Thermoacoustic engines rely on the complex interactions between thermodynamics and acoustics to convert heat of a certain grade into acoustic power, which is one form of mechanical work. As thermoacoustic heat engines are external heat engines, one of their main advantages is their ability to use different sources of input heat, including solar or waste heat energies. However, because of their nature of operation, these engines do not operate unless the temperature gradient along the stack exceeds a certain limit, which may exclude many heat sources. In this work, a simple method is suggested to decrease the onset temperature of an existing standing-wave thermoacoustic engine to allow usage of lower-temperature heat sources if necessary. The method relies on moving the relative position of the stack towards regions of lower dynamic pressures and higher gas parcel velocities. Results show that a stack relative movement of 3.2% of the engine length causes the onset temperature to decrease by 3.4%. The work present the transient and steady-state characteristics of the cases considered in the temperature and dynamic pressure. The benefits and limitations of this method are presented and discussed in terms of its effects on the onset temperature, dynamic pressure amplitude, gas temperature at the hot and cold sides of the stack, interaction between the dynamic pressure amplitude and the heat transfer to/from the stack, harmonic excitation, generated acoustic power contained in the fundamental mode, as well as the operating frequency.
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