Development of a compact simple unpressurized Watt‐level low‐temperature‐differential Stirling engine

Despite the fast advance of modern technology, poverty is still a serious problem in many developing countries; and more than 1 billion people are having no access to electricity. For these people, even a few Watts of electricity supply for lighting can make a big difference. In this study, a simple, compact, unpressurized, Watt-level low-temperature-differential Stirling engine has been developed aiming to solve the lighting problem in developing countries. The engine in this study is compact. Yet, it is capable of delivering useful electrical power. It is a γ-type Stirling engine with twin power pistons. The diameter of the displacer cylinder is 220 mm, comparable to the size of a cooking pot, and the weight of the engine is under 5 kg. Two energy-conservation/heat-transfer enhancement measures have been incorporated into the engine's design: one is adopting a displacer/regenerator unit, and the other is machining engine-turn slotted grooves on its hot- and cold-end plates. CFD analysis showed that the combination of both measures could effectively improve the performance of the engine. Experiments were conducted to examine the engine's performance. In one experiment, the engine produced 3.7 W of electric power as temperature difference was 100°C, and its power was found to be almost linearly proportional to temperature difference. With a higher temperature difference of 140°C, the electric power reached 5.3 W. Another experiment that operated the engine for a prolonged period has proven the reliability of the engine's performance for long-time use. In practice, the engine can be operated by putting it on a stove table, and the residual heat from cooking is good enough to power the engine to produce usable electricity. Or it can be directly put on a wood fire to generate even higher electrical power.