The Achates Power engine, originally developed during World War II, has made a remarkable comeback in the 21st century with a modern twist. This engine features a unique design with two pistons in one cylinder that compress fuel and air, resulting in lower fuel consumption and increased thermal efficiency. What sets this engine apart is its use of synthetic diesel, a cleaner and more efficient fuel derived from renewable resources. The engine's reliance on synthetic diesel marks a significant step towards reducing greenhouse gas emissions, offering a more sustainable energy solution for various applications beyond transportation. Despite current challenges in the production of synthetic diesel, advancements in renewable energy sources are expected to drive down costs, making it a more viable option for the future. Achates Power's engine has been modified to run on hydrogen, showcasing its adaptability and potential to further reduce emissions and transform the automotive industry. While the engine's journey from the past to the present has been met with challenges, its innovative design and sustainable fuel options position it as a key player in shaping a greener future.