Enabling high overall pressure ratios, wave rotors and piston concepts seem to be solutions surpassing gas turbine efficiency. Therefore, a comparison of a wave rotor and three piston concepts relative to a reference gas turbine is offered. The piston concepts include a Wankel, a 2-stroke reciprocating engine and a free-piston. All concepts are investigated with and without intercooling. An additional combustion chamber downstream the piston engine is investigated, too. The shaft power chosen corresponds to large civil turbofans. Relative to the reference gas turbine a maximum efficiency increase of 11.2 percent for the piston concepts and 9.8 percent for the intercooled wave rotor is demonstrated. These improvements are contrasted by a 5.8 percent increase in the intercooled reference gas turbine and a 4.2 percent increase due to improved gas turbine component efficiencies. Intercooling the higher component efficiency gas turbine leads to a 9.8 percent efficiency increase. Furthermore, the study demonstrates the high difference between intercooler and piston engine weight and a conflict between piston concept efficiency and chamber volume, highlighting the need for extreme lightweight design in any piston engine solution. Improving piston engine technology parameters is demonstrated to lead to higher efficiency, but not to a chamber volume reduction. Heat loss in the piston engines is identified as the major efficiency limiter.

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