The Membrane Engine: Concept, Model, and First Results

<div>This study investigates the feasibility of a novel internal combustion engine (ICE) architecture, termed the membrane engine, in which the conventional piston is replaced by a flexible elastic membrane. Although the concept appears in several patent documents proposing reduced friction, improved sealing, and lower heat losses, no empirical data has been published to support these claims. To the authors’ knowledge, this work presents the first membrane engine built and experimentally tested. The primary aim is to verify whether such an engine can operate as a functional ICE, regardless of its current efficiency or performance level.</div> <div>To support concept validation, a simplified mathematical model was developed to describe the membrane’s deformation and its effect on combustion chamber volume. Unlike conventional piston engines, the membrane introduces a pressure-dependent geometry, enabling a variable compression ratio. The model is not intended to predict performance but to assist in interpreting experimental results and assessing feasibility. It combines geometric and pressure-induced volume changes and was constructed conservatively to avoid overestimating deformation effects.</div> <div>A single-cylinder spark-ignition prototype was built by modifying an existing piston engine. Experimental tests were conducted under motored and fired conditions, with comparative measurements taken against the unmodified engine. Results confirmed that the membrane engine can sustain combustion and produce torque. Notably, the exhaust stroke exhibited a steeper pressure drop, suggesting improved scavenging, and the torque trace showed a distinct positive spike post-combustion. These findings support the hypothesis that the membrane’s dynamic behavior influences combustion and gas exchange.</div> <div>While some patent claims remain unverified, the study demonstrates that the membrane engine is a viable concept. The results provide a foundation for further development and refinement, including material selection and advanced modeling. Future work will focus on improving durability, expanding the operating envelope, and exploring hybrid configurations for waste heat recovery.</div>