In this paper we provide insight into the thermophysical properties and the dynamics of cryogenic jets. The motivation of the work is to optimise the use of cryogenic fluids in novel ultra low emission engines. For demonstration, we use conditions relevant to an internal combustion engine currently being developed by Dolphin N2 and the University of Brighton, the CryoPower recuperated split cycle engine (RSCE). The principle of this engine is a split-cycle combustion concept which can use cryogenic injection in the compression cylinder to achieve isothermal compression and thus help maximise the efficiency of the engine. Combined experimental and numerical findings are presented and the effects of atomisation dynamics of the LN ${}_2$ are explored at both sub- and supercritical conditions in order to cover different pressure and temperature conditions representative of the engine compression cycle. For subcritical regimes, we observe that the appearance of the jet coincides with the predicted atomisation regimes based on the Weber, Ohnesorge and Reynolds numbers for other common fluids. For the modelling of supercritical jets, a new methodology within OpenFoam which accounts for Real Fluid Thermodynamics has been developed and the jet behaviour under various pressure and temperature conditions has been investigated. To our knowledge this is the first study where a cryogenic spray process evolution is examined for conditions relevant to the ones prevailing in a compression chamber accounting for both sub and supercritical conditions.

Methane from livestock is a significant source of greenhouse gas emissions. Under the UN Framework Convention on Climate Change (UNFCCC), Annex I countries’ National Inventories report emissions from cattle as enteric or from manure management at ratios of between 3:1 and 9:1 depending on country and cattle type. Field research generally supports the inventories’ assumptions about enteric emissions, but these ratios have focused interest on enteric emissions and diverted attention away from those from manure management. Official calculations about manure management emissions factors are more varied than those for enteric emissions and evidence from field measurements suggests inventories may be underestimating manure management emissions especially in the dairy sector. This paper has three objectives. First, it reviews the science underpinning the international framework for estimating methane emissions from manure management. Second, it presents data from two dairy farms in south-west England where measured emissions of methane from slurry storage facilities are found to be four to five times greater than the assumptions in the UK’s inventory. If these measurements were representative of the UK, the implication is that total methane emissions from the UK dairy herd would be over 40% greater than the level reported to the UNFCCC and the proportion of total methane emissions from dairy cows arising from manure management would be almost a half rather than less than a quarter. Finally, the paper assesses the potential value if methane were captured from slurry storage facilities. Its value as a biogas is estimated to be £500 million per year for the UK dairy industry (at forecourt diesel prices). The paper concludes that the scale of emissions and the potential economic value of lost biogas are sufficient to warrant urgent research and action to reduce emissions from manure management with the beneficial prospect that a valuable new income stream for farm businesses could also be realised.

Decarbonising heavy-duty trucks is challenging due to high journey power and energy requirements. With a growing fleet of commercial vehicles in the UK, biomethane can provide significant reductions in greenhouse gas (GHG) emissions compared to fossil diesel. Methane is a potent GHG with a global warming potential (GWP) of 23–36, therefore reducing levels in the atmosphere can have a significant impact on climate change. There are a range of anthropogenic sources of methane that could be collected and processed to provide sustainable energy (upcycled), e.g., agricultural waste and the waste water system. This paper explores the impact of using upcycled methane in transport in South East England, evaluating local sources of anthropogenic methane and the environmental and economic impact of its use for a heavy-duty truck compared to fossil and battery electric alternatives. Analysis concludes that the use of upcycled methane in transport can provide significant reductions in lifecycle GHG emissions compared to diesel, fossil natural gas or battery electric trucks, and give net negative GHG emissions where avoided environmental methane emissions are considered. Furthermore, upcycling solutions can offer a lower cost route to GHG reduction compared to electrification.

This short piece is a response to the comment by Anthony and colleagues on our paper on methane emissions from manure management published in this journal in 2024. It explains the motive behind publishing our paper – that we judged there was insufficient attention being paid to manure management as a source of methane emissions compared to enteric emissions, and that our field measurements were suggesting levels of emissions significantly higher than what we would expect from the calculations in the National Inventory. Our response clarifies aspects of the methodology and presents further analysis of the claim that covering a slurry storage facility will increase emissions. We reiterate our conclusion that it would be valuable to develop a stronger understanding of the potential variability of methane emissions from manure management under different geographical and environmental conditions.