HCCI Engine Stratified Temperature Control via Segmented EGR
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Solution Overview
Problem
Internal combustion engines operating in homogeneous-charge compression ignition (HCCI) mode face limitations in expanding their operating ranges, generating high NOx emissions, and experiencing rapid combustion and knocking due to high combustion temperatures and ignitability issues.
Innovation Solution
The engine employs a cooling and recirculation system that connects the intake and exhaust passages to create a stratified temperature distribution in the combustion chamber by reintroducing high-temperature and low-temperature exhaust gas mixtures, along with direct fuel injection, to control combustion temperatures and reduce NOx emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If internal EGR or external EGR is used to create stratified fresh intake air and recirculated exhaust gas, then fuel burning velocity is reduced, but the recirculated exhaust-gas region remains high in temperature resulting in high ignitability and interference with combustion slowdown
Solution Approach 1:
The exhaust gas recirculation system is segmented into two separate pathways: a first recirculation pathway that introduces high-temperature exhaust gas to create a high-temperature mixture region, and a second recirculation pathway that introduces cooled exhaust gas to create a low-temperature mixture region. This segmentation allows independent control of temperature and ignitability effects in different combustion chamber zones.
Solution Approach 2:
Different regions of the combustion chamber are given different local qualities by introducing high-temperature exhaust gas in one region and cooled exhaust gas in another region. This creates spatially differentiated temperature and ignitability characteristics, allowing the high-temperature region to provide energy while the low-temperature region controls overall combustion speed and prevents knocking.
2Temperature
If recirculated exhaust gas with high temperature is drawn back in the combustion chamber, then combustion temperature of concentrated charge increases, but this results in generation and exhaust of NOx emissions
Solution Approach 1:
The exhaust gas recirculation is divided into two pathways with different temperature characteristics. The first pathway provides high-temperature exhaust gas that creates localized thermal energy, while the second pathway provides cooled exhaust gas that limits overall combustion temperature. This segmentation prevents excessive NOx formation by controlling peak temperatures.
Solution Approach 2:
The system changes the temperature parameter of recirculated exhaust gas by using a cooler for the second recirculation pathway. By adjusting the temperature of recirculated exhaust gas, the system optimizes combustion efficiency while preventing NOx generation, achieving a balance between power output and emission control.
3Power
If HCCl mode is operated with high load, then power output increases, but abrupt increase in pressure due to knocking or sudden pressure increase causes noise
Solution Approach 1:
The combustion chamber is effectively segmented into regions with different mixture temperatures and ignitability characteristics. The high-temperature mixture region provides energy for power output, while the low-temperature mixture region suppresses combustion speed and prevents knocking, thereby eliminating combustion noise even at high load conditions.
Solution Approach 2:
Different local qualities are created in the combustion chamber by introducing high-temperature and cooled exhaust gas in separate regions. This spatial differentiation allows the combustion process to proceed rapidly in the high-temperature region for power generation while the low-temperature region prevents knocking and combustion noise.
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 approach expands the engine's operating range, lowers combustion temperatures, reduces NOx emissions, and prevents rapid combustion and knocking, thereby enhancing fuel economy and reducing combustion noise.
Implementation Method 1
recirculates a second part of the exhaust gas discharged in the gas exhaust passage, which flows into the recirculation passage from the gas exhaust passage, into the gas intake passage via the recirculation passage while cooling the second part of the exhaust gas
Implementation Method 2
a fuel injector that directly sprays fuel into the combustion chamber
Implementation Method 3
a homogeneous charge of air-fuel mixture is compressed by a piston in a combustion chamber of a cylinder to start ignition
Implementation Method 4
a homogeneous charge of air-fuel mixture is compressed by a piston in a combustion chamber of a cylinder to start ignition
Implementation Method 5
generating, in the combustion chamber, a stratified temperature distribution of the high-temperature mixture of the first fresh air and the first part of the exhaust gas with the high temperature and the low-temperature mixture of the second fresh air and the second part of the exhaust gas with the low temperature
Data Source
AI summary
In an internal combustion engine, a valve actuating mechanism actuates an intake valve member to open an intake port, and actuates an exhaust valve member to return a first part of exhaust gas with a high-temperature from a gas exhaust passage into a combustion chamber via an exhaust port. A cooling and recirculation system recirculates a second part of the exhaust gas from the gas exhaust passage into the gas intake passage via a recirculation passage while cooling the second part of the exhaust gas. This results in a stratified temperature distribution of a high-temperature mixture of first fresh air and the first part of the exhaust gas with the high temperature and a low-temperature mixture of second fresh air and the second part of the exhaust gas with a low temperature in the combustion chamber.