**Meet the editor**

Prof. Dr. Gurrappa is a Senior Scientist in Defence Metallurgical Research Laboratory (DMRL), Hyderabad, India, working in the field of Gas Turbine Engine Materials for about three decades. In addition to defense systems, he has been helping different industries in solving the corrosion problems and stressing the need of prevention of corrosion by using different advanced protective techniques.

He has been recognized globally. He is the recipient of Prestigious Fellowships.He is also the recipient of "Corrosion Awareness Award" and "Meritorious Contribution Award" from NACE International India section in 2004 and 2010 respectively. He has received a number of best paper awards and delivered a number of invited lectures / talks, keynote addresses in various international / national symposia and chaired the technical sessions. He authored 200 publications, 9 books / book chapters and edited two books on Gas Turbines. He is an elected Fellow of Royal Society of chemistry, London and Andhra Pradesh Akademi of Sciences, India.

## Contents

**Preface XI**


Chapter 5 **Combustion Modelling for Training Power Plant Simulators 129** Edgardo J. Roldán-Villasana and Yadira Mendoza-Alegría

## Preface

Modern aero, marine and industrial gas turbines essentially need to exhibit outstanding per‐ formance, reliability and efficiency. This is possible only by selecting advanced materials, coatings and excellent designing. For this, the gas turbine manufactures should adopt mod‐ ern technologies / techniques. This book presents current research in the area of gas tur‐ bines. It is a useful book providing a variety of topics ranging from basic understanding about the materials and coatings selection, designing and modeling of gas turbines to ad‐ vanced technologies for their ever increasing efficiency which is the need of the hour for modern industries.

Chapter 1 presents a work that has been carried out on the modelling of dynamic response of marine GT rotor shaft systems. It is shown that when a system is subjected to force har‐ monic excitation, its vibration response takes place at the same frequency as that of the exci‐ tation. To determine the response of the shaft under vibration, readings were collected from bearings 1, 2, and 3 of GT 17 in Afam thermal station. The engine characteristic obtained in GT 17 is shown. Equation 40 was developed to determine the response of the system under vibration. This mathematical equation is used to run a computer programme with a code in C++programming language. The recommendations are 1. More attention should be paid to shaft vibrations as is the case with vibration on bearing. 2. Some factors which affect the performance of gas turbines on industrial duty should be considered while carrying out vi‐ bration based simulation of GT rotor shafts. 3. Errors and extraneous environmental factors should be put into consideration when modelling the response of rotor shaft under vibra‐ tion. 4. GT rotor shaft systems should be provided with more supports to prevent adverse effects of eccentricity which leads to bow and whirl.

Chapter 2 describes 1. The selection of a location for a gas turbine cogenerative plant impos‐ es climatic conditions and demands adequate technical solutions to meet performance re‐ quirements, especially during summer season when inlet air temperature rises, leading to a decrease in power output and efficiency. 2. Water content modifies thermodynamic proper‐ ties of intake air (density, specific heat) affecting power output and heat mass flow resulted from the gas turbine. If in the past air humidity was neglected, in present day cogenerative gas turbine power increase, but also water/steam injection impose the need for it to be taken into account. 3. The main research directions in the area of cogenerative groups with gas turbines efficiency are: combustion temperature increase; compression ratio increase; im‐ provement of design methods, combustion technology and advanced materials; technologi‐ cal transfer for aviation domain to industrial turbines domain; integrated systems (combined cycles, intake air cooling, exhaust turbine gases heat recovery, afterburning, etc.). 4. Determinant factors concerning the overall efficiency of the cogenerative group are: gas turbine exit temperature, temperature at the heat recovery steam generator stack; ambient

environment temperature. For these the most influential factor upon the increase of the overall efficiency is the temperature at the heat recovery steam generator stack. 5. Operating flexibility of equipment has become a major subject. Gas turbines are designed to function generally at nominal regime, in maximum efficiency conditions and minimum pollutants. At cogenerative groups with heat recovery steam generator, for producing technological steam, is preferable that the flexibility to the process demands to be achieved using after‐ burning installation. 6. Theoretical and experimental research conducted at INCDT COMO‐ TI Bucharest, revealed that, in the case of a gas turbine with intercooling, the performances variation is approximately linear for a compression ratio between 10.2 - 16, with a power decrease of 2.5 % for each 5 degrees increase of the environment temperature; to be obtained a afterburning module with a 30 % reduction of the NOx reduction (at partial load) in com‐ parison with the existing cogenerative power plant 2xST 18 – Suplacu de Barcau; to demon‐ strate the power increase and NOx emissions reduction when injecting water in the intake device of TA2 gas turbine.

Chapter 3 highlights the importance of high temperature corrosion i.e. oxidation, type I and II hot corrosion which are catastrophic for the gas turbines. Hot corrosion is a major prob‐ lem for the gas turbines engines due to which failures take place during service. Though advanced superalloys comprising new alloying elements such as rhenium, ruthenium and iridium (4th and 5th generation) that have been developed recently, exhibit considerably im‐ proved high temperature strength properties, their hot corrosion resistance is found be very poor. Therefore, there is a need to apply appropriate hot corrosion resistant coatings on the superalloys as the gas turbine engine components should exhibit both high temperature strength as well as hot corrosion resistance. Considerable amount of research has been car‐ ried out in the coatings area. As a result, new compositions, graded coatings have been emerged and efforts have also been made to predict their lives. However, no work was re‐ ported to predict the lives of coatings under hot corrosion conditions. Recently, smart coat‐ ings with varied techniques and compositions have been reported, which provides total protection to the superalloy components against high temperature oxidation, type I and II hot corrosion with their intelligent behaviour which in turn enhances the efficiency of gas turbines by eliminating failures during service. Therefore, it is recommended to apply smart coatings for the advanced superalloys as bond coatings used in all types of modern gas tur‐ bines i.e. aero, industrial, and marine in order to obtain ever greater efficiency, which is es‐ sential in the present world. The chapter also presents the future research trends in the field.

Chapter 4 describes the formation and growth behaviour of thermally grown oxide (TGO) at the interface between ceramic thermal barrier coating and metallic bond coating. During thermal aging, a TGO is formed at the TBC/MCrAlY interface. SEM and EDX analysis show that the TGO contains two different oxides. One is alumina closer to the MCrAlY, and the other is mixed oxide closer to the TBC. Thickness of both alumina and mixed oxide in‐ creased with aging time. In the case of aged specimen for a long time, the macro-crack was identified everywhere in the TGO. This reason indicates that thermal expansion mismatch accompanied by formation and growth of alumina is one of the driving forces of macrocracks formation. However, the driving force is not only thermal stress but also decrease in adhesive force or formation of stress concentration site caused by formation of porosity or micro-crack. Almost all macro-cracks passed through the porosity in mixed oxide or microcrack in YSZ layer. It is thought that the delamination or the spalling is initiated and propa‐ gated due to an interaction of these degradation factors such as thermal stress, initiation of

stress concentration sites, and decreasing adhesive force due to formation and growth of alumina, porosities and microcracks. It has been made clear from kinetics of TGO growth that oxidation behaviour of the mixed oxide layer obeys parabolic law. On the other hand, it is thought that the oxidation rate constant of the alumina is a function of thickness of mixed oxide. Consequently, the alumina thickness obeys anomalous parabolic law. Furthermore, improvement technique for bonding strength between TBC and bond coat was suggested. By adding Ce and Si to conventional CoNiCrAlY, morphologies of the thermally grown ox‐ ide changed drastically. Furthermore, the influence became more pronounced when the amount of Ce increased. Ce addition to the bond-coat made the wedge-like oxide. The wedge-like oxide can improve the bonding strength. From these results, if we can control the morphology of the TGO, we can control the bonding strength between TBC and bond coat.

environment temperature. For these the most influential factor upon the increase of the overall efficiency is the temperature at the heat recovery steam generator stack. 5. Operating flexibility of equipment has become a major subject. Gas turbines are designed to function generally at nominal regime, in maximum efficiency conditions and minimum pollutants. At cogenerative groups with heat recovery steam generator, for producing technological steam, is preferable that the flexibility to the process demands to be achieved using after‐ burning installation. 6. Theoretical and experimental research conducted at INCDT COMO‐ TI Bucharest, revealed that, in the case of a gas turbine with intercooling, the performances variation is approximately linear for a compression ratio between 10.2 - 16, with a power decrease of 2.5 % for each 5 degrees increase of the environment temperature; to be obtained a afterburning module with a 30 % reduction of the NOx reduction (at partial load) in com‐ parison with the existing cogenerative power plant 2xST 18 – Suplacu de Barcau; to demon‐ strate the power increase and NOx emissions reduction when injecting water in the intake

Chapter 3 highlights the importance of high temperature corrosion i.e. oxidation, type I and II hot corrosion which are catastrophic for the gas turbines. Hot corrosion is a major prob‐ lem for the gas turbines engines due to which failures take place during service. Though advanced superalloys comprising new alloying elements such as rhenium, ruthenium and iridium (4th and 5th generation) that have been developed recently, exhibit considerably im‐ proved high temperature strength properties, their hot corrosion resistance is found be very poor. Therefore, there is a need to apply appropriate hot corrosion resistant coatings on the superalloys as the gas turbine engine components should exhibit both high temperature strength as well as hot corrosion resistance. Considerable amount of research has been car‐ ried out in the coatings area. As a result, new compositions, graded coatings have been emerged and efforts have also been made to predict their lives. However, no work was re‐ ported to predict the lives of coatings under hot corrosion conditions. Recently, smart coat‐ ings with varied techniques and compositions have been reported, which provides total protection to the superalloy components against high temperature oxidation, type I and II hot corrosion with their intelligent behaviour which in turn enhances the efficiency of gas turbines by eliminating failures during service. Therefore, it is recommended to apply smart coatings for the advanced superalloys as bond coatings used in all types of modern gas tur‐ bines i.e. aero, industrial, and marine in order to obtain ever greater efficiency, which is es‐ sential in the present world. The chapter also presents the future research trends in the field. Chapter 4 describes the formation and growth behaviour of thermally grown oxide (TGO) at the interface between ceramic thermal barrier coating and metallic bond coating. During thermal aging, a TGO is formed at the TBC/MCrAlY interface. SEM and EDX analysis show that the TGO contains two different oxides. One is alumina closer to the MCrAlY, and the other is mixed oxide closer to the TBC. Thickness of both alumina and mixed oxide in‐ creased with aging time. In the case of aged specimen for a long time, the macro-crack was identified everywhere in the TGO. This reason indicates that thermal expansion mismatch accompanied by formation and growth of alumina is one of the driving forces of macrocracks formation. However, the driving force is not only thermal stress but also decrease in adhesive force or formation of stress concentration site caused by formation of porosity or micro-crack. Almost all macro-cracks passed through the porosity in mixed oxide or microcrack in YSZ layer. It is thought that the delamination or the spalling is initiated and propa‐ gated due to an interaction of these degradation factors such as thermal stress, initiation of

device of TA2 gas turbine.

VIII Preface

Chapter 5 covers needs of the GSACS. A generic model of such a combustion process de‐ signed to work in any operators' training simulator. Validation of the model has been in‐ trinsically demonstrated with the inclusion of the model in a gas turbine and a combined cycle power plants simulators for operators' training. In the proper date, CENAC endorsed and accepted as correct the results of the tests in accordance with the testing acceptance pro‐ cedures and the ANSI norm. Some other off-line examples have been presented with the objective to explain the model principles and potential. Consequently, the future work is discussed.

I believe that this book will be highly useful to materials scientists, gas turbine engine de‐ sign engineers, manufacturers, mechanical engineers, undergraduate, post graduate stu‐ dents and academic researchers.

> **Injeti Gurrappa** Defence Metallurgical Research Laboratory Hyderabad, India

**Chapter 1**
