Patent Description:
Rotary engines, such as for example Wankel engines, use the eccentric rotation of a piston to convert pressure into a rotating motion, instead of using reciprocating pistons. In these engines, the rotor includes a number of apex or seal portions which remain in contact with a peripheral wall of the rotor cavity of the engine throughout the rotational motion of the rotor to create a plurality of rotating chambers when the rotor rotates.

Wankel engines are typically used with gasoline or similar fuel, with a single fuel injector or with two spaced apart fuel injectors. The fuel injector(s) may be located in a recess adjacent the combustion chamber and defined integrally through the engine housing, to communicate with an ignition member such as for example a spark plug. However, known arrangements are not optimized for use in a compound cycle engine system and/or for use with so-called heavy fuels, such as kerosene, and thus room for improvement exists.

<CIT> discloses a prior art engine as set forth in the preamble of claim <NUM>.

<CIT> discloses an internal combustion engine.

In one aspect, there is provided a rotary internal combustion engine as recited in claim <NUM>.

Referring to <FIG>, a rotary internal combustion engine <NUM> known as a Wankel engine is schematically and partially shown. In a particular embodiment, the rotary engine <NUM> is used in a compound cycle engine system such as described in <CIT> or as described in <CIT>. 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 <NUM> is used without a turbocharger, with air at atmospheric pressure.

The engine <NUM> comprises an outer body <NUM> having axially-spaced end walls <NUM> with a peripheral wall <NUM> extending therebetween to form a rotor cavity <NUM>. The inner surface <NUM> of the peripheral wall <NUM> of the cavity <NUM> has a profile defining two lobes, which is preferably an epitrochoid.

An inner body or rotor <NUM> is received within the cavity <NUM>, with the geometrical axis of the rotor <NUM> being offset from and parallel to the axis of the outer body <NUM>. The rotor <NUM> has axially spaced end faces <NUM> adjacent to the outer body end walls <NUM>, and a peripheral face <NUM> extending therebetween. The peripheral face <NUM> defines three circumferentially-spaced apex portions <NUM> (only one of which is shown), and a generally triangular profile with outwardly arched sides. The apex portions <NUM> are in sealing engagement with the inner surface of peripheral wall <NUM> to form three rotating working chambers <NUM> (only two of which are partially shown) between the inner rotor <NUM> and outer body <NUM>. A recess <NUM> is defined in the peripheral face <NUM> of the rotor <NUM> between each pair of adjacent apex portions <NUM>, to form part of the corresponding chamber <NUM>.

The working chambers <NUM> are sealed. Each rotor apex portion <NUM> has an apex seal <NUM> extending from one end face <NUM> to the other and protruding radially from the peripheral face <NUM>. Each apex seal <NUM> is biased radially outwardly against the peripheral wall <NUM> through a respective spring. An end seal <NUM> engages each end of each apex seal <NUM>, and is biased against the respective end wall <NUM> through a suitable spring. Each end face <NUM> of the rotor <NUM> has at least one arc-shaped face seal <NUM> running from each apex portion <NUM> to each adjacent apex portion <NUM>, adjacent to but inwardly of the rotor periphery throughout its length. A spring urges each face seal <NUM> axially outwardly so that the face seal <NUM> projects axially away from the adjacent rotor end face <NUM> into sealing engagement with the adjacent end wall <NUM> of the cavity. Each face seal <NUM> is in sealing engagement with the end seal <NUM> adjacent each end thereof.

Although not shown in the Figures, the rotor <NUM> 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 <NUM> and the meshed gears guide the rotor <NUM> to perform orbital revolutions within the stator cavity. The rotor <NUM> performs three rotations for each orbital revolution. Oil seals are provided around the phasing gear to prevent leakage flow of lubricating oil radially outwardly thereof between the respective rotor end face <NUM> and outer body end wall <NUM>.

At least one inlet port (not shown) is defined through one of the end walls <NUM> or the peripheral wall <NUM> for admitting air (atmospheric or compressed) into one of the working chambers <NUM>, and at least one exhaust port (not shown) is defined through one of the end walls <NUM> or the peripheral wall <NUM> for discharge of the exhaust gases from the working chambers <NUM>. 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 one orbital revolution of the rotor <NUM>, each chamber <NUM> moves around the stator cavity <NUM> 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 <NUM> 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.

An insert <NUM> is received in a corresponding hole <NUM> defined through the peripheral wall <NUM> of the outer body <NUM>, for pilot fuel injection and ignition. The peripheral wall <NUM> also has a main injector elongated hole <NUM> defined therethrough, in communication with the rotor cavity <NUM> and spaced apart from the insert <NUM>. A main fuel injector <NUM> is received and retained within this corresponding hole <NUM>, with the tip <NUM> of the main injector <NUM> communicating with the cavity <NUM> at a point spaced apart from the insert <NUM>. The main injector <NUM> is located rearwardly of the insert <NUM> 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 <NUM> sequentially with a tip hole pattern designed for an adequate spray.

Referring particularly to <FIG>, the insert includes an elongated body <NUM> extending across a thickness of the peripheral wall <NUM>, with an enlarged flange <NUM> at its outer end which is biased away from a shoulder <NUM> defined in the peripheral wall <NUM>, and against a gasket (not shown) made of an appropriate type of heat resistant material such as a silica based material. A washer <NUM>, such as for example a steel or titanium washer, and spring <NUM>, such as for example a wave spring or a Belleville spring, are provided between the flange <NUM> and the shoulder <NUM> of the peripheral wall <NUM>. The spring <NUM> biases the body <NUM> against a cover <NUM> having a cross-section greater than that of the hole <NUM> and extending over an outer surface <NUM> of the peripheral wall <NUM>. The cover <NUM> is connected to the peripheral wall <NUM>, 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 <NUM> has an inner surface <NUM> which is continuous with the inner surface <NUM> of the peripheral wall <NUM> to define the cavity <NUM>. The insert hole <NUM> in the wall <NUM> defines a flange <NUM> extending in the insert hole <NUM> adjacent the inner surface <NUM>, and the inner end of the insert body <NUM> is complementarily shaped to engage this flange <NUM>, with a gasket <NUM> being received therebetween.

The insert body <NUM> is made of a material having a greater heat resistance than that of the peripheral wall <NUM>, which in a particular embodiment is made of aluminium. In this particular embodiment, the insert body <NUM> is made of an appropriate type of ceramic.

The insert body <NUM> has a pilot subchamber <NUM> defined therein in communication with the rotor cavity <NUM>. In the embodiment shown, the subchamber <NUM> has a circular cross-section; alternate shapes are also possible. The subchamber <NUM> communicates with the cavity through at least one opening <NUM> defined in the inner surface <NUM>. The subchamber <NUM> has a shape forming a reduced cross-section adjacent the opening <NUM>, such that the opening <NUM> defines a restriction to the flow between the subchamber <NUM> and the cavity <NUM>. The opening <NUM> may have various shapes and/or be defined by a pattern of multiple holes.

The peripheral wall <NUM> has a pilot injector elongated hole <NUM> defined therethrough, at an angle with respect to the insert <NUM> and in communication with the subchamber <NUM>. A pilot fuel injector <NUM> is received and retained within the corresponding hole <NUM>, with the tip <NUM> of the pilot injector <NUM> being received in the subchamber <NUM>.

The insert body <NUM> and cover <NUM> have an ignition element elongated hole <NUM> defined therein extending along the direction of the transverse axis T of the outer body <NUM>, also in communication with the subchamber <NUM>. An ignition element <NUM> is received and retained within the corresponding hole <NUM>, with the tip <NUM> of the ignition element <NUM> being received in the subchamber <NUM>. In the embodiment shown, the ignition element <NUM> is a glow plug. Alternate types of ignition elements <NUM> which may be used include, but are not limited to, plasma ignition, laser ignition, spark plug, microwave, etc..

The pilot injector <NUM> and main injector <NUM> inject heavy fuel, e.g. diesel, kerosene (jet fuel), equivalent biofuel, etc. into the chambers <NUM>. In a particular embodiment, at least <NUM>% and up to <NUM>% of the fuel is injected through the pilot injector <NUM>, and the remainder is injected through the main injector <NUM>. In another particular embodiment, at most <NUM>% of the fuel is injected through the pilot injector <NUM>. In another particular embodiment, at most <NUM>% of the fuel is injected through the pilot injector <NUM>. The main injector <NUM> injects the fuel such that each rotating chamber <NUM> when in the combustion phase contains a lean mixture of air and fuel.

Referring to <FIG>, an insert <NUM> according to another embodiment is shown, engaged to the same outer body <NUM>. The insert <NUM> extends across a thickness of the peripheral wall <NUM>, and includes an inner body portion <NUM> and an outer body portion <NUM> which are attached together, for example through a high temperature braze joint <NUM>. The outer body portion <NUM> has an enlarged flange <NUM> at its outer end which abuts the outer surface <NUM> of the peripheral wall <NUM> 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 <NUM> has an inner surface <NUM> which is continuous with the inner surface <NUM> of the peripheral wall <NUM> to define the cavity <NUM>. The inner end of the inner body portion <NUM> is complementarily shaped to engage the flange <NUM> extending in the insert hole <NUM> adjacent the inner surface <NUM>, with a gasket <NUM> being received therebetween.

In this particular embodiment, the body portions <NUM>, <NUM> are made of an appropriate type of super alloy such as a Nickel based super alloy.

The pilot subchamber <NUM> is defined in the insert <NUM> at the junction between the body portions <NUM>, <NUM>, with the inner body portion <NUM> defining the opening <NUM> for communication between the subchamber <NUM> and the cavity <NUM>. The outer body portion <NUM> has the ignition element elongated hole <NUM> defined therein along the direction of the transverse axis T and in communication with the subchamber <NUM>. The ignition element <NUM> is received and retained within the corresponding hole <NUM>, for example through threaded engagement. As in the previous embodiment, the tip <NUM> of the ignition element <NUM> is received in the subchamber <NUM>.

Referring to <FIG>, an insert <NUM> according to another embodiment is shown. The insert <NUM> is received in a corresponding hole <NUM> defined through the peripheral wall <NUM>. The insert <NUM> includes an inner body portion <NUM> and an outer body portion <NUM> which are attached together, for example through a high temperature braze joint, with the subchamber <NUM> being defined at the junction of the two portions <NUM>, <NUM>. The inner body portion <NUM> defines the opening <NUM> for communication between the subchamber <NUM> and the cavity <NUM>.

The outer body portion <NUM> has the ignition element elongated hole <NUM> defined therethrough in communication with the subchamber <NUM>. The outer body portion <NUM> includes an inner enlarged section <NUM> connected to the inner body portion <NUM> and defining the subchamber <NUM>. The enlarged section <NUM> extends substantially across the width of the hole <NUM> around the subchamber <NUM>, then tapers to a reduced width section <NUM> extending therefrom. The reduced width section <NUM> has at its outer end an enlarged flange <NUM> which abuts a shoulder <NUM> defined in the outer surface <NUM> of the peripheral wall <NUM> around the hole <NUM>. An outer section <NUM>, which in the embodiment shown has a width intermediate that of the sections <NUM> and <NUM>, extends outwardly from the flange <NUM>. 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 <NUM> and shoulder <NUM>. Alternate types of connections can also be used.

The inner body portion <NUM> has an inner surface <NUM> which is continuous with the inner surface <NUM> of the peripheral wall <NUM> to define the cavity <NUM>. The inner body portion <NUM> includes a groove defined therearound near the inner surface <NUM>, in which an appropriate seal <NUM>, for example a silica based gasket tape, is received in contact with the walls of the insert hole <NUM>. In this embodiment, the walls of the insert holes <NUM> are straight adjacent the inner surface <NUM>, i.e. there is no flange adjacent the inner surface <NUM>.

The volume of the subchamber <NUM> in the insert <NUM>, <NUM>, <NUM> 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 <NUM>. The volume of the subchamber <NUM> is at least <NUM>% and up to <NUM>% of the displacement volume, with the displacement volume being defined as the difference between the maximum and minimum volumes of one chamber <NUM>. In a particular embodiment, the volume of the subchamber <NUM> corresponds to from about <NUM>% to about <NUM>% of the displacement volume.

The volume of the subchamber <NUM> may also be defined as a portion of the combustion volume, which is the sum of the minimum chamber volume Vmin (including the recess <NUM>) and the volume of the subchamber V<NUM> itself. In a particular embodiment the subchamber <NUM> has a volume corresponding to from <NUM>% to <NUM>% of the combustion volume, i.e. V<NUM> = <NUM>% to <NUM>% of (V<NUM> + Vmin). In another particular embodiment, the subchamber <NUM> has a volume corresponding to from <NUM>% to <NUM>% of the combustion volume, i.e. V<NUM> = <NUM>% to <NUM>% of (V<NUM> + Vmin).

The subchamber <NUM> may help create a stable and powerful ignition zone to ignite the overall lean main combustion chamber <NUM> to create the stratified charge combustion. The subchamber <NUM> 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 <NUM>, <NUM>, <NUM> made of a heat resistant material may advantageously create a hot wall around the subchamber which may further help with ignition stability.

Claim 1:
A rotary internal combustion engine (<NUM>) comprising:
a rotor body (<NUM>); and
a stator body (<NUM>), wherein the stator body (<NUM>) comprises:
two axially spaced apart end walls (<NUM>);
a peripheral wall (<NUM>) extending between the end walls (<NUM>) and defining an internal cavity (<NUM>) therewith, the cavity (<NUM>) having an epitrochoid shape defining two lobes, wherein the cavity (<NUM>) receives the rotor body (<NUM>) rotatable within the cavity (<NUM>) and defines three working chambers (<NUM>) of variable volume in the cavity (<NUM>) between the rotor body (<NUM>) and the stator body (<NUM>), the volume of each of the three working chambers (<NUM>) is configured to vary between a minimum volume and a maximum volume, a difference between the maximum volume and the minimum volume defining a displacement volume; and
an insert (<NUM>; <NUM>; <NUM>) in the peripheral wall (<NUM>) of the stator body (<NUM>), the insert (<NUM>; <NUM>; <NUM>) being made of a material having a greater heat resistance than that of the peripheral wall (<NUM>), the insert (<NUM>; <NUM>; <NUM>) having a subchamber (<NUM>) defined therein and having an inner surface (<NUM>; <NUM>; <NUM>) bordering the cavity (<NUM>), the subchamber (<NUM>) communicating with the cavity (<NUM>) through at least one opening (<NUM>) defined in the inner surface (<NUM>; <NUM>; <NUM>) and having a shape forming a reduced cross-section adjacent the opening (<NUM>), at least one of the insert (<NUM>; <NUM>; <NUM>) and the peripheral wall (<NUM>) having a pilot fuel injector elongated hole (<NUM>) defined therethrough communicating with the subchamber (<NUM>) and sized to receive a pilot fuel injector (<NUM>) therein, at least one of the insert (<NUM>; <NUM>; <NUM>) and the peripheral wall (<NUM>) having an ignition element elongated hole (<NUM>) defined therethrough communicating with the subchamber (<NUM>) and sized to receive an ignition element (<NUM>) therein, and the peripheral wall (<NUM>) having a main fuel injector elongated hole (<NUM>) defined therethrough spaced apart from the insert (<NUM>; <NUM>; <NUM>) and sized to receive a main fuel injector (<NUM>) therein,
characterised in that
the subchamber (<NUM>) has a volume of at least <NUM>% of the displacement volume and up to <NUM>% of the displacement volume.