Engine Combustion Chamber Layout for Pre-Ignition Suppression
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Solution Overview
Problem
In spark ignited engines, pre-ignition occurs when operating in high load ranges, leading to reduced engine torque and potential ignition failure due to the increased distance between fuel injection and ignition, especially when fuel is injected towards the exhaust side, affecting ignitability.
Innovation Solution
A combustion chamber structure with a piston crown surface featuring a recessed cavity on the exhaust side and a reverse squish flow generation portion, allowing for efficient fuel atomization and guiding the air-fuel mixture towards the ignition plug, while maintaining the ignition plug on the intake side for cooling efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a conventional combustion chamber design is used, then manufacturing is simpler, but thermal stress and thermal fatigue damage increase due to high combustion temperatures
Solution Approach 1:
A thermal barrier coating layer is introduced as an intermediary between the combustion chamber wall and the combustion gases. This coating layer has low thermal conductivity and acts as a thermal insulator, reducing heat transfer to the chamber wall while maintaining high combustion temperatures, thereby reducing thermal stress and improving reliability
Solution Approach 2:
The combustion chamber employs a composite structure combining a metallic substrate with a ceramic thermal barrier coating. The metallic substrate provides mechanical strength while the ceramic coating provides thermal insulation, creating a composite material system that resists both mechanical loads and thermal stress
2Reliability
If a thermal barrier coating is applied, then thermal stress resistance improves, but manufacturing complexity and cost increase
Solution Approach 1:
The thermal barrier coating is designed to be self-healing through the inclusion of sacrificial oxide particles that can migrate to crack sites and seal thermal pathways, automatically repairing minor damage without external intervention and maintaining protective function over time
Solution Approach 2:
The coating system uses controlled porosity and gradient thermal conductivity profiles to optimize performance. By varying the density and composition parameters through the coating thickness, the design achieves optimal balance between thermal insulation and mechanical durability while simplifying manufacturing
3Strength
If the combustion chamber wall thickness is increased, then structural strength improves, but heat dissipation to cooling channels increases
Solution Approach 1:
The combustion chamber wall is segmented into functional zones with different thicknesses and material properties. The thermal barrier coating layer provides insulation where needed, while thinner sections with active cooling channels are positioned strategically to manage heat flow, optimizing both strength and thermal management
Solution Approach 2:
Instead of uniformly increasing wall thickness in one dimension, the design uses a multi-layered approach adding dimensions of material composition and functional layering. The thermal barrier coating adds a dimensional layer that provides thermal management without increasing the structural thickness required for strength
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 enables high-speed and homogeneous combustion throughout the combustion chamber, suppressing pre-ignition and maintaining engine torque by ensuring sufficient fuel atomization and efficient combustion even in high load operating conditions.
Implementation Method 1
The thermal barrier coating layer has a low thermal conductivity and is designed to reduce the transfer of heat from the combustion gases to the combustion chamber wall
Implementation Method 2
Combustion of the fuel/air mixture takes place in the combustion chamber, the combustion process generating combustion gases at a high temperature
Data Source
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AI summary
A structure of a combustion chamber for an engine includes a crown surface of a piston, a combustion chamber ceiling surface, an injector and an ignition plug provided on the combustion chamber ceiling surface, and an intake opening and an exhaust opening opened in the combustion chamber ceiling surface. A side where the intake opening is opened is defined as an intake port side, and a side where the exhaust opening is opened is defined as an exhaust port side, with respect to a center portion of the combustion chamber as a reference, in a plan view from one side in a cylinder axis direction. An ignition portion of the ignition plug is disposed on the intake port side. The ignition plug is ignited at a timing after the piston passes a compression top dead center. The injector is disposed on the center portion, and is configured to inject fuel toward the exhaust port side. A cavity, which is recessed in the cylinder axis direction in a region on the exhaust port side with respect to a position below the ignition portion, is provided on the crown surface of the piston. A reverse squish flow generation portion, which draws an air-fuel mixture toward the intake port side as the piston moves in an expansion stroke, is provided in the combustion chamber.