https://www.sciencedirect.com/science/article/pii/S1876610219308677?ref=pdf_download&fr=RR-2&rr=71f72788ee480c71 https://www.sciencedirect.com/science/article/p

https://www.sciencedirect.com/science/article/pii/S1876610219308677?ref=pdf_download&fr=RR-2&rr=71f72788ee480c71 https://www.sciencedirect.com/science/article/pii/S187661021... This is a nice paper on the different fuel cycles of hydrogen ammonia and methyl. Roundtrip efficiencies for hydrogen and ammonia are both at about 30% plus. Don't know how high it could theoretically go.