The Next Steps in Zero-Carbon Aviation Development

The electrification of commercial modes of transport on the road has been growing rapidly, and now the next natural step is to electrify air travel for the masses. Unfortunately, air travel is expected to increase its carbon emissions by 3-4 times by 2050 due to conventional propulsion systems. The United States is leading the charge in developing alternative fuel options to combat this problem.

The Advanced Research Projects Agency-Energy (ARPA-E) has two major programs working towards achieving zero-carbon aviation feasibility: Range Extenders for Electric Aviation with Low Carbon and High Efficiency (REEACH) and Aviation Class Synergistically Cooled Electric Motors with Integrated Drive (ASCEND). In this series of two articles, let's discuss both programs in more detail.

Both programs have already reached the second phase of testing in the industry and have contacted OEMs in the United States to integrate the models with aircraft. The target aircraft and market are single-aisle aircraft of the Boeing 737 class that operate on short to medium routes.

The estimated cost for REEACH is USD 42 million, and its goal is to improve energy storage efficiency and convert high-energy-density liquid fuel to power with an efficiency of over 70%. REEACH aims to use carbon-neutral renewable fuel sources with high energy density to meet energy requirements for long-range flights. In conjunction with energy conversion for cruising, high-efficiency energy stores will provide the peak power requirements for landing and takeoff.

The technologies of the program are broadly classified in two directions. The first one is a hybrid power plant that uses a solid oxide fuel cell with a gas turbine, which is the most popular in phase one as seven out of nine teams have decided to pursue this approach. The other approach is a heat recovery system from the exhaust gases of the gas turbine. However, one of the biggest challenges that the latter faces are weight consideration, which is naturally aimed to be low for air travel purposes.

Raytheon Technologies Research Center leads both of the projects under REEACH. The first one, ZAPTurbo, uses ammonia-powered turboelectric. It uses the thermal properties of anhydrous ammonia to cool the turbine and then cracks the ammonia molecules to release hydrogen, which is used to drive the turbine. The heat recovery system uses a compactly packed supercritical CO2 heat exchanger to recover waste heat in a hybrid electric propulsion architecture.

As we look towards the future of aviation, it is essential to prioritize the development of sustainable and efficient technologies. The REEACH and ASCEND programs offer exciting possibilities for zero-carbon aviation, and it's crucial that we support these initiatives to ensure their success. Whether you're an industry professional or an aviation enthusiast, we can all play a role in advancing this critical work. Let's stay informed, and engaged, and advocate for a cleaner, more sustainable future for air travel.