In the scenario dependence section of our methodology, we assume deployment with a gaseous precursor to sulfate aerosols — likely SO2. This uncertainty focuses on the feasibility of and timeline to research, develop, and build SO2 disbursement technology, including but not limited to nozzles and in-flight storage.
Metric
Time to design and verify the technology to quickly disperse the gaseous precursor (stored on board as a liquid), and ensure it is entrained into aircraft wake, is more than 5 years from first funding. Note: There has been no academic literature on this topic yet, so the below analysis is based on the Reflective team’s internal expertise along with conversations with external experts.
Uncertainty
While this uncertainty presents a unique engineering challenge, it is one that is technically feasible and therefore is likely to be solved with large enough funding.
Decision relevance
If the timeline were longer than that dictated in the metric, this would materially impact deployment timeline by ≤5 years, and therefore we classify the decision relevance as medium.
Further Information
SO2 would need to be liquified to reduce volume, either by cooling or pressurization; this is not likely to present any significant engineering hurdles. However, there are other questions about ensuring safety; for loading the tank or purging it, for crew safety in the event of a leak, etc. Given industry experience with ground handling of SO2, the only unique challenge here is managing the safety associated with the potential for leaks during flight. We assume that while this is a novel challenge, it is resolvable (not a challenge if there are no pilots; safety concerns for a piloted aircraft could be addressed through a pressurized bulkhead for example).
The largest engineering question here is how to design for the release of SO2 such that it is entrained into the aircraft’s wake as a gas while simultaneously not requiring the aircraft to remain at altitude for too long. There are two potential solutions to this, which are discussed below.
Atomization
The first option here is to release the SO2 as fine liquid particles in a process called atomization, which will subsequently evaporate in the aircraft’s wake. There has been limited research on this, but some analysis has argued that you would need to get the liquid particles to a size of a few 100s of μm for the second step to be successful (without the particles falling out of the wake). It is not quite clear what size is required, nor clear whether the SO2 can be easily atomized to the required size. Nonetheless, we expect these are solvable problems. There may also be a potential to use the heat from the engine exhaust to achieve the required particle size, but the feasibility of this has not been studied.
Venting as a gas
The second option is to vent the SO2 directly as a gas. While this is quite achievable in theory, the limitations here are ensuring that the SO2 does not partially form liquid droplets as it expands and cools, along with the time it takes to release the payload without requiring an excessively large valve. The more time spent at altitude, fuel burn increases, number of flights per plane decreases, and the overall efficiency of injection decreases. To achieve release times of under 20 minutes for a 75 ton payload, a 0.5 m in diameter valve would be required. While not technically infeasible, this is quite large and would present some engineering hurdles. This limitation might be less relevant when injecting at higher latitudes, where the altitude may be the limiting factor on the payload size rather than the release time.
References
0Have feedback on this entry?
Spot something off, missing, or worth adding? We’d love to hear from you.
Share feedback