Modeling and Evaluation of the Olshammar engine. A simulation based approach of a five-stroke turbocharged engine using Siemens Amesim.

Abstract

Internal combustion engines (ICEs) have been used since the 19th century and remain relevant as of 2025, although the field faces major challenges. The future of ICEs will heavily rely on new inventions and technological advancements. This thesis addresses one such invention: the Olshammar engine, a five-stroke engine concept featuring a lowpressure exhaust cylinder. The purpose of this study is to examine how the Olshammar engine performs in comparison to a conventional four-stroke engine. There are several software tools available for modeling and simulating ICEs, and in this study, Siemens Amesim was used. Initially, a two-cylinder petrol baseline engine was modeled and optimized, providing the reference for modeling the Olshammar engine. The results show that the Olshammar engine reduces brake-specific fuel consumption (BSFC) across the operating range of 2000–5000 rpm, with the largest improvement at 3000 rpm, where BSFC is reduced by approximately 4 %. This corresponds to a fuel conversion efficiency of ηf = 35.2% compared to ηf = 33.7% for the baseline engine. Furthermore, the simulations indicate that the improvement in BSFC can be attributed to the power contribution from the exhaust cylinder, resulting from the recovery of expansion work. Additional assessment of key parameters contributing to performance improvements suggests that tuning the exhaust cylinder offset relative to the combustion cylinders, as well as adjusting the bore-to-stroke ratio, can further enhance overall performance. Siemens Amesim proved to be a well-suited tool for ICE modeling, to the extent that it could replace GTPower in the ICE course at Chalmers in the future. Finally, the findings of this study demonstrate how the design and optimization of the Olshammar engine contribute to improved fuel efficiency compared to conventional four-stroke designs.