Generalized comparative analysis of crosshead-free and crosshead schemes of piston hybrid power machines

A generalized analysis of crosshead and crosshead-free piston hybrid power machine (PHPM) is conducted in this research. A comparison of these machines was carried out experimentally by using two created experimental samples for comparison with practically the same working volumes of the compressor and pump sections, crosshead, and crosshead-free piston hybrid power machines. The comparison was performed within the framework of the following units: thermodynamic unit, dynamic unit, comparison unit for weight and size indicators, comparison unit for reliability and durability, comparison unit for the manufacturing technology, and the provision of gaps in the cylinder-piston group. Results of the experimental data were compared in the thermodynamic comparison unit in terms of cooling the compressor section, flow coefficient and its components, volumetric efficiency of the pump section, and cavitation margin. Comparison results show that the temperature of the cylinder-piston group and, in particular, the temperature of the valve body and of the suction gas of the crosshead-free PHPM is lower than those of the crosshead PHPM; the indicator isothermal efficiency of the crosshead-free PHPM is higher than that of the crosshead PHPM; and the volumetric efficiency for a cross-head-free PHPM is 5 %–10 % higher than that for a crosshead PHPM. The comparison of the acting forces and torques of the crosshead and crosshead-free PHPM established that the crosshead PHPM has better dynamic characteristics in terms of maximum effective force and torque unevenness. Moreover, the PHPM crosshead-free scheme has better overall characteristics.