Intellectual Merit: Combustible fuel-air mixtures can be ignited, intentionally or not, by a transient jet, a puff, of hot reactive gas from an adjacent combustion event. This re-ignition phenomenon differs greatly from common electric spark or compression ignition events. Whether or not, and how quickly, re-ignition occurs depends on a complex interaction of physical and chemical processes occurring at different rates: puff vortex spinning, mixing and fuel molecule oxidation. Preliminary experiments show good agreement with gas motion predictions, but also indicate that re-ignition delay time depends on the fuel-air ratio in a way that is as yet unexplained. This project will use computational, experimental, and analytical approaches to investigate re-ignition by transient jets that mix residual or re-injected combustion gases and fresh mixtures, establish the re-ignition delay time for common gaseous fuels, and determine their sensitivities to key parameters. Computational models will be used to predict puff vortex dynamics and reacting mixture temperature in stationary and traversing jets. Experiments will verify vortex dynamics and measure re-ignition delay times for traversing and stationary jets through the use of pressure sensors, visualization, and optical diagnostics. A simplified mathematical model will then be developed to carefully disentangle the gas mixing and chemical processes, and more accurately predict re-ignition. Fuel oxidation theory validated in other types of combustion will be tested for applicability to jet re-ignition. Scientists at a company partnering in this project will not only guide the project itself, but also mentor a doctoral candidate in applying the research findings at the company.
Broad Impacts: This project will enable jet-ignited combustion approaches aimed at dramatic reductions in fuel consumption and greenhouse gas emissions in a wide range of power plants. The success of this project has the potential to transform many of the ways in which fuel has been consumed since the Industrial Revolution. It leads directly to novel combustion methods that create a pressure boost in aircraft and electric power generation engines. By retrofitting or redesigning power generation gas turbines and aircraft jet engines with pressure-boost combustors, the United States can save an estimated $10 billion dollars in fuel and 100 megatons of CO2 emissions each year. The project will help develop pressure-boost combustion technology using a device called a wave rotor combustor. This disruptive technology can also enable innovative medium- and small-scale power generators as well as more efficient hybrid vehicles and portable power units. Additionally, the project enables more reliable ignition in trucks and locomotives using internal combustion engines, allowing the substitution of less expensive, domestic gas fuels for diesel refined from imported petroleum. Transient jets from small pre-chambers can accomplish consistent ignition of natural gas while reducing nitrogen oxide emissions and avoiding diesel smoke. The results of this research will be immediately utilized in concurrent but separate wave rotor combustor experiments, with simplified models being incorporated into design codes usable by industry. The doctoral candidate will assist the industry partner in the development of a wave rotor combustor prototype, the initial goal of which is reducing fuel consumption, carbon emissions, and the weight of gas turbines by about 20% each.
