Fausto Gamma

Regeneration and Intercooling in Gas Turbine Engines for Propulsion Systems

The need to reduce fuel consumption in modern gas turbine engines is evident, and with today’s oil price levels it has become of primary importance. Infact oil price, and consequently aircraft fuel consumption, is one of the most im portant economic element in airlines management. Regeneration and intercooling are two of the most effective practices used in ground based power plants to achieve these goals . However they are not still used in gas turbine engine for propulsion systems ma inly for the extra weight and size due to the presence of the heat exchangers and for the more complicated flow pattern that it comes from it. If we will be able in the near future to overcome these technical problems we can think th at the same benefits o btained for the ground based plants could be transferred to propulsion systems. In particular turboprop engine seems to be the most suited to this purpose thanks to its smaller mass flow rate and its gas path. A thermodynamic cycle analysis is performed to put in evidence the advantages, in terms of power increase and fuel consumption reduction, of the introduction of regeneration and intercooling in a turboprop engine.

Fuel Consumption Reduction and Weight Estimate of an Intercooled-Recuperated Turboprop Engine

Abstract The introduction of intercooling and regeneration in a gas turbine engine can lead to performance improvement and fuel consumption reduction. Moreover, as first consequence of the saved fuel, also the pollutant emission can be greatly reduced. Turboprop seems to be the most suitable gas turbine engine to be equipped with intercooler and heat recuperator thanks to the relatively small mass flow rate and the small propulsion power fraction due to the exhaust nozzle. However, the extra weight and drag due to the heat exchangers must be carefully considered. An intercooled-recuperated turboprop engine is studied by means of a thermodynamic numeric code that, computing the thermal cycle, simulates the engine behavior at different operating conditions. The main aero engine performances, as specific power and specific fuel consumption, are then evaluated from the cycle analysis. The saved fuel, the pollution reduction, and the engine weight are then estimated for an example case.

Numerical Analysis of Intercooled and Recuperated Turbofan Engine

Abstract In the last decades the main efforts of aero engine designers have been focused on the possibility to increase maximum attainable thrust while reducing specific fuel consumption. As consequence, very high bypass ratio turbofan engines have been developed, ensuring the specific fuel consumption reduction by means of the increased propulsion efficiency. However this way to operate cannot be followed indefinitely, and some new techniques need to be thought. In this work it has been considered the possibility to increase the efficiency of the engine modifying the working thermal cycle. In fact, by means of the development of a numeric thermodynamic code, it has been simulated the thermal behavior of a turbofan engine in which the practices of intercooling and regeneration are introduced.

Preliminary analysis of strategies for NOx reduction

Although the LAPCAT II project theoretically demonstrated that the chance for future long range high speed commercial transport ( i.e. Bruxelles-Sydney in less than 2 hrs and 30 min) is real, the impact of these vehicles on the environment is a key point to be investigated. In fact, nevertheless hydrogen has been chosen as fuel and no particulate, CO and CO2 emissions are foreseen, the high temperature within the scramjet combustor rises the issue of the NOx, water vapor and OH emissions. Further, the higher altitudes associated with hyper/supersonic flight make the emission of NOx a critical point for the ozone layer depletion. In fact, at current subsonic flight altitudes (troposphere and lower stratosphere), NOx emissions are associated with ozone production whereas, at the high altitudes of 20000-30000 m, which correspond closely to the maximum ozone density, NOx can catalyze ozone destruction. Thus reduction of the NOx Emission Index (grams of emission produced per kilogram of fuel consumed) remains of primary concern, being responsible for the ozone layer depletion. This study has shown that high level of NOx emissions occurs when burning fuel near stoichiometric air-to-fuel ratios. Hence, a strategy in reducing NOx production could be to burn fuel-rich or lean; also the combustor initial pressure has an impact on the combustor emissions. In this paper the impact of the combustor pressure and equivalence ratio on the ozone NOx emissions has been investigated.

Low-Fuel Consumption Gas Turbine Engines for Extended-Range UAVs

In the last years the interest in Unmanned Air Vehicle systems has greatly raised, thanks to their extended operation capabilities. Among the reasons of this growing interest there is the development of very efficient and reliable guiding systems, that allow a thorough remote vehicle control. The endurance capability is certainly one of the most important UAV characteristics, because some missions are supposed to last even more than one day. For this reason, the engine fuel consumption becomes a fundamental aspect. The turboprop engine is commonly used in this kind of missions, with powers in the range between 300-900 kW. To extend the flight range and the endurance characteristics, it is important to have low-fuel consumption propulsion systems. At this purpose, a turboprop engine with intercooling and regeneration has been studied. A thermodynamic numeric program that simulates the behavior of a turboprop with regeneration and intercooling at different engine and operating conditions has been developed. The program allows to compute the thermodynamic working cycle and hence the main engine performances, as specific power, thermal efficiency and specific fuel consumption. An off-design analysis is performed to evaluate the engine behavior when operating at different conditions respect to the design point. An example case, showing the saved fuel for a particular mission profile, is then reported.

Air vitiation effects in scramjet engines

Vitiation is one of the major sources of uncertainty in testing combustors. In fact, in real flight conditions, there is no water in the air entering the combustion chamber, whereas the air entering the test model contains water and radicals. This makes extrapolation to flight difficult. As the total pressure required for engine testing is high, typically 10 MPa for Mach 8 flight conditions, a vitiation air heater burning fuels is required to increase the air enthalpy. Since the arc heaters become unstable under high pressure operations, they are not suitable for heating air for supersonic engine wind tunnels. In spite of such limitations, these vitiation air heaters are the only options available for driving engine wind tunnels. In this work, the chemical inhibition effect on flame temperature and ignition due to OH and H2O has been numerically investigated by means of the 2D RANS of the LAPCAT 2 European MR2 scramjet. Finally, theoretically laws have been proposed for the ground to flight data extrapolation.

OffDesign Performances of a Gas Turbine Engine With Heat Recovery and Intercooling

The reduction of fuel consumption and pollutant emissions have become one of the main requirements of modern gas turbine aero engines. To pursue this aim engineers are developing new techniques to improve the efficiency of the thermodynamic cycle of new engines. In particular the attention is focused on the possibility to introduce practices as heat regeneration and staged-intercooled compression process on these engines. These practices, that change considerably the features of the working cycle of the engine, are well known and widely used in ground based power plants, but until now they have not been transferred on aero engines, mainly for problems of extra weight and size. However now these problems seem to be overcome by new technology, and the possibility to have intercooled-recuperated gas turbine engines on a plane has become real. A thermodynamic code that simulates the behavior of a gas turbine engine at different engine and operating conditions has been developed. In this paper are presented the main results obtained with the code, simulating the behavior of a turboprop engine in which both intercooling and regeneration are introduced. An off-design analysis is then performed to compare the behavior difference between the two engines when operate at different conditions respect to the design point.

Parametric Thermal Analysis of Regenerated and Intercooled Turboprop Engine

The reduction of fuel consumption and pollutant emissions have become one of the main requirements of modern gas turbine aero engines. To pursue this aim engineers are developing new techniques to improve the efficiency of the thermodynamic cycle of new engines. In particular the attention is focused on the possibility to introduce practices as heat regeneration and staged-intercooled compression process on these engines. These techniques, that change considerably the engine working cycle features, are well known and widely used in ground based power plants, but until now they have not been transferred on aero engines, mainly for extra weight and size problems. However these problems now seem to be overcome by new technology, and the possibility to have intercooled-regenerated gas turbine engines on an aircraft has become real. A thermodynamic code that simulates the behavior of a gas turbine engine at different engine and operating conditions has been developed. In this paper are presented the main results obtained with the code, simulating the behavior at take-off and cruise of a turboprop engine in which both intercooling and regeneration are introduced.

Feasibility of high speed atmospheric flight on Venus

Exploring Venus is difficult, so far, probes have managed to survive only few hours. However, Venus’ atmosphere, composed of 96.5 % CO2 might provide an unique opportunity for a airbreathing vehicle. In this context, this paper intends to study the feasibility of a scramjet/ramjet engine for flying in Venus’ atmosphere at an altitude of ~70 km. The first part of the work focuses on the choice of fuel. The most promising candidates to burn in CO2 are metals and their hydrides. In this context, the analysis of a wider range of these candidates including lithium (Li), beryllium (Be), magnesium (Mg), aluminum (Al), silicon (Si), beryllium hydride (BeH2), magnesium hydride (MgH2) and silane (SiH4) has been done. Once the fuel with better performance was chosen, weight and volume of a supersonic aircraft capable of carrying 200 kg of payload and operating range of 1000 km were estimated. The results showed that with a total weight of 995 kg it is possible to keep the size of the aircraft within the limits imposed by modern launchers, leaving enough room and mass weights for an orbital module to be attached to a future venus sound spacecraft.

Electro-chemical propulsion for space exploration

This paper wants to explore the feasibility and convenience to couple an electromagnetic with a chemical thruster in order to exploit the modest propellant consumption of the first and the high thrust of the second. Coupling the advantages of electric propulsion and chemical allows an electric thruster to perform manoeuvers where higher thrust is required. In fact, in case of a electrochemical thruster that uses hydrogen as working fluid can be reacted with oxygen to get larger thrust increase, of course, for a time limited by mass of LOX (or GOX) on board. While in principle this is feasible, in practice, several points must be considered: in particular, those related to chemical propulsion, that is, mixing between two fluids, reactivity at the low feed pressure, and of course the performance achievable. For this purpose, in order to preliminary estimate performance of this electro-chemical thruster in chemical mode when burning H2 with oxygen and at its same operative conditions of pressure and temperature, a theoretical analysis has been performed. This has shown that, combustion of H2/Ox at typical electric thruster pressures is possible with significant thrust increase, coupling the advantages of electric propulsion.