Patent Application
20180080375
This disclosure relates to the improved gas micro turbine engine, wherein water is evaporated into steam in the exhaust heat exchanger, then is injected into the combustion chamber to maintain preset exhaust temperature for maximum efficiency with minimum waste heat. The burning air-fuel mixture turns the steam into super-heated steam, thereby reducing intake air while maintaining pressure to drive the turbine for useful work.
Over the past one hundred years, gas turbine engine has been the major power engine for aviation apparatus, ships, locomotives, helicopters, and power plants. Industrial gas turbines usually have fewer moving part than internal combustion reciprocating engines found in most of the motorized vehicles. As the result, gas turbines are more reliable and more efficient. Their efficiency ranges from 35% in simple cycle configuration to 90% in co-generation configuration. However, internal combustion engines (ICE) have been dominated in the small application area, like motorized vehicles, emergency electric generators, lawn mowers etc. because an ICE can be designed and built less expensive and more compact in size although the average ICE thermal efficiency is lower at about 20%.
A typical gas turbine engine consists of a compressor section, a combustion section and a turbine section. Gas turbines are described thermodynamically by the Brayton cycle, in which air is compressed isotropically, combustion occurs at constant pressure, and expansion over the turbine occurs isotropically back to the starting pressure. It uses atmospheric air as the working medium. Flammable fuel burns and heats the atmospheric air to very high temperature (usually in 1000° C.) to achieve differential pressure between turbine inlet and exit. During this process, a huge amount of waste heat is generated and released into the atmosphere. To recover this waste heat in exhaust gas for higher efficiency, manufacturers spend a major portion of the resources into heat exchange systems and multiple stage turbine systems. It increases the size of the generator system and the total cost of the gas turbine.
Although micro turbine engines have a great power-to-weight ratio and are small in size compared to internal combustion reciprocating engines, they have not been used in small applications like motorized vehicles, household emergency electric generators except in large applications like jet airplanes and power plants. The prior arts are not able to address the tough problem in designing and manufacturing gas turbines from both the engineering and materials standpoint because of the high operating temperatures.
High combustion temperature in a gas turbine engine also causes Nitric Oxides emission and reduces turbine blade working life. Some common practices, like injecting steam and cool air into the engine have been applied to slightly reduce the temperature at the turbine blade surface. Strict material requirements to withstand higher temperature and pressure contribute to higher design and fabrication cost.
In most of the prior arts, a compressor is driven by the turbine, which establishes a fixed input and output air ratio. In order to adjust the output power to match the load, the controller can only change the fuel injection amount. It takes significant amount of time (in a few seconds) to have the effect triggered down to the turbine. Thus when the turbine engine is used in automotive applications, it is harder to control the dynamic of the overall output to follow fluctuating load. In this embodiment, the compressor is controlled by an electrical motor, which can be controlled rapidly and precisely by a computer system to adjust output according to the load in addition to the adjustment of the fuel injection amount.
Some prior arts address the waste heat issue by adding an intake-exhaust air recuperator as shown in
Some prior arts address the NOx emission issue by adding water or steam injection feature to control the combustion temperature as shown in
One aspect of this disclosure is to improve gas micro turbine efficiency and reduce complexity by using steam as the primary working medium instead of atmospheric air. The primary expansion pressure in the combustion chamber is caused by super-heated steam evaporated in the exhaust heat exchanger instead of high temperature exhaust gases. The waste heat is recovered by evaporating the water into pressurized steam mass to generate mechanical work. The exhaust steam mixture temperature at the turbine intake is controlled at much lower level (like 500° C. instead of 1000° C. in most gas turbines) so that the waste heat is minimized.
It is also an object of this disclosure to significantly reduce NOx pollution by controlling fuel combustion temperature well below 1500° C., at which temperature NOx emissions form in significant amount.
It is also an object of this disclosure to significantly reduce unburned fuel, CO by maintaining richer air to fuel ratio so that the fuel is completely burned in the combustion chamber. At least 5% of the oxygen in the air remains after burned with fuel.
In embodiment disclosed in the present disclosure, the temperature at the turbine inlet is reduced from 700-1000° C. to 350-500° C. The loss of thermal volume (about 50%) is replaced by injected steam. The lower operating temperature reduces NOx formation and equal importantly reduces waste heat. The exhaust heat exchanger and condenser convert steam back into water, reduces mass volume and creates low pressure at the exit of the turbine section. Lower operating temperature also reduces the strength requirements for turbine blades and bearing materials, which are big obstacles, in terms of cost, of applying turbine technology in small application such as motorized vehicles and portable electric generators.
In certain embodiments in this disclosure, with the steam vacuum pump, the cold path of the heat exchanger is at lower pressure than 1 atmosphere resulting in lower water boiling point. It ensures the steam in the hot path is condensed back into water as much as possible.
With reference to
With reference to
A fresh air stream is heated by the exhaust condenser 11 and flows through into the compressor 3. The compressed heated air enters the combustion chamber and is mixed with the fuel that is injected by the fuel nozzle 13. The spark plug 14 ignites the air fuel mixture. The steam injector 10 injects high pressurized steam at the flame front. The exhaust gas quickly heats up the steam into super-heated steam. The steam becomes the primary working fluid with over 50% of the mass volume in the mixture.
The exhaust steam gas mixture enters into the turbine 5. The expansion of this mixture, caused by the differential pressure between the inlet and the ambient pressure, rotates the turbine 5. Useful mechanical work is extracted from this process. It can be used for driving a motorized vehicle or generating electricity through a rotor.
The exhaust steam gas mixture enters the exhaust heat exchanger 7 and is cooled by the water in the cold path of the exhaust heat exchanger 7. The steam in the exhaust mixture is condensed back into water releasing huge amount (>2000 kJ/kg) of heat to evaporate the cold water into steam under low pressure and low boiling point less than 100 degrees Celsius. The condensed water is stored in the water tank 19 for next cycle. The remaining exhaust steam gas goes through the exhaust condenser 11. More thermal energy is transferred to the air flow stream to the compressor in this heat exchange process.
The energy flow diagram is shown in
The controller 6 adjusts the key input parameters of the engine. The fuel solenoid controls the fuel injection amount based on the power demand of the load. The air compressor proportionally follows the fuel injection amount to maintain rich air to fuel ratio for complete combustion. The water solenoid 9 is turned on and lasts for a duration to provide adequate water amount for injection, which is calculated based on the turbine exit temperature and fuel injection amount. The more fuel is injected into the combustion chamber; the more water is needed. Typically, the higher the turbine exit temperature, the more water is needed, and vice versa. Since the steam micro turbine engine has higher efficiency (about 100% improvement), the fuel injection amount is reduced by 50% comparing to a traditional gas micro turbine.
The water amount can be expressed as the following formula.
water volume=a×f+b×(Te−Tp)
where f is fuel volume, Te is turbine exit temperature, Tp is desired turbine exit temperature, a and b is the coefficient based on engine size and thermal dynamics. The target temperature of Tp is less than 200 degrees Celsius to minimize waste heat.
With reference to
With reference to
The above specification, examples and data provide a complete description of the manufacture and use of the composition of the disclosure. Since many embodiments of the disclosure can be made without departing from the spirit and scope of the disclosure, the disclosure resides in the claims hereinafter appended.
