Patent Description:
Although current engine systems have improved propulsive efficiency, aircraft engine manufacturers continue to seek further improvements to engine performance including improvements to thermal, transfer and propulsive efficiencies.

<CIT> discloses a prior art thermal management system.

<CIT> discloses a prior art thermal management system for an electric propulsion engine.

<CIT> discloses a prior art aircraft heating assembly with a liquid cooled internal combustion engine and a heating element using waste heat.

According to a first aspect of the present invention, there is provided an aircraft propulsion system as set forth in claim <NUM>.

In a further embodiment of the foregoing, the first heat exchanger assembly includes a first outlet that communicates the working flow to an inlet of the skin heat exchanger.

In a further embodiment of any of the foregoing, the skin heat exchanger includes a second outlet that communicates the working flow to the first heat exchanger assembly.

In a further embodiment of any of the foregoing, the skin heat exchanger assembly is black.

In a further embodiment of any of the foregoing, the aircraft propulsion system includes a second heat exchanger assembly that is disposed in the aircraft structure. The second heat exchanger is in fluid communication with the skin heat exchanger assembly.

In a further embodiment of any of the foregoing, the aircraft structure includes at least one of an aircraft fuselage or an aircraft wing.

According to a further aspect of the present invention, there is provided a method of transferring thermal energy from an aircraft system working fluid as set forth in claim <NUM>.

<FIG> is a schematic view of an example aircraft heat exchanger system <NUM> disposed in an aircraft structure <NUM>. The aircraft structure <NUM> may be the aircraft fuselage, a wing or other lifting structure. The disclosed example aircraft structure <NUM> includes an imbedded propulsor assembly <NUM> that receives air flow through an inlet duct <NUM>. The propulsor assembly <NUM> creates a high energy propulsive flow that is exhausted through an exhaust duct <NUM>. In one disclosed example, the propulsor assembly <NUM> is electrically powered In another disclosed example embodiment, the propulsor assembly <NUM> is a hybrid system that combines conventional combustion with electric power. It should be understood that although several types of propulsor assemblies are disclosed by way of example that any propulsor assembly would benefit from the heat exchanger system of this disclosure and are within the contemplation of this disclosure.

The inlet duct <NUM> is sized to provide a desired amount of airflow to the propulsor assembly <NUM>. The size over the inlet duct <NUM> is constrained by the size and shape of the aircraft structure <NUM>. Accordingly, exposure to inlet airflow is limited by the size of the inlet duct <NUM>. The constrained amount of airflow may limit a thermal capacity of a heat exchanger system required to cool and transfer heat produced by various aircraft systems <NUM>. The aircraft systems <NUM> are shown schematically and may include lubricant, cooled cooling air, buffer cooling air and any other aircraft systems that transfer thermal energy to operate efficiently. A disclosed example heat exchanger system embodiment provides for increased thermal transfer capacity without modifications to the inlet duct <NUM>.

The example heat exchanger system <NUM> includes a first heat exchanger assembly <NUM> that is disposed in the inlet duct <NUM> and in thermal communication with an airflow <NUM> such that some airflow portion <NUM> is ingested into inlet duct <NUM>. A skin heat exchanger assembly <NUM> is disposed along an outer bottom surface <NUM> of the aircraft structure <NUM> and in thermal communication with the airflow <NUM>. The first heat exchanger assembly <NUM> and the skin heat exchanger assembly <NUM> are in fluid communication such that a working fluid <NUM> flows between the first heat exchanger assembly <NUM> and the skin heat exchanger <NUM>. The working fluid <NUM> may include lubricant, fuel, hydraulic fluid as well as other flows that require thermal transfer of heat for efficient operation.

In one disclosed example, a working fluid <NUM> is communicated first through the first heat exchanger assembly <NUM>. The first heat exchanger assembly <NUM> transfers some quantity of thermal energy into the ingest airflow <NUM>. The amount of thermal energy transferred may be sufficient to provide efficient operation. However, should additional thermal energy transfer be required, the working fluid <NUM> may be communicated to the skin heat exchanger assembly <NUM>. In one disclosed example, the first heat exchanger <NUM> provides between <NUM>% and <NUM>% of the required thermal transfer capacity desired to sufficiently cool the working fluid <NUM> and the skin heat exchanger assembly provides the remaining thermal transfer capacity. In another disclosed embodiment, the first heat exchanger <NUM> provides between <NUM>% and <NUM>% of the required thermal transfer capacity and the skin heat exchanger assembly provides the remaining <NUM>% to <NUM>%. As appreciated, other combinations of heat transfer capacity may be utilized and are within the contemplation of this disclosure.

Referring to <FIG> and <FIG> with continued reference to <FIG>, the example heat transfer system <NUM> includes the skin heat exchanger <NUM> disposed on a bottom surface of the aircraft structure <NUM>. The skin heat exchanger <NUM> may have any shape, width and length that provides a desired thermal transfer capacity. The bottom surface <NUM> is typically not exposed to sunlight for extended periods of time and therefore is where the example skin heat exchanger <NUM> is mounted.

In this disclosed example, the skin heat exchanger <NUM> is disposed on either side of the inlet <NUM>. The offset placement of the skin heat exchanger <NUM> provides for non-heated boundary layer airflow <NUM> to be communicated into the inlet <NUM>. Accordingly, airflow that has accepted heat through contact with the skin heat exchanger <NUM> is not substantially communicated into the inlet <NUM>. The inlet <NUM> and thereby the first heat exchanger <NUM> is not provided with preheated air. It should be appreciated that it is within the contemplation and scope of this disclosure that the skin heat exchanger <NUM> may be located in other portions of the aircraft structure <NUM>, falling within the scope defined by the appended claims, that do not result in preheated air being communicated into the inlet <NUM>.

Moreover, the thermal transfer of heat through the skin <NUM> provided by the disclosed skin heat exchanger <NUM> may be utilized to provide additional functions that make use of the communicated thermal energy. In one disclosed example, the skin heat exchanger <NUM> may provide anti-icing functions to prevent ice build up on portions of the aircraft structure <NUM>. The skin heat exchanger <NUM> may be located, at least partially, on a leading edge of a wing or other lift generating structure of the aircraft structure <NUM> to provide an anti-icing function. Moreover, other beneficial uses of the thermal energy transferred through the skin <NUM> may be utilized by providing a specific location of the skin heat exchanger <NUM> and are within the scope and contemplation of this disclosure.

The skin heat exchanger <NUM> is placed in direct thermal transfer contact with a skin <NUM> of the aircraft structure <NUM>. The direct contact with the skin <NUM> provides for thermal contact with the boundary layer flow <NUM> generated during aircraft operation. The working fluid <NUM> is flowed through the skin heat exchanger <NUM> in a forward direction that opposes the boundary layer flow <NUM>. Stated another way, the working fluid <NUM> is flowed from an aft position toward a forward location that is opposite the flow <NUM> along the outer skin <NUM>. Thermal energy illustrated by arrows <NUM> is transferred into the flow <NUM> and the cooled working fluid <NUM> is communicated back to the corresponding aircraft system <NUM>.

The skin heat exchanger <NUM> may be configured with multiple channels and passages for the working fluid <NUM> that are placed in thermal communication with the skin <NUM> and thereby the flow <NUM>. It should be appreciated, that the skin heat exchanger <NUM> may be constructed of any applicable, known, thermal transfer materials and structures and all such materials and configurations are within the contemplation and scope of this disclosure.

The disclosed example skin heat exchanger <NUM> is black to provide the advantageous thermal absorption properties associated with black body radiation. In this disclosed example, the black body of the skin heat exchanger is schematically indicated at <NUM>.

Moreover, the skin heat exchanger <NUM> provides the increased thermal transfer capacity without introducing any additional aerodynamic drag. Furthermore, the skin heat exchanger is advantageous for cooling working fluids <NUM> that operate most efficiently when brought to ambient temperatures due to the large surface areas and high convective cooling rates during aircraft operation.

Referring to <FIG>, the example heat exchange system <NUM> is shown with the working fluid <NUM> first being communicated to an inlet <NUM> of the skin heat exchanger assembly <NUM>. The working fluid <NUM> is communicated forward and then back to the first heat exchanger assembly <NUM> disposed in the inlet duct <NUM>. Accordingly, in this disclosed embodiment, the working fluid <NUM> is initially cooled and then cooled completely by the first heat exchanger assembly <NUM>. The different configurations of working fluid flow <NUM> are possible to combine the thermal transfer capacities of the first heat exchanger assembly <NUM> and the skin heat exchanger assembly <NUM>. As appreciated, other routing and communication of the working fluid between the first heat exchanger assembly <NUM> and the skin heat exchanger assembly <NUM> are possible and within the scope and contemplation of this disclosure.

Referring to <FIG>, another heat exchanger system <NUM> is schematically shown and includes a second heat exchanger <NUM>. The second heat exchanger <NUM> is in thermal communication with another cooling flow <NUM> and with the working fluid <NUM>. The second heat exchanger assembly <NUM> may include a single heat exchanger or multiple heat exchangers that are utilized to further transfer thermal energy. In this disclosed example, the working fluid <NUM> is communicated from the aircraft systems <NUM> to the second heat exchanger <NUM> where it is cooled by the cooling flow <NUM>. The working fluid <NUM> is then communicated to an inlet <NUM> of the first heat exchanger <NUM> for additional transfer of thermal energy. The working fluid <NUM> is then routed to inlet <NUM> for further thermal transfer by the skin heat exchanger <NUM>. As appreciated, routing of the working fluid <NUM> may be controlled by various valves and conduits to select some combination of the heat exchangers required to transfer thermal energy as desired.

Accordingly, the disclosed example heat exchanger systems provide for increased thermal efficiencies within the size constraint arising from alternate propulsor mounting and limited inlet duct size. Additionally, disclosed heat exchanger system embodiments provide for use of smaller heat exchangers in engine inlet ducts while the skin heat exchanger assembly <NUM> does not increase drag and thereby further provides for increased engine efficiencies.

Claim 1:
An aircraft propulsion system comprising:
an aircraft structure (<NUM>);
a propulsor assembly (<NUM>) disposed in the aircraft structure (<NUM>);
an inlet duct (<NUM>) for communicating airflow to the propulsor assembly (<NUM>);
a first heat exchanger assembly (<NUM>) disposed in the inlet duct (<NUM>) and in thermal transfer communication with an inlet airflow through the inlet duct (<NUM>); and
a skin heat exchanger assembly (<NUM>) disposed along and in thermal communication with a bottom facing
outer surface (<NUM>) of the aircraft structure (<NUM>), wherein the skin heat exchanger assembly (<NUM>) is offset relative to the inlet duct (<NUM>) and the first heat exchanger assembly (<NUM>) and the skin heat exchanger assembly (<NUM>) is in fluid communication with the first heat exchanger (<NUM>) such that a working fluid (<NUM>) is communicated therebetween;
characterised in that the inlet duct is open through the bottom facing outer surface.