Engine Air-Fuel Ratio Control During Load Transients
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Solution Overview
Problem
Internal combustion engines face power lag during sudden load increases due to the limited rate of increase in intake manifold air pressure, which can lead to misfiring or improper combustion when additional compressed air is introduced, especially in gaseous fuel engines burning homogeneous air-fuel mixtures.
Innovation Solution
A system comprising a primary air supply unit, such as a turbocharger, and a secondary air supply unit with an air reservoir and valve, controlled by a controller to selectively introduce compressed air into the intake conduit, maintaining the air-fuel ratio within specific thresholds to quickly increase engine power without causing lean or rich mixtures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If additional compressed air is introduced to quickly increase engine power during sudden load increase, then the response time is improved, but the air-fuel ratio becomes leaner causing misfiring or improper combustion
Solution Approach 1:
An air reservoir is introduced as an intermediary component between the compressor and the engine intake. The reservoir acts as a buffer that can quickly discharge compressed air when needed, decoupling the slow compressor response from the immediate power increase requirement. This allows rapid air delivery without directly disrupting the air-fuel mixing process, thereby maintaining combustion stability while achieving fast response.
Solution Approach 2:
The air reservoir is pre-filled with compressed air during periods when the compressor has excess capacity or when the engine is operating at lower loads. This preliminary accumulation of compressed air ensures that when a sudden load increase occurs, the required additional air is already available in the reservoir, eliminating the delay associated with compressor spool-up and allowing immediate power increase without compromising the air-fuel ratio.
2Speed
If the compressor speed is increased to quickly raise intake manifold air pressure, then the power increase rate is improved, but the time required for compressor acceleration increases due to inherent inertia
Solution Approach 1:
The air reservoir is pre-filled with compressed air during periods when the compressor has excess capacity or when the engine is operating at lower loads. This preliminary accumulation of compressed air ensures that when a sudden load increase occurs, the required additional air is already available in the reservoir, eliminating the delay associated with compressor spool-up and allowing immediate power increase without compromising the air-fuel ratio.
Solution Approach 2:
The air reservoir serves as an intermediary storage device that decouples the compressor's slow response characteristics from the engine's immediate power requirements. By storing compressed air in advance, the system can deliver air rapidly without requiring the compressor to accelerate quickly, thus overcoming the compressor's inertial limitations.
3Power
If more air is supplied to meet increased fuel demand, then the power output is improved, but the air-fuel ratio control becomes more difficult to maintain within optimal thresholds
Solution Approach 1:
A controller continuously monitors the air-fuel ratio and adjusts the valve controlling air reservoir discharge accordingly. When the air-fuel ratio approaches the lean threshold, the controller modulates the amount of additional air from the reservoir to maintain the ratio within optimal bounds. This feedback control mechanism simplifies the overall system by automatically managing air-fuel balance during transient conditions, reducing the complexity of manual or open-loop control approaches.
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 system enables rapid power increase during transient loads by controlling the introduction of additional air to maintain optimal air-fuel ratios, reducing power lag and minimizing misfiring or knocking, while ensuring efficient engine operation.
Implementation Method 1
The engine having a turbocharger may increase the intake manifold air pressure by controlling a compressor
Implementation Method 2
One approach for quickly increasing the intake manifold air pressure is by using an additional air storage unit to provide additional compressed air
Implementation Method 3
A system comprising a primary air supply unit, such as a turbocharger, and a secondary air supply unit with an air reservoir and valve, controlled by a controller to selectively introduce compressed air into the intake conduit
Implementation Method 4
Internal combustion engines often experience sudden increase in loads during operation
Data Source
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AI summary
A method for operating an engine (100a,100) is disclosed. The engine (100a,100) includes an intake conduit (110) configured to supply air to the engine(100a,100), a primary air supply unit (102) configured to supply air to the intake conduit (110), a secondary air supply unit (104) configured to selectively supply air to the intake conduit (110). The method discloses selectively controlling supply of air from the secondary air supply unit (104) to the intake conduit (110) such that air fuel ratio is maintained between a first threshold value and second threshold value during increase in engine (100a,100) load.