Model Based Experimental Study on Next Generation Hybrid Environmental Control Systems (HECS)

航空电子设备的环境温度范围规定在-31 ℃和+70 ℃之间。超出范围的操作会导致故障率呈指数级增加。控制到范围的下限要求环境控制系统（ECS）供应多余的调节空气。过剩的产生需要增加引气和冲压空气的使用，需要额外的发动机功率，并降低飞机的空气动力性能。控制到范围的上限显著地减少了调节的冷空气的量，增加了发动机功率输出，提高了燃料效率，并且提高了飞行器性能。常规引气ECS使用发动机引气和外部冲压空气。这是一种经过验证的可靠技术，但效率很低。它需要额外的发动机功率，降低了飞机的空气动力学性能，并且除了由于地面上和上升/下降期间的过热而导致的其他维护问题之外，还导致发动机上的巨大热功率损失（例如，当冲压空气流必须用风扇、发动机风扇或专用风扇来强制时）。电动ECS使用专用的电动压缩机，该压缩机供给冲压空气以产生调节空气。它消除了发动机引气，提供了如下潜力：（1）提高机体系统利用率并实现更有效的动力装置，（2）减小发动机核心尺寸、总压比和涡轮机入口温度，从而改善发动机性能，导致更有效的飞机，以及（3）消除引气系统，导致飞机整体质量减小。然而，高航空电子设备和雷达热负荷的增加需要过多的冷却功率。目前的电力系统相对不成熟，以满足高要求。一个潜在的解决方案的优化，可以通过一个混合环境控制系统（HECS）的概念，通过添加一个小规模的电动ECS的传统引气系统。这样，引气ECS被减少到仅提供调节空气以将航空电子设备维持在较高的操作温度范围。附加的电动ECS将采用启停式设计，仅在需要时提供过量的空调空气。因此，HECS提供了一种节能而低风险的解决方案。它使发动机引气的需求保持在最低限度，因此显著增加了发动机功率输出，提高了燃油效率，并提高了飞机性能。这是未来飞机实现电动ECS的中间步骤。该项目的目的是根据我们目前对航空电子热需求、ECS建模研究和实验ECS评估的研究成果，将HECS概念发展成一个概念验证示范装置。从该项目开发的HECS概念将提供提高ECS效率的潜力，同时保持低故障率。此外，优化的HECS可以改善飞机性能并增加发动机功率。

The environmental temperature range of the avionics is specified at between -31degreesC and +70degreesC. Operation outside the range leads to exponentially increases in failure rate. Controlling to the lower limit of the range requires the Environmental Control System (ECS) to supply surplus conditioned air. The generation of the surplus requires increased use of bleed and ram air, demands extra engine power and reduces aircraft aerodynamic performance. Controlling to the upper limit of the range significantly reduces the amount of the conditioned cold air, increases engine power output, improves fuel efficiencies, and improves aircraft performance. Conventional - bleed air ECS uses engine bleed air and external ram air. It is a proven and reliable technology but largely inefficient. It demands extra engine power, reduces aircraft aerodynamic performance, and results in an enormous of thermal power penalty over the engine in addition to other maintenance problems due to overheating on ground and during ascent/descent (when ram air flow must be forced with a fan, the engine fan or a dedicated one, for example).Electric ECS uses dedicated electric compressor(s) that feed on ram air to produce the conditioned air. It eliminates engine bleed, offers potentials such as: (1) improve airframe systems utilization and implement more efficient power units, (2) reduce engine core size, overall pressure ratio and the turbine inlet temperature, thus improving engine performance which lead to more efficient aircraft, and (3) eliminate bleed air systems lead to overall aircraft mass reduction. However, the increases in high avionics and radar heat loads demand excessive cooling power. The current electric system is relatively immature to satisfy the high demands. A potential solution of optimisation can be achieved through a hybrid environmental control system (HECS) concept by adding a small-scale electric ECS to the conventional bleed air system. In doing so, the bleed air ECS is reduced to only provide the conditioned air to maintain the avionics at the upper operating temperature range. The add-on electric ECS will be a start-stop design, which only supply the excessive conditioned air when it is needed. The HECS therefore provides an energy efficient yet low risk solution. It keeps the demand of engine bleed air to minimum, therefore significantly increases engine power output, improves fuel efficiencies, and improves aircraft performance. It is an intermediate step towards realisation of electric ECS for future aircrafts. The aim of this project is to develop the HECS concept into a proof-of-concept demonstration unit based on our current research outputs on avionic thermal demands, ECS modelling studies and experimental ECS evaluations. The HECS concept developed from this project will offer the potential of improving the ECS efficiency while maintaining a low failure rate. In addition, the optimised HECS can improve the aircraft performance and increase the engine power.