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Access Type
WSU Access
Date of Award
January 2025
Degree Type
Dissertation
Degree Name
Ph.D.
Department
Mechanical Engineering
First Advisor
Omid Samimi-Abianeh
Abstract
As the global energy landscape transitions towards sustainable alternatives, ammonia and dimethyl ether (NH3/DME) mixtures have emerged as promising, low-carbon surrogate fuels with an existing production infrastructure and the potential for net-zero carbon emissions. However, the combustion behavior of surrogate mixtures at conditions representative of advanced engines and gas combustors remains insufficiently understood. This dissertation addresses this gap by investigating both autoignition and flame propagation in NH3/DME mixtures and by benchmarking its combustion properties against conventional jet fuels (e.g., JP-8 and JP-5) to evaluate their suitability as sustainable aviation fuels.The initial research focuses on investigating autoignition behavior using a rapid compression machine (RCM). Ignition delay times were measured at end-of-compression pressures of 5, 10, and 20 bar, with gas temperatures of 621–725 K, for stoichiometric NH3/DME mixtures with 10% to 50% DME by mole. Results indicated that increasing the DME fraction from 10% to 50% reduced ignition delays by up to 65% across all pressures, underscoring DME’s significant role as an ignition promoter. These experiments provided high-fidelity ignition data at elevated thermodynamics conditions, with the 30% DME mixture’s ignition delay closely matching that of conventional jet fuels under comparable conditions. Subsequently, the research examines laminar flame speeds using a novel RCM–Flame configuration, enabling the study of two distinct regimes: autoignition-assisted flame propagation (affected by pre-flame autoignition chemistry) and conventional laminar flame propagation (unaffected by pre-flame autoignition chemistry). Validation experiments with methane (3.04 bar, 740–765 K) and n-heptane (6.85 bar, 595–621 K) confirmed the reliability and reproducibility of this novel experimental approach. These tests showed that the effects related to chamber size, temperature inhomogeneity, data analysis methodology, and flame stretch on flame dynamics are negligible, ensuring high measurement fidelity. Considering uncertainties, measurement accuracies are within 7.5% of the established literature values, confirming the technique’s robustness and reliability. Comparison with one-dimensional and three-dimensional simulations further validated the technique’s capabilities and revealed limitations in current kinetic mechanisms under autoignition conditions. Building on these validation findings, experiments with stoichiometric NH3/DME mixtures at pressures of 5, 10, and 15 bar and gas temperatures of 540–710 K identified distinct pressure-, temperature-, and density-dependent characteristics and elucidated the effect of first-stage ignition delay on flame propagation. A numerical comparison offered further insight into how effectively existing kinetic models represent the underlying chemistry and flame dynamics of NH3/DME surrogates. The results indicate that 50% DME in an NH3/DME mixture can successfully mimic the combustion characteristics of conventional jet fuel characteristics under analogous conditions. Furthermore, the results show that post-first-stage ignition flame speeds were more sensitive to temperature variations than to changes in pressure and/or unburned gas density. Finally, these findings provide a foundational dataset and deeper understanding of NH3/DME combustion, offering the potential for guiding future fuel formulations, optimizing combustion system design, and improving kinetic mechanism development for cleaner, more efficient propulsion and power generation applications.
Recommended Citation
Goyal, Tushar, "Autoignition-Assisted Flame Regimes In Ammonia And Dimethyl Ether Blends: A Sustainable Aviation Fuel" (2025). Wayne State University Dissertations. 4254.
https://digitalcommons.wayne.edu/oa_dissertations/4254