Engine Intake Valve Timing Control for Lean Combustion Stability
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Solution Overview
Problem
Current engine technologies face challenges in achieving stable partial compression-ignition combustion, particularly under air-fuel lean environments, where flame propagation stability is difficult to maintain, leading to reduced fuel efficiency and combustion instability.
Innovation Solution
A control system that adjusts the open and close timings of the intake valve and exhaust valve to manage the air-fuel ratio and in-cylinder temperature, using advanced valve timing mechanisms to ensure stable spark-ignition combustion, which in turn supports stable compression-ignition combustion, even at lower engine loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the air-fuel ratio is increased to improve fuel efficiency and reduce emissions, then fuel efficiency improves, but flame propagation stability deteriorates making SI combustion unstable
Solution Approach 1:
The combustion process is segmented into two distinct phases: SI combustion for part of the mixture gas and CI combustion for the remaining mixture gas. This segmentation allows the engine to operate with a lean air-fuel ratio for improved fuel efficiency while the SI combustion portion provides stable flame propagation to initiate the combustion process, and the CI combustion portion completes the combustion without requiring stable flame propagation across the entire mixture
Solution Approach 2:
The invention changes the combustion mode parameter from traditional SI combustion to a dual-mode SPCCI combustion, transitioning from relying solely on flame propagation to combining flame propagation with self-ignition. This parameter change enables stable combustion at lean air-fuel ratios by using the CI combustion component which does not depend on flame propagation stability
2Temperature
If the in-cylinder temperature is increased to promote CI combustion, then CI combustion occurs more readily, but excessive temperature causes early CI combustion and reduces fuel efficiency
Solution Approach 1:
The control device uses feedback from detected engine operating conditions (temperature, pressure, load) to dynamically adjust the injection timing and amount of second fuel injection. This feedback control ensures that the in-cylinder temperature is maintained within an optimal range that promotes CI combustion without causing excessive temperature rise that would lead to early combustion and reduced fuel efficiency
Solution Approach 2:
The invention dynamically adjusts the combustion parameters including the timing and amount of second fuel injection based on real-time engine operating conditions. This dynamic control allows the system to optimize the balance between promoting CI combustion and preventing excessive temperature rise, adapting to changing engine loads and temperatures to maintain peak fuel efficiency
3Reliability
If the close timing of the intake valve is retarded to increase the amount of burnt gas in the cylinder, then combustion stability improves, but in-cylinder temperature increases causing early CI combustion
Solution Approach 1:
The control device dynamically adjusts the intake valve close timing based on detected engine operating conditions. This dynamic adjustment allows the system to optimize the trade-off between maintaining combustion stability (by retaining burnt gas) and controlling in-cylinder temperature (to prevent early CI combustion). The timing is varied with engine load and temperature to maintain optimal combustion characteristics across different operating ranges
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 enhances fuel efficiency and combustion stability by maintaining a higher air-fuel ratio, increasing the amount of burnt gas in the cylinder, and optimizing valve timings to prevent excessive in-cylinder temperature and early CI combustion, thereby improving overall engine performance.
Implementation Method 1
a spark plug configured to ignite a mixture gas containing the fuel injected by the injector and air. The engine executes partial compression-ignition combustion in which the mixture gas is spark-ignited with the spark plug to be partially combusted by spark ignition (SI) combustion
Implementation Method 2
The in-cylinder pressure on the compression stroke when the SPCCI combustion is carried out is increased by compression work of a piston
Implementation Method 3
the remaining mixture gas is combusted by self-ignition (CI combustion)
Data Source
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AI summary
A control system for a compression-ignition engine includes an intake variable mechanism and a controller. In a second operating range, the controller controls the intake variable mechanism so that, while partial compression-ignition combustion is performed under an air-fuel ratio (A/F) lean environment, an intake valve open timing takes timing at an advanced side of an exhaust TDC. In a first operating range on a lower load side, the controller controls the intake variable mechanism so that, while the partial compression-ignition combustion is performed under the A/F lean environment, under the same engine speed condition, the intake valve close timing is more retarded within a range on a retarded side of an intake BDC as the engine load decreases, and an absolute value of a change rate of the intake valve close timing to the engine load becomes larger than in the second range.