Valve-Controlled Ignition Prechamber for High EGR Combustion
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Solution Overview
Problem
Spark-ignition engines face challenges with low efficiency and increased nitrogen oxide emissions due to the use of cooled EGR, which makes it difficult to initiate and develop combustion efficiently, especially at high EGR contents, leading to misfires and reduced thermodynamic efficiency.
Innovation Solution
A valve ignition prechamber is designed to minimize the thermal load on the protruding dome, reduce pilot charge dispersion, and maintain low pilot charge pressure, featuring a stratification cavity, injector, and a valve that controls the flow between the prechamber and combustion chamber to ensure efficient ignition and combustion development.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If cooled EGR is used to dilute the charge, then thermodynamic efficiency is improved, but combustion stability deteriorates and misfires occur
Solution Approach 1:
The combustion chamber is segmented into a prechamber and a main chamber. The prechamber contains a pilot charge that is easier to ignite, and upon ignition, it generates high-temperature jets that propagate into the main chamber to ignite the diluted charge. This segmentation allows the use of cooled EGR in the main chamber while maintaining reliable combustion through the prechamber mechanism.
Solution Approach 2:
The prechamber acts as an intermediary between the spark plug and the main diluted charge. It contains a pilot charge that serves as a mediator to transfer the ignition energy from the spark plug to the main chamber, enabling stable combustion even when the main charge is heavily diluted with cooled EGR.
2Use of energy by moving object
If cooled EGR content is increased, then fuel consumption is reduced, but ignition difficulty increases and misfires occur
Solution Approach 1:
The combustion process is segmented into two stages: first, the pilot charge in the prechamber is ignited (which is easy due to its higher fuel concentration and lower EGR content), and second, the high-temperature jets from the prechamber ignite the main diluted charge. This segmentation makes ignition easier even when the main charge has high cooled EGR content.
Solution Approach 2:
The pilot charge is prepared in advance in the prechamber with optimal fuel-air mixture ratios that facilitate easy ignition. This preliminary preparation of a ignitable charge in the prechamber enables subsequent ignition of the heavily diluted main charge without direct difficulty.
3Productivity
If a prechamber is used to ignite the main charge, then combustion development is improved, but thermal load on the dome increases causing hot spots and knocking
Solution Approach 1:
The harmful thermal effects are extracted and isolated from the main combustion chamber by confining them to the prechamber. The prechamber dome absorbs the thermal load from rapid combustion, but this heat is contained within the prechamber structure rather than directly heating the main chamber dome, reducing hot spot formation and knocking in the main combustion space.
Solution Approach 2:
The prechamber dome acts as a thermal intermediary that absorbs and contains the intense heat generated during rapid combustion development. This mediator protects the main chamber dome from direct thermal exposure, preventing hot spots and knocking while still enabling rapid combustion through the jet mechanism.
4Power
If pilot charge is injected into the prechamber, then ignition efficiency is improved, but pilot charge dispersion occurs reducing effectiveness
Solution Approach 1:
The pilot charge is nested within the prechamber, which is itself nested within the main combustion chamber. This nested structure confines the pilot charge to a specific volume where it can be effectively ignited and then release its energy through controlled jets into the main chamber, preventing unwanted dispersion while maintaining high ignition power.
Solution Approach 2:
The fuel injection system is segmented to deliver the pilot charge specifically to the prechamber volume, separating the pilot charge injection function from the main charge injection. This segmentation ensures the pilot charge remains concentrated in the prechamber where it is most effective, preventing dispersion into the main chamber before ignition.
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 valve ignition prechamber enhances combustion efficiency by maintaining a stable and rapid burn of the main charge, even at high EGR contents, reducing energy consumption, and minimizing nitrogen oxide emissions, while preventing hot spots that could cause knocking.
Implementation Method 1
a valve (13) which can block all or part of the stratification duct and which presents a cavity-side face (14) subjected to the pressure of gases prevailing in the stratification cavity and a chamber-side face (15) subjected to the pressure of gases prevailing in the combustion chamber, said valve being able to translate with respect to said duct under the effect of gas pressure
Implementation Method 2
ignition means (11) which open into the stratification cavity and which can ignite the pilot charge
Implementation Method 3
a pilot charge (9) consisting of an oxidizer-fuel mixture (AF) which can be easily ignited by means of a spark
Data Source
AI summary
The valve-controlled ignition pre-chamber (1) is intended for an internal combustion engine (2) which has a combustion chamber (5) in which a main charge (30) more less diluted with a neutral gas is ignited, said prechamber (1) comprising a stratification cavity (6) into which ignition means (11) open and into which a stratification injector (8) can inject a pressurized readily-inflammable pilot charge (9), a stratification valve (13) being able to close off the stratification duct (7) in full or in part, notably under the effect of the pressure of the gases obtaining in the combustion chamber (11).