Ammonia-Powered Aviation Engine AmmoniaJet Deep Dive: Zero-Carbon Flight Alternative Route Catching Up with Hydrogen

In the race toward zero-carbon aviation, hydrogen fuel and sustainable aviation fuel (SAF) command the lion's share of attention. But ammonia, a chemical commodity with global annual production exceeding 180 million tons, is quietly emerging as a third technical route. The AmmoniaJet engine, jointly developed by Rolls-Royce and Germany's MAN Energy Solutions, completed its first prototype ground test stand run on July 16 at Rolls-Royce's Derby testing center.

Ammonia as fuel offers several notable advantages: its volumetric energy density is 1.5 times that of liquid hydrogen, it requires no cryogenic storage, and mature production, transport, and storage infrastructure already exists globally. More importantly, green ammonia synthesized from renewable-energy-produced hydrogen and atmospheric nitrogen has near-zero lifecycle carbon emissions.

However, ammonia's combustion characteristics fall far short of conventional jet fuel or hydrogen. Ammonia burns slowly, has a high ignition temperature, and poor flame stability. AmmoniaJet chief engineer Helen Roberts stated: "Driving a turbofan engine directly with pure ammonia is nearly impossible. Our solution catalytically cracks ammonia into a hydrogen and nitrogen mixture before it enters the combustion chamber, using the resulting hydrogen to assist ammonia combustion."

AmmoniaJet uses a dual-stage architecture called pre-crack assisted combustion. The first stage is a compact catalytic cracking reactor decomposing approximately 30 percent of ammonia into hydrogen and nitrogen at 600 degrees Celsius. The second stage is a modified annular combustion chamber where hydrogen serves as pilot fuel to stabilize ammonia combustion.

Ground test data showed AmmoniaJet achieved a specific fuel consumption of 0.42 kg per kN-minute at maximum thrust of 35 kN, about 15 percent higher than conventional turbofan engines. Compared to hydrogen fuel solutions, AmmoniaJet's advantage lies in not requiring fundamental modifications to aircraft fuel systems. Liquid hydrogen requires bulky cryogenic tanks, while ammonia can be stored as a liquid at approximately 10 atmospheres at ambient temperature, with tank volume only one-third that of liquid hydrogen.

The biggest safety concern is ammonia's toxicity. Ammonia gas leaks can irritate eyes and respiratory tracts even at low concentrations. AmmoniaJet's fuel system features triple seals and real-time ammonia concentration monitoring with leak detection response time under 50 milliseconds.

Rolls-Royce plans to complete first flight testing by 2031 and obtain airworthiness certification by 2033. Initial target aircraft are regional jets with ranges under 2,000 kilometers. Twelve airlines worldwide have expressed interest, including easyJet and AirAsia.