Experimentally Studying a Single-Cylinder Pneumatic Piston Engine Operating in a Rotation Frequency Self-Stabilizing Mode

Abstract

Generation of electricity by standalone sources is one of leading-edge avenues in the development of modern power engineering. Good-looking prospects of developments in this field are stemming from the fact that the use of nothing else but centralized power grids and generating capacities in Russia becomes impossible under the conditions of market economy in the country. Wide use of stand-alone generation of electricity on the basis of well-known heat engines is held back by impossibility to ensure highly accurate stabilization of voltage frequency (at a 50 ±0.2 Hz level) unless expensive equipment is used. The article considers an approach to solving this problem by using a generating set equipped with an expansion piston (reciprocating) engine operating in the rotation frequency self-stabilization mode (RFSS). This phenomenon is studied by taking a pneumatic piston engine as an example. Air is considered as a modeling working fluid. Steam will be used as an actual working fluid in a real cogeneration plant. One of distinctive features pertinent to operation of a piston engine with RFSS is that the working fluid flowrate remains constant irrespective of the load power, which is a positive feature during its operation in a cogeneration mode. This feature eliminates the need to use an adjustable bypass line or a separate boiler and ensures normal operation of the heat supply system when the electrical load decreases. The main objective of the study is to compare the experimental data on the generating set operation with the theoretical data (the latter were obtained on a piston engine’s simplified dynamic model in transient modes). It has been shown that this model describes the real piston engine with accuracy sufficient for engineering purposes. Owing to this circumstance, taken in combination with simplicity of the dynamic model, it became possible to derive for the first time an engineering analytical formula for the overshoot of piston engines with RFSS at a step-wise variation of load. The study results opened the possibility to reliably determine how the rotation frequency of a piston engine with RFSS deviates in response to a step-like change of load. This quantity uniquely determines deviation of the frequency of voltage generated by the electrical generator driven by such engine. The authors have created prerequisites for determining the advisable application field of piston engines with RFSS in cogeneration power supply systems.