of the system when placing next to an existing thermoelectric power plant. The final design provides a first step towards the refinement and development of a system capable of efficiently returning an amount of biomass large enough to replace non-renewable resources. Finally, an innovative methodology applied to the dryer is discussed that could recover water evaporated from the biomass and utilize it for agricultural purposes or within the power plant thermodynamic cycle.Copyright