Patent Description:
It is generally known to completely deactivate some cylinders of a reciprocating internal combustion engine to reduce fuel consumption at part load. Also, dynamic skip fire allows to rapidly stop and restart injection within a cylinder so that a cylinder receives no fuel, and does not undergo combustion, for example for a single combustion event. This is often accompanied with high speed modifications to the valve train to reduce pumping loss during the skipped injections. However, completely stopping combustion in a cylinder may create thermal loading on the engine and impede the ability of the engine for a rapid relight when higher power is required.

<CIT> discloses a non-Wankel rotary engine having an insert in the peripheral wall of the outer body, having a subchamber defined therein and having an inner surface bordering the cavity, the subchamber communicating with the cavity through at least one opening defined in the inner surface, a pilot fuel injector having a tip received in the subchamber, an ignition element having a tip received in the subchamber, and a main fuel injector extending through the housing and having a tip communicating with the cavity at a location spaced apart from the insert.

The present invention provides a method of operating a rotary engine including a rotor engaged to a shaft and rotationally received in a housing to define a plurality of working chambers of variable volume, as defined in claim <NUM>.

The present invention further provides a method of operating a rotary engine including first and second rotor assemblies and a shaft, the first and second rotor assemblies including a rotor engaged to the shaft and rotationally received in a housing to define a plurality of working chambers of variable volume, and a pilot cavity in successive communication with the working chambers, as defined in claim <NUM>.

Referring to <FIG>, a rotor assembly configured as a rotary intermittent internal combustion engine <NUM> is schematically and partially shown. The rotor assembly <NUM> is known as a Wankel engine and comprises an outer body <NUM> having axially-spaced end walls <NUM> with a peripheral wall <NUM> extending therebetween to form an internal cavity <NUM>. The inner surface <NUM> of the peripheral wall <NUM> of the internal cavity <NUM> has a profile defining two lobes, which is preferably an epitrochoid.

An inner body or rotor <NUM> is received within the internal 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 internal cavity <NUM>. Each face seal <NUM> is in sealing engagement with the end seal <NUM> adjacent each end thereof.

Although not shown in <FIG>, the rotor <NUM> is journaled on an eccentric portion of a shaft <NUM> (<FIG>) 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 rotor <NUM> rotates the shaft <NUM> and the meshed gears guide the rotor <NUM> to perform orbital revolutions within the internal cavity <NUM>. The shaft <NUM> performs three rotations for each orbital revolution of the rotor <NUM> in the internal cavity <NUM>. 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 ignitor and fuel injectors (further described below) such that during each revolution of the rotor <NUM>, each chamber <NUM> moves around the internal 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 rotor assembly <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.

A pilot cavity is defined in the outer body <NUM>, for pilot fuel injection and ignition. In the embodiment shown example, the pilot cavity is in the form of a pilot subchamber <NUM>, provided in an insert <NUM> received in a corresponding insert opening defined through the peripheral wall <NUM> of the outer body <NUM> and in communication with the internal cavity <NUM>, for pilot fuel injection and ignition. In a particular embodiment, the insert <NUM> is made of a material having a greater heat resistance than that of the peripheral wall <NUM>, which may be made for example of aluminium. For example, the insert <NUM> may be made of an appropriate type of ceramic or of an appropriate type of super alloy such as a Nickel based super alloy. Other configurations are also possible, including configurations where the pilot cavity (e.g. pilot subchamber <NUM>) is defined directly in the outer body <NUM>, for example in the peripheral wall <NUM>.

The pilot subchamber <NUM> is in communication with the internal cavity <NUM>. In the embodiment shown, the pilot subchamber <NUM> has a circular cross-section; alternate shapes are also possible. The pilot subchamber <NUM> communicates with the internal cavity <NUM> through at least one opening <NUM>, and 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 pilot subchamber <NUM> and the internal cavity <NUM>. The opening <NUM> may have various shapes and/or be defined by multiple holes.

The peripheral wall <NUM> has a pilot injector elongated hole <NUM> defined therethrough in proximity of the pilot subchamber <NUM>, and in communication with the pilot 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> in communication with the pilot subchamber <NUM>.

The insert <NUM> and/or peripheral wall <NUM> have an ignitor elongated hole <NUM> defined therein, also in communication with the pilot subchamber <NUM>. An ignitor or ignition element <NUM> is received and retained within the corresponding hole, with the tip of the ignitor <NUM> communicating with the pilot subchamber <NUM>, for example by having the ignitor <NUM> extending outside of the pilot subchamber <NUM> and the ignitor elongated hole communicating with the pilot subchamber <NUM> through an opening or passage <NUM> aligned with the ignitor tip. In the embodiment shown, the ignitor <NUM> is a glow plug. Alternate types of ignitors <NUM> which may be used include, but are not limited to, plasma ignition, laser ignition, spark plug, microwave, etc..

It is understood that the pilot subchamber <NUM> may be omitted; in a particular embodiment which is not shown, the pilot subchamber <NUM> is replaced by any other suitable type of pilot cavity formed in the outer body <NUM>, for example a recess defined in the peripheral wall <NUM>. The pilot fuel injector <NUM> and the ignitor <NUM> having tips received in or communicating with the pilot cavity so as to perform the fuel ignition therein.

The peripheral wall <NUM> also has a main injector elongated hole <NUM> defined therethrough, in communication with the internal cavity <NUM> and spaced apart from the pilot cavity and pilot injector <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 internal cavity <NUM> at a point spaced apart from the communication between the pilot cavity and internal cavity <NUM> (e.g. from the subchamber opening <NUM>). The main injector <NUM> is located rearwardly of the subchamber opening <NUM> with respect to the direction R of the rotor rotation and revolution, i.e. downstream from the communication <NUM> between the pilot subchamber <NUM> and working chambers <NUM>, and is angled to direct fuel forwardly into each of the rotating chambers <NUM> sequentially with a tip hole configuration designed for an adequate spray.

The pilot injector <NUM> and main injector <NUM> inject fuel, which in a particular embodiment is heavy fuel e.g. diesel, kerosene (jet fuel), equivalent biofuel, etc. into the chambers <NUM>. 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, the pilot injector <NUM> and main injector <NUM> deliver the same type of fuel, for example from a common fuel source; alternately, the pilot injector <NUM> and main injector <NUM> may deliver different type of fuel. In a particular embodiment, up to <NUM>% of a maximum fuel flow (sum of maximum flow of the pilot injector <NUM> and main injector <NUM>) is injected through the pilot injector <NUM> when used; other values are also possible, for example having the pilot injector <NUM> deliver up to <NUM>%, or up to <NUM>%, of the maximum fuel flow when used. The main injector <NUM> injects the fuel such that each working chamber <NUM> when in the combustion phase contains a lean mixture of air and fuel.

The pilot subchamber <NUM> may help create a stable and powerful ignition zone to ignite the overall lean working chamber <NUM> to create the stratified charge combustion. The pilot subchamber <NUM> may improve combustion stability, particularly but not exclusively for a rotor assembly which operates with heavy fuel below the self-ignition of fuel. The insert <NUM> made of a heat resistant material may advantageously create a hot wall around the pilot subchamber <NUM> which may further help with ignition stability.

In a particular embodiment, the rotor assembly <NUM> is operated in accordance with the following. A pilot quantity of fuel is delivered into the pilot subchamber <NUM> and ignited within the pilot subchamber <NUM>, and a main quantity of fuel is delivered into the working chambers <NUM> downstream of their communication with the pilot subchamber <NUM>. When the rotor assembly <NUM> operates at maximum load, both the pilot quantity and the main quantity may correspond to a maximum pilot and main injection fuel flow, respectively. However, when the rotor assembly <NUM> operates at part load, some of the pilot and/or main injections are reduced or skipped, so as to reduce the fuel consumption, noise and/or vibrations on the rotor assembly <NUM>. Accordingly, one or both of the pilot and main quantity is varied between successive rotations of the shaft <NUM>, i.e. between successive working chambers <NUM> (since the shaft <NUM> performs three rotations for each complete revolution of the rotor <NUM>, each shaft rotation corresponds to fuel injection in one of the working chambers <NUM>). For example, the pilot and/or main injection quantity may be zero (skipped injection) for at least one of the successive rotations of the shaft <NUM>, and greater than zero (e.g., maximum value) for at least another one of the successive rotations of the shaft <NUM>.

Various injection patterns may be used to vary the quantity of fuel injected by the pilot and/or main injector(s) <NUM>, <NUM> between the successive rotations of the shaft <NUM>. In a particular embodiment, the injection pattern is repeated for each set of first, second and third successive rotations of the shaft <NUM>, and accordingly each of the three working chambers <NUM> has its particular injection conditions. For example, for the first shaft rotation (first working chamber <NUM>), the main quantity is zero and the pilot quantity is greater than zero, i.e. the main injection is skipped while a pilot injection is performed; for the second rotation (second working chamber <NUM>), the main and pilot quantities are both zero, i.e. both the main and pilot injections are skipped; and for the third rotation (third working chamber <NUM>), the main and pilot quantities are both greater than zero, i.e. a pilot and main injections are both performed.

Various other injection patterns can be used. The following are a few nonlimiting examples, where x is a natural number greater than <NUM>:.

It is understood that the examples of injection patterns for the pilot injection by the pilot injector <NUM> can be combined with a main injection by the main injector <NUM> which is maintained throughout the x successive shaft rotations, whether with a fixed or variable main quantity, or skipped following any suitable injection pattern, and that the examples of injection patterns for the main injection by the main injector <NUM> can be combined with a pilot injection by the pilot injector <NUM> which is maintained throughout the x successive shaft rotations, whether with a fixed or variable pilot quantity, or skipped following any suitable injection pattern. The pilot injection can also be performed in two or more pulses, and the main injection can be performed in more than two pulses; each pulse can be varied, for example as indicated above, without or with variation of the other pulses.

In a particular embodiment, an engine control unit <NUM> (see <FIG>), for example forming part of a full authority digital engine (or electronics) control (FADEC), controls the pilot and main fuel injectors <NUM>, <NUM>, for example through actuation of electronic valves within the fuel injectors <NUM>, <NUM> to control the injection pulses. The flexibility of the engine control software allows for the choice of firing or skipping all injection opportunities. For example, a control algorithm may be created to control the injection and apply injection pattern(s) based on the power demand on the rotor assembly <NUM>, so as to implement an injection pattern (e.g. including pilot and/or main injection skipping) when the power demand is lower than a threshold value, or select between multiple injection patterns each corresponding to a respective range in power demand.

In a particular embodiment, the ability to keep one of the pilot and main injectors <NUM>, <NUM> on while skipping the other of the pilot and main injectors <NUM>, <NUM> allows for the rotor assembly <NUM> to always stay warm and reduce thermal loading, and facilitates engine relight when needed.

In a particular embodiment, an engine includes a single rotor assembly <NUM>, i.e. the rotor assembly <NUM> can be referred to as a rotary intermittent internal combustion engine. In another embodiment, multiple rotor assemblies <NUM> are used together to defined an intermittent internal combustion engine. Referring to <FIG>, an intermittent internal combustion engine <NUM> is schematically shown, including four (<NUM>) rotor assemblies <NUM> engaged to the same shaft <NUM>. It is understood that the engine <NUM> can includes any other suitable number of rotor assemblies <NUM>, i.e. one (<NUM>) rotor assembly <NUM>, two (<NUM>) or three (<NUM>) rotor assemblies, or more than four (<NUM>) rotor assemblies <NUM>.

The pilot and/or main quantities of fuel can be varied as set forth above, for a single one, only some, or all of the rotor assemblies <NUM> forming part of the engine <NUM>. In a particular embodiment, the variation in pilot and main injection is the same for all of the rotor assemblies <NUM>; in another embodiment, at least one of the rotor assemblies <NUM> has a constant pilot and main injection throughout the rotations of the shaft <NUM>, and at least another one of the rotor assemblies <NUM> has a variable pilot and/or main injection between successive rotations of the shaft <NUM>, as set forth above. Accordingly, one or both of the pilot and main quantities of fuel is different between two of the rotor assemblies <NUM> during at least one of the successive rotations of the shaft <NUM>. One or both of the pilot and main quantities of fuel may be different between more than two, for example all, of the rotor assemblies <NUM> during at least one of the successive rotations of the shaft <NUM>. For example, in a particular embodiment one or both of the pilot quantity and the main quantity is different between first, second and third rotor assemblies <NUM> of the engine <NUM> during the at least one of the successive rotations of the shaft <NUM>.

Since the rotor assemblies <NUM> do not include valves at the inlet and outlet ports, and the inlet is not throttled, the injection skipping can be performed without the need for valve train modifications.

In a particular embodiment, implementation of injection patterns (e.g. with pilot and/or main injection skipping) on more than one, for example all, of the rotor assemblies <NUM> of the engine <NUM> allows to distribute the load reduction throughout the engine <NUM>.

In a particular embodiment, implementation of injection patterns (e.g. with pilot and/or main injection skipping) allows for a reduction in fuel consumption, noise, vibrations and/or torque pulsing during operation at part load, while decreasing wear on the engine components, as compared with operation of an engine where injection in one or more of the rotor assemblies <NUM> is completely shut off during part load operation.

In a particular embodiment, the engine <NUM> including one or more rotor assemblies <NUM> is used in a compound cycle engine system or compound cycle engine such as described in Lents et al. 's <CIT> or as described in <CIT>, or as described in <CIT>, or as described in <CIT>. The compound cycle engine 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 rotor assembly, and the engine drives one or more turbine(s) of the compound engine. In another embodiment, the engine <NUM> is used without a turbocharger, with air at atmospheric pressure.

When the engine <NUM> is used with a turbine, for example in a compound cycle engine as mentioned above, a post-injection pulse of the main injector <NUM> can be maintained while the main injection pulse of the main injector <NUM> and/or pilot injection of the pilot injector <NUM> are skipped; maintaining the post-injection pulse may help maintain adequate inlet conditions for the turbine receiving the engine exhaust.

In a particular embodiment, implementation of injection patterns (e.g. with pilot and/or main injection skipping) allows to reduce the power provided by the engine <NUM> without the need to resort to a reduction in the air compression upstream of the engine <NUM> (for example, through control of variable inlet guide vanes of the compressor in the compound cycle engine), and/or a change in the air temperature upstream of the engine <NUM> (for example, by bypassing an intercooler).

For example, in a particular embodiment of compound cycle engine used as a turboprop, the compressor is designed to be efficient in flight (e.g. compression ratio of <NUM>:<NUM> or <NUM>:<NUM>), but may need to have a significantly smaller compression ratio when the compound cycle engine is used at idle on the ground (for example, <NUM>:<NUM>), which may be difficult to obtain with variable inlet guide vanes. Implementation of injection patterns (e.g. with pilot and/or main injection skipping) allows for a reduction of power without reducing the compression ratio of the compressor, which may allow the compressor to function at a higher compression ratio when at idle on the ground (for example, <NUM>:<NUM>). Accordingly, implementation of injection patterns (e.g. with pilot and/or main injection skipping) may allow for an easier match between the requirements of the components of the compound cycle engine.

In another embodiment and still referring to <FIG>, the engine <NUM> is a reciprocating intermittent internal combustion engine including at least two (four in the embodiment shown) cylinders <NUM>' each receiving a reciprocating piston. As illustrated in <FIG>, each piston <NUM>' is received in a corresponding internal cavity <NUM>' of the cylinder housing <NUM>' to define a working chamber <NUM> of variable volume and undergoing the four stroke phases of intake, compression, expansion and exhaust, with the reciprocating pistons <NUM>' engaged to the engine shaft <NUM> (<FIG>). The engine <NUM> includes, for each cylinder <NUM>', a main injector <NUM>, an ignitor <NUM>, a pilot subchamber <NUM> (or other suitable pilot cavity) communicating with the working chamber <NUM> separately from the main injector <NUM>, and a pilot injector <NUM> in communication with the pilot subchamber <NUM>.

The pilot and/or main quantities of fuel can be varied as set forth above, for a single one, only some, or the entirety of the cylinders <NUM>' forming part of the engine <NUM>, as described above, for example using one of the injection patterns described for the rotor assemblies <NUM>, or any other suitable injection pattern. In a particular embodiment, implementation of injection patterns (e.g. with pilot and/or main injection skipping) on more than one, for example all, of the cylinders <NUM>' of the engine <NUM> allows to distribute the load reduction throughout the engine <NUM>.

In another embodiment, the engine <NUM> includes one or more rotor assemblies configured as a non-Wankel engine. A "non-Wankel" engine, as used herein, means a rotary engine suitable for use with the present invention, but excluding Wankel type engines.

In a particular embodiment, the rotor assembly may be a single or eccentric type rotary engine in which the rotor rotates about a fixed center of rotation. For example, the rotor assembly may be a sliding vane engine, such as described in <CIT> or in <CIT>.

Referring to <FIG>, an example of a rotor assembly <NUM> configured as a sliding vane engine is shown. The rotor assembly <NUM> includes an outer body <NUM> defining an internal cavity <NUM> receiving a rotor <NUM> having a number of vanes <NUM>. The rotor <NUM> includes an inner hub assembly <NUM> rotating about a first axis and an outer hub assembly <NUM> rotating about a second axis offset from the first axis, with the two hub assemblies <NUM>, <NUM> being mechanically linked. The vanes <NUM> are pivotally connected to the inner hub assembly <NUM> and are slidingly engaged through slots defined between adjacent sections of the outer hub assembly <NUM>. The sections of the outer hub assembly <NUM> are thus sealingly engaged to the vanes <NUM> at different distances from the first axis of the inner hub assembly <NUM>, defining a plurality of chambers <NUM> of variable volume within the internal cavity <NUM> around the rotor <NUM>.

In the embodiment shown, the pilot subchamber <NUM> of the rotor assembly <NUM> is defined in the insert <NUM> (for example made of a material having a greater heat resistance than that of the peripheral wall <NUM>) received in an insert opening of a peripheral wall <NUM> of the outer body <NUM>; alternately the pilot subchamber <NUM> may be defined directly in the outer body <NUM>, for example in the peripheral wall <NUM>, or the pilot injector <NUM> may be received in any other suitable type of pilot cavity formed in the outer body <NUM>. The peripheral wall <NUM> also has a main injector elongated hole <NUM> defined therethrough, in communication with the internal cavity <NUM> and spaced apart from the insert <NUM>. The peripheral wall <NUM> and/or the insert <NUM> has the pilot injector elongated hole <NUM> and the ignitor elongated hole <NUM> defined therethrough in communication with the pilot subchamber <NUM>.

In another particular embodiment, the rotor assembly 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>, an example of such a rotor assembly is shown. The rotor assembly <NUM> includes an inner rotor <NUM> and an outer body or rotor <NUM> rotating at different angular velocities, the outer rotor <NUM> defining an internal cavity <NUM> in which the inner rotor <NUM> is received. Chambers <NUM> of variable volume are defined within the internal cavity <NUM> around the inner rotor <NUM>.

In the embodiment shown, the pilot subchamber <NUM> of the rotor assembly <NUM> is defined in the insert <NUM> (for example made of a material having a greater heat resistance than that of the peripheral wall <NUM>) received in an insert opening of a peripheral wall <NUM> of the outer body <NUM>; alternately the pilot subchamber <NUM> may be defined directly in the outer body <NUM>, for example in the peripheral wall <NUM>, or the pilot injector <NUM> may be received in any other suitable type of pilot cavity formed in the outer body <NUM>. The peripheral wall <NUM> also has the main injector elongated hole <NUM> defined therethrough spaced apart from the insert <NUM>, and the peripheral wall <NUM> and/or the insert <NUM> has the pilot injector elongated hole <NUM> and the ignitor elongated hole <NUM> defined therethrough.

In another particular embodiment, the rotor assembly is configured as a planetary rotating engine having a different geometry than that of the Wankel engine. Referring to <FIG>, an example of such a rotor assembly is shown. The rotor assembly <NUM> includes an outer body <NUM> forming an internal cavity <NUM> with a peripheral inner surface thereof having an epitrochoid profile defining three lobes. The rotor assembly <NUM> also includes a rotor <NUM> with four apex portions <NUM> in sealing engagement with the peripheral inner surface to form four rotating working chambers <NUM> of variable volume within the internal cavity <NUM> around the rotor <NUM>. The rotor <NUM> is journaled on an eccentric portion of a shaft and performs orbital revolutions within the internal cavity <NUM>.

Claim 1:
A method of operating a rotary engine (<NUM>) including a first rotor assembly, the first rotor assembly including a rotor (<NUM>) engaged to a shaft (<NUM>) and rotationally received in a housing (<NUM>) to define a plurality of working chambers (<NUM>) of variable volume, wherein each shaft rotation corresponds to fuel injection in one of the working chambers (<NUM>), the method comprising:
delivering a pilot quantity of fuel into a pilot cavity (<NUM>) in successive communication with the working chambers (<NUM>);
igniting the pilot quantity of fuel within the pilot cavity (<NUM>); and
delivering a main quantity of fuel into the working chambers (<NUM>) downstream of the successive communication of the pilot cavity (<NUM>) with the working chambers (<NUM>);
characterised in that:
when operating at part load, the pilot quantity (<NUM>) is varied between successive rotations of the shaft (<NUM>), wherein the pilot quantity (<NUM>) of the first rotor assembly is zero for at least one of the successive rotations of the shaft (<NUM>) and greater than zero for at least another one of the successive rotations of the shaft (<NUM>).