The internal combustion engine will remain dominant across high power marine, distributed power generation and off-road vehicles for several decades to come, requiring intensified fundamental research around greener fuels and clean, high efficiency operating modes. The UK has an internationally leading reputation for excellence in fundamental engine research for lighter duty cars, vans and trucks, with clear opportunities now apparent to transfer fundamental knowledge and skills to large engines. At present, the UK academic community is totally lacking large single cylinder engine facilities, with researchers restricted to automotive scale experiments and simulations extrapolated up to larger scale (with significant errors in fundamental predictions). This is a major omission in accelerating Net Zero fuels, disruptive large engine technologies and policies from within the UK. The vision is therefore to establish a world-leading, megawatt scale decarbonised engine experimental facility, with two unique research engines strategically co-located as a new collaborative centre of excellence and nationally accessible asset leveraging existing infrastructure and expertise.