Patent Publication Number: US-11028768-B2

Title: Rotary internal combustion engine with removable subchamber insert

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is division of U.S. application Ser. No. 15/153,277 filed May 12, 2016, which is a continuation-in-part of U.S. application Ser. No. 13/750,523 filed Jan. 25, 2013, which is a continuation-in-part of U.S. application Ser. No. 13/273,534 filed Oct. 14, 2011, which claims priority on provisional U.S. application Ser. No. 61/512,593 filed Jul. 28, 2011, the entire contents of all of which are incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The application relates generally to a rotary internal combustion engine. 
     BACKGROUND OF THE ART 
     Rotary engines, such as for example Wankel engines, use the rotation of a piston to convert pressure into a rotating motion, instead of using reciprocating pistons. In these engines, the rotor typically includes a number of seals that remain in contact with a peripheral wall of the internal cavity of the engine throughout the rotational motion of the rotor to create a plurality of rotating chambers when the rotor rotates. 
     Rotary engines come in many forms. One well-known type, the Wankel engine, has a generally triangular rotor received in a two-lobed epitrochoid cavity. Other non-Wankel rotary engines types exist as well. 
     Rotors and internal cavities of rotary engines may be difficult to inspect, often requiring substantial disassembly to be able to inspect the more critical regions where combustion occurs. 
     SUMMARY 
     In one aspect, there is provided a rotary engine comprising: an outer body having an internal cavity defined by two axially spaced apart end walls and a peripheral wall extending between the end walls, the peripheral wall having an insert opening defined therethrough in communication with the internal cavity, and a plurality of coolant passages defined through the peripheral wall in proximity of the insert opening, the coolant passages forming part of a cooling circuitry for circulating a liquid coolant therethrough; a rotor body rotatable within the internal cavity in sealing engagement with the peripheral wall and defining at least one chamber of variable volume in the internal cavity around the rotor body; and an insert removably received in the insert opening of the peripheral wall, the insert having a subchamber defined therein communicating with the internal cavity; wherein a minimum width of the insert opening is defined along a direction of an axis of rotation of the rotor body, the minimum width of the insert opening being at least 0.75 inches. 
     In another aspect, there is provided an outer body for a rotary engine comprising: two axially spaced apart end walls; a peripheral wall extending between the end walls and defining an internal cavity for receiving a rotor, the peripheral wall having an insert opening defined therethrough in communication with the internal cavity, and a plurality of coolant passages defined through the peripheral wall in proximity of the insert opening, the coolant passages forming part of a cooling circuitry for circulating a liquid coolant therethrough; an insert removably received in the insert opening of the peripheral wall, the insert having a subchamber defined therein communicating with the internal cavity; a fuel injector in fluid communication with the subchamber; and an ignition element in heat transfer communication with the subchamber; wherein a minimum width of a cross-section of the insert opening is at least 0.75 inches. 
     In another aspect, there is provided a method of inspecting in an internal cavity in an outer body of a rotary engine, the method comprising: detaching an insert from the outer body, the insert received in an insert opening of a peripheral wall of the outer body and including a subchamber configured for receiving fuel for ignition; removing the insert from the insert opening; and performing an unaided visual inspection of the internal cavity through the insert opening to determine if a subsequent maintenance or repair operation is required. 
     In another aspect, there is provided a method of performing maintenance on a rotary engine, including inspecting the internal cavity of the rotary engine following the method described above, disassembling at least part of the rotary engine upon determination that a subsequent maintenance or repair operation is required, and then performing the subsequent maintenance or repair operation on the rotary engine. 
     In a further aspect, there is provided a rotary engine comprising: an outer body having an internal cavity defined by two axially spaced apart end walls and a peripheral wall extending between the end walls, the peripheral wall having an insert opening defined therethrough in communication with the internal cavity, and an injector hole defined therein in communication with the insert opening; a rotor body rotatable within the internal cavity in sealing engagement with the peripheral wall and defining at least one chamber of variable volume in the internal cavity around the rotor body; an insert removably received in the insert opening of the peripheral wall, the insert having a subchamber defined therein communicating with the internal cavity and with the injector hole; and a fuel injector having a tip received in the injector hole of the peripheral wall without protruding in the insert opening. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       Reference is now made to the accompanying figures in which: 
         FIG. 1  is a partial, schematic cross-sectional view of a rotary internal combustion engine in accordance with a particular embodiment; 
         FIG. 2  is a schematic cross-sectional view of an insert of the engine of  FIG. 1 ; 
         FIG. 3  is a schematic cross-sectional view of an insert in accordance with another embodiment; 
         FIG. 4  is a schematic cross-sectional view of an insert in accordance with a further embodiment; 
         FIG. 5  is a schematic cross-sectional view of a rotary internal combustion engine in accordance with another embodiment; 
         FIG. 6  is a schematic cross-sectional view of a rotary internal combustion engine in accordance with another embodiment; 
         FIG. 7  is a schematic cross-sectional view of a rotary internal combustion engine in accordance with another embodiment; 
         FIG. 8  is a schematic cross-sectional view of a rotary internal combustion engine in accordance with another embodiment; 
         FIG. 9  is a partial, schematic cross-sectional view of a rotary internal combustion engine including an insert in accordance with a further embodiment; 
         FIG. 10  is a partial, schematic top view of the rotary engine and insert of  FIG. 9 ; 
         FIG. 11  is a partial, schematic top view of the rotary engine of  FIG. 9  with the insert removed, showing part of a rotor of the rotary engine through the insert opening; 
         FIG. 12  is a partial, schematic cross-sectional view of a rotary internal combustion engine in accordance with another embodiment; and 
         FIG. 13  is a partial, schematic top view of the engine of  FIG. 12 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a rotary internal combustion engine  10  known as a Wankel engine is schematically and partially shown. In a particular embodiment, the rotary engine  10  is used in a compound cycle engine system such as described in Lents et al.&#39;s U.S. Pat. No. 7,753,036 issued Jul. 13, 2010 or as described in Julien et al.&#39;s U.S. Pat. No. 7,775,044 issued Aug. 17, 2010, the entire contents of both of which are incorporated by reference herein. The compound cycle engine system may be used as a prime mover engine, such as on an aircraft or other vehicle, or in any other suitable application. In any event, in such a system, air is compressed by a compressor before entering the Wankel engine, and the engine drives one or more turbine(s) of the compound engine. In another embodiment, the rotary engine  10  is used without a turbocharger, with air at atmospheric pressure. 
     The engine  10  comprises an outer body  12  having axially-spaced end walls  14  with a peripheral wall  18  extending therebetween to form an internal cavity  20 . The inner surface  19  of the peripheral wall  18  of the cavity  20  has a profile defining two lobes, which is preferably an epitrochoid. 
     An inner body or rotor  24  is received within the cavity  20 , with the geometrical axis of the rotor  24  being offset from and parallel to the axis of the outer body  12 . The rotor  24  has axially spaced end faces  26  adjacent to the outer body end walls  14 , and a peripheral face  28  extending therebetween. The peripheral face  28  defines three circumferentially-spaced apex portions  30  (only one of which is shown), and a generally triangular profile with outwardly arched sides. The apex portions  30  are in sealing engagement with the inner surface of peripheral wall  18  to form three rotating working chambers  32  (only two of which are partially shown) between the inner rotor  24  and outer body  12 . A recess  38  is defined in the peripheral face  28  of the rotor  24  between each pair of adjacent apex portions  30 , to form part of the corresponding chamber  32 . 
     The working chambers  32  are sealed. Each rotor apex portion  30  has an apex seal  52  extending from one end face  26  to the other and protruding radially from the peripheral face  28 . Each apex seal  52  is biased radially outwardly against the peripheral wall  18  through a respective spring. An end seal  54  engages each end of each apex seal  52 , and is biased against the respective end wall  14  through a suitable spring. Each end face  26  of the rotor  24  has at least one arc-shaped face seal  60  running from each apex portion  30  to each adjacent apex portion  30 , adjacent to but inwardly of the rotor periphery throughout its length. A spring urges each face seal  60  axially outwardly so that the face seal  60  projects axially away from the adjacent rotor end face  26  into sealing engagement with the adjacent end wall  14  of the cavity. Each face seal  60  is in sealing engagement with the end seal  54  adjacent each end thereof. 
     Although not shown in the Figures, the rotor  24  is journaled on an eccentric portion of a shaft and includes a phasing gear co-axial with the rotor axis, which is meshed with a fixed stator phasing gear secured to the outer body co-axially with the shaft. The shaft rotates the rotor  24  and the meshed gears guide the rotor  24  to perform orbital revolutions within the internal cavity  20 . The shaft rotates three times for each complete rotation of the rotor  24  as it moves around the internal cavity  20 . Oil seals are provided around the phasing gear to prevent leakage flow of lubricating oil radially outwardly thereof between the respective rotor end face  26  and outer body end wall  14 . 
     At least one inlet port (not shown) is defined through one of the end walls  14  or the peripheral wall  18  for admitting air (atmospheric or compressed) into one of the working chambers  32 , and at least one exhaust port (not shown) is defined through one of the end walls  14  or the peripheral wall  18  for discharge of the exhaust gases from the working chambers  32 . The inlet and exhaust ports are positioned relative to each other and relative to the ignition member and fuel injectors (further described below) such that during each rotation of the rotor  24 , each chamber  32  moves around the cavity  20  with a variable volume to undergo the four phases of intake, compression, expansion and exhaust, these phases being similar to the strokes in a reciprocating-type internal combustion engine having a four-stroke cycle. 
     In a particular embodiment, these ports are arranged such that the rotary engine  10  operates under the principle of the Miller or Atkinson cycle, with its volumetric compression ratio lower than its volumetric expansion ratio. In another embodiment, the ports are arranged such that the volumetric compression and expansion ratios are equal or similar to one another. 
     As described further below, a subchamber, which in the particular embodiment shown is a pilot subchamber  72 , is defined in the outer body  12 , for pilot fuel injection and ignition. In this example, the subchamber  72  is provided in an insert  34  received in a corresponding insert opening  36  defined through the peripheral wall  18  of the outer body  12  and in communication with the internal cavity  20 , for pilot fuel injection and ignition. The peripheral wall  18  also has a main injector elongated hole  40  defined therethrough, in communication with the internal cavity  20  and spaced apart from the insert  34 . A main fuel injector  42  is received and retained within this corresponding hole  40 , with the tip  44  of the main injector  42  communicating with the cavity  20  at a point spaced apart from the insert  34 . The main injector  42  is located rearwardly of the insert  34  with respect to the direction R of the rotor rotation and revolution, and is angled to direct fuel forwardly into each of the rotating chambers  32  sequentially with a tip hole pattern designed for an adequate spray. 
     Referring particularly to  FIG. 2 , in this example the insert includes an elongated body  46  extending across a thickness of the peripheral wall  18 , with an enlarged flange  48  at its outer end which is biased away from a shoulder  50  defined in the peripheral wall  18 , and against a gasket (not shown) made of an appropriate type of heat resistant material such as a silica based material. A washer  56 , such as for example a steel or titanium washer, and spring  58 , such as for example a wave spring or a Belleville spring, are provided between the flange  48  and the shoulder  50  of the peripheral wall  18 . The spring  58  biases the body  46  against a cover  62  having a cross-section greater than that of the insert opening  36  and extending over an outer surface  64  of the peripheral wall  18 . The cover  62  is connected to the peripheral wall  18 , for example through brazing. Alternate types of connections can also be used, including but not limited to a connection through fasteners such as bolts, to help facilitate replacement of the insert if necessary. 
     The insert body  46  has an inner surface  66  which is continuous with the inner surface  19  of the peripheral wall  18  to define the cavity  20 . The insert opening  36  in the wall  18  defines a flange  68  extending in the insert opening  36  adjacent the inner surface  19 , and the inner end of the insert body  46  is complementarily shaped to engage this flange  68 , with a gasket  70  being received therebetween. 
     In this example, the insert body  46  is made of a material having a greater heat resistance than that of the peripheral wall  18 , which in a particular embodiment is made of aluminium. In this particular embodiment, the insert body  46  is made of an appropriate type of ceramic. 
     The insert body  46  has a pilot subchamber  72  defined therein in communication with the internal cavity  20 . In the embodiment shown, the subchamber  72  has a circular cross-section; alternate shapes are also possible. The subchamber  72  communicates with the cavity through at least one opening  74  defined in the inner surface  66 . The subchamber  72  has a shape forming a reduced cross-section adjacent the opening  74 , such that the opening  74  defines a restriction to the flow between the subchamber  72  and the cavity  20 . The opening  74  may have various shapes and/or be defined by a pattern of multiple holes. As can be seen in  FIG. 2 , the opening  74  has an area smaller than the maximum cross-sectional area of the subchamber  72 , which is defined spaced apart from the opening  74 . 
     The peripheral wall  18  has a pilot injector elongated hole  76  defined therethrough in proximity of the insert  34 , extending at a non-zero angle with respect to a surface of an outer wall of the insert  34  and with respect to the longitudinal direction of the insert (which in the embodiment shown corresponds to the direction of the transverse axis T of the outer body  12 ). The pilot injector hole  76  is in communication with the subchamber  72 . A pilot fuel injector  78  is received and retained within the corresponding hole  76 , with the tip  80  of the pilot injector  78  being received in the subchamber  72 . As can be seen in  FIG. 2 , the insert body  46  has an injector opening defined therethrough providing the communication between the pilot injector elongated hole  76  and the subchamber  72 , and the tip  80  of the pilot injector  78  is received in the subchamber  72  through this injector opening, with a major part of the pilot injector  78  being received in the pilot injector elongated hole  76  outside of the insert  34 . The opening providing the communication between the pilot injector elongated hole  76  and the subchamber  72  has an area smaller than the maximum cross-sectional area of the subchamber  72 . 
     The insert body  46  and cover  62  have an ignition element elongated hole  82  defined therein extending along the direction of the transverse axis T of the outer body  12 , also in communication with the subchamber  72 . As can be seen in  FIG. 2 , the ignition element elongated hole  82  and the subchamber  72  communicate through an opening having an area smaller than the maximum cross-sectional area of the subchamber  72 . An ignition element  84  is received and retained within the corresponding hole  82 , with the tip  86  of the ignition element  84  being received in the subchamber  72 . In the embodiment shown, the ignition element  84  is a glow plug. Alternate types of ignition elements  84  which may be used include, but are not limited to, plasma ignition, laser ignition, spark plug, microwave, etc. 
     The pilot injector  78  and main injector  42  inject fuel, which in a particular embodiment is heavy fuel e.g. diesel, kerosene (jet fuel), equivalent biofuel, etc. into the chambers  32 . Alternately, the fuel may be any other adequate type of fuel suitable for injection as described, including non-heavy fuel such as for example gasoline or liquid hydrogen fuel. In a particular embodiment, at least 0.5% and up to 20% of the fuel is injected through the pilot injector  78 , and the remainder is injected through the main injector  42 . In another particular embodiment, at most 10% of the fuel is injected through the pilot injector  78 . In another particular embodiment, at most 5% of the fuel is injected through the pilot injector  78 . The main injector  42  injects the fuel such that each rotating chamber  32  when in the combustion phase contains a lean mixture of air and fuel. 
     Referring to  FIG. 3 , an insert  134  according to another embodiment is shown, engaged to the same outer body  12 . The insert  134  extends across a thickness of the peripheral wall  18 , and includes an inner body portion  146  and an outer body portion  162  which are attached together, for example through a high temperature braze joint  188 . The outer body portion  162  has an enlarged flange  148  at its outer end which abuts the outer surface  64  of the peripheral wall  18  and is connected thereto, for example through bolts with appropriate sealing such as a gasket or crush seal (not shown). Alternate types of connections can also be used, including but not limited to a brazed connection. 
     The inner body portion  146  has an inner surface  166  which is continuous with the inner surface  19  of the peripheral wall  18  to define the cavity  20 . The inner end of the inner body portion  146  is complementarily shaped to engage the flange  68  extending in the insert opening  36  adjacent the inner surface  19 , with a gasket  70  being received therebetween. 
     In this particular embodiment, the body portions  146 ,  162  are made of an appropriate type of super alloy such as a Nickel based super alloy. 
     The subchamber configured as a pilot subchamber  72  is defined in the insert  134  at the junction between the body portions  146 ,  162 , with the inner body portion  146  defining the opening  74  for communication between the subchamber  72  and the cavity  20 . The outer body portion  162  has the ignition element elongated hole  82  defined therein along the direction of the transverse axis T and in communication with the subchamber  72 . The ignition element  84  is received and retained within the corresponding hole  82 , for example through threaded engagement. As in the previous embodiment, the tip  86  of the ignition element  84  is received in the subchamber  72 . 
     Referring to  FIG. 4 , an insert  234  according to another embodiment is shown. The insert  234  is received in a corresponding insert opening  236  defined through the peripheral wall  18 . The insert  234  includes an inner body portion  246  and an outer body portion  262  which are attached together, for example through a high temperature braze joint, with the subchamber  72  being defined at the junction of the two portions  246 ,  262 . The inner body portion  246  defines the opening  74  for communication between the subchamber  72  and the cavity  20 . 
     The outer body portion  262  has the ignition element elongated hole  82  defined therethrough in communication with the subchamber  72 . The outer body portion  262  includes an inner enlarged section  245  connected to the inner body portion  246  and defining the subchamber  72 . The enlarged section  245  extends substantially across the width of the insert opening  236  around the subchamber  72 , then tapers to a reduced width section  247  extending therefrom. The reduced width section  247  has at its outer end an enlarged flange  248  which abuts a shoulder  250  defined in the outer surface  64  of the peripheral wall  18  around the insert opening  236 . An outer section  249 , which in the embodiment shown has a width intermediate that of the sections  245  and  247 , extends outwardly from the flange  248 . The flange is connected to the shoulder, for example through bolts (not shown) with appropriate sealing such as a crush seal or a gasket (not shown) made of high temperature material, for example a silica based material or grafoil, between the flange  248  and shoulder  250 . Alternate types of connections can also be used. 
     The inner body portion  246  has an inner surface  266  which is continuous with the inner surface  19  of the peripheral wall  18  to define the cavity  20 . The inner body portion  246  includes a groove defined therearound near the inner surface  266 , in which an appropriate seal  251 , for example a silica based gasket tape, is received in contact with the walls of the insert opening  236 . In this embodiment, the walls of the insert openings  236  are straight adjacent the inner surface  19 , i.e. there is no flange adjacent the inner surface  19 . 
     The volume of the pilot subchamber  72  in the insert  34 ,  134 ,  234  is selected to obtain a stoichiometric mixture around ignition within an acceptable delay, with some of the exhaust product from the previous combustion cycle remaining in the subchamber  72 . In a particular embodiment, the volume of the subchamber  72  is at least 0.5% and up to 3.5% of the displacement volume, with the displacement volume being defined as the difference between the maximum and minimum volumes of one chamber  32 . In another particular embodiment, the volume of the subchamber  72  corresponds to from about 0.625% to about 1.25% of the displacement volume. 
     The volume of the pilot subchamber  72  may also be defined as a portion of the combustion volume, which is the sum of the minimum chamber volume Vmin (including the recess  38 ) and the volume of the subchamber V2 itself. In a particular embodiment the subchamber  72  has a volume corresponding to from 5% to 25% of the combustion volume, i.e. V2=5% to 25% of (V2+Vmin). In another particular embodiment, the subchamber  72  has a volume corresponding to from 10% to 12% of the combustion volume, i.e. V2=10% to 12% of (V2+Vmin). 
     The subchamber  72  may help create a stable and powerful ignition zone to ignite the overall lean main combustion chamber  32  to create the stratified charge combustion. The subchamber  72  may improve combustion stability, particularly but not exclusively for a rotary engine which operates with heavy fuel below the self-ignition of fuel. The insert  34 ,  134 ,  234  made of a heat resistant material may advantageously create a hot wall around the subchamber which may further help with ignition stability. 
     The teachings herein are applicable to many rotary engine types, and not just Wankel engines. Therefore, in another embodiment, the rotary engine with subchamber the  72  may be a non-Wankel engine. A “non-Wankel” engine, as used in this description and the appended claims, means a rotary engine suitable for use with the present invention, but excluding Wankel type engines. 
     In a particular embodiment, the rotary engine may be a single or eccentric type rotary engine in which the rotor rotates about a fixed center of rotation. For example, the rotary engine may be a sliding vane engine, such as described in U.S. Pat. No. 5,524,587 issued Jun. 11, 1996 or in U.S. Pat. No. 5,522,356 issued Jun. 4, 1996, the entire contents of both of which are incorporated by reference herein. 
     Referring to  FIG. 5 , an example of a sliding vane engine  100  is shown. The engine  100  includes an outer body  112  defining an internal cavity  20  receiving a rotor  124  having a number of vanes  125 . The rotor  124  includes an inner hub assembly  127  rotating about a first axis and an outer hub assembly  129  rotating about a second axis offset from the first axis, with the two hub assemblies  127 ,  129  being mechanically linked. The vanes  125  are pivotally connected to the inner hub assembly  127  and are slidingly engaged through slots defined between adjacent sections of the outer hub assembly  129 . The sections of the outer hub assembly  129  are thus sealingly engaged to the vanes  125  at different distances from the first axis of the inner hub assembly  127 , defining a plurality of chambers  32  of variable volume within the cavity  20  around the rotor  124 . 
     In the embodiment shown, the engine  100  includes the subchamber  72  described above, in this example defined in the insert  34  received in an insert opening  36  of a peripheral wall  118  of the outer body  112 . The peripheral wall  118  also has a main injector elongated hole  40  defined therethrough, in communication with the internal cavity  20  and spaced apart from the insert  34 . The insert is biased against the cover  62  retaining the insert  34  within the insert opening  36 . The insert  34  is made of a material having a greater heat resistance than that of the peripheral wall  118  and defines the pilot subchamber  72  in communication with the internal cavity  20  through at least one opening  74 . The peripheral wall  118  and/or the insert  34  has the pilot injector elongated hole  76  and the ignition element elongated hole  82  defined therethrough in communication with the subchamber  72 . Other embodiments may be provided for the insert in the engine  100 , including, but not limited to, the other inserts  134 ,  234  described above. 
     In another particular embodiment, the rotary engine may be an oscillatory rotating engine, including two or more rotors rotating at different angular velocities, causing the distance between portions of the rotors to vary and as such the chamber volume to change. Referring to  FIG. 6 , an example of such an engine is shown. The engine  200  includes an inner rotor  224  and an outer body or rotor  212  rotating at different angular velocities, the outer rotor  212  defining an internal cavity  20  in which the inner rotor  212  is received. Chambers  32  of variable volume are defined within the cavity  20  around the inner rotor  224 . 
     In the embodiment shown, the engine  200  includes the subchamber  72  described above, in this example defined in the insert  34  received in an insert opening  36  of a peripheral wall  218  of the outer body  212 . The peripheral wall  218  also has the main injector elongated hole  40  defined therethrough spaced apart from the insert  34 , and the peripheral wall  218  and/or the insert  34  has the pilot injector elongated hole  76  and the ignition element elongated hole  82  defined therethrough. Other embodiments may be provided for the insert in the engine  200 , including, but not limited to, the other inserts  134 ,  234  described above. 
     In another particular embodiment, the rotary engine is a planetary rotating engine having a different geometry than that of the Wankel engine. Referring to  FIG. 7 , an example of such an engine is shown. The engine  300  includes an outer body  312  forming an internal cavity  20  with a peripheral inner surface thereof having an epitrochoid profile defining three lobes. The engine  300  also includes a rotor  324  with four apex portions  330  in sealing engagement with the peripheral inner surface to form four rotating working chambers  32  of variable volume within the cavity  20  around the rotor  324 . The rotor  324  is journaled on an eccentric portion of a shaft and performs orbital revolutions within the cavity  20 . 
     In the embodiment shown, the engine  300  includes the subchamber  72  described above, in this example defined in the insert  34  received in an insert opening  36  of a peripheral wall  318  of the outer body  312 . The peripheral wall  318  also has the main injector elongated hole  40  defined therethrough spaced apart from the insert  34 , and the peripheral wall  318  and/or the insert  34  has the pilot injector elongated hole  76  and the ignition element elongated hole  82  defined therethrough. Other embodiments may be provided for the insert in the engine  300 , including, but not limited to, the other inserts  134 ,  234  described above. 
     The subchamber  72  may be provided integrally within the outer body  12 ,  112 ,  212 ,  312  of the engine  10 ,  100 ,  200 ,  300 , provided the outer body  12 ,  112 ,  212 ,  312  is made of a material having adequate heat resistance and such other properties required to provide a suitable outer body. Referring to  FIG. 8 , the Wankel engine  10  is shown with the subchamber  72 , pilot injector hole  76  and ignition element hole  82  integrally defined in the outer body  12 , more particularly in the peripheral wall  18 . In a particular embodiment, the outer body  12  is made of a material having a heat resistance greater than that of aluminium. In a particular embodiment, the outer body  12  is made of an appropriate type of ceramic or of an appropriate type of super alloy, such as for example a Nickel based super alloy. Though not shown, a wear insert may be provided in the internal cavity  20  for contacting the rotor sliding surfaces. The integral subchamber may be applied to any of the rotary engine configurations contemplated by the present description. 
     Referring to  FIG. 9 , a rotary engine  400  and an insert  434  according to another embodiment is shown. Although the engine  400  is depicted as a Wankel engine, with an outer body including a peripheral wall  418  extending between two axially spaced apart end walls  14  to define an internal cavity  20  receiving a rotor  24 , it is understood that the engine  400  may alternately be any other adequate type of rotary engine, including, but not limited to, the rotary engines described above. 
     The insert  434  is removably received in an insert opening  436  extending across a thickness of the peripheral wall  418  of the outer body of the engine  400 . The insert  434  includes an elongated insert body  446 , with an enlarged flange  448  at its outer end which abuts shoulders  464  defined by the insert opening  436  having an enlarged cross-section adjacent its communication with the outer surface of the peripheral wall  418 . Alternately, the flange  448  can abut the outer surface of the peripheral wall  418 . A seal  448 A is disposed between the flange  448  and the shoulders  464  to seal the insert opening  436 . The seal  448 A can be a C-seal or any other suitable seal. The insert opening  436  is located at or near top dead center, downstream of the main fuel injector  42  communicating with the internal cavity  20  of the engine  400  and upstream of a maximum temperature and pressure region of the internal cavity  20 . The maximum pressure and temperature region is defined as a region of the chambers  32  just after top dead center. The fuel in the internal cavity  20  is ignited before top dead center (BTDC) and releases its energy such that maximum compression of the gas mixture is obtained just after top dead center (ATDC) (i.e. just after the minimum volume for the chambers  32 ). In a particular embodiment, the maximum pressure obtained in this region is in the order of 1500 psi. 
     The insert body  446  has an inner surface  466  which is continuous with an inner surface  19  of the peripheral wall  418  defining the internal cavity  20 . The insert opening  436  has a reduced cross-section adjacent the inner surface  19 , the reduced cross-section being defined by a flange  468  of the peripheral wall  418  surrounding and protruding into the insert opening  436  adjacent the inner surface  19 . The inner end of the insert body  446  is complementarily shaped to engage this flange  468 ; optionally, a gasket may be received between the insert body  446  and flange  468 , for example at  470 . In the embodiment shown, the outer surface of the flange  468  abutting the insert body  446  is frusto-conical such that a thickness of the flange  468  is progressively reduced toward a central axis of the insert opening  436 ; other configurations are also possible. 
     The insert body  446  has a subchamber configured as a pilot subchamber  472  defined therein in communication with the internal cavity  20 . In the embodiment shown, the subchamber  472  has a circular cross-section; alternate shapes are also possible. The subchamber  472  communicates with the cavity  20  through at least one opening  474  defined in the inner surface  466 . 
     In this embodiment, the peripheral wall  418  has a pilot injector elongated hole  476  defined therethrough in proximity of the insert  434  and communicating with the insert opening  436 . The pilot injector elongated hole  476  has a shape similar to the pilot injector elongated hole  76  described above. The pilot injector hole  476  is in communication with the subchamber  472  through an injector opening  488 A defined in the insert body  446 , and which has an area smaller than the maximum cross-sectional area of the subchamber  472 . A pilot fuel injector  478  is received and retained within the corresponding hole  476 . However, in this embodiment, the pilot fuel injector  478  extends with its tip  480  received in the pilot injector hole  476  without any part of the pilot fuel injector  478  protruding in the insert opening  436 ; the injector opening  488 A is thus free of the pilot fuel injector  478 . The pilot fuel injector  478  is clear from the subchamber  472  and the insert opening  436  to allow removal of the insert  434  without the need to removing the pilot fuel injector  478 . 
     Referring to  FIGS. 10 and 11 , a threaded hole  494  is provided (e.g. centrally disposed) in the flange  448  of the insert  434 , configured to receive and having a shape complementary to that of a threaded tool. Upon engagement with the threaded hole  494 , the threaded tool may facilitate removal of the insert  434  from the insert opening  436  when required, for example for inspection or maintenance. 
     In the embodiment shown, the insert  434  is removably retained in the insert opening  436  by four threaded fasteners such as bolts  496  ( FIG. 10 ) engaging the flange  448  of the insert  434  and the peripheral wall  418  through corresponding threaded holes  448 B ( FIG. 11 ) to secure the insert  434  with respect to the peripheral wall  418 . It is understood that other types of fasteners allowing for the insert to be removably retained (e.g. retained such as to be removable without requiring to break, cut or damage the insert, wall or fastening mechanism) and/or different numbers of fasteners can also be used (e.g. one or more). 
     Referring to  FIG. 12 , the peripheral wall  418  has at least one ignition element elongated hole  482  defined therein, angled with respect to the transverse axis T of the outer body  12  and in communication with the subchamber  472  and the insert opening  436 . The ignition element elongated hole  482  and the subchamber  472  communicate through an opening  488 B in the insert body  446  aligned with the hole  182  and having an area smaller than the maximum cross-sectional area of the subchamber  472 . An ignition element  484  is received and retained within the corresponding ignition element elongated hole  482  in heat transfer communication with the subchamber  472 . In the embodiment shown, a tip  486  of the ignition element  484  is received in the subchamber  472 . Alternately, the tip  486  of the ignition element  484  can be outside of the subchamber  472 , opening  488 B and/or insert opening  436  (for example, so that no part of the ignition element  484  penetrates the insert opening  436 ), and the heat transfer communication may be performed with or without a fluid communication between the ignition element elongated hole  482  and the subchamber  472  (for example, the opening  488 B may be omitted). 
     Referring to  FIG. 13 , in a particular embodiment, two ignition elements  484  are provided in communication with the subchamber  472 . The ignition elements  484  are provided in different planes, so that each ignition element  484  is extending along a respective axis  498 , the axes  498  intersecting. In a particular embodiment, the axes are disposed at a 30 degrees angle from each other. Alternately, the number and/or orientation of the ignition elements  484  can differ. 
     As can be seen in  FIGS. 9 and 12 , a plurality of coolant passages  499  are defined throughout the peripheral wall  418  (and although not shown, similar coolant passages may extend through the peripheral walls  18 ,  118 ,  218 ,  318  described above), including, but not limited to, in proximity of the insert  434 . The coolant passages  499  are in fluid communication with one another by being part of a cooling circuitry through which a liquid coolant (e.g. water) circulates in a closed loop with a heat exchanger or any other element suitable to cool the used coolant for recirculation to the engine. The size and number of the coolant passages  499  are selected such as to be able to maintain the peripheral wall  418  at temperatures below the applicable maximum threshold for the material of the peripheral wall  418 . 
     In the embodiment shown in  FIGS. 12-13 , the ignition elements  484  extend within the peripheral wall  418  along most of their length, which may facilitate cooling of the ignition elements  484  using the cooling circuitry provided in the outer body through the peripheral wall  418 . 
     In a particular embodiment, the presence of coolant passages  499  can impede inspection, for example preventing the provision of a dedicated inspection port, particularly for the hotter regions where more cooling is required and where the presence of such a port could disturb the cooling pattern. In a particular embodiment, the presence of the insert  34 ,  134 ,  234 ,  434  allows for the insert opening  36 ,  236 ,  436  to be used as an inspection port, taking advantage of this existing opening to perform visual inspection of the internal cavity  20  through a region of the peripheral wall which includes the cooling passages  499 . Since the insert  34 ,  134 ,  234 ,  434  is located adjacent the fuel injectors which are typically readily accessible in use for maintenance purposes, in a particular embodiment the insert  34 ,  134 ,  234 ,  434  is also readily accessible in use to be removed from the engine without the need to move the engine. Prior methods of rotary engine inspection include inspection through the inlet or outlet ports; the insert opening  36 ,  236 ,  436  is closer to the high pressure and temperature region of the engine than the ports, and accordingly in a particular embodiment provides for a better access to the portions of the internal cavity  20  which are most susceptible to damage. Prior methods of rotary engine inspection also include inspection through the hole left by removal of the ignition element; however, such inspection requires the use of inspection tools, for example a boroscope, since the hole is too small to be usable for visual and/or manual inspection. In a particular embodiment, the insert opening  36 ,  236 ,  436  is advantageously sized to allow for visual and/or manual inspection. 
     In a particular embodiment, inspection in the internal cavity  20  (i.e. of features of the outer body inside the internal cavity  20  and/or of the rotor  24  received therein) is performed in accordance with the following. If the ignition element(s)  484  extend(s) within the peripheral wall  418  and protrude(s) into the insert opening  436 , the ignition element(s)  484  is/are disengaged from the insert  434 . In an embodiment where the ignition element(s) is/are not engaged in the insert  434 , or where the ignition element(s)  84 , is/are received in the insert  34 ,  134 ,  234  without extending through the peripheral wall such as to be removable together with the insert  34 ,  134 ,  234  in a same step, this step may accordingly be omitted. 
     Similarly, if a fuel injector extends within the peripheral wall and protrudes into the insert opening, the fuel injector is disengaged from the insert. In an embodiment where the fuel injector is not engaged in the insert, received in the insert without extending through the peripheral wall such as to be removable together with the insert in a same step, this step may accordingly be omitted. 
     The insert  34 ,  134 ,  234 ,  434  is then removed from the insert opening  36 ,  236 ,  436  of the outer body, thereby providing access to the internal cavity  20  through the insert opening  36 ,  236 ,  436 . To facilitate removal of the insert by a user, a threaded tool may be inserted into the threaded hole  494  provided in the insert  434  (a similar threaded hole may be provided in any of the inserts described herein) and a force is then applied on the threaded tool, for example a pulling force. 
     Once the insert  34 ,  134 ,  234 ,  434  is removed, the internal cavity  20  is inspected through the insert opening  36 ,  236 ,  436 . The inspection can be done visually and/or manually. The inspection can include, but is not limited to, any one or any combination of inspecting the condition of the apex seals  52 , inspecting the condition and/or operation of the spring(s) biasing the apex seals  52 , inspecting the condition of a coating applied to the inner surface  19  of the peripheral wall  18 ,  118 ,  218 ,  318 ,  418  and/or to the inner surface  491  of the end walls  14 , inspecting the condition of the rotor  24  itself (e.g. presence of cracks), verifying if liquid coolant and/or oil is present in the chambers  32 , inspecting the fuel injector (e.g. its tip), particularly for the fuel injector communicating with the chamber but having a configuration allowing the insert to be removed without prior removal of the fuel injector, etc. Inspection of the condition of the coating can include inspection to detect one or more of pitting, erosion, delamination and cracks in the coating surface. 
     Following the results of inspection, appropriate maintenance and/or repair operations may be performed. Non-limiting examples of such operations include, with a prior step of disassembly of the engine in whole or in part when required:
     When the condition of the apex seals  52  and/or of the spring(s) biasing the apex seals  52  is determined to be inadequate following the inspection, replacing damaged ones of the apex seals  52  and the springs;   When the condition of the coating applied to the inner surface  19  of the peripheral wall  18 ,  118 ,  218 ,  318 ,  418  and/or to the inner surface  491  of the end walls  14  is determined to be inadequate following the inspection, recoating the parts where the defects were detected, optionally stripping the existing coating before the recoating operation;   When the condition of the rotor  24  itself is determined to be inadequate following the inspection, performing required repairs to the rotor (e.g. weld repair or replacement) or replacing the rotor as a whole;   When the presence of liquid coolant in the chambers  32  is detected, replacing a broken or defective seal of the cooling (e.g. o-ring), and/or inspecting the outer body to find a crack responsible for the leak and repairing the crack or replacing the damaged part;   When the presence of oil in the chambers  32  is detected, replacing a broken or defective oil seal, or repair or replacement of the element responsible for the leak, with optional pressure testing to determine which element is responsible if the failure is not apparent;   When damage to the fuel injector (e.g. pilot fuel injector) is detected, replacing or repairing the fuel injector.   

     In a particular embodiment, a boroscope is optionally inserted through the insert opening  436 , as a follow-up to a preliminary visual inspection, to further inspect the internal cavity  20 . The use of the boroscope can advantageously provide a wider access to the internal cavity  20 . 
     Referring back to  FIGS. 10 and 11 , the width  490  of the internal cavity is defined as the distance between the inner surfaces  491  of the end walls  14  along a direction parallel to a rotational axis RA of the rotor  24 . In a particular embodiment and referring to  FIG. 11 , the width  492  of the insert opening  436 , i.e. of its cross-section, defined perpendicularly to the thickness of the peripheral wall  418  (e.g. parallel to the rotational axis RA), is sufficiently large throughout the thickness of the peripheral wall  418  to be able to perform an unaided (i.e. without inspection instruments or tools) visual inspection of the internal cavity  20  through the insert opening  436 ; the minimal width is thus sized to correspond to, at least, a minimum dimension required for visual inspection, based on the size of the human eye. 
     In the embodiment of  FIG. 9 , the minimum width  492 ′ of the insert opening  436  is a minimum diameter, since the insert opening  436  has a circular cross-section, and is located adjacent the inner surface  19  of the peripheral wall  418 , i.e. at the radially innermost point of the insert opening  436 . In a particular embodiment, the minimum width  492 ′ is at least equal to ⅓ of the width  490  of the internal cavity  20 . In a particular embodiment, the minimum width  492 ′ of the insert opening  436  is between ⅓ and ½ of the width  490  of the internal cavity  20 . For example, in a particular embodiment, the minimum width or diameter  492 ′ of the insert opening  436  is at least 0.75 inch; in a particular embodiment, such a minimum width is sufficient to allow for visual inspection through the insert opening. In particular embodiments, the minimum width  492 ′ of the insert opening  436  may correspond to any one of the following: at least 0.8 inch; at least 0.85 inch; at least 0.9 inch; at least 0.93 inch; about 0.93 inch; at least 1 inch. It is understood that the particular dimensions provided herein are also applicable to the insert openings  36 ,  236  of the other embodiments discussed. 
     The ability to perform visual inspection is highly desirable, and in a particular embodiment allows for reduction of the costs and/or time associated with preliminary inspections, as opposed to engine configurations which require instruments and/or disassembly of the housing to be inspected; a larger insert opening  36 ,  236 ,  436  provides better exposure of the internal cavity  20  for visual inspection. 
     It is understood that the removable insert  34 ,  134 ,  234 ,  434  allowing inspection of the internal cavity  20  through the insert opening  36 ,  236 ,  436  is not limited to an insert defining a pilot subchamber for pilot ignition. For example, in particular embodiments, the removable insert  34 ,  134 ,  234 ,  434  allowing inspection of the internal cavity  20  through the insert opening  36 ,  236 ,  436  is an insert defining other types of subchambers, such as for example a pre-chamber for combustion, where the whole volume of fuel is injected for ignition—i.e. where the main injector is in communication with the pre-chamber in the insert. Other configurations are also possible. 
     The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the invention(s) disclosed. For example, the mechanical arrangements of the rotary engines described above are merely examples of many possible configurations which are suitable for use with the present invention(s). Any suitable injector configuration and arrangement may be used. Hence, modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.