A Comparative Life Cycle Assessment of Linear Free-Piston and Conventional Engines for Stationary and Automotive Applications

This study presents a Life Cycle Assessment (LCA) conducted to evaluate the environmental performance of a Free-Piston Linear Generator (FPLG) compared to conventional internal combustion engines in two applications: automotive range extenders and stationary generator sets. A cradle-to-grave approach was adopted, covering production, use, and end-of-life phases, with consistent modelling of engine materials, fuel supply chains (gasoline, diesel, hydrogen), and mission profiles. The FPLG, modelled based on key components (e.g., stator, magnets, coils), was evaluated under multiple hydrogen-production pathways, including steam methane reforming, wind- and photovoltaic-powered electrolysis, nuclear-based hydrogen production, and coal gasification. Conventional engine baselines were assessed using gasoline, diesel, and hydrogen pathways. Results highlight that environmental impacts are strongly driven by the fuel supply chain, particularly the Well-to-Tank phase. When hydrogen is produced through wind-powered electrolysis, the FPLG achieves over 90% reduction in fossil fuel consumption and more than 80% reduction in greenhouse gas emissions compared to gasoline. With hydrogen produced through steam methane reforming, benefits are limited in automotive applications but remain significant for stationary systems (>20% reduction in greenhouse gas emissions). However, hydrogen produced through wind-powered electrolysis increases impacts in categories such as resource use and toxicity due to materials and infrastructure required for wind farms and electrolyzers. The extended pathway analysis further showed that nuclear-based hydrogen achieved the lowest global warming potential among the investigated hydrogen scenarios, whereas coal gasification produced the highest climate-change impacts. These results confirm that the environmental performance of hydrogen-fuelled FPLG systems depends strongly on the upstream hydrogen-production pathway.