Exhaust valve for a large sized two stroke diesel engine, process for reduction on NOx-formation in such an engine and such engine
AssigneeMan Diesel & Turbo, Filial Af Man Diesel & Turbo SE, Tyskland
InventorMads Lytje Christensen
Life of this patent
Estimating the term…
Abstract
For reducing the NOx-emission of a large sized two stroke diesel engine having at least one combustion room (3), a reciprocating piston (4) and an exhaust opening (12) controlled by an exhaust valve (13) at each work cyclus a small volume of burnt gas is retained in the combustion room (3) and so added to the fresh air for the next combustion. For achieving this retention of burnt gas the underside of the valve disc (15) off the exhaust valve (13) is provided with a shallow concave face (17) building a basin-like collection room, whose depth is within a range of 2-10% of the outer diameter of the valve disc (15).
Claims15
A large sized diesel engine, having a combustion room (3) delimited by a reciprocating piston (4), comprising:
- an exhaust valve (13) having a valve disc (15) arranged at a lower end of a valve shaft (14),
- the valve disc (15) including an underside which faces the combustion room (3) and being provided with a basin designed as a rotationally symmetric cavity (18) that is surroundingly bordered and downwardly open,
- wherein for retention of burnt gas, the maximum of rise of a concavely shaped underside of the valve disc (15) relative to an imaginary planar face (23) directly supporting the valve disc (15), is within the range of 2-10% of the outer diameter of the valve disc (15),
- at least one said tag being located with a line section of ¾ of the overall axial valve length opposed to the valve disc end,
- the tag of said exhaust valve being exposed for reading by non-contacting means positioned above the combustion room for said exhaust valve, and
- a combustion room volume formed by the cavity (18) on the underside of the valve disc (15) being compensated by raising a top face level of the piston (4) with a shims layer (24).
A process for reduction of NOx-formation in a two stroke large sized diesel engine (1) having:
- at least one combustion room (3) with an exhaust opening (12) coaxially arranged within and controlled by an exhaust valve (13) having a valve disc (15) arranged at a lower end of a valve shaft (14),
- whereby the valve disc (15) includes an underside which faces a combustion room (3) and is provided with a basin designed as a rotationally symmetric cavity (18), being surroundingly bordered and being downwardly open,
- whereby for retention of burnt gas, the maximum of rise of a concavely shaped underside of the valve disc (15) relative to an imaginary planar face (23) directly supporting the valve disc (15), is within the range of 2-10% of the outer diameter of the valve disc (15), the process comprising:
- carrying out, in the combustion room (3) at each work cycle, a fuel injection, a combustion of fuel, an ejection of burnt gas, a scavenging and filling with fresh air, and a compression of the filling of the combustion room (3),
- further comprising adding some burnt gas to the air before combustion in such a way that at least some of the burnt gas added to the air is conserved in the combustion room (3) in the manner of a nest (19) of burnt gas built within a rim area of the underside of the said exhaust valve (13) being concavely shaped on the underside.
Dependencies are inferred from the claim text.