Analysis of air impact on aircraft engine lubrication system performance

Taras Mykhailenko, Oleksandr Goridko, Illia Petukhov

Abstract


A distinctive feature of an aircraft gas turbine engine (GTE) oil system is that an oil-air mixture, rather than pure oil, circulates through almost all of its components. The presence of air in the oil significantly influences the thermohydraulic processes in the oil system and leads to a deterioration of its performance. Dissolved and free air can substantially alter the physicochemical properties of the working medium. This is manifested in reduced heat transfer efficiency, changes in viscosity, deterioration of lubricating properties, and may also cause cavitation in pumps, unstable bearing operation, and even local thermal degradation of the oil. Thus, neglecting the gas content of the oil in oil system design may adversely affect its operability. The focus of this study is on the interactions between air and oil in an aircraft GTE oil system, as well as their influence on the system’s thermohydraulic characteristics, efficiency, and reliability. The goal of this article is to highlight the differences in thermohydraulic behaviour between two-phase and single-phase media and to emphasize the importance of considering these effects during oil system design. The objective of the work is to determine the nature and degree of the influence of air in the oil on the operation of the aircraft GTE oil system through analysis of thermohydraulic processes. The main results are as follows. The study examines the characteristics of thermohydraulic processes in the oil-air mixture within the oil system. It presents calculations of the effects of pressure and temperature on the solubility of air in oil. Using a homogeneous multiphase mechanics model, the impact of air content on the performance of the oil cooler was analyzed. The scientific novelty of the obtained results lies in establishing the quantitative influence of the flow gas content on the thermal and hydraulic processes in the oil system of an aircraft gas turbine engine. For the first time, it has been shown that when the gas content increases to a level of about 70%, the thermal capacity of the oil cooler decreases by approximately 20%, while hydraulic losses increase by more than two times. This leads to deterioration in oil cooling efficiency, as well as a reduction in the reliability and overall operability of the system. In conclusion, it can be stated that, to enhance the efficiency of the oil system, it is crucial to identify and account for the patterns of thermohydraulic processes, taking into consideration the peculiarities of two-phase oil-air flow during system design.

Keywords


oil system; gas turbine engine; two-phase flow; thermo-hydraulic processes; solubility; gas content

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DOI: https://doi.org/10.32620/aktt.2026.1.05