Research Plan: a Carbon-free Future with Ammonia-Hydrogen Combustion
University of Southern California
Benjamin Cohen, Zhenghong Zhou & Professor Paul David Ronney
With the urgency to reduce our carbon footprint, eco-friendly energy alternatives are taking the front seat. Ammonia sourced through eco-conscious methodologies, priced around $45/GJ [1], emerges as a green alternative fuel. However, the combustion of pure ammonia doesn't consistently meet the requirements of the maritime and aviation sectors. Hybrid engines leveraging diesel and NH3 are now on the rise. Ammonia stored can undergo auto-thermal reforming for enhanced efficiency, producing NH3-H2 mixtures for combustion. Investigating the viability of these mixtures can revolutionize our energy systems, steering towards sustainability.
Historically, combustion studies have been centered on open environments. But practical applications, like in engines, necessitate confined combustion. This research is anchored in Fernández-Galisteo et al.'s (2018) [2] findings, seeking to delve deeper into NH3-H2 combustion within enclosures. The Hele-Shaw apparatus stands out as the preferred tool to observe flame behavior under confinement.
Figure 1: Hele-Shaw Apparatus
Constructed with two polycarbonate plates, this apparatus creates a thin space, adjustable between 3mm to 15mm. The Nova FASTCAM Phantom camera makes invisible-to-eye ammonia-hydrogen flames detectable in the near-infrared spectrum. The depicted flame from this apparatus represents data from an H2-N2-O2 flame with an adiabatic temperature of 1200K at an equivalence ratio of 0.7. The unique flame texture results from differential diffusion rates of heat and reactants.
Research Goals
Precision Data Acquisition - Ensuring consistency in adiabatic flame temperatures is crucial, given its significant influence on chemical kinetics. By integrating a series of solenoid valves with sophisticated pressure settings and leveraging periodic vacuum chamber operations, I aim to achieve the desired consistency in the adiabatic flame temperature. This meticulous approach would generate over five thousand videos, leading to around ten terabytes of data.
Developing a Public Database - Given the extensive data, I am working on creating a streamlined video database designed for efficient data retrieval and parallel video analysis. Integration with Cantera is in progress, facilitating rapid access for researchers to extinction thresholds during the initial stages of internal combustion engine development. Check back here for the database link once it's live.
Incorporating a Multi-Layer Perceptron (MLP) - The prowess of neural networks in image recognition tasks is well-established. My vision is to employ these techniques to classify distinct flame morphologies. This system would offer researchers a platform to introduce their data, enabling the MLP to systematically index, fetch, or assimilate it into the primary database.
Throughout my tenure at USC's Combustion Physics Laboratory, my collaboration with Ph.D. candidate Zhenghong Zhou has pivoted to investigating the instabilities of dilute H2 flames. The prevalent computational models, albeit robust, often fall short in predictive accuracy, rendering our experimental data-driven approach indispensable. I am set on broadening this scope to encompass diluted NH3-H2 mixtures.
The adoption of green ammonia and the influx of diesel-ammonia hybrids in the shipping sector underscores the profound potential of this research. It promises not only eco-conscious transport solutions but also positions ammonia-hydrogen mixtures as pivotal players in the quest for greener, large-scale power generation
[1] IRENA and AEA (2022). Innovation Outlook: Renewable Ammonia. International Renewable Energy Agency, Abu Dhabi, Ammonia Energy Association, Brooklyn.
[2] Fernández-Galisteo, D., et al. (2018). Analysis of premixed flame propagation between two closely spaced parallel plates. Combustion and Flame, 190, 133-145.
Hele-Shaw Flame Visualizations
All videos are presented in real-time, showcasing the combustion of clean fuel. The mixtures depicted below consist of hydrogen flames diluted with nitrogen.
Above, we observe a lean flame with an equivalence ratio of 0.884. This indicates that, at the conclusion of the reaction, there will be residual unburned oxygen, even as all the fuel is consumed. Additionally, this flame propagates downward, requiring it to counteract buoyancy forces due to gravity. Unequal rates of heat diffusion and product diffusion also play a role, leading to the transitions seen in the visualization.
In the video above, we observe a fuel-lean flame once again. However, this time, it is burning in a horizontal direction, meaning it isn't hindered by buoyancy forces resulting from density changes and gravity. As a result, we notice a much faster flame speed compared to the previous video.