The invention relates to a mixer for an engine exhaust system according to the preamble of claim 1.

Such a mixer is known from US-Al -2018/023446. In this known mixer a diverter duct is fixed to the mixer housing and has a first duct end open to the interior cavity and a second duct end at least partially

overlapping the window opening such that a portion of the engine exhaust gas in the interior cavity is directed to enter the first duct end, to flow through the at least one window and then to flow into the cone inlet opening to be mixed with a fluid injected through the injector opening. The cone of this known mixer has a body of which at least a portion of the body increases in diameter in a direction extending from the base end toward the outlet end. In addition, the base end is spaced apart from an inner surface of the mixer housing that surrounds the injector opening to create a gap between the base end of the cone and the mixer housing to allow exhaust gases exiting the window opening to flow into the gap and enter the cone inlet opening. In this known mixer, during operation of the engine, the exhaust gas flows past the injector and the diverter duct scoops and directs a small portion of the exhaust gas through the window opening to introduce this small portion of the exhaust gas into the gap between the cone and an inner surface of the wall of the mixer housing and is directed to the cone inlet opening. A gaseous or liquid reducing agent is injected by the injector into the cone inlet opening and is mixed with this introduced small portion of exhaust gas after which the mixture exits the cone outlet opening into the interior cavity where the mixture is further mixed with the remainder of the exhaust gas, which remainder was not scooped by the diverter duct into the cone. In particular when using a liquid reducing agent it however appears that mixing of the liquid reducing agent and the introduced small portion of exhaust gas sometimes is not sufficiently thorough and that droplets of liquid reducing agent exit the cone outlet opening. These droplets of liquid reducing agent can lead to so called wetting of inner surfaces of the mixer housing and surfaces of components arranged therein and to crystallization of liquid agent, which wetting and crystallization can have a negative effect on the operation of the mixer and in the end even the engine.

It is therefore the object of the invention to provide a mixer for an engine exhaust system in which wetting of surfaces and crystallization growth is reduced.

According to the invention this object is obtained by providing a mixer for an engine exhaust system according to claim 1. As a result of the combination of the decreasing diameter of the cone body in a direction towards the outlet end, the turbulent flow amplifying opening and the flow direction reversal scoop associated with each window opening, during operation of the engine, the small portion of exhaust gas passing through the window opening becomes highly turbulent. Reducing agent injected into the cone inlet opening comes into contact with this highty turbulent exhaust gas and is thoroughly mixed therewith. In case a liquid reducing agent is used mixing of this liquid reducing agent with the turbulent exhaust gas is sufficiently thorough to significantly reduce the risk of or even to prevent droplets of liquid being injected into the interior cavity. In addition, the mixture of reducing agent and the small portion of exhaust gas introduced into the cylindrical member exiting the cone outlet opening maintains its turbulent property when being injected into the interior cavity which further improves mixing of this mixture with the remainder of the exhaust gas, which remainder passed the cylindrical member without being led into the window opening thereof. In this manner wetting and crystallization growth is at least reduced substantially.

In an embodiment of a mixer according to the invention the cylindrical member includes a first number of window openings and the cone includes a second number of turbulent flow amplifying openings, wherein the first number and the second number are equal. It has appeared that by using an equal number of window openings and turbulent flow amplifying openings the turbulence imposed on the small portion of exhaust gas introduced through the window openings is improved.

In a further embodiment of a mixer according to the invention the cylindrical member includes six window openings and the cone includes six turbulent flow amplifying openings. By using this number of window openings not only the turbulence imposed on the small portion of exhaust gas introduced through the window openings is found to be sufficient in all operation modes of an engine but also no additional components, such a diverter ducts external to the cylindrical member, are necessary to direct a sufficient small portion of exhaust gas into the cylindrical member to obtain an effective mixture with the reducing agent injected by the injector.

The invention will be further explained with reference to the Figures, in which non-limiting exemplar embodiments of an arrangement for introducing a liquid medium, e.g. urea, into exhaust gases from a diesel combustion engine for suppfy to a selective catalytic reduction device according to the invention are shown:

Fig. 1 schematically shows an embodiment of a mixer for an engine exhaust system in perspective in which an injector is mounted into the injector opening;

Fig. 2 schematically shows an enlargement of the embodiment of Fig. 1 in perspective in which the injector has been left out;

Figs. 3A, 3B and 3C schematically show an embodiment of the cylindrical element and the cone of the embodiment shown in Fig. 1 in perspective, in side view and in front view, respectively. In Fig. 1 an embodiment of a mixer 1 for an engine exhaust system is schematically shown in perspective. The mixer 1 comprises a mixer housing 2 enclosing an interior cavity 3 for engine exhaust gases. The mixer 1 comprises reducing agent injection sj^stem comprising an injector 4 for injecting a gaseous or liquid reducing agent into the interior cavity 3. An injector opening 5 (Fig. 2) is formed in an outer peripheral wall 6 of the mixer housing 2 for receiving the injector 4.

As shown in Figures 3A-3C the mixer 1 for an engine exhaust system further comprises a cone 7 having a cone inlet opening 8 aligned with the injector opening 5 and a cone outlet opening 9 into the interior cavity 3. Thus with regard to the outer peripheral wall 6 the cone 7 is arranged opposite to the injector 4. The cone 7 has a cone body 10 having a base end 11 defining the cone inlet opening 8 and an outlet end 12 defining the cone outlet opening 9. A cylindrical member 13 surrounds at least a portion of the cone 7, in the embodiment shown in Figures 3A-3C the cylindrical element 13 completely surrounds the cone 7. The cylindrical member 13 has a central axis 14 and, in the shown embodiment, includes at six window openings 15. In other, not shown embodiments the cylindrical element 13 can include another number of window openings. Each of the window openings 15 is defined by opposite axial window edges 16, 16’ and opposite tangential window edges 17, 17’.

A portion of the cone body 7 decreases in diameter in a direction extending from the base end 11 towards the outlet end 12, as indicated in Figure 3B by the dotted line. The outlet end 12 has a portion of relatively small dimension in which the diameter does not decrease. In the shown embodiment the cone 7 comprises six turbulent flow amplifying openings 18. In other not shown embodiments, the cone can include another number of turbulent flow amplifying openings. However, it is preferred that the number of turbulent flow amplifying openings equals the number of window openings. Associated with each window opening 15 is a flow direction reversal scoop 19 (Fig. 3A) which is attached to one of the axial window edges 17’ and projects radially inward from said axial window edge 17’.

During operation of the engine, the majority of the exhaust gas flowing within the interior cavity 3 of the mixer housing 2 will pass by the cylindrical member 13 and only a small portion of the exhaust gas enters the cylindrical member 13 in a radial direction through the window openings 15, as indicated by the arrows 20. As a result of the combination of the decreasing diameter of the cone body 10 in a direction towards the outlet end 12, the turbulent flow amplifying openings 18 and the flow direction reversal scoops 19 associated with each window opening 15 the small portion of exhaust gas introduced via the window openings 15 becomes highly turbulent and is forced into the axial direction (i.e. parallel to the central axis 14). Reducing agent injected by the injector 4 into the injector opening 5 and thus into the cone inlet opening 8, upon exiting the cone outlet opening 9 comes into contact with this highly turbulent exhaust gas and is thoroughly mixed therewith. This mixture keeps its turbulent property when exiting the cylindrical member 15 and is further mixed with the remainder of the exhaust gas which passed by the cylindrical member 14. In case a liquid reducing agent is used mixing of this liquid reducing agent with the turbulent exhaust gas is sufficiently thorough to significantly reduce the risk of or even to prevent wetting and crystallization growth.