Development of Heat Engines Powered by Twisted and Coiled Polymer Fiber Actuators

ABSTRACT Engines powered by artificial muscles have great potential for environmental energy harvesting. Here we show for the first time an engine generating continuous rotary motion powered by twisted and coiled polymer (TCP) fiber actuators. When stimulated by a temperature gradient of only 60°C the engine generated a maximum speed of 27 revolutions per minute; a stall torque of 74 Nmm; and a peak power of 42 mW or 9 W/kg based on the mass of TCP. One TCP heat engine ran for more than 16 000 cycles, which was more than 13 times longer than a comparable shape memory alloy (SMA) engine. Optimizing the energy output and efficiency required tuning the engine design to the tensile characteristics of the actuators. Two simple analytical models are introduced to predict the stall torque of four different engines verified in experiments using the same SMA actuator. The stall torque can predict the engine's full performance envelope described by its torque‐speed and power‐speed curves. The developed models were used to design the TCP engine and improve performance. The models can also be used as a general design guide for all types of rotating engine driven by any type of tensile actuator.