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WO2008156913A2 - Moteur harmonique - Google Patents

Moteur harmonique Download PDF

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Publication number
WO2008156913A2
WO2008156913A2 PCT/US2008/061285 US2008061285W WO2008156913A2 WO 2008156913 A2 WO2008156913 A2 WO 2008156913A2 US 2008061285 W US2008061285 W US 2008061285W WO 2008156913 A2 WO2008156913 A2 WO 2008156913A2
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WO
WIPO (PCT)
Prior art keywords
expander
compressor
working fluid
engine
valve
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/US2008/061285
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English (en)
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WO2008156913A3 (fr
Inventor
Charles L. Bennett
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Lawrence Livermore National Security LLC
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Lawrence Livermore National Security LLC
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Publication date
Application filed by Lawrence Livermore National Security LLC filed Critical Lawrence Livermore National Security LLC
Publication of WO2008156913A2 publication Critical patent/WO2008156913A2/fr
Publication of WO2008156913A3 publication Critical patent/WO2008156913A3/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02G—HOT GAS OR COMBUSTION-PRODUCT POSITIVE-DISPLACEMENT ENGINE PLANTS; USE OF WASTE HEAT OF COMBUSTION ENGINES; NOT OTHERWISE PROVIDED FOR
    • F02G1/00—Hot gas positive-displacement engine plants
    • F02G1/04—Hot gas positive-displacement engine plants of closed-cycle type
    • F02G1/043—Hot gas positive-displacement engine plants of closed-cycle type the engine being operated by expansion and contraction of a mass of working gas which is heated and cooled in one of a plurality of constantly communicating expansible chambers, e.g. Stirling cycle type engines
    • F02G1/044—Hot gas positive-displacement engine plants of closed-cycle type the engine being operated by expansion and contraction of a mass of working gas which is heated and cooled in one of a plurality of constantly communicating expansible chambers, e.g. Stirling cycle type engines having at least two working members, e.g. pistons, delivering power output

Definitions

  • This invention relates to heat powered engines, and more particularly to a highly efficient form of heat powered, reciprocating- piston, harmonically acting engine having, in one embodiment, harmonic oscillator valves automatically controlling working fluid flow into and out of an expander at a resonant frequency, and in another embodiment, a shunt channel connecting a buffer chamber of the expander to the outlet of an expansion chamber of the expander, to minimize pressure perturbation in the engine fluidic circuit.
  • Heat powered engines are known in which heat is supplied externally of the working cylinders rather than internally, in contrast to internal combustion engines.
  • a working fluid flows in a loop sequentially through a compressor, a heater, an expander, a cooler and finally back to the compressor.
  • air is the working fluid and the ambient atmosphere performs the role of the cooler.
  • a heat interchanger transfers heat from the working fluid flowing between the expander and the cooler to the working fluid flowing between the compressor and the heater.
  • FIG. 1 An early example of such a heat powered engine is described in U.S. Pat. No. 14690, entitled “Air Engine” by John Ericsson.
  • Figure 1 A schematic illustration of this type of engine, but drawn with modernized mechanisms to facilitate comparison with the present invention, is shown in Figure 1.
  • This is an open cycle, heat powered engine having a single cylinder 57 with a single reciprocating piston dividing the internal cylinder volume into an expander chamber 54 and a compressor chamber 52.
  • Incoming air 51 is drawn into compressor chamber 52 and raised in pressure, then sent to heater 53 and raised in temperature, then admitted to expander chamber 54 and dropped in pressure, and finally outgoing air 55 is released back to the ambient atmosphere.
  • a heat interchanger 56 is provided to transfer some of the heat of the outgoing air to the pressurized air emerging from the compressor on its way to the heater.
  • the arrows in Figure 1 indicate the direction of flow of the air during the upstroke of the piston in this engine.
  • a drawback of this single cylinder arrangement is the significant flow of heat from the high temperature expander chamber to the low temperature compressor chamber via the cylinder wall and the piston, which incurs a significant loss of thermal efficiency.
  • Figure 2 illustrates one particular phase in the engine cycle in which the volume within the expander, the transport volume that passes through the cooler, and the volume within the compressor are all contiguous. Arrows in this figure indicate the direction of the gas flow at this particular phase.
  • the valves in the gas flow circuit provide a means for isolating the portion of the gas mass involved in expansion and compression, from the portion of the gas involved in exchanging heat with heaters or coolers.
  • very efficient heat transfer can be achieved without attenuation of the pressure swings involved in gas expansion and compression inside of the working cylinders, in sharp contrast to the case with Stirling engines.
  • the Bush reference teaches the use of header volumes, both at the expander inlet 58 and at the expander outlet 59.
  • header volumes need to be substantially larger than the displacements of the compressor and expander.
  • the header volumes need to be approximately 100 times greater than the working cylinder volume throughput per cycle. Since the volume throughput associated with the high pressure side is much less than for the low pressure side, the header volume at the exit of the expander, in particular, entails a significant engine mass and volume penalty in order to achieve high efficiency.
  • poppet valves such as those described in the Bush reference, avoid sliding contact, and are very highly developed in the field of internal combustion engines.
  • Such poppet valves typically involve components such as cams, tappets, rockers and followers, as in conventional automobile engines, or pneumatic actuators, such as described by the Bush reference, or may involve electromagnetic actuators.
  • the expander inlet valve may be opened automatically in response to either the increasing pressure within the expander cylinder as the expander piston approaches the top of the cylinder, or by actual contact with the expander piston itself.
  • Bush does not teach how the expander inlet and outlet valves may be made to act fully automatically, as has long been known in the art for compressor valves.
  • One aspect of the present invention includes an engine comprising: a reciprocating-piston expander comprising: an expander cylinder; an expander piston head axially slidable in said expander cylinder and together enclosing an expansion chamber; a piston rod connected at one end to the expander piston head; an inlet valve for controlling the flow of working fluid into the expansion chamber to effect a power stroke of the expander, said inlet valve being a harmonic oscillator having an equilibrium position outside the expansion chamber so that the inlet valve is open at equilibrium and displaceable to a closed position against an equilibrium restoring force; latch means for automatically re-latching the inlet valve in the closed position after being unlatched to experience a harmonic oscillation; an outlet valve for controlling the flow of working fluid out from the expansion chamber during a return stroke of the expander, said outlet valve being a harmonic oscillator having an equilibrium position inside the expansion chamber so that the outlet valve is open at equilibrium and displaceable to a closed position against an equilibrium restoring force; an intake header connectable
  • Another aspect of the present invention includes an engine comprising: an expander having an expansion chamber, an expander inlet leading into the expansion chamber, an expander outlet leading out from the expansion chamber, valve means for controlling flow of working fluid into and out of the expansion chamber via the expander inlet and the expander outlet, respectively; a compressor having a compression chamber, a compressor inlet leading into the compression chamber, a compressor outlet leading out from the compression chamber, and valve means for controlling flow of working fluid into and out of the compression chamber via the compressor inlet and compressor outlet, respectively; a fluidic channel connecting the compressor outlet to the expander inlet for supplying pressurized working fluid from the compressor to the expander; throttle valve means for controlling the flow rate of working fluid entering the compressor inlet based on an absolute temperature ratio of the working fluid leaving the expander and the working fluid entering the compressor; and throttle valve means for controlling the flow rate of working fluid coming from the exhaust header of the expander.
  • Figure 1 is a schematic view of a prior art air engine disclosed in U.S. Pat. No. 14690 to Ericsson.
  • Figure 2 is a schematic view of a prior art heat powered engine disclosed in U.S. Pat. No. 3,708,979 to Bush et al.
  • Figure 3 is a schematic view of a prior art tandem compound hot air engine similar to that disclosed in U.S. Pat. No. 1,038,805 to Webb.
  • Figure 4 is a schematic cross-sectional view of a first exemplary embodiment of the harmonic engine of the present invention, having a tandem arrangement.
  • Figure 5 is a perspective view of the harmonic engine of Figure 4.
  • Figure 6 is a partial view of the expander head of figure 4, showing the fully relaxed state of the automatic expander valves.
  • Figure 7 is a graph showing the valve lifts and piston position of the harmonic engine of Figure 4 as a function of crankshaft angle. A horizontal dashed line indicates the neutral position, corresponding to a fully relaxed spring, for each of the expander valves.
  • Figure 8 is a detail view of the semi-automatic embodiment of the expander inlet and outlet valves both in the un-latched configuration.
  • Figure 9 is a detail view of the semi-automatic embodiment of the expander inlet and outlet valves both in the latched configuration.
  • Figure 10 is a partial view of a second embodiment of the present invention with reed valves in both the expander and the compressor. The position of the reeds in this figure corresponds to the fully relaxed state for all four reeds.
  • This figure also illustrates a third exemplary embodiment, having a linear induction motor.
  • Figure 11 is a schematic cross-sectional view of a fourth exemplary embodiment of the present invention, having a parallel arrangement of the expander and the compressor.
  • Figure 12 is a graph showing the compressor valve and compressor piston positions of the steady running, parallel embodiment of the harmonic engine illustrated in figure 11, with the compressor valve and compressor piston positions shown in solid lines, and with the expander piston position shown as a dashed line for reference.
  • Figure 13 is a graph showing the expander valve and expander piston positions of the steady running, parallel embodiment of the engine of Figure 11, with the expander valve and expander piston positions shown in solid lines, and the compressor piston position shown as a dashed line for reference.
  • Figure 14 is a schematic cross-sectional partial view of a fifth exemplary embodiment of the present invention comprising a double acting expander.
  • the present invention is a high efficiency, heat powered reciprocating-piston engine designed to maximize thermal efficiency by minimizing thermal losses and pressure hysteresis losses as much as reasonably achievable, as well as enabling automatic self- acting expander valve actuation for simplified and cost-effective operation.
  • the engine expander and compressor cylinders of the engine are separated in order to minimize the heat loss from the hot end to the cold end of the engine.
  • the separation enables the harmonic engine to operate at very high thermal efficiency by allowing a high ratio between the hot side temperature and the cold side temperature in the engine.
  • thermal efficiency substantially exceeding 60% the current state of the art value attained with gas turbine plus steam turbine combined cycle engines, is enabled. Experiments with a laboratory prototype based on the engine described herein have shown that this configuration has the capability to exceed an indicated efficiency of 60%.
  • the present invention preferably uses resonant harmonic oscillator valves for controlling working fluid flow into and out of the expander, which has typically been mechanically or otherwise controlled externally (e.g. by cams, or driven by hydraulic, pneumatic or solenoidal means), to simply the expander valve actuation mechanism and its operation, and improve cost effectiveness.
  • the present invention uses harmonic oscillators as self-acting automatic valves, and as such is characterized as a harmonic engine.
  • harmonic engine can be used to characterize either the simple combination of an expander (for producing the power stroke) driven by a supply of pressurized working fluid and a periodic or cyclical means for effecting the return stroke, or a self-contained power generating system having additional components such as a compressor, heater, cooler, fluidic conduits, etc.
  • Figures 4 and 5 together show a first exemplary system having various component parts and sub- assemblies which together as a whole or in various sub-combinations may be characterized as the "harmonic engine" of the present invention.
  • the system is shown having the following components and sub-assemblies: a reciprocating-piston expander assembly 150 with valves 101 and 104 for controlling flow into and out of an expander chamber 162 and a shunt line 100 fluidically connecting an exhaust header duct 105 to a buffer chamber 154; a reciprocating- piston compressor assembly 190 arranged to operate in tandem with the expander assembly via a piston rod 195 and having valves 103 and 102 for controlling flow into and out of a compression chamber 151; fluidic channels 157 and 158 for transporting a working fluid between the compressor assembly and the expander assembly; a heater 163 for heating the working fluid prior to entering the expander assembly; a cooler 187 for cooling the working fluid prior to entering the compressor assembly; a heat interchange
  • the reciprocating-piston expander assembly 150 is shown in Figure 4 having an expander cylinder 161, an expander piston head 160 dividing the internal volume of the expander cylinder into an enclosed expansion chamber 162 above the piston head and an enclosed buffer chamber 154 below the piston head, and valves 101 and 104 leading into and out of the expansion chamber 162, respectively.
  • flow ducts such as expander intake header 125 and expander exhaust header 105, are provided to direct working fluid arriving from the fluidic channel 158 into the expander inlet at inlet valve 101, and to direct working fluid exhausted from the expander outlet at outlet valve 104 into the fluidic channel 157.
  • shunt line 100 is shown connecting the buffer chamber 154 to the expander exhaust header 105.
  • Most components of the expander assembly 150 are preferably constructed of high temperature compatible stainless steel, by virtue of resistance to oxidation at high temperature and low thermal conductivity.
  • the single representative expander piston ring 164 shown surrounding the expander piston head 160 to contact the inner cylinder surface of the expander cylinder 161 is preferably a low porosity graphite, such as Poco graphite, that may be used in air beyond 500 0 C, and far higher in an inert atmosphere.
  • Expander valves 101 and 104 are shown in Figure 4 as poppet valves.
  • expander outlet valve 104 that controls the flow of working fluid out of expansion chamber 162 preferably has a conventional poppet valve arrangement commonly used in automobile engines with a chamfer that occludes from the inside out, i.e. the outlet valve 104 occludes when pulled away from the center of expander cylinder 161, and opens when pushed into the expander cylinder.
  • expander inlet valve 101 that controls the flow of working fluid into expansion chamber 162 preferably has a reversed chamfer arrangement which occludes from the outside in (similar to a conventional automotive wastegate valve known in the art), i.e. the inlet valve 101 occludes when pushed toward the expander cylinder 161, and opens when pulled away from the center of the expander cylinder.
  • expander inlet valve 101 is connected to spring 107 to form a spring-mass system of a harmonic oscillator which, when displaced from its equilibrium position, experiences a restoring force proportional to the displacement according to Hooke's law, as known in the art.
  • expander outlet valve 104 is connected to spring 106 to form another spring-mass system characterized as a harmonic oscillator.
  • the expander valves 101 and 104 are arranged so that the valves are open ( Figure 6) when in their respective neutral/ equilibrium positions, and closed ( Figure 4) when displaced from their respective neutral/ equilibrium positions.
  • the preferred neutral spring position is near half the desired maximum valve open position.
  • inlet valve 101 when inlet valve 101 is in its neutral position with spring 107 relaxed and latch 109 disengaged from indent 110, the position of inlet valve 101 in this state represents approximately half of the fully opened lift height under steady running conditions.
  • spring 107 when valve 101 is closed, as shown in Figure 4, spring 107 is stretched with respect to its neutral position, and when valve 104 is closed, spring 106 is compressed with respect to its neutral position.
  • the spring-loaded latches 109 and 112 are used to keep the expander valves 101 and 104, respectively, in the closed position until overcome by a sufficient change in pressure differential on opposite sides of the valves.
  • valves 101 and 104 When the latches are released from the closed positions, it is appreciated that in the absence of working fluid flow past the valves and ignoring friction and the action of the latches, both valves 101 and 104 would execute simple harmonic oscillatory motion, at resonant frequencies determined by the valve masses and spring strengths, about the neutral positions displayed in Figure 6.
  • inlet valve 101 there is normally a higher pressure acting on the outside surface of inlet valve 101 than on the interior surface facing the expansion chamber, and thus it is normally held shut by a combination of the engaged latch and this pressure difference.
  • outlet valve 104 there is normally a higher pressure acting on the inside surface of outlet valve 104 than on the exterior surface, and thus it is normally held shut by a combination of the engaged latch and this pressure difference.
  • the reciprocating-piston compressor assembly 190 shown in Figure 4 is preferably of a form well known to those skilled in the art, and is shown having a compressor cylinder 155, a compressor piston head 182 positioned in the compressor cylinder 155 to form a compression chamber 151, and automatic valves 102 and 103. Similar to the expander assembly 150, header flow ducts provide connection to the fluidic conduits 157 and 158, and serve to lead/ direct working fluid out to conduit 158, or in from conduit 157. Most components of the compressor assembly are preferentially constructed of aluminum, by virtue of the strength, corrosion resistance, lightness, and relatively low cost. And conventional metal rings 171 and splash oil lubrication from a sump may be used for the compressor piston.
  • an automatic valve 103 governs flow into compression chamber 151, while a second automatic valve 102 governs flow out of chamber 151.
  • Valves 102 and 103 are conventional automatic compressor valves, activated by the flow of working fluid into and out of compression chamber 151. That is, valve 102 opens only when the pressure in expansion chamber 151 sufficiently exceeds the pressure on the external side of valve 102, while valve 103 opens only when the pressure in expansion chamber 151 has dropped sufficiently below the pressure on the external side of valve 103.
  • reed valves (as illustrated in Figure 10) are preferred, since the mass that is moved in the actuation of the valve is only that of the reed material itself, and thus by proper design, it is feasible to have very rapid acting valves, with very little complexity or expense.
  • many variations in the design of compressor valves are known, and almost any of the many forms that are suitable for use in compressors may be used for the present invention.
  • the reciprocating-piston expander assembly 150 and the reciprocating-piston compressor assembly 190 are shown in Figure 4 arranged in tandem with and spaced from each other.
  • the expander cylinder 161 and the compressor cylinder 155 are preferably structurally connected to and thermally isolated from each other by a suitable rigid structure, such as tripod 170 shown in Figure 5.
  • the thermal resistance of the tripod is preferably sufficiently great that only a negligible fraction of the supplied heat is lost by conduction from the hot side to the cold side of the engine. This tripod supports and positions the two cylinders and allows access to tighten the packing seals as needed,
  • Piston rod 195 is shown connecting expander piston head 160 to compressor piston head 182 so that work performed by the expansion of working fluid is transferred by piston rod 195 to the compressor piston head 182 in an axial direction and the compressor piston head moves in phase with the expander piston head.
  • the length of piston rod 195 is suitably great so that the loss of heat by thermal conduction from the hot expander cylinder to the cold compressor cylinder through the material of the piston rod is negligible.
  • tandem reciprocating motions of the expander piston head 160, the compressor piston head 182, and the piston rod 195 are preferably centered and supported by conventional shaft packing seals (not shown) at the bottom of the expander cylinder and at the top of the compressor cylinder (through which the piston rod 195 extends) by means well known in the art of tandem cylinders.
  • shaft packing seals on the expander cylinder and compressor cylinder allow piston rod 195 to reciprocate up and down without significant loss of pressure past the seals.
  • an additional tube (not shown) surrounding piston rod 195 prevents loss of working fluid from the engine.
  • Such packing seals are well known in the art, and many choices are available, but woven graphite material is particularly suitable.
  • the packing material for both of the shaft seals is preferably a braided carbon fiber with graphite lubrication, such as the Style 98 material available from Garlock Sealing Technologies. This material is good up to 455°C in air, 650 0 C in steam, and is expected to be good far beyond 700 0 C in a nitrogen or argon environment. This material is also suitable for use at temperatures as low as -200 0 C.
  • the harmonic engine is shown as a closed system, such that working fluid is cycled between the compressor assembly 190 and the expander assembly 150.
  • channel 158 fluidically connects the compressor outlet (at valve 102) to the expander inlet (at valve 101), and channel 157 fluidically connects the expander outlet (at outlet valve 104) to compressor inlet (at valve 103).
  • an open system embodiment of the present invention is also possible such that fluidic channel 157 would not be necessary. In such an open system embodiment, air would be drawn from the ambient environment into the compressor inlet and exhausted from the expander outlet out to the ambient environment.
  • Heat is preferably supplied by heater 163 to the engine working fluid in fluidic channel 158 to further increase the temperature of the working fluid coming from the compressor, ⁇ t is appreciated that the heat supplied by the heater 163 may be generated by the heater itself, or provided by any number of high temperature external heat sources coupled to the heater.
  • concentrated sunlight from a solar thermal heat collector, external combustion, chemical reaction, nuclear reactions (radioisotope decay heat), or heat transfer from a thermal energy storage medium, either with or without the use of a distinct heat transfer fluid are all viable options in the present invention.
  • the heat transfer surface area may be made arbitrarily large relative to the dimensions of the expander, and thus the efficiency of heat transfer may be made arbitrarily high without degrading the work produced by the expander piston per cycle.
  • the choice of materials for the heater is quite broad, as the mechanical stresses within the heater region may be made much less than in the expander cylinder itself.
  • the highest temperature component in the engine is the heater. This component may advantageously be made of ceramic or a high temperature, high strength metal alloy, for applications involving extreme high temperatures.
  • Working fluid is also preferably cooled in the harmonic engine by cooler 187 prior to entering the compressor assembly 190.
  • the cooler 187 is preferably exposed or otherwise thermally coupled to the ambient environment. This is particularly advantageous when the ambient environment is a low temperature external heat sink, such as high altitude air, or with radiative coupling to cold sky/ space which enables high thermodynamic efficiency.
  • the ambient environment is a low temperature external heat sink, such as high altitude air, or with radiative coupling to cold sky/ space which enables high thermodynamic efficiency.
  • heater 163 is not explicitly required as the ambient environment may provide adequate heating to achieve high thermodynamic efficiency.
  • cooler 187 is not explicitly required in open cycle embodiments, for which the ambient atmosphere itself provides pressure reference 166.
  • compressor 190 serves to increase the pressure of the working fluid, but with only minimal decrease in the volume of the working fluid.
  • the cooler is normally called a condenser
  • the heater is normally called a boiler
  • the compressor is normally called a pump.
  • a heat interchanger 180 is also shown provided in Figure 4, which functions to heat the working fluid emerging from compressor chamber 151 using the hot working fluid output from expander chamber 162.
  • the heat interchanger 180 shown in Figure 5 is shown as a conventional, counter-flow shell and tube heat exchanger.
  • High pressure working fluid flow from compressor assembly 190 to heater 163 flows up through the tubes inside of heat interchanger 180, while low pressure working fluid from the outlet of expander chamber 162 flows down through the shell portion of heat interchanger 180 to cooler 187.
  • the volume within the tube side of interchanger 180 and connected conduits is preferably significantly greater than the volume of working fluid admitted each stroke to expander chamber 162. This promotes substantially isobaric filling of expander chamber while inlet valve 101 is open.
  • the interchanger assembly 180 and most components of expander assembly 150 are preferentially constructed of stainless steel, by virtue of the strength, relatively low cost, and corrosion resistance at the higher temperatures typically involved in the hot side of the engine. [0050] Similarly, with an efficient heat exchanger, the volume within the shell and associated conduits tends to be significantly greater than the volume of working fluid admitted each stroke to compression chamber 151 and this tends to promote substantially isobaric filling of the compression chamber.
  • the working fluid may either remain in gas phase throughout the engine working cycle, or may be in a liquid state in certain portions of the engine working cycle.
  • Air is the most readily available gaseous working fluid, and the only viable choice for an open cycle embodiment.
  • Water is the most readily available phase- change working fluid, and is preferred for modest operating temperatures, between approximately 300 K and 600 K.
  • Hydrogen gas features one of the highest thermal conductivities among gases, and this aspect enables the external heat exchangers to be relatively smaller, but also requires that the engine be approximately hermetically sealed to prevent loss of working fluid.
  • Helium has almost as high a thermal conductivity as hydrogen, but is in addition an inert gas, and thus enables extremely high and or low operating temperatures, without corrosion or condensation.
  • ORC Organic Rankine Cycle
  • FIGs 4 and 5 also show a crank assembly including crankshaft 186 connected to the compressor piston head 182 in a conventional manner known in the art for converting reciprocating piston motion to rotary power output.
  • flywheel 185 is connected to the crankshaft 186 and serves to momentarily store some of the energy produced during the power stroke of expander piston head 160 to be returned during the return or exhaust stroke. In this manner, the inertial moment of the rotating flywheel functions to drive the expander piston head (and compressor piston head in the tandem arrangement) back toward the top dead center position to effectuate the return stroke.
  • Figures 4 and 5 show an optional starting motor 188 ope r ably connected to crankshaft 186 for starting the engine.
  • the starting motor 188 may also be a generator for producing electrical power once the engine is running.
  • starter motor generator 188 is preferably a squirrel cage induction motor compatible with the 60 Hz alternating current power in the United States.
  • crankshaft 186 is driven to rotate at a frequency very nearly equal to an integer fraction (with the integer depending on the motor pole structure) of the power grid frequency.
  • the engine overdrives motor 188, and instead generates electrical current that is forced to be in phase with the electric grid current.
  • the resonant frequency of the expander inlet and outlet valve and spring assemblies to be near integer multiples of the desired electrical output power frequency.
  • the shunt channel 100 enables pressure variations in the volume between the expander outlet and the compressor inlet to be minimized, so that pressure hysteresis losses may be lowered and the engine efficiency may be increased.
  • FIG. 7 A detailed timing diagram illustrating the phasing of the motions of fully automatic valves 101, 102, 103, and 104 together with the position of piston 160, is shown in Figure 7, as a function of crankshaft angle on the abscissa.
  • the sequencing and conditions described here are those for the nominal, full power, steady operation with a highly compressible gaseous working fluid, and the ordering of the valve curves from top to bottom in the figure is approximately in the order of their opening.
  • the angular range displayed covers one complete 360° cycle, and starts at a point for which piston head 160 is at its uppermost position, TDC, "top dead center". At this point, inlet valve 101 opens up out of expansion chamber 162, while all other valves are closed.
  • inlet valve 101 After undergoing a full cycle of oscillation about neutral position 114, located above and outside cylinder 161, inlet valve 101 returns to its seat and is latched closed. This event is indicated by arrow 140 in Figure 7, The phasing of this valve closure effectively determines the peak pressurization ratio of the engine, with longer valve opening corresponding to lower pressurization.
  • spring constant for spring 107 in conjunction with the mass of inlet valve 101, and accounting for the slowing effects of friction and the speeding up effects of the in-rushing gas, the period of the valve motion is made equal to the design open time ⁇ in the case shown here this is approximately one quarter of the full engine period).
  • outlet valve 104 The timing of the closure of outlet valve 104 is determined by the choice of spring constant and valve mass, as described for the case of the expander inlet valve, but in the case of outlet valve 104 this open time is approximately one half of the full engine period. After outlet valve 104 closes, the pressure in the expander chamber rapidly increases as piston head 160 approaches TDC.
  • valve 102 At the point that the pressure of the working fluid in compression chamber 151 sufficiently exceeds the pressure of the working fluid on the opposite side of automatic valve 102, valve 102 is forced open, and working fluid in chamber 151 is expelled to high pressure conduit 158. Under steady running conditions valve 102 remains open just long enough to expel the steady state equilibrium mass charge per cycle of working fluid from chamber 151. In the case of working fluid that is condensed to liquid phase by the cooler, the opening of valve 102 occurs instead very shortly after BDC, by virtue of the low degree of compressibility of most liquid working fluids. [0063] As piston head 182 comes to TDC, valve 102 closes, as the outward flow of working fluid, and the pressure drop across valve 102 ceases.
  • the pressure ratio between the high pressure and low pressure conduits would be lower than in the case described above.
  • smaller fractional periods would correspond to smaller phase delays and higher pressure ratios. It is, however, quite helpful for the period of the expander inlet valve to be close to an integer fraction of the engine period, in order to facilitate the process of starting the engine.
  • the pressure pulsations produced at the outlet of the compressor arrive at the inlet to the expander with an optimal phase delay, approximately 90° for the timing diagram shown in Figure 7. With this delay, the pressure pulse produced at the outlet of compressor 190 during the open phase of valve 102 arrives at the inlet to expander 150 during the open phase of inlet valve 101.
  • this phase delay is produced by providing that high pressure conduit 158 has a total length, from compressor outlet to expander inlet, substantially equal to one quarter acoustic wavelength at the design engine frequency. It is also preferable for high pressure conduit 158 to have smooth bends and avoid sudden discontinuities, such as illustrated in figure 5, in order to minimize sonic reflections.
  • the pressure pulsations produced at the outlet of the expander may arrive at the inlet to the compressor with an optimal phase delay.
  • the strongest pressure pulses that pass from the expander to the compressor occur on the down stroke, with outlet valve 104 closed.
  • the phase delay in this case may advantageously be either 0° or some integer multiple of 360°.
  • the fully automatic valve embodiment is particularly well suited for an engine designed to operate at a single speed, such as is desirable for a prime mover for the generation of alternating current at a fixed frequency, such as 60 Hz in the United States, or 50 Hz in Europe.
  • a fixed frequency such as 60 Hz in the United States, or 50 Hz in Europe.
  • the electrical frequency may be any desired integer factor higher than the design engine frequency. This harmonic resonance with the operating frequency of induction motor generator 188 is particularly helpful in the startup of the engine discussed below.
  • Figure 6 shows an initial state prior to engine startup for which the expander piston head is not near TDC and the valves 101 and 104 are in their respective neutral positions.
  • both the expander inlet and outlet valves normally open at their equilibrium positions, there is little resistance to the acceleration of the starter motor generator 188, and with the connection of motor 188 to a source of AC electrical power, crankshaft 186 is rapidly brought up to the unloaded operating speed for motor 188. Since this speed is by design in harmonic resonance with the valves, they oscillate with increasingly greater amplitudes, until they reach the full amplitude and phase indicated in Figure 7, and operate as described above for the steady running condition.
  • a closed cycle embodiment as known in the art, varying the pressure of the working fluid contained within the engine fluidic circuit varies the power output from the engine.
  • a power control system is described in U.S. Pat. No. 3,708,979 to Bush, for example.
  • Pressure reference assembly 166 in the closed cycle embodiment comprises this power control system.
  • Figure 4 shows an implementation of such a system, in which high pressure reservoir 172 is connected through valve 175, and low pressure reservoir 173 is connected through valve 176 to low pressure conduit 157. Pump 174 keeps the pressure in reservoir 173 low and the pressure in reservoir 172 high.
  • Pressure control actuator 177 on command from controller 197, opens valve 175 momentarily to increase the engine pressure and thereby increase power or opens valve 176 momentarily to reduce the engine pressure and thereby decrease power.
  • the pressure reference assembly 166 in an open cycle embodiment may be nothing more than a port to the ambient atmosphere through a dust filter (not shown) with the ambient atmosphere itself serving the role of low pressure reservoir 173.
  • FIG. 4 also shows a throttle valve 196 which is varied by actuator 194 in response to controller 197 based on changes in the ratio of the hot temperature sensed at the exit of expander 150 by thermocouple 153, to the cold temperature sensed at the inlet to compressor 190 by thermocouple 152. Partially closing throttle valve 196 produces a drop in the pressure admitted to the compressor relative to pressure reference 166. It is found by numerical models that the net power output of the engine illustrated in figure 4 varies almost not at all with changes in the pressure drop across compressor inlet throttle 196, for a fixed pressure at pressure reference 166, but varies approximately linearly with the pressure drop across expander outlet throttle 199.
  • the setting of throttle 196 is used to accommodate variations in the hot to cold temperature ratio between the expander outlet and compressor inlet, while the setting of throttle 199 is used for power demand accommodation (in the open cycle case in which pressure reference 166 is fixed at the value of the ambient atmospheric pressure) or speed regulation (in the closed cycle case, in which pressure reference 166 may accommodate power demands for a given fixed speed). It is useful to be able to tolerate rapid changes in the volumetric expansion ratio between the compressor and the expander, especially in the context of a solar powered engine, in which the temperature produced at the heater by solar illumination may vary substantially with the fluctuating solar insulation conditions from minute to minute, or in which the temperature produced at the cooler may vary with the ambient wind speed or temperature. This is in contrast to the case of a conventional external combustion engine, for which the temperature of the heater is generally thermostatically controlled.
  • semi-automatic expander valves may be employed for controlling the flow of working fluid into and out of the expansion chamber of the expander assembly.
  • semi-automatic operation employs an actively controlled mechanism for releasing the expander valves from their latched positions, while the return mechanism for re-engaging the latch remains automatic, with a period determined by the resonant frequency of the spring strength and valve mass combination.
  • FIGs 8 and 9 show an exemplary embodiment of the semiautomatic expander valves of the present invention having release lever 108 associated with inlet valve 101, and release lever 111 associated with outlet valve 104.
  • Latch 112 is preferably released by latch release lever 111 at a pre-determined engine phase near BDC, rather than in response to the diminishing pressure differential.
  • latch release lever 111 releases latch 112 and allows outlet valve 104 to commence oscillation.
  • Latch 112 is reengaged as piston head 160 and outlet valve 104 approach TDC as in the fully automatic case.
  • latch 109 is released by latch release lever 108 as piston head 160 approaches TDC rather than in response to the pressure spike as piston head 160 reaches TDC.
  • release lever 108 releases latch 109 from a catch 110 and causes inlet valve 101 to commence oscillation under the combined force of spring 107 and the aerodynamic force of the working fluid flow past inlet valve 101.
  • the oscillation period of spring 106 and outlet valve 104 in the face of the out rushing working fluid should be just under half the design engine period. Also as in the fully automatic mode, the oscillation period of spring 107 and inlet valve 101 in the face of the in rushing working fluid determines the engine pressurization ratio in normal operation. For ease of starting, it is desirable for the frequency of inlet valve 101 to be near an integer multiple of the engine frequency. The exemplary timing illustrated in figure 7 corresponds to a factor of four between the frequency of inlet valve 101 and the engine frequency.
  • Figure 10 schematically illustrates another exemplary harmonic engine system which uses reed valves instead of poppet valves as the automatic harmonic oscillator valves, and a linear induction motor/ generator 388 instead of a conventional crank assembly.
  • the oscillating functionality provided by the discrete springs used with the poppet valves in Figure 4 and 5 may be provided instead by the flexibility and resiliently biasing properties of the reeds themselves.
  • Figure 10 shows a reed valve 301 positioned at the inlet of expander 350, a reed valve 304 positioned at the outlet of the expander, a reed valve 303 at the inlet of compressor 390, and a reed valve 302 at the outlet of the compressor.
  • the state shown in Figure 10 corresponds to the fully relaxed state for all four reed valves.
  • the expander valves are in their relaxed state while open, in contrast to the compressor valves, which are closed in their fully relaxed state.
  • the expander inlet reed valve 301 is shown positioned outside the expansion chamber to occlude from the outside in
  • the expander outlet reed valve 304 is positioned inside the expansion chamber to occlude from the inside out.
  • FIG. 10 illustrates that reed valve 304 may function without need of a latch, by virtue of the presence of piston head 360 tending to hold it closed near TDC until sufficient pressure differential has been produced / via the opening of valve 301 and the admission of high pressure working fluid to the expansion chamber, to hold valve 304 closed.
  • the length of high pressure conduit 358 in this case is preferably tuned to produce a phase delay of 270° between the pressure pulse delivered at the compressor outlet and the pressure pulse received at the expander inlet. With this tuning, the pressure pulse from the compressor arrives at the expander at the time that valve 301 is open.
  • a linear induction motor generator 388 rather than the crankshaft, flywheel and rotary induction motor shown in figure 4.
  • Suitable devices for this application are commercially available, such as the STAR motor/ alternator, for example, produced by the Clever Fellows Innovation Consortium (CFIC) corporation. Such devices may be used both for initially starting the engine as well as for extracting single- phase, 60 Hz alternating current electrical power from the engine.
  • Figure 11 shows a sectional view of an alternative system configuration with a parallel arrangement of the compressor 290 and expander 250 cylinders linked by crankshaft 286. Since the phases of the motion of compressor piston head 282 and expander piston head 260 are not necessarily completely in step, as in either of the tandem arrangements shown in Figure 4 or Figure 10, the optimal time delay between the outlet of the compressor and the inlet of the expander may be arranged by having a combination of crankshaft phase difference, and pressure wave transit time generated phase difference based on total length of the fluidic conduit connecting the compressor outlet to the expander inlet. In the example displayed in Figure 11, most of the desired 90° phase difference between the compressor and the expander is provided mechanically. This mechanical component of the 90° phase delay is independent of engine speed, in contrast to the propagating wave component of the phase delay.
  • valve 204 acts without a latch in the following way. While the pressure inside expander chamber 162 is higher than the pressure at the outlet, valve 204 is held shut by the differential pressure overcoming the force of spring 106. As piston head 260 reaches BDC, and the force from the pressure differential across valve 204 becomes less than the spring force, spring 106 pushes valve 204 into the expander chamber. During the upstroke of piston head 260, valve 204 executes a full oscillation. Just at TDC, valve 204 returns to its closed position. As valve 204 closes, the pressure of the small quantity of working fluid left in expander chamber 162 rapidly increases as piston head 260 more closely approaches TDC.
  • valve 204 it is helpful for the head of valve 204 to be slightly concave, as shown in Figure 11, in order to prevent the valve from being sucked back down with piston head 260 as it leaves TDC.
  • the small concavity produces a small repelling gas spring, replacing the function of the latch of the first embodiment, between the bottom of valve 204 and the top of piston head 260 that helps keep valve 204 sealed shut as piston head 260 passes through the TDC position.
  • valve 201 Just after piston head 260 reaches TDC, with valve 201 open, the pressure within expansion chamber 162 remains high, and valve 204 is held closed until piston head 260 once again approaches BDC.
  • any other source of high pressure working fluid may be employed, as for example from a rotating compressor or pump, electrically driven by the output of generator 288.
  • a separate electric motor (not shown) having only an electrical connection instead of crankshaft 286 may drive the compressor.
  • a simple source of compressed gas as from a pressure vessel or other reservoir (not shown) may be used to supply the inlet to the expander.
  • Figure 12 is a graph showing the compressor valve and compressor piston positions of the steady running, parallel embodiment of the harmonic engine illustrated in figure 11, with the compressor valve and compressor piston positions shown in solid lines, and with the expander piston position shown as a dashed line for reference. Dotted line 305 corresponds to the fully closed positions for each of the valves.
  • Figure 13 is a graph showing the expander valve and expander piston positions of the steady running, parallel embodiment of the engine of Figure 11, with the expander valve and expander piston positions shown in solid lines, and the compressor piston position shown as a dashed line for reference.
  • the expander assembly of the present invention may be implemented in a double acting configuration 450, as shown in figure 14.
  • the joint role of buffer chamber 154 and shunt channel 100 described in connection with figure 4 is instead served by having an additional expansion chamber 454 below the expander piston head.
  • a second expander inlet valve 401 controls the admission of high pressure working fluid to lower expansion chamber 454, while a second expander outlet valve 404 controls the expulsion of low pressure working fluid from the lower expansion chamber.
  • the operation of valve 401 is 180° out of phase with respect to the operation of valve 101, and similarly, valve 404 is 180° out of phase with respect to valve 104.
  • the action of the expander valves may each be fully automatic, or semi-automatic, as described above.
  • the strength of spring 407, together with the mass of valve 401 are chosen to provide the same resonant frequency as for valve 101.
  • the strength of spring 406, considering the mass of valve 404 is chosen to match the resonant frequency of valve 104.
  • the timing of latch 409 is then 180° out of phase with latch 109, but otherwise acts in an identical fashion.
  • outlet manifold 405 experiences two pulses of emerging working fluid per engine cycle, and inlet manifold 425 preferably supplies two pulses of entering working fluid per engine cycle.
  • the heat-powered engine may be operated as a refrigerator based on the reversed operation of the current invention, i.e. supply power and produce cooling.
  • the engine described here may, with the supply of work, act as a refrigerator rather than an engine. In this case, the roles of the heater and cooler are reversed. Heat is rejected at the high temperature point and accepted at the low temperature point.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Compressors, Vaccum Pumps And Other Relevant Systems (AREA)

Abstract

L'invention concerne un moteur harmonique à efficacité élevée sur la base d'un détendeur à piston alternatif de manière résonante qui extrait une action à partir de la chaleur et met sous pression un fluide de travail dans un compresseur à piston alternatif. Le moteur comprend de préférence des soupapes d'oscillateur harmonique pouvant osciller à une fréquence de résonance pour réguler le flux de fluide de travail dans le détendeur et à l'extérieur de celui-ci, ainsi que de préférence une ligne de dérivation reliant une chambre de détente du détendeur à une chambre tampon du détendeur pour réduire à un minimum les variations de pression dans les circuits hydrauliques du moteur. Le moteur est spécialement conçu pour fonctionner à une entrée de température très élevée vers le détendeur et à une entrée de température très basse vers le compresseur, afin de fournir une efficacité de conversion thermique très élevée.
PCT/US2008/061285 2007-05-11 2008-04-23 Moteur harmonique Ceased WO2008156913A2 (fr)

Applications Claiming Priority (2)

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US11/801,253 2007-05-11

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WO2008156913A3 WO2008156913A3 (fr) 2009-08-20

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
ITUD20120093A1 (it) * 2012-05-22 2013-11-23 Spectrum Engineering Di Eugenio Cos Olo Motore termico con fonte di calore esterna e valvola per detto motore
CN103485928A (zh) * 2012-09-19 2014-01-01 摩尔动力(北京)技术股份有限公司 分置相循环发动机
DK201300628A1 (da) * 2013-11-06 2015-05-18 Kresten Haaning Varmluftmotor/kølemaskine
US9068484B2 (en) 2013-03-11 2015-06-30 Lawrence Livermore National Security, Llc Double-reed exhaust valve engine

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Publication number Priority date Publication date Assignee Title
GB191419130A (en) * 1914-08-27 1915-04-22 Lindsay Stewart Eglinton An Improvement in Auxiliary Exhaust Valves for Internal Combustion Engines.
US1926463A (en) * 1923-07-18 1933-09-12 Elliott J Stoddard Apparatus for obtaining power from compressed air
US3708979A (en) * 1971-04-12 1973-01-09 Massachusetts Inst Technology Circuital flow hot gas engines
JPH05179901A (ja) * 1991-12-26 1993-07-20 Kazuo Kuroiwa 自然循環熱移動発電高低熱源システム
DE4209590C1 (en) * 1992-03-25 1993-05-13 Mtu Friederichshafen Gmbh Piston-type valve actuator - is used on ic engine poppet valve and has small inlet and release valves for high-pressure compressible fluid
DE10107698C1 (de) * 2001-02-19 2002-08-22 Bosch Gmbh Robert Gaswechselventileinrichtung für eine Brennkraftmaschine

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
ITUD20120093A1 (it) * 2012-05-22 2013-11-23 Spectrum Engineering Di Eugenio Cos Olo Motore termico con fonte di calore esterna e valvola per detto motore
CN103485928A (zh) * 2012-09-19 2014-01-01 摩尔动力(北京)技术股份有限公司 分置相循环发动机
US9068484B2 (en) 2013-03-11 2015-06-30 Lawrence Livermore National Security, Llc Double-reed exhaust valve engine
DK201300628A1 (da) * 2013-11-06 2015-05-18 Kresten Haaning Varmluftmotor/kølemaskine

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