Patent Description:
Turbine engine manufacturers continue to seek further improvements to engine performance including improvements to reduce environmental impact while improving propulsive efficiencies.

Document <CIT> discloses a prior art turbine engine.

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

In a further embodiment of the foregoing, the energy extraction system further includes a liquid pump that is configured to increase a pressure of the liquid ammonia fuel to a pressure that is greater than a pressure of the liquid ammonia fuel in the ammonia fuel storage tank.

In a further embodiment of any of the foregoing, the ammonia fuel storage tank assembly is configured to store the liquid ammonia fuel under a temperature and pressure that is different than an ambient temperature and pressure.

In a further embodiment of any of the foregoing, the energy extraction system further includes a liquid pump that is configured to increase a pressure of the liquid ammonia fuel to a first pressure that is greater than a pressure of the liquid ammonia fuel in the ammonia fuel storage tank. The first pressure is greater than a pressure of the vaporized ammonia based fuel that is communicated to the combustor.

In a further embodiment of any of the foregoing, the thermal transfer assembly is in communication with a core flow to the turbine.

In a further embodiment of any of the foregoing, the thermal transfer assembly is configured to heat the ammonia fuel to decompose at least a portion of the ammonia fuel into hydrogen and nitrogen.

In a further embodiment of any of the foregoing, the thermal transfer assembly is disposed before the turbo-expander.

In a further embodiment of any of the foregoing, the energy conversion device includes a fuel cell that is configured to generate electric power to drive an electric motor.

According to a further aspect of the present invention, there is provided a method of operating an energy extraction system as set forth in claim <NUM>.

In a further embodiment of any of the foregoing, the method includes pressurizing the ammonia fuel in the liquid form to a first pressure greater than a pressure of the ammonia fuel stored in a fuel storage tank.

In a further embodiment of any of the foregoing, the method includes transforming the ammonia fuel within a thermal transfer assembly in thermal communication with a heat source.

In a further embodiment of any of the foregoing, the method includes transforming the ammonia fuel in liquid form within a thermal transfer assembly in thermal communication with a core flow.

In a further embodiment of any of the foregoing, the method includes decomposing at least a portion of the ammonia fuel into hydrogen and nitrogen with exposure to heat in the thermal transfer assembly.

Although the different examples have the specific components shown in the illustrations, embodiments of this invention are not limited to those particular combinations.

<FIG> schematically illustrates one example disclosed alternate fueled turbine engine assembly <NUM>. The engine assembly <NUM> uses a vaporized ammonia based fuel mixed with a core gas flow <NUM> in a combustor <NUM> to generate a high energy gas flow <NUM> that expands through a turbine section <NUM> to drive a compressor section <NUM> of a main turbine engine <NUM>. The disclosed vaporized ammonia based fuel may include ammonia, decomposition products of ammonia and/or a mixture of ammonia and decomposition products.

Ammonia (NH<NUM>) does not contain carbon, but does have a fuel energy similar to alcohols such as methanol. Ammonia can also be transported and stored in liquid form at moderate pressure and temperature. For example, ammonia is a liquid at a pressure of about <NUM> atm and a temperature of <NUM>. Alternatively, ammonia is a liquid at a pressure of <NUM> atm and a temperature of -<NUM>. These properties make ammonia attractive as alternate fuel that produces no carbon dioxide.

The disclosed engine assembly <NUM> uses heat to transform ammonia fuel in a liquid state into a vaporized ammonia based fuel. The vaporized ammonia based fuel <NUM> is expanded through a turbo-expander <NUM> to create shaft work and then delivered to the combustor <NUM> to generate additional power and shaft work utilized to generate a thrust producing flow <NUM> by the main engine <NUM>.

The vaporized ammonia based fuel <NUM> is generated from a liquid ammonia fuel <NUM> stored in a fuel storage tank <NUM>. The fuel storage tank <NUM> stores ammonia fuel <NUM> in a liquid state at a pressure and temperature that maintains the ammonia fuel <NUM> in a liquid state. The specific pressure and temperature required to maintain the ammonia fuel <NUM> in the liquid state may vary in different embodiments. In one disclosed example, the ammonia fuel <NUM> is maintained in the liquid state by storing at a temperature below about -<NUM> and at a pressure at or below approximately <NUM> atm. In another disclosed embodiment, the ammonia fuel <NUM> is maintained in the fuel storage tank at a pressure of about <NUM> atm at a temperature of <NUM>. In another disclosed embodiment, the ammonia fuel is maintained in a liquid form at a pressure of about <NUM> atm and a temperature of about -<NUM>. It should be appreciated that the specific temperature and pressure of ammonia may vary depending on application specific conditions.

Ammonia fuel <NUM> in a liquid state is pressurized to a first pressure by a liquid pump <NUM>. The liquid pump <NUM> raises the pressure to a point where the ammonia fuel <NUM> is of a pressure greater than is needed for communication into the combustor <NUM>. The pressurized liquid ammonia fuel <NUM> is then heated within a thermal transfer assembly <NUM>. Thermal energy is drawn from various heat sources including heat producing engine systems as is schematically shown at <NUM>. Heat producing systems can include electric systems, combustion systems, turbine systems, lubrication systems and air cooling systems. The work required to pressurize ammonia fuel <NUM> in a liquid state to a high pressure is relatively small compared to the work created by turbo-expanding the heated, gaseous ammonia (or its decomposition products) in the turbo-expander <NUM>. As a result, the heat used to raise the temperature of the ammonia fuel produces additional work that can be captured to reduce the load on the main engine <NUM> that in turn enables more work or thrust to be produced from a given quantity of fuel. Additionally, heat producing systems onboard an aircraft may also be utilized to supply heat required to vaporize the ammonia fuel <NUM>.

Ammonia fuel exhausted from the thermal transfer assembly <NUM> is in a gas state and is communicated to an inlet <NUM> of a turbo-expander <NUM> and exhausted through an outlet <NUM> to the combustor <NUM>. The turbo-expander <NUM> drives a shaft <NUM> that is coupled though a mechanical coupling <NUM> to drive engine and/or aircraft systems as is schematically shown at <NUM>. The engine and/or aircraft systems can include pumps, generators, gearboxes and any other systems that would normally be powered through a coupling to a main engine shaft.

In this disclosed example, the turbo-expander <NUM> is further coupled to drive a low pressure compressor section <NUM> of the main turbine engine <NUM>. As is schematically shown, the high pressure compressor section <NUM> is coupled by way of shaft <NUM> to a high pressure turbine section <NUM>. The high pressure compressor section <NUM>, combustor <NUM> and high pressure turbine <NUM> provide a gas generator that produces the high energy exhaust flow <NUM> utilized to produce thrust. Any load placed on the main engine <NUM> reduces the amount of thrust that can be produced. The turbo-expander <NUM> uses energy in the vaporized ammonia based fuel <NUM> to reduce the amount of fuel required to produce the exhaust flow, thereby improving engine efficiency.

In the main engine <NUM>, the thrust producing flow <NUM> can be directed through a nozzle <NUM> to generate thrust. Additionally, the exhaust gas flow <NUM> can be used to drive a turbine that in turn would drive a fan to produce a bypass flow that increases thrust. A controller <NUM> is provided to control operation of the pump <NUM> and the turbo-expander <NUM> to desired engine operating demands and conditions. It should be appreciated, that the main engine <NUM> is shown schematically and that other structures and engine configurations such as <NUM>-spool, <NUM>-spool and geared turbofan engines would benefit from this disclosure and are within the contemplation and scope of this disclosure. Moreover, a land based turbine engine would also benefit from application of the features of this disclosure.

Referring to <FIG>, another example engine assembly <NUM> is schematically shown. The example engine assembly <NUM> includes the turbo-expander <NUM> that produces additional shaft work from the expansion of products from the cracking or decomposition of an ammonia based fuel <NUM>. The engine assembly <NUM> includes a main engine <NUM> and a thermal transfer system <NUM> that utilizes heat from the high energy exhaust gas flow <NUM> generated in the combustor <NUM> to thermally decompose the ammonia fuel <NUM>. In this example, the thermal transfer system <NUM> includes heat exchangers <NUM> in thermal communication with the exhaust gas flow <NUM> generated by the combustor <NUM>. The higher heat energy generated aft of the combustor <NUM> elevates the temperature of the liquid ammonia fuel <NUM> and helps to decompose the ammonia into hydrogen and nitrogen according to the chemical equation:
<CHM>.

Depending upon the final temperature and pressure and the rate of decomposition in the presence of a catalyst, all of the ammonia or some portion of the ammonia may become cracked to form nitrogen and hydrogen. Cracking the ammonia fuel into nitrogen and hydrogen captures waste heat and provides an increased amount of work in the turbo-expander <NUM>.

Moreover, because the cracking process is endothermic, the cracked fuel has increased fuel chemical energy and can therefore provide increased engine work output or thrust output without increased fuel flow and thereby improves engine fuel efficiency. The cracking process is endothermic and therefore additional heat absorption capacity becomes available at a given fuel temperature, thereby enabling greater heat absorption before the fuel temperature approaches the temperature of the heat source.

The cracking process increases the number of moles, with one mole of ammonia NH<NUM> becoming two moles of cracked gas, per NH<NUM> = ½ N<NUM> + <NUM>(½ H<NUM>), the resulting cracked gas occupies more volume and can provide more work output when turbo-expanded than can the original ammonia fuel for the same turbo-expander inlet temperature and pressure conditions. Because the cracked gas is less dense and has a higher specific heat capacity it can produce more work as enthalpy is extracted during turbo-expansion.

Furthermore, the cracking process changes the chemical composition of the ammonia fuel and thereby also changes its vapor-liquid equilibrium properties which provide greater turbo-expansion of the cracked gas. As appreciated, for a given pressure, the saturation temperature, where vapor begins to condense to liquid, is much lower for H<NUM> and N<NUM> than it is for NH<NUM>. As a result, the conversion of some or all of the NH<NUM> to H<NUM> and N<NUM> allows a larger temperature drop and more work extraction across the turbo-expander <NUM> without crossing the vapor-liquid equilibrium line than would be possible with pure NH<NUM> as the working fluid in the turbo-expander.

This property can be advantageously used when cracking is included in the process by pumping the liquid fuel to a higher pressure before it is heated and cracked, thereby enabling a greater pressure and temperature drop during turbo-expansion. Cracking at least some of the ammonia fuel to form hydrogen further improves the flammability of the fuel, thus facilitating both ignition and stabilization of combustion in the main engine <NUM>.

The example main engine <NUM> includes a free power turbine <NUM> that drives an output shaft <NUM>. The free power turbine <NUM> is driven by expansion of the exhaust gas flow <NUM> aft of the high pressure turbine <NUM>. The free power turbine <NUM> is not coupled to drive other structures of the main engine <NUM> and therefore may more efficiently drive accessory components or a propulsive fan <NUM>, at their desired speeds, as is schematically shown. As appreciated, some portion of shaft power from a turbine is typically required to drive accessory components and/or other compressor sections such as the low pressure compressor <NUM>. However, the turbo-expander <NUM> uses energy from the cracked ammonia based fuel <NUM> to drive an accessory component <NUM> and/or the low pressure compressor <NUM>. Accordingly, power generated by the power turbine <NUM> to drive the shaft <NUM> is increased and the overall engine efficiency is improved.

Referring to <FIG>, another example engine assembly <NUM> is schematically shown. The engine assembly <NUM> includes a fuel cell system <NUM> that is supplied with vaporized ammonia based fuel <NUM> to generate electric power schematically shown at <NUM>. The fuel cell system <NUM> may be a direct-ammonia fuel cell, or a system that includes conversion of ammonia to hydrogen for use in a hydrogen fuel cell. The electric power <NUM> in this example is utilized to drive an electric motor <NUM>. The electric motor <NUM> includes an output shaft <NUM> that drives an engine and/or aircraft system schematically indicated at <NUM>. Vaporized ammonia based fuel <NUM> expands through the turbo-expander <NUM> to power the shaft <NUM>. The shaft <NUM> can be coupled to drive various needed aircraft and/or engine accessories as is schematically shown at <NUM>. The aircraft/engine accessory <NUM> may be a pump, a generator and/or any other structure utilizing rotary shaft power. The heat <NUM> for vaporizing the ammonia fuel <NUM> may be provided by any heat producing structure or device associated with an engine, fuel cell system, and/or aircraft. The disclosed engine assembly <NUM> may be utilized as a standalone engine or as an accessory unit in concert with a turbine engine to increase overall engine efficiency.

Accordingly, the disclosed assemblies provide for the advantageous use of ammonia fuel to improve engine efficiency and reduce carbon emission. The disclosed systems use advantageous properties of ammonia to convert ammonia fuel into useful work prior to combustion that enables improved engine efficiencies.

Claim 1:
An energy extraction system, comprising:
an ammonia fuel storage tank assembly (<NUM>) configured to store a liquid ammonia fuel;
a thermal transfer assembly (<NUM>; <NUM>) configured to transform the liquid ammonia fuel into a vaporized ammonia based fuel;
a turbo-expander (<NUM>) configured to expand the vaporized ammonia based fuel to extract work;
a low pressure compressor (<NUM>), the turbo-expander (<NUM>) coupled to drive the low pressure compressor (<NUM>); and
an energy conversion device including a combustor (<NUM>), the energy conversion device configured to use the vaporized ammonia based fuel from the turbo-expander (<NUM>) to generate a work output, wherein the low pressure compressor (<NUM>) is in flow communication with the combustor (<NUM>), the low pressure compressor (<NUM>) pressurizing air to be mixed with the vaporized ammonia based fuel in the combustor (<NUM>), and the vaporized ammonia based fuel is mixed with air and ignited in the combustor (<NUM>) to generate a high energy exhaust gas flow that is expanded through a turbine (<NUM>).