Thermal Propulsion Systems Research, Department of Engineering Science, University of Oxford - Green Ammonia
Green Ammonia for Propulsion
Ammospray
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.
This project, AmmoSpray, aimed to supply data to enable the design of energy conversion systems specific to ammonia. AmmoSpray provided, for the first time, fundamental data on liquid ammonia sprays into nitrogen. This data obtained included spray break-up (how liquid ammonia breaks up and evaporates upon injection) and how ammonia and air mix under realistic conditions including spray particle size and spray penetration length. In addition, significant advances were made in safe handling and disposal of ammonia under laboratory conditions. A new spray rig was designed, built and commissioned, which can handle ammonia at up to 220 bar / 110C and background (nitrogen) conditions up to 15 bar.
The rig is modular enabling a wide variety of different ammonia injectors to be tested. The chamber has optical access along three axes, facilitated by five 80 mm viewable diameter fused silica (quartz) windows, two pairs on the side and one at the bottom. Spray images are recorded by a high speed camera at 10 000 FPS using shadowgraphy by back-illuminating the spray with a white (i.e., broadband) LED shining through a diffusing screen giving a uniform backlighting to the images. Spray particle size is measured using a Malvern Spraytec device, which uses the laser diffraction technique. It provides a spatial measurement on the bulk behaviour of the spray at a given time - all the droplets within the measurement region (defined as the intersection between the laser beam and the plume) at the time when the measurement was taken would contribute to the final droplet size distribution. It provides measurement of droplet size ranging from 0.1−900 μm, most often reported as the Sauter Mean Diameter (SMD).
Here are some example images we get out of our rig:
Some recent publications from the experimental part of this project are available here:
There are more publications to come!
This experimental approach is complemented with parallel modelling activity - using the experimental data to improve models. The data obtained have been used to code new models into commercial modelling software (computational fluid dynamics (CFD)) provided by project partner, Convergent Science. Its CONVERGE CFD software is used by companies globally. The focus has been on both evaporation and breakup models used with ammonia sprays.
Some recent publications from the modelling part of this project are available here:
There are more publications to come!