Patent Application
20140069090
U.S. Pat. No. 7,398,841 B2 (2008) Kaufman, Jay S.
1. Chrysler Technical Information Office, “History of Chrysler Corporations Gas Turbine Vehicles”, Chrysler Corporation Publication (Jan. 1979)
2. Antoine, H., “Is There a Future For Micro-turbines?, Proceedings of Second International Conference on Industrial Gas Turbine Technologies, Bled, Slovenia (April 2004)
3. DeFrate, L. and Hoerl, A. “Optimum Design of Ejectors Using Digital Computers”, Chemical Engineering Progress, Symposium Series, 21 (1959)
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.
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:
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.
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.
Accordingly, objects of the prime mover of the present invention are:
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:
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.
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:
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
Thus the scope of the invention should be determined by the appended claims and their legal equivalents, rather than by the examples given.
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.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13374861 | Jan 2012 | US |
| Child | 14082221 | US |
