As a result of growing concerns about the carbon emissions associated with the combustion of conventional hydrocarbon fuels, hydrogen is gaining more attention as a clean alternative. The combustion of hydrogen in air produces no carbon emissions. However, hydrogen-air combustion does have the potential to produce oxides of nitrogen (NOx), which are harmful pollutants. The production of NOx can be significantly curbed using lean premixed combustion, wherein hydrogen and air are mixed at an equivalence ratio (the ratio of stoichiometric to actual air in the combustion process) significantly less than 1.0 prior to combustion. Hydrogen is a good candidate for use in lean premixed systems due to its very wide flammability range. The potential for the stable combustion of hydrogen at a wide range of equivalence ratios makes it particularly well-suited to application in gas turbines, where the equivalence ratio is likely to vary significantly over the operating range of the machine.
The strong lean combustion stability of hydrogen-air flames is due primarily to high reaction rates and the associated high turbulent burning velocities. While this is advantageous at low equivalence ratios, it presents a significant danger of flashback — the upstream propagation of the flame into the premixing device — at higher equivalence ratios. An investigation has been conducted into the operation of a specific hydrogen-air premixer design in a gas turbine engine. Laboratory tests were first conducted to determine the upper stability limits of a single premixer. Tests were then carried out in which eighteen premixers and a custom-fabricated combustor liner were installed in a modified Pratt and Whitney Canada PT6A-20 turboprop engine. The tests examined the premixer and engine operability as a result of the modifications. A computer cycle analysis model was created to help analyze and predict the behavior of the modified engine and premixers. The model, which uses scaled component maps to predict off-design engine performance, was integral in the analysis of premixer flashback which limited the operation of the modified engine. / Master of Science
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/43532 |
| Date | 24 July 2009 |
| Creators | Perry, Matthew Vincent |
| Contributors | Mechanical Engineering, O'Brien, Walter F. Jr., LePera, Stephen D., Vandsburger, Uri |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | Thesis_7_22.pdf |
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