Investigation into the Performance and Emissions of Ammonia / Hydrogen Blends in a Spark Ignition Engine and Demonstration of Improved Engine Thermal Efficiency using Oxidative Coupling of Methane Pretreatment
2022-09
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Investigation into the Performance and Emissions of Ammonia / Hydrogen Blends in a Spark Ignition Engine and Demonstration of Improved Engine Thermal Efficiency using Oxidative Coupling of Methane Pretreatment
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2022-09
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Reducing the impact of internal combustion engines on the global climate is a principal concern of the 21st century. Increasing thermal efficiency and reducing specific emissions are both ways to decrease greenhouse gas emissions from engines and therefore reduce their environmental impact. This thesis presents experimental and simulation studies of two promising concepts for reducing emissions and fuel consumption. The first study identified favorable operating regimes of a spark ignited (SI) engine using ammonia and hydrogen fuels. These fuels are rapidly gaining interest because they contain no carbon and therefore allow an engine to operate without producing any CO2, CO, or hydrocarbons (HC). Because these fuels are a new topic for IC engine research, and burn differently than typical HC fuels, an exploratory study must identify important engine performance trends. With these trends identified, favorable operating conditions may be selected to optimize the engine performance. The experiments show that high thermal efficiency (>40%) and low NOx (<100 ppm) is achievable using rich equivalence ratios. They also show that, unlike a traditional HC fuel, increasing the peak cylinder temperature decreases NOx emissions by facilitating the thermal deNOx mechanism. The fuel blends tested demonstrated a tendency to autoignite - characterized by a two-stage heat release, despite having a high ignition energy. Interestingly, auto-ignition did not lead to intense ringing as it would in a HC engine, which will be the topic of future research.
The second study explored how a pretreatment strategy for natural gas could be used to increase the efficiency of a heavy-duty engine. The pretreatment strategy would use an on-board reactor to convert natural gas, primarily CH4, into more reactive C2 species. This process would increase the reactivity of the natural gas fuel and enable natural gas engines to operate in premixed compression ignition (PCI) combustion modes. These combustion modes have a high thermal efficiency but are difficult to realize with natural gas due to its naturally high resistance to autoignition. The analysis done in this thesis will test this strategy by estimating the efficiency gain that could be realized using OCM fuel treatment. First, Cantera simulations found that an engine scale reactor could provide sufficient C2 conversion to enhance the natural gas reactivity significantly. GT-Power software simulated the performance of a natural gas SI engine and found that CI combustion modes were up to 7% more efficient than SI combustion, even when the reactor and required heaters are considered. The benefit is attributed to faster combustion associated with CI combustion, which is accessed more easily using OCM products than with pure natural gas. Future work on this subject will need to investigate alternative combustion control methods and improve reactor performance.
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University of Minnesota M.S. thesis. 2022. Major: Mechanical Engineering. Advisors: William Northrop, David Kittelson. 1 computer file (PDF); 97 pages.
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Swift, Evan. (2022). Investigation into the Performance and Emissions of Ammonia / Hydrogen Blends in a Spark Ignition Engine and Demonstration of Improved Engine Thermal Efficiency using Oxidative Coupling of Methane Pretreatment. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/250018.
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