Browsing by Author "Sharvelle, Sybil E., committee member"

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Open Access
Development of portable recycled vertical flow constructed wetlands for the sustainable treatment of domestic greywater and dairy wastewater
(Colorado State University. Libraries, 2011) Roberts, Bronte Marie, author; Goodridge, Lawrence D., advisor; Engle, Terry E., committee member; Sharvelle, Sybil E., committee member; Wickramasinghe, Sumith Ranil, committee member
To view the abstract, please see the full text of the document.
Open Access
Experimental & analytical evaluation of knock characteristics of producer gas
(Colorado State University. Libraries, 2010) Arunachalam, Aparna, author; Olsen, Daniel B., advisor; Marchese, Anthony, committee member; Sharvelle, Sybil E., committee member
Amongst the popular gaseous bio-fuels is producer gas. Evaluation of knock properties of producer gas enhances efficient utilization of this renewable energy resource in an internal combustion engine. A literature review revealed that producer gas is formed from a set of combustion-reduction reactions in a gasifier and is typically composed of 18-20% H2, 18-20%CO, 2-3% CH4, 12% CO2 and 48-50%N2. It is seen that a production process where the combustion and reduction reactions are effectively separated yields a gas rich in hydrogen. Hence based on the production method and range in gas composition five different producer gas compositions are chosen for knock evaluation. Knock evaluation for gaseous fuels has been done by previous researchers using the Methane Number method. This method requires the use of a Cooperative Fuel Research (CFR) F2 engine installed in Colorado State University’s Engines and Energy Conversion Laboratory. It was seen that the methane number of producer gas ranged from 54-131. Further it was quantitatively evaluated that addition of CO2 increases the critical compression ratio while H2 decreases it. Overall, the effect of CO2 on changing the critical compression ratio was found to be over twice that of H2. It was attempted to evaluate the methane number of producer gas using chemical kinetics software CHEMKIN. A Methane Number evaluation process was developed using CHEMKIN’s internal combustion engine model. There were significant differences between model and experiment. Recommendations for future work are discussed.
Open Access
Landfill gas analysis to support an assessment of organic waste stability
(Colorado State University. Libraries, 2016) Mantell, Steven C., author; Bareither, Christopher A., advisor; von Fischer, Joe C., committee member; Sharvelle, Sybil E., committee member
Organic stability is defined as the state of near complete decomposition of organic waste constituents such that human health, environmental, and financial risks associated with undecomposed waste are reduced. An assessment of organic stability was completed based on comparison between collected and predicted landfill gas. There were two main objectives of the study: (i) assess landfill organic stability for an entire site and specific landfill phases to evaluate how operational practices influence organic stability and (ii) develop recommendations for conducting organic stability assessments based on gas collection and modeling. Landfill gas generation is frequently assessed on a site-wide basis; however, the process of waste disposal and subsequent gas generation varies temporally and spatially within a landfill. In this study, landfill gas modeling was conducted on a site-wide and phase-specific basis (i.e., multiple phases constitute the entire landfill site) for a non-hazardous solid waste landfill in the U.S. The U.S. EPA's LandGEM model for methane generation was used for the gas model simulations. LandGEM calculates the rate of methane generation based on the mass of solid waste, methane generation potential of the waste, and first-order rate coefficient (k). Models were completed that considered the following factors: (i) constant methane generation potential; (ii) methane flow rates representative of monthly and annual averages; (iii) collection efficiency of the landfill gas collection system; and (iv) optimization of k to reduce the sum of squared residuals between measured and predicted methane flow rates. Collection efficiency of the landfill gas collection system was accounted for in the models via assuming a constant collection efficiency of 85% and assuming a temporally varying collection efficiency. The temporally varying collection efficiency was used to represent temporal installation of a gas collection system and placement of interim and final cover. Site-wide decay rates varied from 0.068 to 0.070 1/yr while phase-specific rates varied from 0.021 to 0.12 1/yr. Observations reinforce previous studies showing that moisture enhancement has potential to create favorable landfill conditions that may lead to higher rates of methane generation and shorter durations to achieve organic stability.
Open Access
Policies versus perception: estimating the impact of drought awareness on residential water demand
(Colorado State University. Libraries, 2011) Stone, Janine, author; Goemans, Christopher G., advisor; Constanigro, Marco, committee member; Sharvelle, Sybil E., committee member
In response to the water shortages of 2002, Colorado utilities adopted numerous policies promoting water conservation. However, despite this demand-management emphasis, utilities are still distinguishing between the impacts of conservation programs and the psychological impacts of the drought itself. That is, water managers are unsure if post-drought decreases in water consumption are solely due to utility-controlled policies or if they result from a combination of drought awareness and/or permanent changes in water-use behaviors. For this reason, gauging the effectiveness of conservation policies requires answering the following: First, did awareness of the drought lead consumers to conserve more water than predicted, given utility policies alone? Next, if drought awareness did influence demand, is continued awareness--as opposed to utility policies or permanent changes in water use--the reason water demand has failed to return to pre-drought levels? To answer these questions, this research estimates an econometric water demand model using billing data from a major Colorado utility. Results show that drought awareness did decrease water demand both during and after the height of the drought; however, baseline demand still appears to be trending downward even after we control for both drought awareness and utility policies.
Open Access
Waste heat recovery from a high temperature diesel engine
(Colorado State University. Libraries, 2017) Adler, Jonas E., author; Bandhauer, Todd M., advisor; Olsen, Daniel B., committee member; Sharvelle, Sybil E., committee member
Government-mandated improvements in fuel economy and emissions from internal combustion engines (ICEs) are driving innovation in engine efficiency. Though incremental efficiency gains have been achieved, most combustion engines are still only 30-40% efficient at best, with most of the remaining fuel energy being rejected to the environment as waste heat through engine coolant and exhaust gases. Attempts have been made to harness this waste heat and use it to drive a Rankine cycle and produce additional work to improve efficiency. Research on waste heat recovery (WHR) demonstrates that it is possible to improve overall efficiency by converting wasted heat into usable work, but relative gains in overall efficiency are typically minimal (~5-8%) and often do not justify the cost and space requirements of a WHR system. The primary limitation of the current state-of-the-art in WHR is the low temperature of the engine coolant (~90°C), which minimizes the WHR from a heat source that represents between 20% and 30% of the fuel energy. The current research proposes increasing the engine coolant temperature to improve the utilization of coolant waste heat as one possible path to achieving greater WHR system effectiveness. An experiment was performed to evaluate the effects of running a diesel engine at elevated coolant temperatures and to estimate the efficiency benefits. An energy balance was performed on a modified 3-cylinder diesel engine at six different coolant temperatures (90°C, 100°C, 125°C, 150°C, 175°C, and 200°C) to determine the change in quantity and quality of waste heat as the coolant temperature increased. The waste heat was measured using the flow rates and temperature differences of the coolant, engine oil, and exhaust flow streams into and out of the engine. Custom cooling and engine oil systems were fabricated to provide adequate adjustment to achieve target coolant and oil temperatures and large enough temperature differences across the engine to reduce uncertainty. Changes to exhaust emissions were recorded using a 5-gas analyzer. The engine condition was also monitored throughout the tests by engine compression testing, oil analysis, and a complete teardown and inspection after testing was completed. The integrity of the head gasket seal proved to be a significant problem and leakage of engine coolant into the combustion chamber was detected when testing ended. The post-test teardown revealed problems with oil breakdown at locations where temperatures were highest, with accompanying component wear. The results from the experiment were then used as inputs for a WHR system model using ethanol as the working fluid, which provided estimates of system output and improvement in efficiency. Thermodynamic models were created for eight different WHR systems with coolant temperatures of 90°C, 150°C, 175°C, and 200°C and condenser temperatures of 60°C and 90°C at a single operating point of 3100 rpm and 24 N-m of torque. The models estimated that WHR output for both condenser temperatures would increase by over 100% when the coolant temperature was increased from 90°C to 200°C. This increased WHR output translated to relative efficiency gains as high as 31.0% for the 60°C condenser temperature and 24.2% for the 90°C condenser temperature over the baseline engine efficiency at 90°C. Individual heat exchanger models were created to estimate the footprint for a WHR system for each of the eight systems. When the coolant temperature increased from 90°C to 200°C, the total heat exchanger volume increased from 16.6 × 103 cm3 to 17.1 × 103 cm3 with a 60°C condenser temperature, but decreased from 15.1 × 103 cm3 to 14.2 × 103 cm3 with a 90°C condenser temperature. For all cases, increasing the coolant temperature resulted in an improvement in the efficiency gain for each cubic meter of heat exchanger volume required. Additionally, the engine oil coolers represented a significant portion of the required heat exchanger volume due to abnormally low engine oil temperatures during the experiment (~80°C). Future studies should focus on allowing the engine oil to reach higher operating temperatures which would decrease the heat rejected to the engine oil and reduce the heat duty for the oil coolers resulting in reduced oil cooler volume.