Abstract:
A turbojet engine and a method for its operation which reduces NOx emissions, improves engine thermal efficiency, increases thrust and helps prevent engine performance deterioration. The turbojet engine includes two series of water injection nozzles which inject an atomized water stream into the compressor of the turbojet engine prior to the low pressure portion of the compressor and the high pressure portion of the compressor. The water injection nozzles that provide the atomized water stream to the low pressure portion of the compressor may be selectively disabled to inhibit water from being fed into the low pressure portion of the compressor based upon various criteria, such as the current atmospheric conditions.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention generally relates to turbojet engines and more particularly to a turbojet engine having multiple series of water injection nozzles for injecting streams of atomized water into the airflows entering both a low pressure compressor and a high pressure compressor to reduce NOx emissions, increase thrust and prevent engine performance deterioration.  
         BACKGROUND OF THE INVENTION  
         [0002]    The focus of point-source emissions regulations has expanded relatively recently from automotive vehicles and electric power generating plants to include almost every device that employs fossil fuel to generate power. These ever more stringent regulations necessitate that both aircraft and turbojet engine manufacturers continually strive to improve the efficiency of their products, as well as decrease their emissions generating capacity. As those skilled in the art will readily understand, however, these two objectives frequently pull relevant design criteria in opposite directions. For example, higher combustion temperatures are generally viewed as assisting a turbojet engine to achieve a relatively high degree of efficiency. High combustion temperatures, however, typically increase the amount of NOx that is produced during combustion by a significant degree.  
           [0003]    Previous attempts to increase efficiency and reduce emissions in turbojet engines include ground-based engine wash systems and engine combustor water injection. The ground-based engine wash systems are employed to clean the rotating components of a turbojet engine to thereby obtain a 0.5% to 1.0% increase in fuel efficiency. Such systems, however, are costly to procure and operate, given that an expensive water recovery system is likely needed for capturing the wash effluent and that such systems take aircraft out of service while the turbojet engines are being cleaned.  
           [0004]    The older engine combustor water injection systems, which inject water directly into the combustion chamber of a turbojet engine, are known to improve the thrust of a turbojet engine, but typically suffer from draw backs such as an increase in maintenance costs, increased smoke and reduced thermal efficiency.  
         SUMMARY OF THE INVENTION  
         [0005]    In one preferred form, the present invention provides a method for reducing NOx emissions while simultaneously increasing the thrust and thermal efficiency on hot days from a turbojet engine. The turbojet engine has a high pressure compressor axially spaced between a low pressure compressor and a turbine. The method includes the steps of: providing a series of water injection nozzles between the low pressure compressor and the high pressure compressor; operating the turbojet engine to produce thrust; operating the series of water injection nozzles to input a finely atomized stream into the high pressure compressor; wherein the stream is comprised of atomized water.  
           [0006]    In another preferred form, the present invention provides turbojet engine having an air intake, a compressor, a first series of water injection nozzles and a second series of water injection nozzles. The compressor is coupled to the air intake and receives an inlet flow of air therefrom. The compressor includes a low pressure portion, which compresses the inlet flow, and a high pressure portion, which receives and further compresses the airflow from the low pressure portion. The first series of water injection nozzles is coupled to the air intake and injects a first stream of finely atomized water into the airflow entering the low pressure portion of the compressor. The second series of water injection nozzles is configured to inject a second stream of finely atomized water into the airflow entering the high pressure portion of the compressor.  
           [0007]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims, taken in conjunction with the accompanying drawings, wherein:  
         [0009]    [0009]FIG. 1 is a schematic illustration of an aircraft having a water misting intercooler system constructed in accordance with the teachings of the present invention; and  
         [0010]    [0010]FIG. 2 is a schematic illustration of a portion of the aircraft of FIG. 1 illustrating one of the turbojet engines and the nozzles of the water misting intercooler system in greater detail. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0011]    With reference to FIGS. 1 and 2 of the drawings, a water misting intercooler system  10  constructed in accordance with the teachings of the present invention is illustrated in operative association with the turbojet engines  12  of an exemplary aircraft  14 . The aircraft  14  is illustrated to conventionally include a fuselage  16  and a pair of wing assemblies  18  that are attached to the opposite sides of the fuselage  16 . In the particular embodiment illustrated, two of the turbojet engines  12  are conventionally mounted to each wing assembly  18  and the water misting intercooler system  10  is coupled to each of the turbojet engines  12 . While the water misting intercooler system  10  of the present invention is illustrated in conjunction with an aircraft having four turbojet engines, those skilled in the art will understand that the water misting intercooler system  10  of the present invention may be used in conjunction with aircraft of various different configurations and having any number of turbojet engines  12 . Furthermore, the water misting intercooler system  10  of the present invention need not be used in conjunction with each of an aircraft&#39;s turbojet engines.  
         [0012]    With specific reference to FIG. 1, each turbojet engine  12  is illustrated to include an intake  20 , a compressor  22 , a combustor  24 , and a turbine  26 . As the construction and operation of turbojet engines is generally well known in the art, the turbojet engine need not be discussed in exhaustive detail. Briefly, an intake airflow entering the turbojet engine through the intake  20  is directed to the compressor  22 . The compressor  22  is segregated into two portions, a first, low pressure portion  28  and a second, high pressure portion  30 . Each of the low and high pressure portions  28  and  30  of the compressor  22  include a plurality of axially spaced apart stators  32  that are fixedly coupled to the housing  34  of the compressor  22 , and a plurality of rotors  36  that are supported for rotation in the housing  34 . The rotors  36  are staggered axially such that a stator  32  is disposed between each adjacent pair of rotors  36 . Interaction between the rotors  36  and the stators  32  of the low pressure portion  28  of the compressor  22  applies work to compress the intake airflow, while interaction between the rotors  36  and the stators  32  of the high pressure portion  30  of the compressor  22  apply work to compress the airflow exiting the low pressure portion  28 . Air exiting the compressor  22  enters the combustor  24  where fuel is mixed with the airflow and thereafter burned to produce a high velocity exhaust stream that is directed into the turbine  26  which is used to power the rotors  36  of the low and high pressure portions  28  and  30  of the compressor  22 .  
         [0013]    In FIG. 2, the water misting intercooler system  10  is illustrated to include a remote service panel  40 , a pair of water tanks  42 , a pair of tank fill conduits  44  for coupling in fluid connection water tanks  42  and the remote service panel  40 , a plurality of high pressure pumps  46  each of which being in fluid connection with one of the water tanks  42 , a plurality of nozzle assemblies  48  each of which being associated with a different one of the turbojet engines  12 , and plurality of water supply conduits  50 , each of which coupling in fluid connection one of the high pressure pumps  46  and one of the nozzle assemblies  48 .  
         [0014]    The remote service panel  40  is mounted to the fuselage  16  and provides maintenance technicians with a convenient means for filling the water tanks  42 . The remote service panel  40  includes a fill connection  52  and a tank fill valve  54 . The tank fill valve  54  is illustrated to be a two-way, three position valve; two of the valve positions permit water to be directed from the fill connection  52  and associated one of the tank fill conduits  44 , while the other valve position inhibits fluid flow between the fill connection  52  and both of the tank fill conduits  44 . Preferably, de-mineralized water, such as that which is provided through reverse osmosis filtering, is utilized in the water misting intercooler system  10 .  
         [0015]    In the particular example provided, each of the water tanks  42  is illustrated to have a capacity of about  150  gallons and be mounted within an associated wing assembly  18  offset somewhat from the fuselage  16 . Each high pressure pump  46  is mounted to one of the water tanks  42  and supplies water under high pressure to one of the nozzle assemblies  48  via a water supply conduit  50 . Each nozzle assembly  48  includes a first series of nozzles  60 , a second series of nozzles  62 , a shutoff valve  64  and a first valve  66 . The first series of nozzles  60  includes a plurality of water injection nozzles  60  that are coupled to the air intake  20  and oriented so as to inject a first stream  80  of atomized water into the airflow entering the low pressure portion  28  of the compressor  22 . The second series of nozzles  62  includes a plurality of water injection nozzles  70  that are coupled to the compressor  22  and oriented to inject a second stream  82  of atomized water into the airflow entering the high pressure portion  30  of the compressor  22 . The shutoff valve  64  is coupled to the water supply conduit  50  and is selectively operable between a closed condition, for inhibiting the flow of water to the first valve  66  and the second series of nozzles  62 , and an open condition for permitting water to flow from the water supply conduit  50  to the first valve  66  and the second series of nozzles  62 . The first valve  66  is coupled to the first series of nozzles  60  and is operable between a closed condition, for inhibiting the flow of water to the first series of nozzles  60 , and an open condition, for permitting water to flow to the first series of nozzles  60 .  
         [0016]    The water misting intercooler system  10  is operable in an unenergized mode, a first energized mode, and a second energized mode. When operated in the unenergized mode, the shutoff and first valves  64  and  66  in each nozzle assembly  48  are positioned in the closed position to inhibit the flow of water to the water injection nozzles  70 . In this configuration, the turbojet engine  12  functions conventionally.  
         [0017]    When the water misting intercooler system  10  is operated in the first energized mode, both the shutoff and first valves  64  and  66  of each nozzle assembly  48  are positioned in the opened position to permit water to flow to the water injection nozzles  70  in each of the first and second series of nozzles  60  and  62 . The water in the stream that is produced by the first series of nozzles  60  is atomized such that the droplets that make up the stream have a size of about 20 microns or less. Similarly, the water in the stream that is produced by the second series of nozzles  62  is atomized such that the droplets that make up the stream have a size of about 20 microns or less. In contrast to the operation of the first series of nozzles  60 , however, atomization of water from the second series of nozzles  62  is assisted by high pressure air from the high pressure portion  30  of the compressor  22 . Such air may be directed directly from a desired stage of the high pressure portion  30  of the compressor  22 , or may be a flow of bleed air that is redirected from the compressor  22  into the nozzle assemblies  48 .  
         [0018]    Operation of the water misting intercooler system  10  in the first energized mode advantageously cleans the low and high pressure portions  28  and  30  of the compressor  22 , increases the thrust of the turbojet engine  12 , and reduces the temperature of the high pressure compressor  30  to thereby reduce NOx emissions in the combustor  24 . The water misting intercooler system  10  is particularly useful to reduce the emissions of an aircraft during takeoff, since higher levels of thrust are typically needed during takeoff. Furthermore, since atomized water is being input to the compressor  22 , rather than the combustor  24 , the water misting intercooler system  10  does not cause the turbojet engine  12  to generate smoke as seen in previous water injection systems wherein water was injected directly into the combustion chamber  24 . Furthermore since water is introduced into the compressor  22 , the water acts as a heat sink to reduce compressor inlet temperatures and improve compressor efficiency as opposed to reducing engine thermal efficiency by injecting water directly into the combustor  24 .  
         [0019]    As those skilled in the art will understand, the input of a stream of atomized water into the low pressure portion  28  of the compressor  22  may not be desirable under all circumstances, such as when atmospheric conditions would promote freezing. In such situations, the water misting intercooler system  10  may be operated in the second energized mode, wherein the shutoff valve  64  of each nozzle assembly  48  is positioned in the opened position and the first valve  66  of each nozzle assembly  48  is positioned in the closed position to permit water to flow to the water injection nozzles  70  in only the second series of nozzles  62 .  
         [0020]    Operation of the water misting intercooler system  10  in the second energized mode advantageously cleans the high pressure portion  30  of the compressor  22 , increases the thrust of the turbojet engine  12 , and reduces the compressor exit temperature of the high pressure compressor  30  to thereby reduce NOx emissions in the combustor  24 . Thrust and NOx emissions, however, are not affected to the same degree as when the water misting intercooler system  10  is operated in the first energized mode.  
         [0021]    While the invention has been described in the specification and illustrated in the drawings with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention as defined in the claims. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment illustrated by the drawings and described in the specification as the best mode presently contemplated for carrying out this invention, but that the invention will include any embodiments falling within the foregoing description and the appended claims.