Engine Control System for Stable SPCCI Mode Transitions
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Solution Overview
Problem
Existing engine control systems face challenges in maintaining stable combustion efficiency and reducing NOx emissions during mode changes between SPCCI combustion modes, particularly due to fluctuations in EGR gas amounts, which affect flame propagation and in-cylinder temperature.
Innovation Solution
A control system that adjusts the EGR gas amount before mode changes, ensuring the air-fuel ratio is optimized at the stoichiometric or slightly leaner levels, and uses a three-way catalyst to purify exhaust gases, while adjusting the throttle valve and fuel injection to maintain constant torque and stabilize SI combustion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the air-fuel ratio is made leaner to reduce NOx emissions and improve thermal efficiency, then fuel efficiency is improved, but stable SI combustion becomes difficult to maintain, especially under low water temperature or low intake air temperature conditions
Solution Approach 1:
The system dynamically changes the air-fuel ratio parameter based on operating conditions. Under normal conditions, a lean air-fuel ratio (25:1 or higher) is used to maximize fuel efficiency and reduce NOx emissions. When water temperature or intake air temperature is low, the system transitions to a stoichiometric air-fuel ratio to ensure stable SI combustion, thereby resolving the contradiction between fuel efficiency and combustion stability through parameter adaptation.
2Loss of energy
If EGR gas amount is increased to improve fuel efficiency through CI combustion, then thermal efficiency is improved, but flame propagation speed of SI combustion decreases, making it difficult to reach ignition temperature
Solution Approach 1:
The EGR gas amount is dynamically adjusted based on the combustion mode and operating conditions. During SPCCI combustion under normal conditions, EGR gas is introduced to improve thermal efficiency by promoting CI combustion. However, when SI combustion stability is compromised or under low temperature conditions, the EGR gas amount is reduced or eliminated to ensure adequate flame propagation speed, thus dynamically balancing thermal efficiency and flame propagation requirements.
3Adaptability or versatility
If mode change is performed quickly to respond to operating conditions, then adaptability is improved, but torque shocks occur and combustion stability deteriorates during transition
Solution Approach 1:
Before executing a mode change, the system performs preliminary adjustments to the air-fuel ratio and EGR gas amount. This preliminary action ensures that the combustion parameters are gradually transitioned to the target state, preventing abrupt changes that would cause torque shocks or combustion instability. The gradual transition maintains combustion stability while still achieving timely mode changes in response to operating conditions.
4Reliability
If stoichiometric air-fuel ratio is used to ensure stable SI combustion under low temperature conditions, then combustion stability is improved, but NOx emissions increase and three-way catalyst purification is required
Solution Approach 1:
The system applies different air-fuel ratio strategies to different operating conditions. Under low water temperature or low intake air temperature conditions, a stoichiometric air-fuel ratio is locally applied to ensure stable SI combustion. Under normal operating conditions, a lean air-fuel ratio is applied to reduce NOx emissions and improve fuel efficiency. This localized quality adjustment resolves the contradiction by matching the air-fuel ratio to the specific operating context.
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 maximizes thermal efficiency and fuel efficiency by stabilizing SI combustion, reducing NOx emissions, and preventing torque shocks during mode transitions, thereby improving overall engine performance.
Implementation Method 1
uses a three-way catalyst to purify exhaust gases
Implementation Method 2
an EGR passage 52 connected between the intake passage 40 and the exhaust passage 50, and an EGR valve 54 disposed in the EGR passage 52
Implementation Method 3
a pressure buildup by a compression work of a piston during a compression stroke
Implementation Method 4
SI (Spark Ignition) combustion is combustion accompanied by the flame propagation started by forcibly igniting the mixture gas inside a combustion chamber
Implementation Method 5
unburnt mixture gas inside the combustion chamber then combusts by compression ignition due to a pressure buildup caused by generation of heat and flame propagation of SI combustion
Data Source
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AI summary
A control system for a compression ignition engine is provided, which includes a combustion chamber, a throttle valve, an injector, an ignition plug, an EGR system, a sensor device and a controller. The controller includes a first mode module, a second mode module and a changing module configured to change an engine mode from a first mode to a second mode in response to a change demand. The changing module outputs signals to the throttle valve and the injector in response to the demand so that an air-fuel ratio of mixture gas becomes a stoichiometric air-fuel ratio or a substantially stoichiometric air-fuel ratio, and outputs a signal to the EGR system so that an EGR gas amount decreases more than before the demand, and when the EGR gas amount is determined to be decreased to a given amount, the changing module permits that the second mode module starts the second mode.