Skip to main content

Thermal Propulsion Systems Research, Department of Engineering Science, University of Oxford - Green Ammonia

Green Ammonia Propulsion


Ammonia (NH3) is a promising zero-carbon fuel for future transportation. Today transportation emits around 8.9 billion tonnes of CO2 annually. Whilst some sectors (e.g. cars) can be decarbonised using batteries, heavier transport (marine or freight) are less likely to use batteries due to their cost and energy density.

Ammonia is a hydrogen carrier, and (by volume) contains 50% more hydrogen than liquid hydrogen (which alone is extremely energy intensive to liquefy and store). Ammonia has among the highest energy densities of any non-hydrocarbon (traditionally fossil) fuel. Ammonia is particularly attractive because it can be made using the well-established Haber-Bosch process, which today is used to make 230 million tonnes of ammonia per year. Ammonia production can be 100% renewable when powered by solar and wind. This means that ammonia production can be scalable and can be undertaken repurposing a large amount of existing infrastructure.

A number of pilot projects are underway worldwide with Ammonia, including for energy storage, shipping and freight transportation. Many of these are in the UK, including at the Rutherford Appleton Laboratory, Cardiff University and the University of Nottingham. There is a significant lack of fundamental data to enable the design of energy conversion systems specific to ammonia.

This project, AmmoSpray, aims to fill this gap. AmmoSpray will provide, for the first time, fundamental data on ammonia sprays into air. Ammonia can be sprayed into air either as a liquid or as a gas, and both will be investigated in this project. The fundamental data obtained will include spray break-up (how liquid ammonia breaks up and evaporates upon injection) and how ammonia and air mix under realistic conditions.

These studies will be undertaken on three different pieces of test equipment:

1. An ambient conditions spray rig

2. A Cold Driven Shock Tube (CDST)

3. An optical access thermal propulsion system (TPS)

The spray rig is fast and cheap to run, and will enable the development of the experimental systems required for this project, the testing of large numbers of spray test conditions, and will be used to undertake a scoping exercise to identify project boundaries.

The CDST is a unique facility in the UK, able to replicate conditions found during combustion (150 bar pressure, 1500 K temperature) without turbulence, and with space for test equipment. This will enable for the first time imaging and break-up studies of ammonia sprays at conditions that will be seen in-use - key fundamental data.

The optical TPS tests are the logical next step, adding turbulence, and replicating as closely as possible 'real' conditions, whilst still allowing access for imaging and test equipment. The key tests here will be on mixing, using a laser-based technique (PLIF) to obtain ammonia:air ratio measurements throughout the combustion volume. This will link the sprays information developed earlier to their combustion characteristics. The tests on the optical access TPS will also enable studies of how these different spray and mixing methodologies influence emissions formation for ammonia combustion, with NH3 and NOx the key emissions which will be measured.

This step-by-step nature is perfectly suited for improving existing models. The data obtained will be coded into commercial modelling software (computational fluid dynamics (CFD)) provided by project partner, Convergent Science. Its CONVERGE CFD software is used by companies globally. The data obtained will be used to develop models for ammonia spray break-up, mixing, and emissions formation upon combustion. This will all happen in parallel with the experimental program and will ensure that the project's utility well beyond the project itself, with the models developed being available to be used by any of the global users of the software.