Abstract:

The continuous combustion multi-cylinder engine has promising application prospects in mini unmanned aerial vehicles and torpedoes because of its high thermal efficiency and power density, and low vibration and noise. The engine works with separate cylinders for the compression, combustion and expansion processes. The technologies of water induction, unequal bore size, recuperator and continuous external combustion are also adopted. It is considered to have high potential in heat-work conversion. However, the lack of research on its thermodynamic cycle means the lack of theoretical guidance for the design of the engine. The engine working stages can be equivalent to 5 processes: isothermal compression, constant volume combustion, isentropic expansion, exhaust heat release and recuperation. A new theoretical thermodynamic cycle is constructed and the equation of its indicated thermal efficiency is derived. It is found that: the indicated thermal efficiency is mainly determined by the working medium’s thermo-physical property, compression ratio, expansion ratio and recuperation ratio; with the increase of compression ratio and the reduction of expansion ratio, the indicated thermal efficiency is improved; especially, isothermal compression can enlarge the recuperative temperature difference which leads to a significant increase of indicated thermal efficiency; meanwhile, the temperature and pressure in the cylinder is not increased; this engine is proved to have higher thermal efficiency and operation reliability than traditional gasoline and diesel engines; the calculation results show that the indicated thermal efficiency of the engine can reach more than 65%.

Key words: continuous combustion multi-cylinder engine, theoretical thermodynamic cycle, indicated thermal efficiency, isothermal compression