Patent Description:
The present disclosure relates generally to aftertreatment systems for use with internal combustion (IC) engines.

Exhaust aftertreatment systems are used to receive and treat exhaust gas generated by engines such as IC engines. Conventional exhaust gas aftertreatment systems include any of several different components structured to reduce the levels of harmful exhaust emissions present in exhaust gas. For example, certain exhaust aftertreatment systems for diesel-powered IC engines include a selective catalytic reduction (SCR) system which includes a catalyst formulated to convert NOx (NO and NO<NUM> in some fraction) into harmless nitrogen gas (N<NUM>) and water vapor (H<NUM>O) in the presence of ammonia (NH<NUM>). A reductant is often inserted into exhaust conduits communicating the exhaust gas to the SCR system and/or other components of the aftertreatment system.

Natural gas as a fuel for heavy duty engines is receiving attention due to its potential to reduce pollutant and greenhouse gas emissions. Generally, natural gas engines comprise diesel engines converted to operate on natural gas, for example operating the diesel engine on natural gas using spark ignition (SI) stoichiometric parameters. For example, some natural gas engines may comprise diesel engines spanning a range from <NUM> to <NUM> in displacement converted to operate as natural gas engines. Such natural gas engines may be operated using stoichiometric combustion with cooled exhaust gas recirculation and three-way catalysis. However, simply converting diesel engines to operate on natural gas may cause the engine to experience high thermal stresses; relatively low efficiency due to low volumetric efficiency and compression ratio; unequal backpressure on engine cylinders, which may cause knock; and poor performance in terms of power and torque density, and transient response.

<CIT> discloses an exhaust device for internal combustion engines.

<CIT> discloses an internal combustion (IC) power plant that includes an IC engine and an exhaust system carrying exhaust gasses from the IC engine to an outlet communicating to the atmosphere.

Embodiments described herein relate generally to systems and methods for equalizing exhaust gas backpressure across a plurality of cylinders of an engine and, in particular, to exhaust manifolds structured to equalize backpressure of an exhaust gas across the plurality of cylinders of the engine. This is achieved with an exhaust manifold according to claim <NUM>.

In a first set of embodiments, an exhaust manifold comprises a plurality of exhaust intake conduits. Each of the plurality of exhaust intake conduits is structured to be fluidly coupled to an engine and structured to receive exhaust gas from a corresponding cylinder of the engine. At least one of the plurality of exhaust intake conduits may provide a reduction in an exhaust intake conduit cross-sectional area of the respective exhaust intake conduit from an exhaust intake conduit inlet to an exhaust intake conduit outlet of the respective exhaust intake conduits. The exhaust manifold also comprises a plurality of bends. Each of the plurality of bends is defined by a respective one of the exhaust intake conduit outlets. The exhaust manifold also comprises an exhaust intake manifold fluidly coupled to the exhaust intake conduit outlet of at least a portion of the plurality of exhaust intake conduits. Each of the plurality of bends is shaped so as to define an angle of approach of exhaust gas flowing through the respective exhaust intake conduit outlet. A first angle of approach of the first bend relative to the exhaust intake manifold flow axis is smaller than a second angle of approach of a second bend of the plurality of bends. The first bend is structured to receive exhaust gas from a first cylinder of the engine and the second bend is structured to receive exhaust gas from a second cylinder of the engine. The first cylinder is positioned in an outer position on the engine relative to the second cylinder.

In another set of embodiments, a system comprises an engine comprising a plurality of cylinders. Each of the plurality of cylinders is structured to burn a fuel so as to produce an exhaust gas. The system also includes an exhaust manifold comprising a plurality of exhaust intake conduits. Each of the plurality of exhaust intake conduits is structured to be fluidly coupled to an engine and structured to receive exhaust gas from a corresponding cylinder of the engine. The exhaust manifold also includes at least one exhaust intake manifold. The exhaust intake conduit outlet of at least a portion of the plurality of exhaust intake conduits is fluidly coupled to the at least one exhaust intake manifold. The exhaust manifold also includes a means for equalizing a pressure pulse amplitude caused by combustion in each of the plurality of cylinders.

In another set of embodiments, an exhaust manifold includes a first exhaust intake conduit structured to be fluidly coupled to an engine and structured to receive exhaust gas from a first cylinder of the engine. A second exhaust intake conduit is structured to be fluidly coupled to an engine and structured to receive exhaust gas from a second cylinder of the engine. The engine has a plurality of cylinders with the first cylinder being positioned in an outer position on the engine relative to the second cylinder. The first bend defines an oval-shaped cross-section. The first bend is shaped so as to define a first angle of approach of exhaust gas flowing through the first exhaust intake conduit outlet. A second bend is defined by a second exhaust intake conduit outlets of the second exhaust intake conduit. The second bend is shaped so as to define a second angle of approach of exhaust gas flowing through the second exhaust intake conduit outlet. An exhaust intake manifold is fluidly coupled to each of the first and second exhaust intake conduits. The exhaust intake manifold defines a first cross-sectional area proximate the first exhaust intake conduit and a second cross-sectional area proximate the second exhaust intake conduit. The first cross-sectional area is larger than the second cross-sectional area. The exhaust intake manifold defines an exhaust intake manifold flow axis. The first angle of approach relative to the exhaust intake manifold flow axis is smaller than the second angle of approach.

In another set of embodiments, an exhaust manifold includes a plurality of exhaust intake conduits. Each of the plurality of exhaust intake conduits is structured to be fluidly coupled to an engine and structured to receive exhaust gas from a corresponding cylinder of the engine. An exhaust intake manifold is fluidly coupled to an exhaust intake conduit outlet of at least one of the plurality of exhaust intake conduits. Each of the plurality of exhaust intake conduits and the exhaust intake manifold define an exhaust intake manifold core volume. Each of the plurality of exhaust intake conduits and the exhaust intake manifold are shaped so as to define the exhaust intake manifold core volume based on each of the displacement of the engine, the intended operating power of the engine, and the intended flow rate of the exhaust gas through the exhaust manifold.

In another set of embodiments, an intake manifold includes a first inlet structured to be fluidly coupled to a turbocharger so as to receive pressurized intake air from the turbocharger. A second inlet is structured to be fluidly coupled to an exhaust gas recirculation (EGR) system so as to receive EGR gas from the EGR system. A third inlet is structured to be fluidly coupled to a fuel line so as to receive fuel from the fuel line. A plurality of outlets are structured to be fluidly coupled to an engine. An intake manifold passage extends between each of the first, second, and third inlets, and the plurality of outlets. The intake manifold passage is shaped so as to cause at least two reversals in flow direction of each of the intake air, the EGR gas, and the fuel through the intake manifold passage so as to improve mixing of each of the intake air, the EGR gas, and the fuel.

The foregoing and other features of the present disclosure will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. Understanding that these drawings depict only several implementations in accordance with the disclosure and are, therefore, not to be considered limiting of its scope, the disclosure will be described with additional specificity and detail through use of the accompanying drawings.

Reference is made to the accompanying drawings throughout the following detailed description. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative implementations described in the detailed description, drawings, and claims are not meant to be limiting. Other implementations may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, and designed in a wide variety of different configurations, all of which are explicitly contemplated and made part of this disclosure.

Embodiments described herein relate generally to systems and methods for equalizing exhaust gas backpressure across a plurality of cylinders of an engine and, in particular, to exhaust manifolds structured to equalize backpressure of an exhaust gas across the plurality of cylinders of the engine.

Natural gas as a fuel for heavy duty engines is receiving attention due to its potential to reduce pollutant and greenhouse gas emissions. Generally, natural gas engines comprise diesel engines converted to operate on natural gas, for example operating the diesel engine on natural gas using SI stoichiometric parameters. For example, some natural gas engines may comprise diesel engines spanning a range from <NUM> to <NUM> in displacement converted to operate as natural gas engines. Such natural gas engines may be operated using stoichiometric combustion with cooled exhaust gas recirculation and <NUM>-way catalysis.

However, simply converting diesel engines to operate on natural gas may cause the engine to experience high thermal stresses; relatively low efficiency due to low volumetric efficiency and compression ratio; unequal backpressure on engine cylinders which may cause knock; and poor performance in terms of power and torque density, and transient response. For example, the backpressure exerted by the exhaust gas flowing out of individual cylinders of engines (e.g., natural gas engines converted from diesel engines) may vary across the plurality of cylinders. This may lead to inconsistent temperatures across the plurality of cylinders, which may cause at least a portion of the plurality of cylinders included in the engine to run "hot" (e.g., at a temperature exceeding a design temperature of the respective cylinder). This can cause engine "knock" or pre-ignition, which further reduces the efficiency of the engine.

Various embodiments of the systems and methods described herein may provide benefits over conventional engine systems, including, for example: (<NUM>) equalizing pressures across cylinders, such as via an exhaust manifold structured to equalize a backpressure exerted by the exhaust gas on each of a plurality of cylinders of an engine; (<NUM>) maintaining a consistent temperature across all of the plurality of cylinders of the engine so as to reduce knock, thereby increasing engine efficiency; (<NUM>) providing continuous area reduction of exhaust gas flow to a turbine fluidly coupled to the engine so as to maintain exhaust gas momentum and reduce flow losses; (<NUM>) aligning a trajectory of the exhaust gas flow into an EGR system so as to maximize momentum recovery into the EGR flow path; and (<NUM>) defining cross-sections structured to maintain attachment of the exhaust gas flow to walls of the exhaust manifold or components thereof, thereby reducing turbulence and/or momentum losses.

<FIG> is a schematic illustration of a system <NUM>, according to an embodiment. The system <NUM> comprises an engine <NUM>, an exhaust manifold <NUM>, and optionally a turbine <NUM> and an EGR assembly <NUM>.

The engine <NUM> comprises an engine block <NUM> within which a plurality of cylinders <NUM> are defined. Each of the plurality of cylinders <NUM> is structured to burn fuel (e.g., natural gas) so as to produce an exhaust gas. The engine <NUM> may include a diesel engine, a natural gas engine, a gasoline engine, a biodiesel engine, an LPG engine, a dual-fuel engine, or any other suitable engine. In particular embodiments, the engine <NUM> may include a diesel engine converted to operate on natural gas. In other embodiments, the engine <NUM> is specifically designed to operate on natural gas.

The exhaust manifold <NUM> is fluidly coupled to the engine <NUM> and structured to receive the exhaust gas from the engine <NUM>. The exhaust manifold <NUM> is structured to equalize a pressure pulse amplitude caused by combustion in each of the plurality of cylinders <NUM> of the engine <NUM>. This is also referred to herein as equalizing a backpressure exerted by the exhaust gas on each of the plurality of cylinders <NUM>. As used herein, the term "equalize" refers to achieving less than <NUM>% variation in pressure pulse amplitudes in the exhaust manifold <NUM> caused by combustion in each of the plurality of cylinders <NUM>. In particular implementations, the exhaust manifold <NUM> is structured such that equalizing pressure pulse amplitude achieves less than <NUM> % variation between cylinders <NUM>. In further implementations, the exhaust manifold <NUM> is structured such that equalizing pressure pulse amplitude achieves less than <NUM> % variation between cylinders <NUM>. In some embodiments, the exhaust manifold <NUM> may also cause a temperature of each of the plurality of cylinders <NUM> to be substantially the same (e.g., within +/-<NUM>% to +/-<NUM>% of each other, inclusive of all ranges and values therebetween). The consistent pressure and temperature across the plurality of cylinders <NUM> may reduce knock, thereby minimizing losses in the efficiency of the engine <NUM>.

Expanding further, the exhaust manifold <NUM> may comprise a plurality of exhaust intake conduits <NUM>. Each of the plurality of exhaust intake conduits <NUM> is structured to be fluidly coupled to the engine <NUM> and structured to receive exhaust gas from a corresponding cylinder <NUM> of the engine <NUM>. Each of the plurality of exhaust intake conduits <NUM> may provide a reduction in an exhaust intake conduit cross-sectional area of the exhaust intake conduit <NUM> from an exhaust intake conduit inlet to an exhaust intake conduit outlet thereof. The exhaust manifold <NUM> also comprises at least one exhaust intake manifold <NUM>. The exhaust intake conduit outlet of at least a portion of the plurality of exhaust intake conduits <NUM> is fluidly coupled to the at least one exhaust intake manifold <NUM>.

For example, as shown in <FIG> and <FIG>, the exhaust manifold <NUM> may comprise a first exhaust intake manifold 114a and a second exhaust intake manifold 114b (collectively referred to as "the exhaust intake manifolds <NUM>"). The exhaust manifold <NUM> may also comprise a first set of exhaust intake conduits 112a and a second set of exhaust intake conduits 112b (collectively referred to herein as the "exhaust intake conduits <NUM>"). The first set of exhaust intake conduits 112a is fluidly coupled to the first exhaust intake manifold 114a and structured to receive exhaust gas from a first portion of the plurality of cylinders <NUM>. Furthermore, the second set of exhaust intake conduits 112b are fluidly coupled to the second exhaust intake manifold 114b and structured to receive exhaust gas from a second portion of the plurality of cylinders <NUM>.

A cross-section of the exhaust intake conduit inlet may be larger than a cross-section of the exhaust intake conduit outlet, thereby causing the exhaust intake conduit cross-sectional area of each of the exhaust intake conduits <NUM> to decrease from the exhaust intake conduit inlet to the exhaust intake conduit outlet thereof. This may accelerate the exhaust gas flow towards the exhaust intake manifolds <NUM>, thereby preventing any loss in momentum or pressure of the exhaust gas as it flows into the exhaust intake conduits <NUM>.

In some embodiments, the exhaust intake conduit outlet of each of the plurality of exhaust intake conduits <NUM> comprises a bend <NUM> where it is coupled to the corresponding exhaust intake manifold <NUM>. Moreover, in some embodiments, the exhaust intake conduit outlet of at least one the plurality of exhaust intake conduits <NUM> defines a non-circular cross-section (e.g., an elliptical or oval-shaped cross-section), for example at the bend <NUM>. The non-circular cross-section may prevent the exhaust gas from separating from inner surfaces of sidewalls of the exhaust intake conduits <NUM> as the exhaust gas enters the exhaust intake manifolds <NUM>, thereby preventing flow losses.

The reduction in the cross-sectional area of the exhaust intake conduits <NUM> and/or the bends <NUM> provided therein may serve to equalize a backpressure exerted by the exhaust gas on each of the plurality of cylinders <NUM>. This may also cause a temperature in each of the plurality of the cylinders <NUM> to be substantially the same, thereby reducing knock.

In some embodiments, the exhaust intake manifolds <NUM> may also define a cross-sectional area that reduces from a portion where the exhaust gas enters the exhaust intake manifolds <NUM> to a portion where the exhaust gas exits the exhaust intake manifold <NUM>. The reducing cross-sectional area of the exhaust intake manifold <NUM> may further facilitate equalizing of a backpressure exerted by the exhaust gas on each of the plurality of cylinders <NUM>, for example by preventing momentum losses of the exhaust gas.

A first outlet port 116a and a second outlet port 116b (collectively referred to herein as "the outlet ports <NUM>") may be fluidly coupled to the first exhaust intake manifold 114a and the second exhaust intake manifold 114b. Each of the outlet ports <NUM> defines an outlet port flow axis <NUM>, which is positioned orthogonal to an exhaust intake manifold flow axis <NUM> of the exhaust intake manifolds <NUM>. In some embodiments, the outlet port flow axis <NUM> may be parallel to and/or in line with an exhaust intake conduit flow axis <NUM> of the plurality of exhaust intake conduits <NUM> so as to minimize the number of turns the exhaust gas experiences from the exhaust intake conduits <NUM> to the turbine <NUM>.

The outlet ports <NUM> may provide a reduction in an outlet port cross-sectional area of the outlet ports <NUM> from an outlet port inlet to an outlet port outlet of each of the outlet ports <NUM>. Furthermore, each of the outlet ports <NUM> may define a non-circular (e.g., an elliptical or oval-shaped) cross-section. The reduction in cross-sectional area and/or the elliptical or oval cross-section of the outlet ports <NUM> may also serve to equalize the backpressure exerted by the exhaust gas on each of the plurality of cylinders <NUM>.

The outlet ports <NUM> may be fluidly coupled to the turbine <NUM> (e.g., a turbine included in a turbocharger). The reducing cross-sectional area and/or the elliptical or oval cross-section of the outlet ports <NUM> may provide uniform flow of the exhaust gas into the turbine <NUM>. The first outlet port 116a and the second outlet port 116b may provide a fully divided flow of the exhaust gas received from the respective first set and the second set of the plurality of cylinders <NUM> to the turbine <NUM>, which may also serve to equalize the backpressure of the exhaust gas on each of the plurality of cylinder <NUM>.

According to the invention, at least one pull-off conduit is fluidly coupled to the at least one exhaust intake manifold <NUM>. At least a portion of the at least one pull-off conduit defines a pull-off conduit flow axis <NUM> positioned orthogonal to each of the exhaust intake manifold flow axis <NUM> and the outlet port flow axis <NUM>. In various embodiments, a pull-off conduit first portion of the at least one pull-off conduit may define a reducing pull-off conduit cross-sectional area from a pull-off conduit first portion inlet to a pull-off conduit first portion outlet of the pull-off conduit first portion.

For example, as shown in <FIG>, the exhaust manifold <NUM> may include a first pull-off conduit 118a and a second pull-off conduit 118b (collectively referred to herein as "the pull-off conduits <NUM>") fluidly coupled to the first exhaust intake manifold 114a and the second exhaust intake manifold 114b, respectively.

At least a portion of the pull-off conduits <NUM> which is fluidly coupled to the exhaust intake manifolds <NUM> may be positioned orthogonal to each of the exhaust intake manifold flow axis <NUM> of the exhaust intake manifolds <NUM> and the outlet port flow axis <NUM> of the outlet ports <NUM>. For example, the pull-off conduits <NUM> may be positioned orthogonal to the exhaust intake manifolds <NUM> in a first plane (e.g., in an X-Y plane) and orthogonal to the outlet ports <NUM> in a second plane (e.g., in a Y-Z plane).

A pull-off conduit first portion 119a/b of the pull-off conduits 118a/b may define a reducing pull-off conduit cross-sectional area from a pull-off conduit first portion inlet to a pull-off conduit first portion outlet of the pull-off conduit first portion 119a/b. The reducing cross-sectional area may serve to maintain the momentum of the exhaust gas flowing through the pull-off conduit first portion 119a/b, thereby reducing flow losses.

The pull-off conduit first portion 119a/b of the pull-off conduits 118a/b are fluidly coupled to each other at a joint <NUM> so as to define a single flow path for the exhaust gas downstream of the joint <NUM>. The single flow path reduces in cross-sectional area until it reaches a pull-off conduit first portion outlet <NUM> or throat. The sidewalls of the first portion 119a/b of the pull-off conduits 118a/b are joined with each other at the joint <NUM> at a sufficiently small angle (e.g., less than <NUM> degrees) so that the portions of the exhaust gas flowing into the joint <NUM> towards the pull-off conduit first portion outlet <NUM> from each of the pull-off conduit first portions 119a/b may experience minimal turbulence and smoothly mix with each other. A cross-sectional area of the pull-off conduit first portion outlet <NUM> may be optimized so as to prevent the exhaust gas from experience sudden momentum of flow losses, which may change the backpressure exerted by the exhaust gas on one or more of the plurality of cylinders <NUM>.

The exhaust manifold <NUM> may also include a diffuser <NUM>. The diffuser <NUM> may have a larger cross-sectional area relative to a cross-sectional area of the pull-off conduits <NUM> so as to reduce a velocity of the exhaust gas flowing therethrough, expand the exhaust gas, and/or reduce a temperature thereof. The diffuser <NUM> may be coupled to an EGR assembly <NUM>, which may be structured to communicate the portion of the exhaust gas entering the pull-off conduits <NUM> to the plurality of cylinders <NUM>, for example, to cool the combustion temperature of the air/fuel mixture therein (e.g., to reduce knock).

The pull-off conduits <NUM> may include a pull-off conduit second portion <NUM> fluidly coupled to each of the diffuser <NUM> and the pull-off conduit first portion outlet <NUM>. The pull-off conduit second portion <NUM> may define an expanding cross-sectional area from the pull-off conduit first portion outlet <NUM> to a pull-off conduit second portion outlet of the pull-off conduit second portion <NUM>. The pull-off conduit second portion outlet is fluidly coupled to the diffuser <NUM>.

The expanding cross-sectional area of the pull-off conduit second portion <NUM> may provide smooth reduction in pressure and flow velocity of the exhaust gas from the pull-off conduits <NUM> to the diffuser <NUM>. This may prevent vortices, flow losses, or sudden variations in backpressure of the exhaust gas. The pull-off conduit second portion <NUM> may also include a first bend <NUM> and a second bend <NUM> leading to the diffuser <NUM>. The first bend <NUM> and the second bend <NUM> may define an elliptical or oval cross-section which may cause the exhaust gas flow to remain attached to an inner surface of the sidewalls of the pull-off conduit second portion <NUM>, thereby preventing flow losses.

In some embodiments, an upstream portion of the pull-off conduit second portion <NUM> may define a smaller change in cross-sectional area from an inlet to an outlet thereof, relative to a downstream portion of the pull-off conduit second portion <NUM>. The smaller change in cross-sectional area of the upstream portion relative to the downstream portion may provide a controlled reduction in exhaust gas momentum and velocity leading to the diffuser <NUM> so as to prevent sudden changes in backpressure of the exhaust gas.

<FIG> is a side view of at least a portion of the engine <NUM> and the exhaust manifold <NUM> of <FIG>. <FIG> is a bottom view of at least a portion of the exhaust manifold <NUM> of <FIG>. As illustrated in <FIG>, the cylinders <NUM> of the engine <NUM> include a first cylinder <NUM>, a second cylinder <NUM>, a third cylinder <NUM>, a fourth cylinder <NUM>, a fifth cylinder <NUM>, and a sixth cylinder <NUM>. All of the cylinders <NUM> are arranged in the engine <NUM> in a line, with the first and sixth cylinders <NUM>, <NUM> being positioned in an outer-most position on the engine <NUM>, the third and fourth cylinders <NUM>, <NUM> being positioned in an inner-most position on the engine <NUM>, and the second and fifth cylinders <NUM>, <NUM> being positioned in an intermediate position on the engine <NUM> between the outer-most and inner-most cylinders <NUM>. As used herein, the terms "outer" and "inner," in regard to the position of the cylinders <NUM> on the engine <NUM>, refers to the position of each of the cylinders <NUM> on the engine relative to the other cylinders <NUM>. An outer-most cylinder <NUM> (e.g., the first cylinder <NUM>) is positioned adjacent one other cylinder (e.g., the second cylinder <NUM>). Inner cylinders (e.g., the second cylinder <NUM>) are positioned adjacent two other cylinders (e.g., the first and third cylinders <NUM>, <NUM>).

Similarly, the exhaust intake conduits <NUM> of the exhaust intake manifolds <NUM> include a first exhaust intake conduit <NUM>, a second exhaust intake conduit <NUM>, a third exhaust intake conduit <NUM>, a fourth exhaust intake conduit <NUM>, a fifth exhaust intake conduit <NUM>, and a sixth exhaust intake conduit <NUM>. The first exhaust intake conduit <NUM> is structured to be fluidly coupled to the first cylinder <NUM>; the second exhaust intake conduit <NUM> is structured to be fluidly coupled to the second cylinder <NUM>; the third exhaust intake conduit <NUM> is structured to be fluidly coupled to the third cylinder <NUM>; the fourth exhaust intake conduit <NUM> is structured to be fluidly coupled to the fourth cylinder <NUM>; the fifth exhaust intake conduit <NUM> is structured to be fluidly coupled to the fifth cylinder <NUM>; and the sixth exhaust intake conduit <NUM> is structured to be fluidly coupled to the sixth cylinder <NUM>. Accordingly, the first and sixth exhaust intake conduits <NUM>, <NUM> are positioned in an outer-most position on the engine <NUM>; the third and fourth exhaust intake conduits <NUM>, <NUM> are positioned in an inner-most position on the engine <NUM>; and the second and fifth exhaust intake conduits <NUM>, <NUM> are positioned in an intermediate position on the engine <NUM> between the outer-most and inner-most exhaust intake conduits <NUM>. As mentioned above, at least one of the exhaust intake manifolds <NUM> define a cross-sectional area that reduces from a portion where the exhaust gas enters the respective exhaust intake manifolds <NUM> to a portion where the exhaust gas exits the respective exhaust intake manifolds <NUM>. Additionally, in some embodiments, the exhaust intake manifolds <NUM> define cross-sectional areas that are different based on the intended position of the exhaust intake manifolds <NUM> on the engine <NUM>. For example, in some embodiments, the exhaust intake manifolds <NUM> define a cross-sectional area that reduces from an outer-most position to an inner-most position, as defined based on the intended configuration of the exhaust intake manifolds <NUM> when installed on the engine <NUM>. This is most clearly shown in <FIG>. In other words, the exhaust intake manifolds <NUM> define a larger cross-sectional area proximate an outer cylinder <NUM> than proximate an inner cylinder <NUM>. For example, in some embodiments, the first exhaust intake manifold 114a defines a first cross-sectional area proximate the first exhaust intake conduit <NUM> and a second cross-sectional area proximate the third exhaust intake conduit <NUM>, the second cross-sectional area being smaller than the first cross-sectional area.

<FIG> is a side view of a portion of the exhaust manifold <NUM> of <FIG>. As mentioned above, the exhaust manifold <NUM> includes several design features that are implemented to achieve various design objectives, such as equalizing a backpressure exerted by the exhaust gas on each of a plurality of cylinders of the engine <NUM> or equalizing a pressure pulse amplitude at a point in the exhaust manifold <NUM> (c. , proximate the outlet ports <NUM>) caused by combustion in each of the plurality of cylinders of the engine <NUM>. Another design objective is to maximize the total pressure of the exhaust gas so as to optimize operation of the turbine <NUM> and the EGR assembly <NUM>. For example, in some embodiments, the shape of various portions of each of the exhaust intake conduits <NUM> and the exhaust intake manifolds <NUM> is defined so that exhaust gas flowing through the respective exhaust intake conduits <NUM> and exhaust intake manifolds <NUM> causes the same pressure pulse amplitude at a point in the exhaust manifold <NUM>. In other words, the exhaust gas "acts the same" regardless of the cylinder from which it was expelled. Additionally, the shape of various portions of each of the exhaust intake conduits <NUM> and the exhaust intake manifolds <NUM> is defined so as to maximize the pressure of the exhaust gas flowing through the respective exhaust intake conduits <NUM> and exhaust intake manifolds <NUM>.

As will be explained in further detail below, in some embodiments, at least three design parameters are defined so as to equalize the pressure pulse amplitude in the exhaust manifold <NUM>. First, at least one of the bends of the respective exhaust intake conduit outlets has a non-circular (e.g., oval or elliptical) cross-section. Second, at least one of the exhaust intake conduits defines a cross-sectional area that reduces from the exhaust intake conduit inlet to the exhaust intake conduit outlet. Third, each of the plurality of bends are shaped so as to define particular angles of approach of exhaust gas flowing through the respective exhaust intake conduit outlet. As will be appreciated, each of these design parameters was defined so as to achieve the design objectives.

As illustrated in <FIG>, each of the exhaust intake conduits <NUM> includes an exhaust intake conduit inlet and an exhaust intake conduit outlet. In operation, exhaust gas flows from the exhaust intake conduit inlet, through the exhaust intake conduit <NUM>, out of the exhaust intake conduit outlet, and into the exhaust intake manifold <NUM>. For example, as illustrated in <FIG>, the first exhaust intake conduit <NUM> includes a first exhaust intake conduit inlet <NUM> and a first exhaust intake conduit outlet <NUM>; the second exhaust intake conduit <NUM> includes a second exhaust intake conduit inlet <NUM> and a second exhaust intake conduit outlet <NUM>; and the third exhaust intake conduit <NUM> includes a third exhaust intake conduit inlet <NUM> and a third exhaust intake conduit outlet <NUM>.

As also mentioned above, each of the exhaust intake conduit outlets <NUM>, <NUM>, <NUM> define a bend where the respective exhaust intake conduit outlets <NUM>, <NUM>, <NUM> is coupled to the exhaust intake manifold <NUM>. For example, as illustrated in <FIG>, the first exhaust intake conduit outlet <NUM> defines the first bend <NUM>, the second exhaust intake conduit outlet <NUM> defines a second bend <NUM>, and the third exhaust intake conduit outlet <NUM> defines a third bend <NUM>.

In some embodiments, at least one of the first, second, and third bends <NUM>, <NUM>, <NUM> defines a non-circular (e.g., oval or elliptical) cross-section. For example, in some embodiments, the first bend <NUM> defines a non-circular cross-section. In some embodiments, the second and third bends <NUM>, <NUM> do not define a non-circular cross-section. In other embodiments, each of the first, second, and third bends <NUM>, <NUM>, <NUM> defines a non-circular cross-section.

In some embodiments, at least one of the exhaust intake conduits <NUM> defines a cross-sectional area that reduces from the exhaust intake conduit inlet to the exhaust intake conduit outlet. For example, in one embodiment, the third exhaust intake conduit <NUM> defines a cross-sectional area that reduces from the third exhaust intake conduit inlet <NUM> to the third exhaust intake conduit outlet <NUM>. In some embodiments, the first exhaust intake conduit <NUM> defines a cross-sectional area that does not reduce from the first exhaust intake conduit inlet <NUM> to the first exhaust intake conduit outlet <NUM>. In some embodiments, the exhaust intake conduits <NUM> that are configured to be positioned proximate inner cylinders on the engine <NUM> define a cross-sectional area that reduces from the exhaust intake conduit inlet to the exhaust intake conduit outlet to a greater extent than those exhaust intake conduits <NUM> positioned on outer cylinders of the engine <NUM>.

In some embodiments, each of the exhaust intake conduits <NUM> include a cross-sectional area that defines an area schedule between the exhaust intake conduit inlet and the exhaust intake conduit outlet. For example, the first exhaust intake conduit <NUM> includes a first cross-sectional area that varies along its length, thereby defining a first area schedule between the first exhaust intake conduit inlet <NUM> and the first exhaust intake conduit outlet <NUM>; the second exhaust intake conduit <NUM> includes a second cross-sectional area that defines a second area schedule between the second exhaust intake conduit inlet <NUM> and the second exhaust intake conduit outlet <NUM>; and the third exhaust intake conduit <NUM> includes a third cross-sectional area that defines a third area schedule between the third exhaust intake conduit inlet <NUM> and the third exhaust intake conduit outlet <NUM>. In some embodiments, the area schedules are defined by both the exhaust intake conduits <NUM> and the exhaust intake manifold <NUM>. For example, in some embodiments, the first area schedule is defined by the cross-sectional diameter of the first exhaust intake conduit <NUM> from the first exhaust intake conduit inlet <NUM> to the first exhaust intake conduit outlet <NUM>, and further to the first exhaust intake manifold 114a to a point proximate (e.g., upstream of) the first outlet port 116a.

In some embodiments, the first area schedule is linear. In other words, the cross-sectional area of the first exhaust intake conduit <NUM> decreases at a linear rate from a first cross-sectional diameter at the first exhaust intake conduit inlet <NUM> to a smaller second diameter at the first exhaust intake conduit outlet <NUM>. In some embodiments, the second and third area schedules are non-linear. In other words, for example, the cross-sectional area of the second exhaust intake conduit <NUM> decreases from a first cross-sectional diameter at the second exhaust intake conduit inlet <NUM> to a smaller second diameter at the second exhaust intake conduit outlet <NUM> at a non-linear rate. The non-linear area schedule is most clearly shown by the third exhaust intake conduit <NUM>. As shown in <FIG>, the "necking" at the third exhaust intake conduit outlet <NUM> causes the third area schedule to be non-linear due to the sharp reduction in cross-sectional diameter proximate the third bend <NUM>.

The area schedules also define an exhaust intake manifold core volume. For example, in one embodiment, a first exhaust intake manifold core volume is the internal volume of the structure that defines the plurality of exhaust intake conduits 112a and the first exhaust intake manifold 114a of the exhaust manifold <NUM>. In one embodiment, the first exhaust intake manifold core volume is the volume of the plurality of exhaust intake conduits 112a and the first exhaust intake manifold 114a upstream of the first outlet port 116a. In some embodiments, the exhaust manifold <NUM> is sized so as to define the exhaust intake manifold core volume relative to the displacement of the engine <NUM>, based on a volume ratio. In other embodiments, the exhaust manifold <NUM> is sized based on other factors, such as intended operating power of the engine <NUM> or intended flow rate of exhaust gas through the exhaust manifold <NUM>. For example, in some embodiments, the exhaust manifold <NUM> is sized larger for larger engine displacement, higher intended operating power, and/or higher intended exhaust gas flow rate.

Each of the first, second, and third bends <NUM>, <NUM>, <NUM> are also shaped so as to define an angle of approach of exhaust gas flowing through the respective exhaust intake conduit outlet <NUM>, <NUM>, <NUM>. The angles of approach may be defined, for example, relative to the exhaust intake manifold flow axis <NUM>. For example, the first bend <NUM> is shaped so as to define a first angle of approach <NUM>; the second bend <NUM> is shaped so as to define a second angle of approach <NUM>; and the third bend <NUM> is shaped so as to define a third angle of approach <NUM>. The angles of approach <NUM>, <NUM>, <NUM> are defined so as to minimize recirculation caused by the exhaust gas impacting the walls of the exhaust intake manifold <NUM>. In some embodiments, the first angle of approach <NUM> is smaller than each of the second and third angles of approach <NUM>, <NUM>. In other words, in some embodiments, the angle of approach is smaller for exhaust intake conduits <NUM> structured to be positioned in outer positions on the engine <NUM>. While <FIG> and <FIG> show an exhaust manifold structured to reduce exhaust gas backpressure which may lead to reduced knock and increase in efficiency of the engine (e.g., a diesel engine converted into a natural gas engine) various other parameters and structures of the engine may also be structured to improve an efficiency of the engine. For example, <FIG> shows a family tree of various parameters of an engine that may be structured to increase an efficiency of an engine, for example a diesel engine converted into a natural gas engine.

<FIG> is a top perspective view of a system <NUM>, according to another embodiment. The system <NUM> includes an engine <NUM>, an exhaust manifold <NUM>, an intake manifold <NUM> and a turbine <NUM>. In some embodiments, the engine <NUM> may include a <NUM> liter engine having six in-line cylinders having a bore of <NUM> and stroke of <NUM>, a power of up to <NUM> kW, and torque of up to <NUM>,<NUM> at <NUM>,<NUM> rpm.

The exhaust manifold is fluidly coupled to the engine <NUM>. The exhaust manifold <NUM> may be substantially similar to the exhaust manifold <NUM> (<FIG>) and, therefore, not described in further detail herein. Various portions of the system <NUM> and their novel features which lead to an increase in efficiency of the engine <NUM> are described below.

One objective of increasing engine <NUM> efficiency is to reduce variations in operational parameters from cylinder-to-cylinder and from cycle-to-cycle. The major contributors impacting efficiency of the engine <NUM> include the intake manifold <NUM>, the exhaust manifold <NUM> and ports for more efficient air handling. The intake manifold <NUM> and the ports are structured so as to increase the efficiency of the engine <NUM>. For example, the intake manifold <NUM> is structured so as to receive each of pressurized intake air from the turbocharger, EGR gas, and fuel injection. As shown in <FIG>, the intake manifold <NUM> is "S-shaped" such that the intake charge air including EGR gas and fuel is subjected to at least two flow reversals before entering the engine <NUM>, which improves constituent mixing of the intake charge air, the EGR gas, and the fuel.

In one embodiment, the intake manifold <NUM> includes first, second, and third inlets. The first inlet is structured to be fluidly coupled to a turbocharger so as to receive pressurized intake air from the turbocharger. The second inlet is structured to be fluidly coupled to an EGR system so as to receive EGR gas from the EGR system. The third inlet is structured to be fluidly coupled to a fuel line so as to receive fuel from the fuel line. The intake manifold <NUM> also includes a plurality of outlets structured to be fluidly coupled to the engine <NUM>. The intake manifold further includes an intake manifold passage extending between each of the first, second, and third inlets, and the plurality of outlets. The intake manifold passage is shaped so as to cause at least two reversals in flow direction of each of the intake air, the EGR gas, and the fuel through the intake manifold passage so as to improve mixing of each of the intake air, the EGR gas, and the fuel.

The intake ports may have a patterned design, and are exactly the same and all exhaust ports are exactly the same. The intake manifold <NUM> includes individual, drop-down runners from the plenum thereof to the intake ports thereof. All cylinders of the engine <NUM> pull off charge flow in exactly the same manner and there is no crosstalk between cylinders.

The intake manifold <NUM> provides a long mixing length so as to achieve flow uniformity. The intake ports of the intake manifold <NUM> are sufficiently large so as to reduce flow losses into the cylinder. Furthermore, exhaust ports of the exhaust manifold <NUM> are smaller for higher velocity flow to support the pulse EGR system <NUM> (see <FIG>). The exhaust manifold <NUM> provides a fully divided, pulse capture flow to the EGR <NUM> and isolates the front bank from the rear bank. Moreover, the trajectory and area schedule of exhaust and EGR system components is optimized to reduce backpressure of the exhaust gas.

The cylinder head of the engine <NUM> comprises a Big Intake Small Exhaust (BISE) diamond valve pattern. The diamond pattern allows for generation of swirl and the bigger intake valves enable bigger intake ports, contributing to improved engine breathing. The intake ports have high flow capability and low losses. The intake manifold may comprise a front end-inlet design with the plenum above the intake port center line, as shown in <FIG>. Individual, equal length runners may pull off of the plenum to feed each cylinder of the engine <NUM> for consistent charge distribution. The runners may be angled towards the incoming charge where they connect to the plenum in order to help direct flow down the runners to feed each cylinder. The individual runners offer additional benefits such as further separation of cylinders, so as to reduce or eliminate fuel cross-talk with a Port Fuel Injection (PFI) architecture.

The exhaust ports also include the BISE diamond valve pattern. Smaller exhaust valves and ports result in higher exhaust flow velocities that positively affect performance of the pulse EGR system <NUM>. The pulse EGR system <NUM> performance may be improved by efficient exhaust flow passages and junctions in order to minimize losses. The exhaust manifold <NUM> provided a drastically lower loss factor to the turbine <NUM> and EGR system <NUM>.

<FIG> is a perspective view of the exhaust manifold <NUM> of the system of <FIG> fluidly coupled to a turbine <NUM> and <FIG> shows the exhaust manifold <NUM> and turbine <NUM> assembled with covers positioned thereon. The turbine <NUM> is structured to provide every cylinder of the engine <NUM> the same experience and minimize loss coefficient. The loss coefficient may be minimized by optimizing the trajectory and the area schedule of the exhaust manifold <NUM>.

Each cylinder of the engine <NUM> may be provided the same exhaust gas backpressure by maintaining fully divided flows up to the turbine <NUM>. In some embodiments, the turbine may comprise a twin port electronically controlled waste gate to enable intake of exhaust gas flow from both banks of the exhaust manifold <NUM> (e.g., the plurality of outlet ports <NUM>), further providing an identical breathing experience for all cylinders.

<FIG> is a perspective view of an EGR system <NUM> included in the system <NUM> of <FIG>. The engine <NUM> operates with a stoichiometric air/fuel ration (AFR) and charge diluted with up to <NUM>% EGR, while minimizing residuals. In addition to the exhaust manifold features already discussed, a very efficient flow junction to combine the flows may be implemented. The hot components of the EGR system <NUM> were developed concurrently and coupled to the exhaust manifold <NUM>. Concurrent with CFD analysis of the flow domain, thermal mechanical fatigue analysis of the designs was also performed to ensure durability.

A stable spark-ignited architecture may be achieved by eliminating sources of knock and pre-ignition. One cause of knock and pre-ignition may include oil control and particularly from piston rings and valve stem seals. To address oil intrusion from the valve stem, a seal which is four times drier than conventional seals is used. The seal is also rated for vacuum, which may be beneficial on a throttled engine (e.g., the engine <NUM>) which frequently operates with a vacuum in the intake manifold (e.g., the intake manifold <NUM>). Oil intrusion past the piston rings of the cylinders was prevented using a three piece oil ring which has improved ring dynamics (compared to a two piece oil ring), therefore providing improved oil control.

A potential source of pre-ignition addressed in various embodiments is an overheated spark plug. <FIG> are finite element analysis (FEA) models showing heat transfer coefficients in water jackets around valve seats, bridges and an ignitor core of a cylinder included in the engine of <FIG> (<FIG>) and predicted combustion face temperature and location of max temperature (<FIG>).

As seen in <FIG>, the heat transfer coefficients are highest in the bridges and surrounding the entire ignitor bore. The engine ignitor bore is structured such that all of the coolant flows past the ignitor bores, thereby providing exceptional cooling to the spark plug. Furthermore, the combustion face, particularly edges, are also effectively cooled so as to prevent hot spots and pre-ignition. As shown in <FIG>, the combustion face is relatively cool. This not only prevents pre-ignition, it also ensures a durable and robust cylinder head with tolerance to brief periods of knock and temperature rise.

The engine <NUM> hardware allows placement of port fuel injectors in two possible locations and using two possible injectors. The injectors may be placed in the intake manifold <NUM> runners and/or above the intake ports in the cylinder head of the engine <NUM>. In some embodiments, the engine <NUM> operates with <NUM>% single point fuel injection (SPFI) or upstream mixed, or <NUM>% multi point fuel injection (MPFI) injected in the individual ports. Additionally, in various embodiments, the engine <NUM> may run with any mix of SPFI and MPFI. Combustion CFD predicted a benefit to using a port fuel distribution tube and engine <NUM> testing proved this to be the case.

An additional benefit of locating the fuel injectors above the port is intake manifold over pressure (IMOP), that is, intake backfire mitigation. With a single point injection near the intake throttle, the entire intake manifold <NUM> contains a stoichiometric combustible mixture. With a MPFI system, most of the intake manifold <NUM> may be filled with air or possibly a very lean mixture beyond the ignition limits.

Stoichiometric gas engines are throttled by air (opposed to a diesel engine throttled by fueling) which may pose a challenge for the turbine <NUM> (e.g., a turbocharger compressor). When the engine <NUM> quickly transitions from a high boost condition to a no boost condition (tip-out), the throttle plate may slam shut and the high speed, high pressure charge between the compressor and the throttle may have to be relieved, otherwise the pressure may spike and find a low pressure path back through the compressor. This is known as compressor surge and may cause a loading reversal of the compressor blades, which may quickly lead to fatigue failures.

In order to prevent this, an electronically controlled compressor recirculation valve (CRV) was implemented. <FIG> is a schematic illustration of a compressor recirculation system <NUM>, according to an embodiment. The compressor recirculation system <NUM> includes a CRV <NUM> that is controllably actuated to prevent back flow of the intake air to a compressor <NUM>. The CRV <NUM> is structured to be controllably opened to provide a path to bleed off the high pressure air to prevent compressor surge, particularly during tip-out events or at any suitable time to help prevent surge. The CRV <NUM> is controlled based on various parameters, such as air pressure, compressor operating parameters, engine operating parameters, etc..

A stoichiometric with cooled EGR combustion system was coupled to the engine <NUM> as it has the capability to deliver high BMEP, extremely low emissions and robust operation. The performance optimization and development of the engine <NUM> subsystems was split into three critical areas: combustion system, fuel system, and charging system.

Development of the combustion system was focused on improvements in closed cycle efficiency, reduced heat transfer and capability of short burn durations under highly dilute conditions and short ignition delay times. High dilution was chosen in order to control component temperatures and to realize closed cycle efficiency improvements through reduced heat transfer as shown in <FIG>.

Initial combustion system work was done using a full combustion cycle analysis on a calibrated combustion CFD model. A baseline combustion system delivered <NUM>% to <NUM>% burn durations capable of tolerating high levels of EGR dilution. The system <NUM> was structured to maintain that burn duration with improved efficiency and ignition delay. <FIG> is a plot of impact of EGR on gross indicated efficiency of the engine. <FIG> is a plot of burn duration and <FIG> is a plot of ignition delay vs. crank angle of <NUM>% (CA50) variations.

The progression from iteration #<NUM> to iteration #<NUM> as shown in <FIG> represents the investigation of swirl level along with charge motion development during the cycle and the impact to combustion. Iteration #<NUM> represents the best efficiency that was achieved because charging penalties were minimized representing the entitlement for efficiency. Iteration #<NUM> - #<NUM> represent iterations to improve the burn duration with minimal impact to efficiency by influencing the in cylinder charge motion. Trends in burn duration and ignition delay are shown in <FIG>. Iteration #<NUM> was chosen as the combustion system for this engine as it was the best tradeoff for key deliverables. Fuel consumption trends are shown in <FIG> for constant EGR levels.

The benefit of a premix combustion system may comprise homogeneity of the fuel and air mixture. The disadvantages may comprise transport delays, catalyst dither amplitude attenuation, and mitigation techniques in the event of cylinder misfire. Challenges of port fuel injection are mixture stratification, number of physical parts and injection pressure requirements. The benefits to MPFI may comprise cost, fuel control cylinder by cylinder, transient response time and three-way catalyst (TWC) control. <FIG> are plots of premix air/fuel mixture injection and port fuel injection (PFI) in each cylinder of the engine of <FIG>. Degraded combustion due to PFI was observed as shown in <FIG>.

Further work was done to understand if MPFI stratification could be improved to match performance of the premixed combustion. <FIG> is a plot of apparent heat release vs. crank angle of a crank shaft of the engine of <FIG> operated using PFI. Many iterations of mixing devices as well as injection strategies were assessed via combustion CFD in order to compare combustion performance as shown in <FIG>. The MPFI mixing observations yielded a design and injection strategy that was transparent to the premix injection strategy allowing for advantages of PFI to be realized.

The charging system was structured to provide a uniform and equal mixture of air and EGR to each cylinder of the engine <NUM>. In addition, the charging system was designed such that it could minimize the trapped residuals. Additionally the turbine <NUM> was sized such that it could accommodate the lower flow rates of a stoichiometric engine <NUM> with EGR <NUM> and provide the necessary pressure balance to drive the desired EGR levels. The intake system was assessed for charge delivery and mixture uniformity. With stringent requirements for charge uniformity and charge distribution a final intake configuration as shown in the CFD model of <FIG> was chosen.

The exhaust system was extensively tested and developed in order to ensure good cylinder balance as well as facilitate an efficient exhaust event. <FIG> shows a summary of iterations assessed using a novel modeling approach in CFD to determine turbine loss factors. The iterations were focused on geometric changes that improved losses in the manifold and balanced the losses cylinder by cylinder. Iteration #<NUM> was chosen as the exhaust manifold <NUM> configuration for the engine <NUM>.

<FIG> is a schematic diagram of an air handling (AH) system <NUM>, according to an embodiment. The air handling system <NUM> includes the engine <NUM> <FIG> and the CRV <NUM> of <FIG>. The fresh air coming from the atmosphere enters the system <NUM> through an air filter <NUM>. Pressure is raised by a compressor <NUM> of a turbocharger <NUM> and temperature reduced by a charge air cooler (CAC) <NUM>. This air reservoir together with an Intake Air Throttle (IAT) <NUM> is used to control the air flow going into the intake manifold <NUM>. Similarly, the EGR flow diverted from the exhaust manifold <NUM> is controlled by an EGR Valve (EGV) <NUM>. Both air and EGR are mixed in the intake manifold <NUM> at rates controlled by the valves. Lastly, the compressor <NUM> is maintained away from the surge region by actuating the CRV <NUM>.

The exhaust gas not diverted to the intake manifold <NUM> is communicated to a waste-gated turbine <NUM> of the turbocharger <NUM> where a waste gate valve (WG) <NUM> is used to control what portion of the flow is bypassed. By doing so, the energy going to the turbine <NUM> and consequently the boost can be controlled within certain limits. The control comprises calculating the IAT <NUM>, EGV <NUM>,and WG <NUM> actuator commands to achieve the target engine Fresh Air Flow (FAF), EGR fraction and/or boost.

In stoichiometric engines, FAF is directly related to engine power so the target FAF is calculated from the driver torque request and engine speed. EGR fraction, on the other hand, is used to reduce knock and PMEP and NOx. The EGR fraction target is usually calibrated as a function of (at least) load and engine <NUM> speed. Finally, having three actuators allows the tracking of three references (when feasible). The last target for the air handling control is turbocharger boost, which allows to trade off transient performance with pumping efficiency. A common target to exercise this tradeoff is the pressure drop on the IAT <NUM>, which may be stored, for example as a function of engine <NUM> load and speed.

The control was designed using physical models of the AH components, which significantly reduced the need for empirical table lookups to address system nonlinearities and changes in environmental conditions. The FAF and EGR fraction control performance is shown in <FIG> is a plot of fresh air flow and <FIG> is a plot of EFR Fraction tracking during a federal testing procedure (FTP) cycle. Overall, the FAF and EGR Fraction remain on top of the reference with few exceptions, most of them related to turbo spooling. The large EGR fraction deviation during idle regions corresponds to EGR flow measurement errors at low flows. The actual tracking error is zero since the EGR valve <NUM> remains close during those regions.

The conversion efficiency of the TWC is directly related to the AFR. Therefore, AFR is a strong lever to control the system out emissions. <FIG> is a schematic illustration of an air/fuel ratio control system, according to an embodiment. The AFR control system comprises a cascade control system with two loops (inner loop and outer loop). The inner loop adjusts the on-time of the fuel injectors to precisely track the AFR target, while the outer loop determines the AFR target based on the catalyst states for best conversion efficiency of the emission constituents.

The inner loop consists of feedforward and feedback fuel scheduling. The feedforward fueling schedules fuel injector on-time based on the estimated air mass in the cylinder, while the feedback trims the feedforward calculation based on a wideband lambda sensor located after the turbocharger. Due to the slow response of the feedback loop, the transient performance of the AFR control is mainly determined by the feedforward fueling. The dynamics of the injectors can be neglected due to its fast response time compared to the air dynamics. Therefore, accuracy of the air estimator plays the most important role in defining the inner loop control performance. A physics-based approach, which utilizes a charge virtual sensor and an EGR flow sensor, was developed to accurately predict air flow to the cylinder. <FIG> shows the on-engine validation of the air estimator at different engine speeds.

The outer loop consists of a feedforward mean AFR target table. A feedback control trims the AFR target based on a wideband O<NUM> sensor located at midbed (between the first catalyst TWC1 and second catalyst TWC2). The feedforward mean lambda values are pre-determined via steady state catalyst characteristic testing at various engine <NUM> operating conditions. The objective is to maintain a constant AFR target at the midbed location that optimizes the conversion of all the emissions constituents. <FIG> are plots demonstrating the influence of outer loop control on constituents of an exhaust gas emitted from the system <NUM> of <FIG>. <FIG> shows the influence of the outer loop control on the system out emissions. The benefit of having the outer loop control can be seen clearly from the individual plots. However, to meet the ultra-low NOx requirement, a trade-off among the emissions constituents may also be observed.

Various embodiments include a close-coupled after treatment architecture to meet system out ultralow NOx emission requirement. The after treatment architecture consists of both a close-coupled TWC and underfloor TWCs. This architecture provides a suitable compromise between high system efficiency and packaging constraints. The close coupled aftertreatment architecture demonstrates excellent performance in managing both cold-start and warm-start transient emissions control. Furthermore, through benchmarking evaluation, "TWC technology A" was selected to achieve both high NOx conversion and methane (CH<NUM>) conversion at near stoichiometric lambda (i.e., air/fuel ratio). The platinum-group metal (PGM) loading of the after treatment system was engineered differently between the close-coupled and underfloor TWCs.

<FIG> are plots of NOx, (<FIG>), CH<NUM> (<FIG>) and CO (<FIG>) emissions during heavy-duty cold FTP transient cycle. The emissions were reported at engine out (EO), close-coupled catalyst out (CC) and system out (SO) locations. During the cold FTP transient cycle as shown in <FIG>, the close-coupled TWC effectively managed the first <NUM>-<NUM> seconds NOx emissions control before warming up the underfloor catalyst. CH<NUM> emissions was largely controlled through close-coupled TWC for the first <NUM> seconds. The close-coupled TWC successfully converted over <NUM>% of the cumulative engine out NOx emissions and over <NUM>% of the cumulative engine out CH<NUM> emissions during the cold FTP cycle.

<FIG> are plots of NOx, (<FIG>), methane (<FIG>) and CO (<FIG>) emissions during heavy-duty warm FTP transient cycle. The emissions were reported at EO, CC and SO locations. During the warm FTP transient cycle as shown in <FIG>, the close-coupled architecture converted over <NUM>% of the cumulative engine out NOx emissions and over <NUM>% of the cumulative engine out CH<NUM> emissions during the warm FTP cycle.

Various embodiments include a TWC model that is capable of closely predicting the application cycles emissions for natural gas application. Key challenges of developing such a model include dynamic oxygen storage mechanism, complex CH<NUM> oxidation and reforming kinetics and its interaction with the oxygen storage dynamics, and the highly transient nature of the air-fuel ratio control during the TWC application. The accuracy of such a TWC model may also depend on obtaining the right kinetic mechanisms through well-designed tests and reliable data collection.

A global-kinetic TWC model was developed and validated using a production natural gas engine with an underfloor only after treatment system during transient emissions cycles (e.g. cold Federal Test Procedure cycle, warm Federal Test Procedure cycles and World Harmonized Transient Cycles). <FIG> is a plot of cumulative NOx and <FIG> is a plot of cumulative CH<NUM> cold FTP transient cycle conversion performance predictions against testing data. As shown in <FIG>, the model has a high predictability of aftertreatment CH<NUM> and NOx performance during the cold FTP cycle against engine bench testing results.

A system approach was used to develop a system that was capable of <NUM>% reduction in NOx below current standards and has equivalent efficiency to a diesel engine. With the intake manifold <NUM>, EGR assembly <NUM>, exhaust manifold <NUM> and combustion systems as described herein, the robustness of the engine <NUM> was dramatically improved. Robustness of the engine <NUM> is depicted in <FIG> which includes plots of a peak cylinder pressure (PCP) and CA50 variations of a baseline and the engine <NUM> (also referred to as "the new engine") and show improvements in cylinder to cylinder and cycle to cycle variation at peak torque with three sigma error bars for reference. The reduction in variation across the engine <NUM> allows for better control of the engine <NUM>, enables lower emissions capability, improved robustness/operating range, higher engine efficiency and capability for increased power density.

In addition to variation reduction, component durability was also addressed. An important component involved in engine durability is the cylinder head. A comparison of the head temperatures is shown in <FIG> which are FEA models comparing a combustion face temperature of the baseline engine (<FIG>) and the new engine (<FIG>). The head temperatures were improved through a revised design so as to reduce the maximum temperatures as well as provide uniform cooling of the combustion face. A comparison of the baseline and the new engine are shown below.

In addition to the cylinder head the exhaust system utilized improved high temperature materials for durability as well as revised designs to improve the loss coefficient of the manifold and improve the relationship between EGR fraction and engine delta p as shown in <FIG>.

The ability to drive large amounts of EGR with low engine delta p may allow for reduced residuals supporting a wide operating range for EGR at high load conditions which provides further robustness to knock. An example of the EGR Range at high load is shown in <FIG> for the peak torque condition.

With a significantly improved engine design, controls were redesigned as well to enable improved air handling, combustion and air/fuel ratio controls. The control system is capable of delivering the transient response, robustness and efficiency while at the same time delivering tight control for NOx emissions reduction. The tracking performance of the air handling system is shown in <FIG>.

Claim 1:
An exhaust manifold (<NUM>), comprising:
a plurality of exhaust intake conduits (<NUM>), each of the plurality of exhaust intake conduits (<NUM>) structured to be fluidly coupled to an engine (<NUM>) and structured to receive exhaust gas from a corresponding cylinder (<NUM>) of the engine (<NUM>);
an exhaust intake manifold (<NUM>) fluidly coupled to an exhaust intake conduit outlet (<NUM>, <NUM>, <NUM>) of at least one of the plurality of exhaust intake conduits (<NUM>);
wherein each of the plurality of exhaust intake conduits (<NUM>) and the exhaust intake manifold (<NUM>) define an exhaust intake manifold core volume, and
wherein each of the plurality of exhaust intake conduits (<NUM>) and the exhaust intake manifold (<NUM>) are shaped so as to define the exhaust intake manifold core volume based on at least one of the displacement of the engine (<NUM>), the intended operating power of the engine (<NUM>), and the intended flow rate of the exhaust gas through the exhaust manifold (<NUM>);
characterized by at least one outlet port (<NUM>) fluidly coupled to the exhaust intake manifold (<NUM>), the at least one outlet port (<NUM>) defining an outlet port flow axis (<NUM>) positioned orthogonal to an exhaust intake manifold flow axis (<NUM>) of the exhaust intake manifold (<NUM>); and
at least one pull-off conduit (<NUM>) fluidly coupled to the exhaust intake manifold (<NUM>), at least a portion of the at least one pull-off conduit (<NUM>) defining a pull-off conduit flow axis (<NUM>) positioned orthogonal to each of the exhaust intake manifold flow axis (<NUM>) and the outlet port flow axis (<NUM>).