Patent Description:
This disclosure relates to exhaust recirculation (EGR) systems for internal combustion engines.

Exhaust gas recirculation, especially cooled EGR, can be added to internal combustion engine systems to reduce NOx emissions and reduce knock tendency. In such a system, an amount of exhaust gas is added to the air and/or fuel mixture within the air-intake manifold of the engine. The challenge is that there is a cost to deliver the cooled EGR (cEGR), especially for high efficiency engines which generally are most efficient when the exhaust manifold pressure is lower than the intake manifold pressure. The pressure difference creates a positive scavenging pressure difference across the engine which scavenges burn gas from the cylinder well and provides favorable pressure-volume pumping loop work. It is particularly challenging to deliver cEGR from its source at the exhaust manifold to the intake manifold without negatively impacting the residual gas scavenging and efficiency of the engine cycle via the pumping loop. The "classic" high pressure loop cEGR system plumbs the exhaust gas directly to the intake manifold, which requires either design or variable turbocharging to force the engine exhaust manifold pressure to be higher than the intake manifold, which in turn, unfavorably reduces scavenging of hot burned gases and engine P-V cycle and loses efficiency. It is particularly counterproductive since the purpose of the cEGR is to reduce the knock tendency to improve efficiency and power density. But, this classic method to drive EGR actually increases the knock tendency through residual gas retention and reduces efficiency thru negative pressure work on the engine - in a manner of diminishing returns, i.e., two steps forward to reduce knock with cEGR, but one step back due to how it is pumped, leading to a zero gain point where the cost of driving cEGR counteracts the benefits of delivering it.

<CIT> describes a device for generating a gas mixture. A combustion chamber surrounded by an air chamber and a gas chamber is supplied with air and gas under pressure in a controllable quantity, so that due to the small difference in pressure inside and outside the wall, the latter is kept very thin and can reach high temperatures, whereupon the combustion products suck a part of the exhaust gases of the engine out of the pipe into the mixing and cooling chamber in the manner of a jet pump.

<CIT> describes an exhaust gas recirculation apparatus that includes: a fresh air throttle portion that continues from a fresh air inlet portion and is configured to throttle the flow of fresh air; an inner side tube portion that continues from the fresh air throttle portion, has a tubular shape and has an opening end disposed on a side opposite to the fresh air throttle portion; an exhaust gas inlet portion configured to receive a flow of exhaust gas; a surrounding portion that continues from the exhaust gas inlet portion, surrounds the inner side tube portion, and defines a circumference direction flow path for the exhaust gas extending along an outer circumference surface of the inner side tube portion; and an outlet portion that continues from the surrounding portion, has a tubular shape, and defines a merging flow path configured to receive the flow of the fresh air flowing out from the opening end of the inner side tube portion and the flow of the exhaust gas flowing out from the circumference direction flow path.

<CIT> describes a venturi type mixer that is equipped with a fuel gas supply pipe and an exhaust gas supply pipe, a barrel part in which an internal space passing intake air is arranged is connected to an intake pipe on the intake air side of an engine, an inner wall whose cross section along the flow direction of the intake air is formed into a hourglass shape from an intake air inflow side toward an intake air outflow side is arranged in the inside of the internal space, a space into which fuel gas and exhaust gas are led to flow and a hourglass-shaped space in which intake air flows are formed between the inner wall and the inside of the barrel part, and an ejection hole through which fuel gas and exhaust gas are ejected to the hourglass-shaped space is arranged in the part of the inner wall where the hourglass-shaped space is narrowed down.

<CIT> describes an EGR device for an engine having a supercharger, including an EGR passage for returning a part of exhaust gas discharged from the engine to an exhaust passage to an intake passage, and a branch from the EGR passage. A bypass passage that connects the upstream side and the downstream side of the supercharger in the intake passage, and an ejector that generates a negative pressure in the intake bypass passage.

This disclosure describes technologies relating to recirculating exhaust gas.

Claim <NUM> provides an exhaust gas recirculation mixer according to the invention. The dependent claims provides details about preferred embodiments.

Claim <NUM> provides a method according to the invention. The dependent claims provides details about preferred embodiments.

Particular implementations of the subject matter described herein can have one or more of the following advantages. The exhaust gas recirculation mixer can allow recirculating exhaust gas into a pressurized engine intake, such as in a supercharged or turbocharged engine, when the exhaust gas source is at a lower pressure than the intake. In certain instances, the mixer can enable admission of exhaust gas even when the internal combustion engine is running under high-load and high boost. At such high-load high boost conditions, EGR is needed the most but it is also most difficult to supply the EGR, due to the higher pressure in the intake system over the exhaust. Moreover, the mixer can mitigate high back pressure in the exhaust system, which prevents burned gas from effectively leaving the combustion chamber and, itself, promotes knock. The mixer is a passive pump, relying on the area reduction of the primary gas stream to accelerate the gas to a high velocity. The accelerated gas causes a low pressure using the Bernouli's effect, followed by the creation of a free jet of the gas into a receiver chamber. The free jet generated low pressure acts as a suction in the receiver chamber, which when connected to the EGR path, manifests as a pressure below the exhaust manifold creating a favorable pressure gradient for the EGR to flow to the lower pressure to admit exhaust gas into the mixer. Following the mixer, the reverse Bemouli effect converts the high velocity gas mixture to a high pressure when it is decelerated into the engine intake manifold. Thus, it mitigates system efficiency losses attributable to the pumping work needed to operate more conventional EGR systems and the negative scavenging pressures across the engine. The mixer is also quite simple in construction, and needs no working parts to operate. The mixer can also be mechanically designed to have different primary flow nozzles which can be modular (e.g., threaded on/off the change out), interchangeably fitted for a wide range of engine displacement families. Further, the mixer creates internal turbulence that promotes mixing of the EGR, air and fuel. Further, the mixer can receive fuel, and operate to mix the fuel, air and EGR. Thus, some implementations <NUM>) reduce the pressure difference across the engine to drive EGR from the exhaust manifold to the intake manifold - under any back pressure to intake pressure ratio, <NUM>) including the special case when it is desirable to maintain the back pressure equal to or below the intake pressure - which (a) improves efficiency (due to the reduction of Pumping Mean Effective Pressure (PMEP) and (b) reduces the retention of hot burned gases trapped inside the combustion chamber which themselves increase the very knock tendency that the active cooled EGR is attempting to reduce, (<NUM>) the addition of high velocity fuel enhances the Jet and suction effect, (<NUM>) can simplify the fuel delivery system by eliminating the pressure regulator and preheater circuit since the mixer favors high pressure fuel and cold fuel to cool the EGR using the Joules-Thomson effect (fuel jetting will cause the temperature to drop - which is favorable since cooled EGR and cooled intake air are beneficial to engine operation).

Exhaust gas recirculation (EGR) can have parasitic effects on an engine system, that is, it can reduce the effective power output of an engine system as energy is required to move exhaust gas from an exhaust manifold and into an intake manifold. This is especially problematic on forced induction engines where the intake manifold pressure can be higher than the exhaust manifold pressure. Ironically, EGR is most needed when the intake manifold pressure is high, such as when the engine is running at high load. In the case of a turbo-charged engine, increased back-pressure within the exhaust manifold can also contribute to knock under high loads.

The concepts herein relate to an EGR system that can be used on an internal combustion engine, including a forced induction internal combustion engine. A jet pump is added to the air intake system of the engine between the throttle and the intake manifold. If a compressor is provided in the intake system, the jet pump can be placed downstream of the compressor (although it could alternatively be placed upstream of the compressor, too). Air, the primary fluid, is flowed through a central flow path of the jet pump from the throttle towards the intake manifold. In a low pressure receiver region within the jet pump, recirculated exhaust gas is added to the air stream from the exhaust manifold. The lower effective pressure in the receiver allows for a pressure differential to form between the exhaust manifold and the receiver. The reverse Bernoulli effect recovers the pressure by slowing down the high velocity/low pressure gas to create a pressure in the intake manifold that is equal to or higher than the exhaust manifold. So at the system level, the jet pump enables the exhaust gas to flow from the exhaust manifold to the intake manifold even when the exhaust manifold is at a lower pressure. Fuel can be added to the air stream upstream of the convergent end of a convergent nozzle. Turbulence is produced as the three streams combine within the jet pump leading to a well-mixed, combustible mixture flowing into the manifold.

<FIG> shows an example engine system <NUM>. The engine system <NUM> includes an intake manifold <NUM> configured to receive a combustible mixture to be combusted within a combustion chamber of the engine <NUM>. That is, the intake manifold is fluidically coupled to a source of oxygen and a source of fuel. The combustible mixture can include air and any combustible fluid, such as natural gas, atomized gasoline, or diesel. While the illustrated implementation includes a four-cylinder engine <NUM>, any number of cylinders can be used. Also, while the illustrated implementation includes a piston engine <NUM>, aspects of this disclosure can be applied to other types of internal combustion engines, such as rotary engines or gas turbine engines.

A throttle <NUM> is positioned upstream of the intake manifold <NUM>. The throttle <NUM> is configured to regulate an air flow into the intake manifold from the ambient environment <NUM>, for example, by changing a cross-sectional area of a flow passage going through the throttle <NUM>. In some implementations, the throttle <NUM> can include a butterfly valve or a disc valve. Reducing the cross-sectional area of the flow passage through the throttle <NUM> reduces the flowrate of air flowing through the throttle <NUM> towards the intake manifold <NUM>.

An exhaust manifold <NUM> is configured to receive combustion products (exhaust) from a combustion chamber of the engine <NUM>. That is, the exhaust manifold is fluidically coupled to an outlet of the combustion chamber. An EGR flow passage <NUM> or conduit fluidically connects the exhaust manifold <NUM> and the intake manifold <NUM>. In the illustrated implementation, an EGR throttle valve <NUM> is located within the EGR flow passage <NUM> between the exhaust manifold <NUM> and the intake manifold <NUM> and is used to regulate the EGR flow. The EGR throttle valve <NUM> regulates the EGR flow by adjusting a cross-sectional area of the EGR flow passage <NUM> going through the EGR throttle valve <NUM>. In some implementations, the EGR throttle valve <NUM> can include a butterfly valve, a disc valve, a needle valve, or another style of valve.

The EGR flow passage feeds into an EGR mixer <NUM> that is located downstream of a throttle <NUM> and upstream of the intake manifold <NUM> in the illustrated implementation. The EGR mixer <NUM> is in the engine intake system, fluidically connected to the throttle <NUM>, the intake manifold <NUM>, and the EGR flow passage <NUM>. The fluid connections can be made with conduits containing flow passages that allow fluid flow. In some implementations, the EGR mixer <NUM> can be included within a conduit connecting the intake manifold <NUM> to the throttle <NUM>, within the intake manifold <NUM> itself, within the EGR flow passage <NUM>, integrated within the throttle <NUM>, or integrated into the EGR throttle valve <NUM>. Details about an example EGR mixer are described later within this disclosure.

In the illustrated implementation, an exhaust gas cooler <NUM> is positioned in the EGR flow passage <NUM> between the exhaust manifold <NUM> and the EGR mixer <NUM>. The exhaust gas cooler can operate to lower a temperature of the exhaust gas prior to the EGR mixer. The exhaust gas cooler is a heat exchanger, such as an air-air exchanger or an air-water exchanger.

In some implementations, the engine system <NUM> includes a compressor <NUM> upstream of the throttle <NUM>. In an engine with a compressor <NUM> but no throttle, such as an unthrottled diesel engine, the throttle is not needed and the mixer can be down stream of the compressor. The compressor <NUM> can include a centrifugal compressor, a positive displacement compressor, or another type of compressor for increasing a pressure within the air EGR flow passage <NUM> during engine operation. In some implementations, the engine system <NUM> can include an intercooler <NUM> that is configured to cool the compressed air prior to the air entering the manifold. In the illustrated implementation, the compressor <NUM> is a part of a turbocharger. That is, a turbine <NUM> is located downstream of the exhaust manifold <NUM> and rotates as the exhaust gas expands through the turbine <NUM>. The turbine <NUM> is coupled to the compressor <NUM>, for example, via a shaft and imparts rotation on the compressor <NUM>. While the illustrated implementation utilizes a turbocharger to increase the intake manifold pressure, other methods of compression can be used, for example an electric or engine powered compressor (e.g., supercharger).

<FIG> is a half cross-sectional schematic diagram of an example EGR mixer <NUM>. The EGR mixer <NUM> is made up of one or more housings or casings. Openings in the end walls of the casings define an air inlet <NUM> and an outlet <NUM> of an interior flow passage <NUM> defined by casing(s) <NUM>. The interior flow passage <NUM> directs flow from the air inlet <NUM> to the outlet <NUM> to allow flow through the mixer <NUM>. Within the casing(s) <NUM>, the EGR mixer <NUM> includes a convergent nozzle <NUM> in a flow path from the air inlet <NUM> of the mixer <NUM> and the outlet <NUM> of the EGR mixer <NUM>. The convergent nozzle <NUM> converges in the direction of flow toward a convergent end <NUM>. That is, the downstream end (outlet) of the convergent nozzle <NUM> has a smaller cross-sectional area, i.e., a smaller flow area, than the upstream end (inlet) <NUM> of the convergent nozzle <NUM>. The EGR mixer <NUM> includes an exhaust gas receiver housing <NUM> and the housing <NUM> includes one or more exhaust gas inlets <NUM> fed from and fluidically connected to the EGR flow passage <NUM> and into an interior receiver cavity <NUM> of the exhaust gas housing <NUM>. In the illustrated implementation, the housing <NUM> surrounds the convergent nozzle <NUM>, such that a portion of the convergent nozzle <NUM> is within the interior receiver cavity <NUM>. The convergent nozzle <NUM> is positioned to form a free jet of gas out of the convergent end208 of the nozzle <NUM>. Also, the exhaust gas inlet <NUM> is upstream of an outlet, the convergent end <NUM>, of the convergent nozzle <NUM>. While the illustrated implementation shows the convergent nozzle <NUM> to be at least partially within the exhaust gas receiver housing <NUM>, other designs can be utilized. In some implementations, the air inlet <NUM> and the outlet <NUM> are provided with attachments or fittings to enable connection to the intake manifold <NUM> of the engine <NUM> and/or the EGR mixer <NUM>. In some instances, the nozzle <NUM> can be modularly interchangeable with nozzles <NUM> of different the inlet area <NUM> and convergent area <NUM>, making the system readily changeable to fit multiple engine sizes. For example, the nozzle <NUM> can be provided with threads or another form of removable attachment to the remainder of the mixer casing <NUM>.

A convergent-divergent nozzle <NUM> is downstream of the convergent end <NUM> of the convergent nozzle <NUM> and is fluidically coupled to receive fluid flow from the convergent end <NUM>, the exhaust gas inlet <NUM>, and a fuel supply <NUM>. In other words, the convergent-divergent nozzle <NUM> can act as an air-fuel-exhaust gas inlet for the intake manifold <NUM>. To help facilitate mixing, an inlet <NUM> of the convergent-divergent nozzle <NUM> has a greater area than an exit of the convergent nozzle <NUM>. The convergent-divergent nozzle includes three parts: the inlet <NUM>, the throat <NUM>, and the outlet <NUM>. The throat <NUM> is the narrowest point of the convergent-divergent nozzle and is located and fluidically connected downstream of the inlet <NUM> of the convergent-divergent nozzle. The narrowing of the convergent-divergent nozzle at the throat <NUM> increases a flow velocity of a fluid flow as it passes through the convergent-divergent nozzle <NUM>. The outlet <NUM> of the convergent-divergent nozzle is fluidically connected to and upstream of the intake manifold <NUM>. Between the throat <NUM> and the outlet <NUM>, the cross-section of the flow passage through the convergent-divergent nozzle increases. The increase in cross-sectional area slows the flow velocity and raises the pressure of the fluid flow. In certain instances, the increase in cross-sectional area can be sized to increase a pressure within the mixer <NUM> so that the pressure drop across the mixer <NUM> is zero, nominal or otherwise small. The convergent-divergent nozzle <NUM> can include threads or another form of removable attachment at the inlet <NUM>, the outlet <NUM>, or both to allow the convergent-divergent nozzle <NUM> to be installed and fluidically connected to the remainder of the intake of the engine system <NUM>. Like, the convergent nozzle <NUM>, the convergent-divergent nozzle <NUM> can be modularly interchangeable with nozzles <NUM> of different inlet <NUM>, throat <NUM> and outlet <NUM> areas too make the system readily changeable to fit multiple engine sizes.

The illustrated implementation shows the convergent nozzle and the convergent-divergent nozzle aligned at a same center axis <NUM>, but in some implementations, the center axis of the convergent nozzle and the convergent-divergent nozzle might not be aligned or parallel. For example, space constraints may require the EGR mixer to have an angle between the axis of the convergent nozzle and the convergent-divergent nozzle. In some implementations, rather than having a substantially straight flow passage as shown in <FIG>, the flow passage may be curved.

As illustrated, the fuel supply <NUM> includes a fuel supply tube <NUM> terminating parallel and centrally within the air flow path. The fuel supply tube <NUM> is configured to supply fuel into the air flow path in a direction of flow through the mixer <NUM>, and upstream of the convergent nozzle. In some implementations, the fuel supply tube <NUM> can be a gaseous fuel supply tube, coupled to a source of gaseous fuel. However, the fuel delivered by the fuel supply tube <NUM> can include any combustible fluid, such as natural gas, gasoline, or diesel. While shown as a single tube, the fuel supply tube <NUM> can be configured in other ways, for example as a cross through the flow area of the mixer, as fuel delivery holes along the perimeter of the flow area, or in another manner. While the illustrated implementation shows a fuel supply tube <NUM> configured to inject fuel upstream of the convergent end <NUM> of the convergent nozzle <NUM>, fuel can also be added with a fuel supply port <NUM> upstream of the exhaust gas inlet <NUM>. Such a port can include a gaseous fuel supply port. In some instances, the fuel can be delivered at high velocity, with velocities up to including sonic flow at the fuel tube exit <NUM>, such that a fuel - air jet pump is also created, allowing the fuel to provide additional motive force for the primary air flow into and thru the nozzle. In such a case, the higher the pressure the better, such that a sonic jet can be generated, further enhancing mixing of the fuel and air. This reduces the need for the fuel pressure regulator. Additionally, if the fuel jet is cold via the Joules-Thompson effect, this is favorable as it will cool the air/fuel stream, thus reducing the air path charge air cooler heat removal requirements as well.

The illustrated implementation operates as follows. The convergent nozzle <NUM> increases a velocity and decreases a pressure of an air flow <NUM> in the EGR mixer <NUM>. An exhaust flow <NUM> is drawn into the EGR mixer <NUM> through the exhaust gas inlet <NUM> in response to (e.g., because of) the decreased pressure of the free jet air flow <NUM> exiting the convergent nozzle <NUM>. The exhaust flow <NUM> is directed from the exhaust manifold <NUM> eventually to the point downstream of the convergent nozzle <NUM>. The air flow <NUM>, the exhaust flow <NUM>, and a fuel flow <NUM> are mixed to form a combustion mixture <NUM> with a second convergent nozzle 214a positioned downstream of the convergent nozzle <NUM>. A pressure of the combustion mixture is increased and a velocity of the combustion mixture is reduced with a divergent nozzle 214b. While the second convergent nozzle 214a and the divergent nozzle 214b are illustrated as a single convergent-divergent nozzle <NUM>, the second convergent nozzle 214a and the divergent nozzle 214b can be separate and distinct parts.

Claim 1:
An exhaust gas recirculation mixer (<NUM>), the mixer comprising:
a convergent nozzle (<NUM>) in a flow path from an air inlet (<NUM>) of the mixer to an outlet (<NUM>) of the mixer, the convergent nozzle converging toward the outlet of the mixer;
an exhaust gas housing (<NUM>) comprising an exhaust gas inlet (<NUM>) into an interior of the exhaust gas housing; and
a convergent-divergent nozzle (<NUM>) comprising an air-fuel exhaust gas inlet (<NUM>) for receiving an air flow, a fuel flow, and an exhaust gas flow, the convergent-divergent nozzle being in fluid communication to receive fluid flow from the convergent nozzle and the interior of the exhaust gas housing, and
a fuel supply (<NUM>) coupled to the mixer and in communication with the air-fuel exhaust gas inlet, the fuel supply comprising a fuel supply tube (<NUM>) positioned parallel to and centrally within the air flow path, the fuel supply tube configured to supply fuel into the air flow path in a direction of flow and upstream of the convergent nozzle.