Development of a method to improve the calculation accuracy of specific fuel consumption for performance modeling of air-breathing engines

Abstract

Determination of specific fuel consumption of air-breathing engines is one of the problems of modeling their performance. As a rule, the estimation error of the specific fuel consumption while calculating air-breathing engine performance is greater than that of thrust. In this work, this is substantiated by the estimation error of the fuel-air ratio, which weakly affects thrust but significantly affects the specific fuel consumption. The presence of a significant error in the fuel-air ratio is explained by the use of simplified methods, which use the dependence of enthalpy as a function of mixture temperature and composition without taking into account the effect of pressure. The developed method to improve the calculation accuracy of specific fuel consumption of air-breathing engines is based on the correction of the fuel-air ratio in the combustor, determined by the existing mathematical models. The correction of the fuel-air ratio is made using the dependences of enthalpy on mixture temperature, pressure and composition. The enthalpy of the mixture is calculated through the average isobaric heat capacity obtained by integrating the isobaric heat capacity, depending on mixture temperature, pressure and composition. The calculation accuracy of the fuel-air ratio was verified by comparing it with the known experimental data on the combustion chamber of the General Electric CF6-80A engine (USA). The average calculation error of the fuel-air ratio does not exceed 3 %. The developed method was applied for correcting the specific fuel consumption for calculating the altitude-airspeed performance of the D436-148B turbofan engine (Ukraine), which made it possible to reduce the estimation error of the fuel-air ratio and specific fuel consumption to an average of 3 %

Working process model development of the gas turbine engine combustor fueling on methanol

“…In [11], a mathematical model for the combustor fueling on aviation kerosene was developed based on the second approach. However, the system of chemical thermodynamics equations for kerosene and methanol differs.…”

“…However, the system of chemical thermodynamics equations for kerosene and methanol differs. Additionally, the work [11] lacks justification for the necessity of considering the equivalent chemical reaction path for non-standard temperature and pressure. Therefore, it is necessary to develop a mathematical model for the working process of a GTE combustor fueling on methanol, taking into account pressure, thermal dissociation of combustion products, and a correctly formulated equivalent chemical reaction path of the combustion process.…”

“…From the law of conservation of energy in [11], the equation for the fuel air ratio q f was obtained:…”

“…where G f and G air , kg/s -fuel consumption and air mass flow rate; H u , kJ/kg -the specific lower calorific value of the fuel, given its known composition, is determined, for example, by Mendeleev's formula; η g -the fuel combustion efficiency coefficient; h air * , kJ/kg -the specific enthalpy of air at temperature and pressure at the inlet to the combustor; h g * , kJ/kg -the specific enthalpy of combustion products at temperature and pressure at the outlet of the combustor. The specific enthalpy of combustion products at the outlet of the combustor is determined as [11]:…”

“…The dependencies с ра = f(T, p) for the main components of air and combustion products, averaged over pressure and temperature, obtained in [11] are used in the study.…”