Exhaust Valve Concave Underside for NOx Reduction
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Solution Overview
Problem
Existing two-stroke diesel engines face challenges in reducing NOx formation due to the dilution of recirculated exhaust gas with scavenging air, which increases oxygen content and requires complex and space-consuming recirculation devices.
Innovation Solution
An exhaust valve with a rotationally symmetric concave underside, designed to retain burnt gas in a basin-like cavity, allowing it to be conserved and reused in the combustion chamber, reducing oxygen content and NOx formation, and incorporating a method for manufacturing such valves to be used in large-sized two-stroke diesel engines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If exhaust gas is recirculated to reduce NOx formation, then NOx emissions are reduced, but the exhaust gas is diluted with scavenging air which increases oxygen content and leads to higher NOx formation
Solution Approach 1:
The exhaust valve underside is divided into distinct functional zones: a central exhaust opening and a surrounding circumferential cavity. This segmentation allows the cavity to trap and retain burnt gas separately from the main exhaust flow, preventing dilution with scavenging air and maintaining low oxygen content for effective NOx reduction.
Solution Approach 2:
The circumferential cavity is nested within the rim area of the exhaust valve underside, creating a nested structure where the cavity is contained within the overall valve geometry. This nested design allows burnt gas to be conserved within the cavity like a nest, providing a concentrated source of low-oxygen gas for reducing NOx formation without requiring external recirculation devices.
2Object-generated harmful factors
If a recirculation device is used to recirculate exhaust gas, then NOx formation is reduced, but the device is expensive and complex
Solution Approach 1:
The exhaust valve itself serves dual functions: controlling exhaust gas flow and trapping/retaining burnt gas through its integrated circumferential cavity. This self-service design eliminates the need for separate recirculation devices, reducing system complexity and cost while maintaining the ability to reduce NOx formation through burnt gas recirculation.
Solution Approach 2:
The exhaust valve structure merges the exhaust control function with the burnt gas retention function by integrating the circumferential cavity directly into the valve underside. This combination eliminates the need for separate recirculation equipment, simplifying the overall system while achieving NOx reduction.
3Object-generated harmful factors
If a recirculation device is used to recirculate exhaust gas, then NOx formation is reduced, but the device occupies hardly available space near the engine
Solution Approach 1:
The burnt gas retention cavity is merged with the exhaust valve structure, utilizing the valve's own geometry to provide the retention function. This integration eliminates the need for separate recirculation equipment that would occupy additional space, as the cavity is formed within the existing valve component footprint.
Solution Approach 2:
The circumferential cavity is nested within the rim area of the exhaust valve, utilizing the available space within the valve structure itself. This nested design allows burnt gas retention without requiring external space, as the cavity is contained within the valve's own dimensions.
4Object-generated harmful factors
If the maximum rise of the concave underside is increased to retain more burnt gas, then NOx reduction is improved, but the mass of the exhaust valve increases
Solution Approach 1:
The maximum rise of the concave underside is optimized to a specific parameter range (2-10% of the outer diameter) that provides sufficient burnt gas retention for effective NOx reduction while minimizing unnecessary material usage. This parameter optimization balances NOx reduction performance with weight reduction.
Solution Approach 2:
The concave underside features localized depth variations with a maximum rise limited to 2-10% of the outer diameter. This local quality optimization ensures adequate burnt gas retention in the circumferential cavity without uniformly increasing the entire valve's mass, achieving weight efficiency.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively reduces NOx emissions and peak combustion temperatures by conserving burnt gas with low oxygen content, minimizing the need for complex recirculation devices and optimizing exhaust valve material temperature distribution.
Implementation Method 1
the valve disc's underside that faces a combustion room is provided with a basin designed as a rotationally symmetric cavity surroundingly bordered and being downwardly open, and in which, for retention of burnt gas
Implementation Method 2
peaks of combustion temperature and herewith the generation of NOx can be reduced when some burnt gas is added to the new air filling of the combustion room
Data Source
AI summary
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).