# 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  
From the historical review presented plus some general consideration of efficiency, energy management and coolant properties, it is possible to identify four different systematic concepts for the future of the TMS design and development as follows:  
* **Class I. ** Classic Development. This class of development would concentrate on the improvement of conventional TMS structure (Figure 1) for GTEs. This improvement could be applied on minor system structure changes in order to get better efficiency, replacement of the components with more advanced and smart ones (e.g., new, effective heat exchangers [59; 60]) and changing the oil and fuel path to get better thermal management efficiency. The advantages of this approach are that the theoretical fundamentals and the implementation infrastructures are well-developed and these modifications would not dictate huge cost to manufacturers. However, the main disadvantage of this approach is that probably it would just bring marginal improvement for the TMS as this area is already well investigated. * **Class II. ** Centralized Development. This class would investigate the integrated TMS for the engine and airframe. It results in a centralized system that manages the thermal loads of the airframe and the engine simultaneously. So, the control algorithm and strategy would have more degree of freedom to deal with thermal loads. However, the main disadvantage is that it would be a high dimension multidisciplinary design problem with many parameters to select and tune simultaneously. Especially, in new advanced aircraft and engines it could be hardly affordable. * **Class III. ** Revolutionary Development. This class of development would cover new ideas with major changes in the TMS. Using new coolants for the engine ([50] and Figure 7) and ACC system ([35] and Figure 2) are examples of this class. The positive points about this class of development is that it may be possible to get a noticeable jump in TMS effectiveness. In other words, a revolutionary approach may result in a revolutionary achievement. But, the problem with this class of development is that implementation of these approaches requires a significant change in the system manufacturing and infrastructures and it may not be interesting for the airliners and manufacturers. * **Class IV. ** Cost-effective Development. This type of approaches will focus on the cost-effective solutions to enhance the TMS behaviour in the GTEs. The driving idea is to keep the hardware structure of the TMS unchanged (if possible) and to work on the solutions that could be implemented easily and/or with minimum changes in the current working systems. Enhancement of the control algorithms [61], splitters, valves and mixers [62] are some examples of cost-effective solutions. The relative merits of this class to the other classes is clear as the cost consideration is one of the most important issues in real-world applications. However, the correlation between the complexity and impact is the matter that should be discussed in these methods. With respect to the above systematic approaches, the main drawbacks of the TMS development classes for the future aircraft engines are summarized in Table 2.  
Considering that the above-listed drawbacks in some classes could be sorted out with using ideas of other classes, the potential solutions for the improvement of the aircraft engine TMS for the future could be proposed as follow:  
1. The first effective solution could be utilizing both class I and IV simultaneously. It means that concentration of new studies should be on some minor modification on the hardware as well as working on algorithms and strategies. The superposition of these classes of development would enable the TMS designers to deal with several challenges in parallel. In one hand, the main architecture of the TMS would be kept approximately unchanged as the manufacturers and airliners prefer.