# Thermal Management Systems for Civil Aircraft Engines: Review, Challenges and Exploring the Future
## 5 TMS Design Challenges and Potential Solutions for the Next Generation of Aircraft Engines
On the other hand, minor changes in the components and cooling paths will give a huge degree of freedom to the control structure designers to play with more parameters in order to enhance the performance indices of the TMS and the engine noticeably. As an illustrative example, change the circulation path of the oil in parallel with defining a smart control algorithm for the variable valve positions may result in a noticeable enhancement in the TMS performance. 2. Another solution could be defining the classes II and III as a unique approach in an engineering optimization problem format. The main idea would be to define the structure of the integrated TMS, the order of components, the oil and fuel paths, the air flowrate and path and so forth, as the indices of a comprehensive objective function; then to use a powerful optimizer to deal with the \begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{2}{c}{**Class of**} & \multicolumn{2}{c}{**Main Drawbacks**} \\  & \multicolumn{2}{c}{**Development**} & & \\ \hline I & \multirow{4}{*}{Classic} & \(\bullet\) & The new aircraft engines designs are being more complicated with much more extra heat to be dissipated [59; 62]. \\  & & \(\bullet\) & Geared Turbofans have power gearbox which makes the extra heat of the engine at least twice [59; 62]. \\  & & \(\bullet\) & Current TMS for aircraft engines are already working on their limits and any modification would probably lead to just marginal improvements. \\ \hline II & \multirow{4}{*}{ Centralized} & \(\bullet\) & New architectures for airframe and engines are more compact and have less space to accommodate conventional TMS components. \\  & & \(\bullet\) & A multidisciplinary design optimization problem with many parameters should be solved in this approach. \\  & & \(\bullet\) & A centralized complicated control algorithm is required to satisfy both engine and airframe TMS requirements simultaneously. \\ \hline III & \multirow{4}{*}{ Revolutionary} & \(\bullet\) & The chance of successfulness of a new idea is not too much in comparison with the time that should be spent on its development and investigation. \\  & & \(\bullet\) & The industry is reluctant to change the infrastructure as it would be expensive and time consuming. \\  & & \(\bullet\) & A new system requires its own certificates and reliability tests before it can go into the production. \\ \hline IV & \multirow{4}{*}{ Cost-effective} & \(\bullet\) & Keeping the main structure and architecture and achieving noticeable improvement in the efficiency is not a simple straightforward task. \\  & & \(\bullet\) & Detailed and probably complicated control algorithms should be developed, simulated and tested in different scenarios to confirm the effectiveness of these methods. \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Drawbacks of the classes of TMS development for the future aero-engines. defined objective function. By tuning the mutation operator probability, the potential evolutionary developments would be investigated as well. However, definition of very smart constraints, penalty functions, penalty factors and objective function indices coefficients is a very vital step in successfulness of this approach. So, the main step in this solution is to define the problem statement very clear and with high level of details and accuracy; and then to select a suitable optimizer which can deal with such a big optimization problem with affordable run time. Associated with this classification, it is helpful to consider some form of evaluation and ranking of proposed solutions. For this purpose, it is worthwhile to analyse the complexity-impact (CI) correlation which is a practical index in selecting the feasible approach for dealing with challenges [63; 64; 65]. It is an assessment to value the effort that should be spend on a problem with respect to impacts of the results. Based on whole review, analyses and discussion presented so far, Figure 10 summarizes the development classes and proposed solutions with their CI index. * **Class I.