Piston Crown Cavity and Raised Portions for Engine Combustion Flow Control
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Solution Overview
Problem
In high compression ratio engines, it is challenging to maintain swirl and tumble flows until the later period of the compression stroke, which is essential for improving combustion properties in partial compression ignition combustion (SPCCI) modes.
Innovation Solution
A combustion chamber structure with a pent roof-shaped ceiling surface and a crown surface on the piston, featuring a bowl-shaped cavity and mound-shaped raised portions, where the ratio of the height of the raised portions to the cavity diameter (H1/D) is set between 0.05 and 0.36, facilitating the maintenance of swirl and tumble flows.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high compression ratio of 15 or more is used to enable SPCCI combustion, then CI combustion can be easily caused, but it becomes difficult to maintain swirl flow until the later period of the compression stroke
Solution Approach 1:
The invention applies local quality by creating raised portions with specific geometric characteristics (height H1, diameter D) at localized positions on the piston crown surface. These raised portions have controlled dimensions (H1/D ratio between 0.05 and 0.36) that locally modify the flow characteristics to maintain swirl flow while accommodating the high compression ratio environment.
Solution Approach 2:
The invention changes geometric parameters of the combustion chamber by introducing raised portions with specific height-to-diameter ratios. By controlling H1/D within the range of 0.05 to 0.36, the design optimizes the balance between maintaining high compression ratio (for CI combustion) and preserving swirl flow characteristics throughout the compression stroke.
2Device complexity
If a conventional combustion chamber structure is used, then the design is simple, but both tumble flow and swirl flow cannot be maintained satisfactorily until the later period of the compression stroke
Solution Approach 1:
The invention maintains relative structural simplicity while introducing localized raised portions on the piston crown surface. These localized features (with specific H1/D ratios) provide the necessary flow control functionality without requiring a complete redesign of the entire combustion chamber structure, thus balancing simplicity with improved flow maintenance.
3Stability of the object's composition
If the height of raised portions H1 is increased relative to cavity diameter D, then swirl flow maintenance is improved, but the geometrical compression ratio decreases
Solution Approach 1:
The invention optimizes the parameter relationship between raised portion height H1 and cavity diameter D by establishing a specific ratio range (H1/D between 0.05 and 0.36). This parameter optimization allows the design to achieve adequate swirl flow maintenance while preserving the required geometrical compression ratio of 15 or more for SPCCI combustion.
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
This configuration allows for the effective maintenance of both swirl and tumble flows until the later compression stroke, enhancing combustion efficiency and ensuring a geometrical compression ratio of 15 or more, necessary for SPCCI combustion.
Implementation Method 1
a swirl flow can be maintained until a later period of a compression stroke
Implementation Method 2
partial compression ignition combustion in which mixture gas combusts by flame propagation and then combusts by compression ignition
Data Source
AI summary
A combustion chamber structure for an engine includes a combustion chamber where SI combustion by spark ignition and CI combustion by self-ignition are conducted. A crown surface includes a cavity recessed to have a bowl-shape, and a pair of raised portions. The cavity includes a bottom portion which is a lower region of the recessed part, the bottom portion having an outer circumferential edge which is circular in a top view. With a height of the raised portion relative to a height position of a deepest portion of the cavity being represented as H1 and a diameter of an outer circumferential edge of the bottom portion of the cavity being represented as D, H1/D as a ratio of the height H1 of the raised portion to the diameter D of the cavity is set to be in a range of 0.05 or more and 0.36 or less.