Scalable power generation using a pulsed detonation engine

A scalable power generator is described. A scalable, portable pulsed detonation engine is coupled to a turbine which drives a generator and using commonly available fuels, electric energy is provided. Additional embodiments incorporate a mechanical compressor at the intake of the pulsed detonation engine which is driven by a second turbine, the second turbine drives a shaft that powers the mechanical compressor. Other enhancements to the invention and additional embodiments are described.

BACKGROUND

There is a constant need for improved and efficient electric power generation from clean and readily available fuels. Power generation for villages, buildings, hospitals, homes, construction sites, and other operations is desirable in remote areas without infrastructure, in new construction where no power grid or distribution system is available, and as alternative power in response to increasingly frequent blackouts or brownout situations on a main power grid. In some remote areas, due to costs and physical barriers, a traditional power grid may never be built for the distribution of centrally generated electric power. In other situations the existing power grid may be unreliable due to weather events such as ice storms, hurricanes, severe thunderstorms and the like, or a poor infrastructure, a weak local economy, or political or military operations which interfere from time to time with use of the existing power grid as an electrical power source.

In the prior art, gas turbine technology is a known source for generated electrical power. Gas turbines burn natural gas, typically, or other similar fuels to drive turbines which turn a generator and thus produce power. In a gas turbine engine, a flame burns fuel and air and expands combustion products to turn a turbine coupled to a shaft, which itself turns a series of compressors located ahead of the engine to compress incoming air to a high pressure, in a power generation application the thrust power remaining in the exhaust turns a turbine which drives a generator for electrical power generation. The heated exhaust expands and creates thrust energy as the hot gases move towards the exhaust port of the engine. (For propulsion applications, the thrust from the engine exhaust is used to push the vehicle forward, as in a jet engine.)

Pulsed detonation engine technology is a newer technology for producing thrust from the process of burning fuel. In a pulsed detonation engine known in the prior art, thrust is produced as the result of a series of rapidly pulsed detonations to produce an approximately constant volume pressure wave traveling at supersonic speeds to an exhaust point in an engine chamber. This type of engine is currently being considered for flight propulsion, for satellite power, for generating satellite electric power using a magnetohydrodynamic (MHD) power generation which depends on an ionic current flow in the exhaust, for satellite and military operations where high levels of “short burst” power is required, for example, as for so-called “space weapons” which require an extremely high amount of energy in a short burst.

In a pulsed detonation engine, a series of detonations are created in a combustion chamber. If the detonations are not sufficiently rapid, then, the reaction is basically a deflagration or “fast flame” combustion process. However, if certain critical parameters are met, the velocity of the pressure waves being generated at and moving away from the ignition point reaches a critical value, the Chapman-Jouguet velocity. If the velocity of the pressure wave reaches the critical Chapman-Jouguet velocity, the engine undergoes a deflagration to detonation transition, known as “DDT” in the art. Once the combustion process has transitioned to detonation, that is the velocity of the pressure waves traveling away from the ignition point is greater than the critical Chapman-Jouguet velocity, the engine is said to be in detonation mode. In order to maintain this mode, fuel, air or oxygen, and the ignition system all have to be pulsed at a frequency which is rapid enough to support and maintain the pulsed detonation mode, which may be as low as 20 Hz, more typically in the vicinity of 50-60 Hz for example and may be optimally over 100 Hz. Now, instead of a flame, the engine exhibits a series of rapid and continuous explosions, the energy from which is added to the pressure wave traversing the tube. The pressure wave velocity will be supersonic, and may reach Mach 4-5. The thrust available from a pulsed detonation engine is believed to be several times that of a gas turbine or jet engine for the amount of fuel consumed.

In a conventional jet engine or gas turbine, a great deal of the available energy is required to produce the high pressures needed to drive the process. For example, in an engine used in a commercial airliner, the Boeing 747, it is estimated that 70,000 horsepower are used to drive the many mechanical air compressors at the intake of the engine. As a result, a substantial amount of the total energy produced is used to drive the compressors, and this limits the amount of output energy available for other purposes, such as propulsion and power generation.

In contrast, a pulsed detonation engine uses the detonations themselves to produce a pressure wave. Thus, much less energy is needed to compress the air at the intake, which results in a more efficient engine for a given amount of thrust.

An ideal pulsed detonation engine produces a constant volume output pressure wave. In a propulsion system, for example as applied to flight propulsion, the pulsed detonation engine is known to have the capacity to produce more thrust per unit time than a conventional jet or rocket engine. Thus the pulsed detonation engine is a more efficient method to produce the thrust needed for a given application.

There is a need for an improved, scalable, efficient and portable power generation system which can use a variety of readily available fuels to produce electric energy. The applications for such a technology range from power generation plants to portable personal use systems for providing energy to a home or building due to storms, for use in remote locations, or temporarily to replace power during power grid failures caused by a variety of events. Further, there is a need for small, efficient and portable electric power generators for a home, a single building, or a remote village. The various embodiments of the invention described in this application address this need.

SUMMARY OF THE INVENTION

The present invention provides an electric power generation system which is driven by a scalable, portable and efficient pulsed detonation engine, or a combination of such engines operated together, which drives a generator for the production of electricity from commercially available fuels such as butane, methane, propane, hydrogen or like similar fuels. The generator of the invention may be quite small and portable. Alternatively it may be scaled to a larger size if desired.

In accordance with one aspect of the present invention a scalable pulsed detonation engine is provided which receives compressed air at its intake, receives propane at fuel intake valve and mixes the propane with the compressed air, and through the use of a high energy, high frequency ignition system, rapidly transitions from deflagration to detonation combustion to produce a nearly constant volume output in a pulsed detonation mode. The exhaust of the pulsed detonation engine drives a turbine which is used to mechanically turn a generator and thus produce electric power. The electric power may also be used, in part, to drive an electric air compressor to provide the compressed air at the intake and to power the ignition system, so that the power generating process is self-sustaining.

In accordance with another aspect of the invention, the fuel used by the electric generation system of the invention may be modified and may be any one of a number of alternatives, including without limitation methane or natural gas, butane, hydrogen, coal dust or other similar fuels.

In accordance with another aspect of the present invention a mechanical compressor such as is used in a small jet engine is attached to an air intake of the pulsed detonation engine, eliminating the need for supplying the compressed air at the intake. The mechanical compressor is turned by a rotating shaft which is itself turned by the turbine at the output of the pulsed detonation engine referred to above. The exhaust output from the first turbine is then used to turn a second turbine, and this turbine is now used to drive the generator and so derive the electric power output by the system. Thus an efficient and scalable “air breathing” generator using the pulsed detonation engine of the invention is provided.

Still further, additional features of the present invention may be applied to increase the efficiency of the power generation system. As an example multiple detonation tubes of small size may be used instead of a single detonation tube. Additional complexity to the fuel and ignition systems may also further increase efficiency. A Shchelkin spiral coil, or other disturbing elements in the main tube, may be used in the ignition chamber to increase the transition speed from deflagration to detonation and thus increase the efficiency. Some remaining exhaust energy may be claimed by using an afterburner to burn some of the exhaust from the engine, or, by thermal exchange to capture exhaust heat in a heat exchanger, or by other means. Multiple sidewall ports may be used to inject fuel and oxidizing agents to improve the engine performance over a single fuel and oxidizer valve.

The present invention provides a scalable power generation system that can be operated using readily available fuel supplies. The power generator may be portable and quite small, or, it may be increased in scale to provide a gas fired or propane power generation plant with increased efficiency. It may be used as an emergency power supply, a backup generator, a remote use generator, for recreational use, for military use, and especially in areas without a power grid, as a residential or village power source. Multiple pulsed detonation engine tubes may be used in a parallel arrangement to increase the scale and the corresponding power output may be proportionally increased as well. The system could be sized to be a truck or trailer mounted system for small villages and buildings, or may be sized to be carried by one or two people, or supplied in a wheeled fashion for easy manual delivery to a desired site.

Those skilled in the art will further appreciate the above-noted features and advantages of the invention together with other important aspects thereof, upon reading the detailed description which follows in conjunction with the drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the description which follows like parts are marked throughout the specification and drawing with the same reference numerals, respectively. The drawing FIGURES are not necessarily to scale and certain features may be shown exaggerated in scale or in somewhat generalized or schematic form in the interest of clarity and conciseness.

Referring toFIG. 1, there is illustrated a portion of a first preferred embodiment of a pulsed detonation engine11for use in the invention. Pulsed detonation engine11is illustrated having detonation tube10coupled by flanges2to an ignition chamber tube4. Igniter5is mounted to tube4adjacent a rotary valve7which receives a fuel and oxygen mixture which is provided into the ignition chamber4. Flange8then couples air intake mount9to an end cap3. The components may be made, for example, of steel, stainless steel or another alloy steel, a prototype has been fabricated of simple bulk steel. The components may be made of any of several sizes, the tube1may have an inner diameter of as short as 10-20 mm and is scalable to any maximum size desired, and lengths may vary from as short as 60 cm or less in length, and are scalable up to any desired size. Cooling may be provided by air, forced air, or typically in a preferred embodiment, a water jacket (not shown) circulating coolant around the exterior of the engine and having a water pump and a conventional radiator for cooling the hot water before returning it to the engine water jacket may be used. The valves used in the preferred embodiment are simple and robust, requiring very little maintenance and lubrication in use.

Ignition is a critical component in achieving and maintaining the deflagration to detonation transition (“DDT”) which is required to create a detonation engine process with the increased thrust advantageously provided by such an engine. It has been discovered by the inventors hereto that prior art approaches to detonation engine ignition may not provide sufficient frequency and/or sufficient instantaneous energy required to quickly achieve and maintain a detonation pressure wave in the engine. The igniter5used in a preferred embodiment of this invention is based on a large capacitive discharge and a control circuit has been designed to operate an off-the-shelf overvoltage type triggered spark gap device driven by the capacitive discharge, this igniter can achieve operating frequencies of over 100 Hz and power levels of up to 28 Joules, with an energy of 18 Joules being used typically in one preferred embodiment. The triggered spark gap device is commercially available from suppliers and may be commercially known as a “trigatron.” Use of the igniter apparatus of the invention enables a rapid transition from the inefficient deflagration mode of combustion to the desired detonation mode of combustion. Further, use of this igniter allows for a shorter detonation tube than would otherwise be required to achieve a detonation mode of combustion, as tube length is a factor in the ease and speed of transition to the detonation mode. A shorter tube length is desirable but use of a shorter detonation tube requires the high frequency, high energy ignition of the invention, otherwise a longer tube is needed to achieve a detonation mode of operation. Longer tube lengths create additional inefficiencies as velocity of the gas flow is slowed by the additional tube length.

In operation, the engine of the preferred embodiment shown inFIG. 1is initially started by beginning a cyclical supply of the fuel, air and oxidizer and the igniter is operated in phase with the rotary valves to start the engine. The frequency of the ignition is then increased synchronously with the fuel, oxidizer and air valve frequency in order to achieve the operating frequency. The frequency of operation may be as little as 10-20 Hz, reliable operation of a prototype has been observed at 60 Hz, and may also be run at faster operation of over 100 Hz. The air intake is used to supply air for ignition cycles and also to purge the tube10between detonation cycles.

InFIG. 2, a second preferred embodiment of a pulsed detonation engine of the invention is depicted. InFIG. 2, the tube10ofFIG. 1is again provided with flange2coupling the tube10to an ignition chamber4with igniter5. Flange8couples the ignition chamber4to an end cap which receives three inputs, one for fuel, one for an oxidizer such as oxygen, and one for compressed air. Now theFIG. 2shows in detail the supply valves. Valve21provides the fuel, valve23provides the compressed air, and valve25provides the oxidizer.

The valves required for air intake, fuel and oxidizer may be, for example, mechanically driven rotary type valves. As shown inFIG. 2, a separate valve may be provided for fuel, a second for oxygen, and a third valve may be used to purge the tube between detonation cycles. In detonation mode the fuel, oxidizer, air intake valve and igniter are all operated synchronously together to produce pulsed detonations with and purge cycles in between, at a frequency of from 10-20 Hz to over 100 Hz. In the preferred embodiment ofFIG. 2, a trapezoidal manifold mount may be used to mount three rotary valves at the closed end of the tube, these are maintained in correct positional relation by a single belt27, and in one arrangement contemplated as part of the invention and depicted inFIG. 2, there is a single rotary motor29driving the belt. Other arrangements are possible for the valves and the drive motor. Alternate arrangements may be used such as eliminating the oxygen valve25if the compressed air and fuel are mixed correctly without it, or using separate drive motors for the valves and using multiple belts, and other modifications can be made as will be apparent to those skilled in the art.

In operation of the pulsed detonation engine ofFIG. 2, the compressed air valve23is used both to supply the compressed air for ignition cycles as determined by the frequency of operation of the igniter5, and to purge the tube10between detonation cycles. This may be accomplished several ways, for example through the use of gearing to turn the valve23at a rate that is twice that of the valves21and25, or by manufacturing the rotary valve23to provide twice the number of valve ports so that it opens twice as often in a given rotation of the motor29, or by other means which will be apparent to those skilled in the art.

Referring toFIG. 1A, there is illustrated a portion of a first preferred embodiment of a pulsed detonation engine11for use in the invention. Pulsed detonation engine11is illustrated having detonation tube10coupled by flanges2to an ignition chamber tube4. Igniter5is mounted to tube4adjacent a rotary valve7which receives a fuel and oxygen mixture which is provided into the ignition chamber4. Flange8then couples air intake mount9to an end cap3. The components may be made, for example, of steel, stainless steel or another alloy steel, a prototype has been fabricated of simple bulk steel. The components may be made of any of several sizes, the tube1may have an inner diameter of as short as 10-20 mm and is scalable to any maximum size desired, and lengths may vary from as short as 60 cm or less in length, and are scalable up to any desired size. Cooling may be provided by air, forced air, or typically in a preferred embodiment, a water jacket12circulating coolant around the exterior of the engine and having a water pump13and a conventional radiator14for cooling the hot water before returning it to the engine water jacket may be used, as shown for example inFIG. 1B. The valves used in the preferred embodiment are simple and robust, requiring very little maintenance and lubrication in use.

Other enhancements may also be added to the engine11ofFIG. 1to increase the efficiency. For example, obstacles in the main tube such as a Shchelkin spiral in the main tube, baffles, orifices or other obstacles may be used which result in enhanced operational efficiency by aiding the transition from deflagration to detonation mode. In a preferred embodiment of the invention, a Shchelkin spiral having a volume of, for example, about 20% of the open tube volume, is placed inside the tube in near proximity to the igniter5and this has been found to improve the rapid transition to detonation mode.

FIG. 3depicts a cross sectional view of the pulsed detonation engine ofFIG. 2incorporating the Shchelkin spiral of this additional preferred embodiment. Tube10is shown with Shchelkin spiral31in place positioned near to igniter5. Mixer33is shown receiving the air, oxidizer and fuel from the rotary supply valves. Spiral31disturbs the flow and thereby enhances the efficiency of the engine operation and speeds the transition to detonation mode at startup.

InFIG. 2, a second preferred embodiment of a pulsed detonation engine of the invention is depicted. InFIG. 2, the tube10ofFIG. 1is again provided with flange2coupling the tube10to an ignition chamber4with igniter5. Flange8couples the ignition chamber4to an end cap which receives three inputs, one for fuel, one for an oxidizer such as oxygen, and one for compressed air. Now theFIG. 2shows in detail the supply valves. Valve21provides the fuel, valve23provides the compressed air, and valve25provides the oxidizer.FIG. 8shows an alternative embodiment with solenoid valves. Valve81provides the fuel, valve83provides the compressed air, and valve85provides the oxidizer.

FIG. 5adepicts another preferred embodiment of a pulsed detonation engine of the invention81. Shown in cross section, chamber83has multiple sidewall ports for fuel injection85controlled by a rotary valve87for supplying fuel into the ports, oxidizer injection ports89which are controlled by a rotary valve91for supplying an oxidizer, preferably oxygen, into the chamber, drive shaft97is coupled to a pulley95which operates the air input valve93which operates by rotating action over an intake port99to receive compressed air into the chamber. Ignitor103is placed into the chamber83to provide the energy required to initiate and sustain detonation.

In operation, a belt or chain92, only partially shown inFIG. 5a,is used to synchronously operate the fuel valve87, the oxidizing valve91, and the air valve93by means of drive pulley95. Ignitor103is used to cause the pulsed detonation cycles as described above and air valve93is also used to purge chamber83between detonation cycles.

As a further alternative to the mechanical rotary valves shown inFIG. 2, solenoid electrical valves may be used instead to provide the pulsed fuel, compressed air and oxidizer required to the ignition chamber, as shown inFIG. 8. A commercially available solenoid valve that partially fulfills the requirements stated above is one in the Numatech.RTM. TM series, which has a maximum operating frequency of 50 Hz, as quoted by the manufacturer. These valves are also commercially available from suppliers. The fuel can be any one of several known fuels, preferably a locally available and economical fuel, such as propane or methane (natural gas), may be used. Other known alternatives such as hydrogen or butane may be used as well as other hydrocarbon-based fuels. In one preferred embodiment, propane is used plus oxygen is used as an oxidizer, and these are combined with the incoming compressed air. The compressed air should be at about 2-3 atmospheres, or more, for efficient operation. Other oxidizers and fuels can be used as is known to those skilled in the art. The oxidizer enhances operational efficiency but is not necessarily required, and for simplicity in remote areas, the fuel may be chosen so as to eliminate the need for a separate oxidizer or the fuel may be enhanced prior to use in the engine by adding oxidizing compounds.

FIG. 6depicts a preferred embodiment of a power generator using the pulsed detonation engine ofFIG. 2orFIG. 3. InFIG. 6, a mechanical compressor41is shown receiving ambient air at an intake. (As an alternative, the air intake and mechanical compressor could be replaced with a source of compressed air as inFIG. 1.) The mechanical compressor41may be an existing off-the-shelf component, for example, for a small scaled detonation engine of the invention, it may be a compressor from a commercially available remote controlled model jet engine; or at a larger scale it could be a compressor such as is used in a cruise missile engine, as are known to be available from Williams International, among other suppliers. A detonation engine43, as for example the one shownFIG. 2, then receives at least a part of the airflow (now, compressed air) output by compressor41. Check valve42allows air to flow from compressor41into pulsed detonation engine43but checks any undesired flow from the detonation tube back to compressor41. Part of the compressed air from the output of compressor41is sent to the detonation tube43, the remaining flow is sent downstream to a turbine. The pulsed detonation engine43again requires rotary or electrical fuel valves which supply propane, methane or another fuel, oxygen, and mixes them and delivers the fuel and oxidizer mix into tube. Again as inFIG. 1a high energy igniter is used to cyclically create detonations at an appropriate frequency, which could be as low as a few Hz or as high as 200 Hz, again using the high energy arc of the preferred embodiment, typically 18 Joules of energy is delivered. A pulsed detonation wave is created in engine43which is used to drive a first turbine45, this turns shaft47which in turn drives the compressor at the intake41. The exhaust is then directed to and drives a second turbine49, which is used to mechanically power generator51. The turbines and generator may be for example commercially available components, for example the turbines may be similar to those used in turbochargers for automotive applications.

In an enhanced preferred embodiment, the remaining exhaust flow may be used in a heat exchanger to capture additional thermal energy as heat before being released into the environment as exhaust. Additional enhanced features may include some burning of the exhaust using an afterburner to provide a cleaner exhaust product with little or no remaining fuel or other combustible elements in it.

The embodiment ofFIG. 7may have additional features added to provide another preferred embodiment, as shown inFIG. 6. A multiple chamber pulsed detonation engine may be used, each chamber52being fired in a predetermined order at a different time in an overall cycle. Each chamber is a pulsed detonation engine as depicted inFIGS. 2 and 3. This enhancement of the earlier embodiment provides additional thrust to the turbines and thereby enables the generator to produce additional electric power. In this embodiment, multiple pulsed detonation engines drive the first turbine by firing in a phased fashion to provide proportionally increased thrust. Each one of the engines has an air intake, a rotary valve or solenoid fuel valve, and preferably a corresponding oxidizer or oxygen valve, for receiving the fuel and supplying it to the individual chamber as shown inFIG. 2. InFIG. 7a plenum53is provided at the output of the now multiple detonation tubes. The plenum53is used, in part, to dampen the individual pulsed output at the detonation tube exhausts and further to provide a kinetic energy to enthalpy conversion which functions to slow the gases down and to simultaneously increase the pressure. The plenum53also functions to prevent pulsations from the several pulsed detonation engines from reaching the turbine45and prevents damage to the turbines downstream due to vibrations or mismatched detonation waves. Again, the turbine49is used to turn shaft47which drives the mechanical compressor41. The exhaust gas flowing from the first turbine is directed to the second turbine49which drives the generator51.

The generator of the invention may be used in a variety of applications. Smaller sized generators of the preferred embodiments might be used to generate 1 kW, or larger ones with multiple tubes may be used to generate 10 kW, or more. A properly scaled mechanical compressor may be used, or previously compressed air could be used to supply the air needed for the process. Oxygen or other known oxidizers are supplied in a preferred embodiment but may not be used for simplicity in other embodiments. The intake valves could be replaced with intakes along the sidewalls of the detonation tubes. Additional power generation could be achieved by ionization of the exhaust stream by adding ionized particulates or other means, and using a magnetohydrodynamic (MHD) generator to capture the resulting energy from the ionic flow.

Those skilled in the art will recognize that other modifications and substitutions may be provided with respect to the invention disclosed herein without departing from the scope and spirit of the appended claims.