Riti Singh

Engine maintenance costs are a major contributor to the direct operating costs of aircraft. Therefore, the minimization of engine maintenance costs per flight-hour is a key aspect for airlines to operate successfully under challenging market conditions. Minimization can be achieved by increasing the on-wing time or by reducing the shop-visit costs. Combining both provides optimum results and can only be achieved by thorough understanding of the engine. In the past, maintenance optimization was mainly an experience-based process. In this work, a novel analytical approach is presented to optimize the maintenance of commercial turbofan engines. A real engine fleet of more than 100 long-haul engines is used to demonstrate the application. The combination of advanced diagnostic and simulation methods with classical hardware-based failure analysis enables linking of overall engine performance with detailed hardware condition and, thus, an effective optimization of the overall maintenance process.

Sub-idle is a very challenging operating region as the performance of a gas turbine engine changes significantly compared with design conditions. In addition, the regulations for new and existing engines are becoming stricter and the prediction of engine relight capability is essential. In order to predict the performance of an engine, detailed component maps are required. The data obtained from rig tests are insufficient at low speeds, creating the need for generation of maps within the sub-idle regime. The first step toward this direction is the use of an extrapolation process. This is a purely mathematical process and the results are not usually of sufficient accuracy. In addition, this method does not provide any insight on the physical phenomena governing the operation of the compressor at low speeds. The accuracy of the resulting compressor map can be increased with a better low speed region definition; this can be achieved via the thorough study of a locked rotor compressor, enabling the derivation of the zero rotational speed line and allowing an interpolation process for the generation of the low speed part of the characteristic. In this work, an enhanced sub-idle compressor map generation technique is proposed. The suggested methodology enables the generation of characteristics at far off-design conditions with enhanced physical background. Alternative parameters for map representation are also introduced. Provided that the all the blade rows of the compressor are of known geometry, a numerical analysis is used for the calculation of the characteristic of the half stage and a stage stacking method is employed to create the entire compressor characteristic. This way, the sub-idle region of the map can be calculated through interpolation, which provides a more accurate and predictive technique. Application of the method for compressor map generation showed that the proposed interpolation approach is robust and capable of enhancing any performance simulation tool used for the prediction of transient altitude relight or ground-starting maneuvers.

In this paper economic and scenario analyses of new gas turbine combined cycles with no emissions of carbon dioxide CO2 and nitrogen oxides are described. The cycles, already presented in a recent paper (ASME GT 2002-30117), have water/steam as a working fluid, the compression phase both in liquid and vapor phase, the internal combustion between pure oxygen O2 and chemically heated natural gas-based syngas, and the CO2 capture and sequestration by water condensation from the exhaust gas. The aim of the economic analyses is to estimate the investment per MW and the levelized discounted cost of the electricity (COE) produced by a power plant based on the cycles proposed here in comparison with a standard reference combined cycle power plant (SRCC). To evaluate the equipment costs, several cost functions of the most important operative parameters have been introduced and tuned with the actual data. Using the least square regression technique, explicit functions of the COE have been proposed to highlight the cheapest operative conditions with a derivative approach. Moreover, a wide scenario analysis has been carried out, varying the most important investment parameters, as, for example, the discount rate. In particular, some maps of the COE and break-even carbon tax (BECT) behavior have been constructed to test the importance of the market uncertainty on the economic results obtained. Finally, the possible technological progress effect on the BECT with a cost reduction of some innovative equipment and the O2 production has been investigated in depth with the 2k factorial design scenario analysis. The O2 production has resulted as the most important parameter from an economic point of view.