Abstract:
A prime mover with recovered energy driven compression for stationary and motor vehicle application. Efficient low compression operation, especially beneficial to small gas turbines, is enabled with either ambient or cryogenic intake air. Two features, exhaust gas recirculation by a jet-compressor and a heat of fusion sink to liquefy motive air to the jet-compressor, decrease regenerative heat exchanger terminal temperature difference relative to turbine temperature drop in low pressure operation while reducing heat exchanger surface area.

Description:
CLAIM OF PRIORITY 
       [0001]    This Application is a continuation in part of co-pending U.S. Non-Provisional patent application Ser. No. 13/374,861, filed on Jan. 20, 2012. 
     
    
     U.S. PATENT DOCUMENTS 
       [0002]    U.S. Pat. No. 7,398,841 B2 (2008) Kaufman, Jay S. 
       OTHER REFERENCES 
       [0003]    1. Chrysler Technical Information Office, “History of Chrysler Corporations Gas Turbine Vehicles”, Chrysler Corporation Publication (Jan. 1979) 
         [0004]    2. Antoine, H., “Is There a Future For Micro-turbines?, Proceedings of Second International Conference on Industrial Gas Turbine Technologies, Bled, Slovenia (April 2004) 
         [0005]    3. DeFrate, L. and Hoerl, A. “Optimum Design of Ejectors Using Digital Computers”, Chemical Engineering Progress, Symposium Series, 21 (1959) 
       FIELD OF THE INVENTION 
       [0006]    The present invention relates to the use of recovered energy to provide minimal compression work in low compression motor vehicle and stationary engines, and in particular to systems for exhaust gas recirculation by a jet-compressor with liquefaction of the motive fluid by a heat of fusion sink. 
       BACKGROUND 
     Description of Prior Art 
       [0007]    A high efficiency prime mover with renewable energy storage has long been a goal of motor vehicle and stationary engine design to provide energy independence, conserve fossil fuels, and reduce emission of combustion products. While the expansion engine of the present invention is applicable to both reciprocating and rotary engines, it is especially beneficial to the gas turbine. The gas turbine offers several advantages over other engines including simplicity, reliability, low maintenance, low emissions, low weight and ability to burn most any fuel or to run on recovered heat. It has the potential to provide a universal prime mover, however it is inefficient in the motor vehicle and stationary distributed electric generation size range, especially with respect to variable speed operation. This is because of two factors:
       rotor stress limitations imposed by the pressure-speed relationship, wherein rotor speed is directly proportional to working fluid flow rate and compression ratio, and indirectly proportional to rotor diameter   high heat exchanger terminal temperature difference relative to turbine temperature drop.       
 
         [0010]    Both of these factors begin to adversely effect cycle efficiency at a pressure ratio less than about 3. As a result turn-down is inefficient, exhaust temperature and rotor stresses are high with rotational speeds exceeding 100,000 rpm, and a large expensive heat exchanger is needed. 
         [0011]    Previous efforts to adapt a gas turbine to motor vehicle use, notably the Chrysler turbine [1] have been unsuccessful. Present efforts to employ micro-turbines [2] for distributed electric generation are proving successful, but with marginal cost advantage. In general, problems with smaller gas turbine applications are attributable to high compression work with low density ambient intake air and exhaust gas heat recovery with large and complex regenerative heat exchangers. Several cryogenic compression engines have been built and tested to reduce compression work by, in effect, transferring compression to production and storage of liquefied air or nitrogen for compression cooling. Liquefaction work is by renewable energy or other low cost means such as off-peak electricity, therefore not chargeable to cycle efficiency. Both Brayton and Rankine cycles, either fired or with fuel-less ambient heating have been tried, however consumption of the liquefied coolant has proved to be excessive and high efficiency liquefaction is still sought after. Similarly, a highly effective regenerative heat exchanger is also sought after. Most gas turbines have a heat exchanger for recovering exhaust heat to improve cycle efficiency. Large surface area and enhanced heat transfer features are combined to attain high effectiveness. Fixed area recuperators constructed of numerous tubes, brazed or welded in complex header arrangements and with enhanced heat transfer are difficult to manufacture and expensive. Another kind of heat exchanger, the rotary regenerator, attains higher effectiveness than recuperators by providing passage of the atmospheric and pressurized flow streams, alternately over the same heat transfer matrix. Seals to minimize leakage between the streams are difficult to maintain and application is limited to low compression systems. 
       OBJECTS OF THE INVENTION 
       [0012]    Accordingly, objects of the prime mover of the present invention are:
       to provide high cycle efficiency in a low compression prime mover of a transport vehicle drawing ambient atmospheric working fluid, while utilizing recovery of vehicle braking energy and other recoverable energy to reduce compression work of the prime mover;   to provide high cycle efficiency throughout the speed range of a low compression prime mover of a transport vehicle, utilizing recovery of vehicle braking energy and other recoverable energy to drive a heat of fusion sink for absorbing heat from and liquefying the working fluid to reduce compression work of the prime mover;   to provide high cycle efficiency of a low compression prime mover for distributed electric generation, drawing ambient atmospheric working fluid, while utilizing recovery of wind, solar and other recoverable energy to reduce compression work of the prime mover;   to provide high cycle efficiency of a low compression prime mover for distributed electric generation utilizing recovery of wind, solar and other recoverable energy to drive a heat of fusion sink for absorbing heat from and liquefying the working fluid to reduce compression work of the prime mover;   to provide minimal heat transfer surface area of the regenerative heat exchanger of the prime mover of the present invention;   to provide minimal liquefied working fluid consumption of the prime mover of the present invention; and   to provide a selection of working fluid and heat sink cryo-coolant combinations for the prime mover of the present invention.       
 
       SUMMARY OF THE INVENTION 
       [0020]    The prime mover and associated energy recovery systems of the present invention have application in a capacity range of approximately 20 kW(e to 150 kW(e) in which speed of an expansion engine such as a gas turbine is reduced by operation in a compression ratio range of approximately 1.1 to 2.5. Problems and deficiencies of the prior art described above are improved by the present invention, wherein:
       A feature of the prime mover in accordance with the present invention lies in providing a jet compressor to circulate exhaust gas for increasing thermodynamic cycle efficiency in low compression operation while reducing the size and complexity of a regenerative heat exchanger;   another feature of the prime mover in accordance with the present invention lies in providing recovered energy available to a transport vehicle or a distributed electric generator to drive an ambient primary air compressor to offset motive compression work of a jet compressor;   another feature of the prime mover in accordance with the present invention lies in providing recovered energy available to a transport vehicle or a distributed electric generator to reduce motive compression work of a jet compressor by liquefying the motive fluid;   another feature of the prime mover in accordance with the present invention lies in providing a heat of fusion sink with a slush compressor driven by recovered energy to provide suction pressure for solidifying a melt cryo-coolant during liquefaction of the working fluid;   another feature of the prime mover in accordance with the present invention lies in providing two parallel working fluid flow paths, a lower pressure primary working fluid path and a motive fluid path to minimize consumption of the liquefied working fluid;   another feature of the prime mover in accordance with the present invention lies in maintaining the melt cryo-coolant of a heat of fusion sink between a subliming solid-vapor and a liquid state;   another feature of the prime mover in accordance with the present invention lies in providing on-stream liquefaction of boiled-off working fluid by circulation through the heat of fusion sink;   another feature of the prime mover in accordance with the present invention lies in providing partial make-up of the melt cryo-coolant of a heat of fusion sink by reliquefaction of vented cryo-coolant in a liquefier powered by recovered energy;   another feature of the prime mover in accordance with the present invention lies in providing make-up of the melt cryo-coolant of a heat of fusion sink by Dewar exchange; and still another feature of the prime mover in accordance with the present invention lies in providing a selection of working fluid and melt cryo-coolant combinations for economizing coolant consumption.       
 
         [0030]    Accordingly, the principal object of the present invention is to provide a prime mover with high cycle efficiency and economic consumption of heat sink coolant and liquefied working fluid in vehicle and stationary application. Still further objects and advantages will become apparent from a consideration of the ensuing description and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    The above and other objects and advantages of the present invention will become apparent from the following description when read in conjunction with the accompanying drawings wherein: 
           [0032]      FIG. 1  is a schematic illustrating a preferred embodiment of a gas turbine engine of the present invention with a recovered energy driven heat of fusion sink for working fluid liquefaction and compression cooling. 
           [0033]      FIG. 2  is a schematic illustrating a transport vehicle powered by two jet compression gas turbine engines of the present invention with recovered energy driven compression. 
           [0034]      FIG. 2A  is a schematic illustrating a preferred embodiment of a jet compression gas turbine engine of the present invention with recovered energy driven compression of ambient atmospheric air. 
           [0035]      FIG. 3  is a schematic illustrating an alternate preferred embodiment of a jet compression gas turbine engine of the present invention with a recovered energy driven heat of fusion sink for working fluid liquefaction and compression cooling. 
           [0036]      FIG. 4  is a schematic illustrating an alternate preferred embodiment of a cryogenic cooling system of the gas turbine engine of the present invention with recovered energy driven make-up for evaporated working fluid and heat sink cryo-coolant. 
       
    
    
     DESCRIPTION 
     FIGS.  1  to  4   
       [0037]      FIG. 1  is a schematic illustrating a preferred embodiment of a gas turbine  100  of the present invention wherein a turbine-generator  102  fired from a fueled combustor  104  with a recuperator  106  provides electrical power to an electrical controller  108  for distribution. The products of combustion  110  of the working fluid continue through the atmospheric side of recuperator  106  and exhaust to atmosphere. A heat of fusion sink  112  of a cryogenic cooling system  114  provides liquefaction of a bypass portion of cryogenic intake combustion air  116  drawn through the atmospheric side of a chiller  118  by a cryogenic primary motor-compressor  120 . A bypass valve  122  controls the flow of air to the working fluid side of a freeze Dewar  124  of sink  112 . The remaining combustion air from chiller  118  combines with the liquefied portion from a liquid air Dewar  126  via a liquid air valve  128  to motor-compressor  120 . 
         [0038]    In sink  112 , a slush compressor  130  powered by a storage battery  132 , circulates nitrogen slush  134  through the shell side of Dewar  124  wherein entering frozen nitrogen alternately melts due to heat absorption from the working fluid and solidifies due to suction pressure of compressor  130 . Condensed nitrogen is imported into the shell side of Dewar  124  and nitrogen vapor is vented through a vent  126 . Liquefied working fluid air  136  for start-up and boil-off replacement is imported to Dewar  126 . 
         [0039]    An open cycle fired system is selected to illustrate design point performance of an 8 kW (10.7 HP) gasoline fired turbine-generator for vehicle or stationary application. Cycle efficiency is 54% at 50,000 rpm with the turbine compression ratio of 1.5, turbine inlet gas temperature of 825° C. (1515° F.), air compressor inlet temperature of −172° C. (−280° F.) and recuperator effectiveness of 95%. Under these conditions fuel consumption is 33 km/L 1.2 kg/hr (2.7 lb/hr), liquefied air consumption is 44 kg/hr (97 lb/hr) and excess air ratio is 24. For comparison a typical reciprocating engine in the same application has a cycle efficiency of 18% at 5,000 rpm and compression ratio of 10, and efficiency of a typical micro-turbine is 28% at 96,000 rpm with a compression ratio of 3.6. 
         [0040]    The sink is filled with solidified nitrogen and maintained below the boiling point of −196° C. (−325° F.). Reduction of vapor pressure from 0.7 to 0.1 atmospheres by the suction compressor provides circulation of the alternately melting and solidifying nitrogen. Work input to the slush compressor is 2.6 kW (3.5 HP), requiring recovered energy equal to 33% of turbine-generator shaft power. A continuous and sufficient supply of liquefied air is maintained as recovered energy charges the battery to drive the slush compressor. 
         [0041]    A small [28 kWe (21 HP) peak] recuperated gas turbine, which can be modified to incorporate cryogenic features of the present invention, is available from the Capstone Corporation of Chatsworth, Calif. Cryogenic components including chiller, compressor and Dewar are available from Chart Industries of Garfield Heights, Ohio, Barber-Nichols of Arvada, Co. and Technifab Products of Brazil, Indiana, respectively. 
         [0042]      FIG. 2  is a side elevation view illustrating a preferred embodiment of a transport vehicle  240  of the present invention with propulsion provided to two motorized wheels  242  by two 4 Kwe (5.4 HP) jet compression gas turbines  200 . An electrical controller  208  distributes recovered energy from a storage battery  232 , charged by a braking generator  244  for pressurization of the gas turbines  200 . A regenerative braking system, which can be adapted to the vehicle of the present invention, is available from the Ford Motor Company of Dearborn, Mich. 
         [0043]      FIG. 2A  is a schematic illustrating a preferred embodiment of a gas turbine  200  of the present invention wherein a turbine-generator  202  fired from a fueled combustor  204  with a recuperator  206  provides electrical power to an electrical controller  208  for distribution. The working fluid of gas turbine  200  consists of a motive combustion air portion  246  which drives a jet compressor  248 , a circulated exhaust portion  250  which is entrained into the motive air, and an emission portion  210  which continues to atmosphere through recuperator  206 . A motive compressor  252  provides combustion air through recuperator  206  to a motive nozzle  254  which entrains the circulated exhaust, under control of an exhaust valve  256 , for delivery through a discharge nozzle  258  to combustor  204 . 
         [0044]    An open cycle fired system is selected to illustrate performance of a gasoline fired gas turbine as prime mover in a compact car operating at an 80 km/hr (50 mph) design point requiring 8 kW (10.7 HP). Compression work, normally provided by turbine-generator output, is supplemented by 33% recovered vehicle braking energy. Cycle efficiency is 44% at 50,000 rpm with motive compression ratio of 5, turbine inlet gas temperature of 825° C. (1515° F.), air compressor inlet temperature of 20° C. (68° F.) and recuperator effectiveness of 95%. Under these conditions fuel economy is 33 km/L (78 mpg) and excess air ratio is 22. High excess air ratio associated with the low turbine pressure ratio obviates the effect of combustion products in the recirculating suction flow. For comparison a typical reciprocating engine in the same application has a cycle efficiency of 18% at 5,000 rpm and compression ratio of 10, and efficiency of a typical micro-turbine is 28% at 96,000 rpm with a compression ratio of 3.6. 
         [0045]      FIG. 3  is a schematic illustrating an alternate preferred embodiment  300  of gas turbine  200  of vehicle  201  ( FIG. 2 ), in which the working fluid is cooled to cryogenic temperature by a heat of fusion sink  306  of a cryogenic cooling system  314 . The sink  306  is powered by recovered braking energy of vehicle  201  ( FIG. 2 ). A turbine-generator  302  fired from a fueled combustor  304  with a recuperator  306  provides electrical power to an electrical controller  308  for distribution. The working fluid of gas turbine  300  consists of a combustion air portion  316  following two parallel flow paths, a circulated exhaust portion  350  which is entrained into the motive air, and an emission portion  310  which continues to atmosphere through recuperator  306 . The first combustion air path provides primary air from a cryogenic motor-compressor  320 , drawing air through the atmospheric side of a chiller  318  and discharging to combustor  304  via recuperator  306 . The second path provides motive air, which is drawn through chiller  318  and a bypass valve  322  for liquefaction and storage in a liquid air Dewar  326 . The liquid is discharged, as required, back through chiller  318  to recuperator  306  by a motive pump  352  to a jet compressor  348 . A motive nozzle  354  entrains the circulated exhaust into the motive air, under control of an exhaust valve  356 , for delivery through a discharge nozzle  358  to combustor  304 . 
         [0046]    In sink  312 , a slush compressor  330  powered by a battery  332 , circulates a two phase melt cryo-coolant  334  through the shell side of freeze Dewar  324  wherein entering cryo-coolant alternately melts due to heat absorption and solidifies due to suction pressure of compressor  330 . Condensed melt cryo-coolant is imported into the shell side of Dewar  324  and liquefied air is imported into Dewar  326  for boil-off replacement. 
         [0047]    An open cycle fired system is selected to illustrate performance of a gasoline fired gas turbine as prime mover in a compact car operating at an 80 km/hr (50 mph) design point requiring 8 kW (10.7 HP). Compression work for combustion air is provided by turbine-generator output and cryo-coolant compression work is provided by recovered vehicle braking energy, which is limited to 33% of turbine-generator shaft power. Cycle efficiency is 70% at 46,000 rpm with primary air compression ratio of 1.4, motive compression ratio of 20, turbine inlet gas temperature of 825° C. (1515° F.), air compressor inlet temperature of −172° C. (−280° F.) and recuperator effectiveness of 95%. Under these conditions fuel economy is 60 km/L (140 mpg), liquefied air consumption is 40 kg/hr (88 lb/hr) and excess air ratio is 27. High excess air ratio associated with the low turbine pressure ratio obviates the effect of combustion products in the recirculating suction flow. For comparison a typical reciprocating engine in the same application has a cycle efficiency of 18% at 5,000 rpm and compression ratio of 10, and efficiency of a typical micro-turbine is 28% at 96,000 rpm with a compression ratio of 3.6. 
         [0048]    The sink is filled with solidified nitrogen coolant and maintained at below the boiling point of −196° C. (−325° F.). Reduction of vapor pressure from 0.7 to 0.1 atmospheres by the slush compressor provides circulation of the melting and solidifying nitrogen. Recovered vehicle braking energy to the slush compressor is 2.4 kW (3.2 HP), equal to 30% of turbine-generator shaft power, while the freeze Dewar provides required working fluid reliquefaction of 35 kg/hr (76 lb/hr). A continuous and sufficient supply of liquefied air is maintained as recovered energy charges the battery to drive the slush compressor. A high temperature jet compressor suitable for exhaust gas recirculation in the present invention is available from the Fox Company of Dover, N.J. Other components to enable features of the present invention are available as listed for  FIG. 1  above. 
         [0049]      FIG. 4  is a schematic illustrating an alternate preferred embodiment of a cryogenic cooling system  414  of gas turbine  300  ( FIG. 3 ), in which boil-off vapor of the working fluid air and vented nitrogen cryo-coolant is made-up. A boil-off compressor  458  powered by recovered braking energy of vehicle  201  ( FIG. 2 ) returns the evaporated working fluid to the tube side of Dewar  424  for reliquefaction. Vented melt cryo-coolant is made-up with solidified nitrogen by removal and replacement of Dewar  424  at flanges  460 . Supplementary liquefied nitrogen is provided by a braking energy driven reliquefier  462  powered from a controllar  428 . The vent rate for solidified nitrogen cryo-coolant is estimated at 12%, sufficient for a 100 kg (205 lb) initial inventory to provide 16 hours of vehicle operation at 80 km/hr (50 mph). 
       SUMMARY, RAMIFICATIONS AND SCOPE 
       [0050]    Accordingly, it is shown that the recovered energy driven compression engine of this invention improves cycle thermal efficiency in both motor vehicle and stationary application. In particular, it overcomes problems of the gas turbine in small low pressure applications. 
         [0051]    Although the description above contains many specific details, these should not be construed as limiting the scope of the invention but as merely providing illustration of some of the preferred embodiments of this invention. For example, turbines, either radial or axial types having either electrical or mechanical output, can be connected in series to lower expansion ratio and speed, or connected in parallel to increase power. In addition, the motive compressor, motive pump, primary compressor and liquefier may be powered by recovered energy of vehicle braking or draft loss, as well as by solar radiation and wind. The heating source may be solar radiation as well as combustion in either open or closed working fluid systems. The heat of fusion sink may absorb compression heat from within the compressor and from the compressor outlet, as well as absorbing heat from the working fluid at the compressor inlet. 
         [0052]    Thus the scope of the invention should be determined by the appended claims and their legal equivalents, rather than by the examples given.