TECHNICAL FIELD

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

BACKGROUND

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. However, 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.

SUMMARY

This disclosure describes technologies relating to recirculating exhaust gas.

An example implementation of the subject matter described within this disclosure is an engine exhaust gas recirculation mixer with the following features. Multiple convergent nozzles define multiple flow passages that extend alongside one another in a flow path from an engine intake air inlet of the mixer to an outlet of the mixer. The convergent nozzles each converge toward the outlet of the mixer. An exhaust gas housing includes an exhaust gas inlet leading into an interior of the exhaust gas housing. Multiple convergent-divergent nozzles each correspond to one of the plurality of convergent nozzles. The convergent-divergent nozzles each include an air-exhaust gas inlet in fluid communication to receive fluid flow from a corresponding convergent nozzle and the interior of the exhaust gas housing.

Aspects of the example engine exhaust recirculation mixer, which can be combined with the example engine exhaust recirculation mixer alone or in combination with other aspects, include the following. Inlets of each of the convergent nozzles are in a same, first plane, and corresponding outlets of the convergent nozzles are in a same, second plane.

Aspects of the example engine exhaust recirculation mixer, which can be combined with the example engine exhaust recirculation mixer alone or in combination with other aspects, include the following. The air-exhaust gas inlet of each of the convergent-divergent nozzles is in a same, third plane. The corresponding outlet of each of the convergent-divergent nozzles are in a same, fourth plane.

Aspects of the example engine exhaust recirculation mixer, which can be combined with the example engine exhaust recirculation mixer alone or in combination with other aspects, include the following. The air-exhaust gas inlet of each of the convergent-divergent nozzles is an air-fuel-exhaust gas inlet in communication with a fuel supply into the mixer.

Aspects of the example engine exhaust recirculation mixer, which can be combined with the example engine exhaust recirculation mixer alone or in combination with other aspects, include the following. The fuel supply further includes a fuel supply port positioned upstream of the convergent-divergent nozzle.

Aspects of the example engine exhaust recirculation mixer, which can be combined with the example engine exhaust recirculation mixer alone or in combination with other aspects, include the following. The fuel supply port includes a gaseous fuel supply port.

Aspects of the example engine exhaust recirculation mixer, which can be combined with the example engine exhaust recirculation mixer alone or in combination with other aspects, include the following. Each of the convergent-divergent nozzles are aligned on a same center axis as a corresponding convergent nozzle.

Aspects of the example engine exhaust recirculation mixer, which can be combined with the example engine exhaust recirculation mixer alone or in combination with other aspects, include the following. Each one of the air-exhaust gas inlets is upstream of a corresponding outlet of one the convergent nozzles.

Aspects of the example engine exhaust recirculation mixer, which can be combined with the example engine exhaust recirculation mixer alone or in combination with other aspects, include the following. The convergent nozzles extend at least partially within the exhaust gas housing.

Aspects of the example engine exhaust recirculation mixer, which can be combined with the example engine exhaust recirculation mixer alone or in combination with other aspects, include the following. Each of the air-exhaust gas inlets has a greater area than the corresponding outlet of the corresponding one of the convergent nozzles.

Aspects of the example engine exhaust recirculation mixer, which can be combined with the example engine exhaust recirculation mixer alone or in combination with other aspects, include the following. The convergent nozzles include four convergent nozzles, and the convergent-divergent nozzles include four corresponding convergent-divergent nozzles.

Aspects of the example engine exhaust recirculation mixer, which can be combined with the example engine exhaust recirculation mixer alone or in combination with other aspects, include the following. A divergent portion of the convergent-divergent nozzle diverges no more than 7°.

Aspects of the example engine exhaust recirculation mixer, which can be combined with the example engine exhaust recirculation mixer alone or in combination with other aspects, include the following. Pressure ports are located at a convergent end of each of the convergent nozzles.

An example implementation of the subject matter described within this disclosure is a method with the following features. A velocity of an air flow is increased and a pressure of an engine intake air flow is deceased using a first set of convergent nozzles to form a multiple free jets exiting a corresponding one of the converging nozzles. An engine exhaust flow is drawn downstream of the first plurality of convergent nozzles in response to the decreased pressure of each of the free jets. Each of free jets and the exhaust flow are mixed using a second set of convergent nozzles, downstream of the first set of convergent nozzles, to form a set of mixed flows corresponding to the free jets. Each of the second set of convergent nozzles corresponds with a different one of the first set of convergent nozzles. A pressure of the mixed flows is increased and a velocity of the mixed flows is reduced using a set of divergent nozzles, each corresponding to a different one of the second set of convergent nozzles.

Aspects of the example method, which can be combined with the example method alone or in combination with other aspects, include the following. Mixing one of the free jets and the exhaust flow to form one of the mixed flows includes mixing a portion of the air flow, a portion of the exhaust flow, and a portion of a fuel flow, to form a combustion mixture.

Aspects of the example method, which can be combined with the example method alone or in combination with other aspects, include the following. The fuel flow is supplied upstream of the convergent ends of the first set of convergent nozzles.

Aspects of the example method, which can be combined with the example method alone or in combination with other aspects, include the following. The fuel flow includes a gaseous fuel flow.

Aspects of the example method, which can be combined with the example method alone or in combination with other aspects, include the following. The exhaust flow is directed from an exhaust manifold to a point downstream of the first set of convergent nozzles.

An example implementation of the subject matter described within this disclosure is an engine system with the following features. An engine intake manifold is configured to receive a combustible mixture configured to be combusted within an engine combustion chamber. A throttle is upstream of the intake manifold. The throttle is configured to regulate an air flow into the intake manifold. An exhaust manifold is configured to receive combustion products from the combustion chamber. An exhaust gas recirculation mixer is downstream of the throttle and upstream of an intake manifold. The exhaust gas recirculation mixer includes convergent nozzles that extend alongside one another defining a flow passages in a flow path from an engine air intake air inlet of the mixer to an outlet of the mixer. The convergent nozzles each converge toward the outlet of the mixer. An exhaust gas housing includes an exhaust gas inlet leading into an interior of the exhaust gas housing. A plurality of convergent-divergent nozzles in the flow path each corresponding to one of the plurality of convergent nozzles, the plurality of convergent-divergent nozzles extending alongside one another, the plurality of convergent-divergent nozzles each comprising an air-exhaust gas inlet in fluid communication to receive fluid flow from a corresponding convergent nozzle and the interior of the exhaust gas housing.

Aspects of the example system, which can be combined with the example system alone or in combination with other aspects, include the following. A compressor is upstream of the throttle. The compressor is configured to increase a pressure within the flow path.

Aspects of the example system, which can be combined with the example system alone or in combination with other aspects, include the following. A turbine is downstream of the exhaust manifold. The turbine is coupled to the compressor and configured to rotate the compressor.

Aspects of the example system, which can be combined with the example system alone or in combination with other aspects, include the following. An exhaust gas cooler is positioned within a flow path between the exhaust manifold and the exhaust gas recirculation mixer. The exhaust gas cooler is configured to lower a temperature of the exhaust gas prior to the exhaust gas recirculation mixer.

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 Bernoulli'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 Bernoulli 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 1) 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, 2) 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, (3) the addition of high velocity fuel enhances the Jet and suction effect, (4) can simplify the fuel delivery system by eliminating the pressure regulator and pre-heater 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). By using four barrels, a similar total inlet area and outlet area can be used as compared to a single-barrel exhaust gas recirculation mixer, while reducing the total length of the mixer to be substantially half that of a single-barrel mixer.

The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages will become apparent from the description, the drawings, and the claims.

