Dual-Recess Piston Crown for Stratified Charge Combustion
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Solution Overview
Problem
Existing fuel injection systems for spark-ignited cylinder engines face challenges in achieving improved ignitability and combustion stability during stratified charge combustion while maintaining performance during uniform combustion.
Innovation Solution
A fuel injection apparatus with a piston featuring a first recess for enhancing gas flow and a second recess with straight guide steps to deflect fuel sprays and form a rich air-fuel mixture around the ignition plug, where at least 50% of the last fuel injection is directed into the second recess during the compression stroke.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a recess is formed on the piston crown surface to form a rich air-fuel mixture area around the ignition plug for stratified charge combustion, then ignitability and combustion stability are improved, but uniform combustion performance deteriorates due to uneven air-fuel ratio distribution
Solution Approach 1:
The piston crown surface is segmented into multiple recesses with different depths: a first recess with a greater depth and a second recess with a smaller depth. This segmentation allows different regions to serve different functions - the first recess promotes stratified charge combustion while the second recess helps maintain uniform air-fuel ratio distribution, thus resolving the contradiction between combustion stability and air-fuel uniformity.
Solution Approach 2:
Different regions of the piston crown surface are given different local qualities through varying recess depths. The first recess creates a deeper cavity for rich mixture formation around the ignition plug, while the second recess provides a shallower cavity for more uniform mixture distribution. This local differentiation allows simultaneous optimization of both stratified charge combustion and uniform combustion performance.
2Reliability
If a deep cavity is provided on the piston to enhance stratified charge combustion, then ignitability is improved, but device complexity increases and manufacturing difficulty increases
Solution Approach 1:
Instead of providing a single deep cavity, the piston crown surface is segmented into multiple recesses with different depths. The first recess provides the necessary depth for ignitability improvement, while the second recess with smaller depth simplifies the overall structure and eases manufacturing. This segmentation resolves the contradiction between ignitability and structural simplicity.
3Reliability
If fuel injection is optimized for stratified charge combustion, then combustion stability is improved, but performance during uniform combustion deteriorates
Solution Approach 1:
The dual-recess piston structure serves multiple functions: the first recess enables stratified charge combustion for improved combustion stability, while the second recess contributes to uniform combustion performance. This multi-functionality allows the same piston structure to optimize for both combustion modes, resolving the contradiction between combustion stability and engine performance.
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 improves ignitability and combustion stability during stratified charge combustion and ensures stable uniform combustion by forming a rich air-fuel mixture around the ignition plug, maintaining the air-fuel ratio within an allowable range.
Implementation Method 1
an injector that is disposed at a position offset from the ignition plug toward the intake port and injects a fuel spray toward a crown surface of the piston
Implementation Method 2
forming an air-fuel-mixture rich area in a periphery of an ignition plug is required at the time of ignition, which enables desirable stratified charge combustion
Data Source
AI summary
A fuel injection apparatus includes: an injector disposed at a position offset from an ignition plug toward an intake port and injecting a fuel spray toward a crown surface of a piston, and an injection controller causing the injector to perform injection in accordance with an amount and timing of fuel injection preset in accordance with an operating state of an engine. The piston includes: a first recess formed by recessing a central portion of the crown surface and a second recess formed by recessing part of the first recess on an injector side further than the first recess. The injector injects 50% or more of fuel to be injected for the last fuel injection toward the second recess during a compression stroke, and injects part of the fuel to be injected for the last fuel injection toward an area of the first recess other than the second recess.