EGR Control System Managing Compressor Surge and NOx Trade-offs
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Solution Overview
Problem
The existing exhaust recirculation gas systems in diesel engines, comprising both low pressure (LP-EGR) and high pressure (HP-EGR) systems, face challenges in managing emission control under new homologation cycles like WLTP and RDE, which require extended operating ranges without hardware upgrades, often exceeding temperature and space velocity limits, leading to potential compressor surge and suboptimal after-treatment conditions.
Innovation Solution
A method to optimize the rate split between LP-EGR and HP-EGR by temporarily adjusting the LP-EGR ratio based on compressor, after-treatment, and intake manifold parameters, ensuring constant total EGR rate, thereby managing emission levels and preventing compressor surge while optimizing space velocity and temperature for effective NOx trapping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the EGR rate is increased to reduce NOx emissions, then emission control is improved, but compressor surge risk increases and after-treatment operating parameters are exceeded
Solution Approach 1:
The patent implements dynamic adjustment of the LP-EGR ratio based on real-time verification of compressor operating parameters (pressure ratio, inlet humidity, outlet temperature) and after-treatment parameters (exhaust gas temperature, space velocity). The control system continuously monitors these parameters and temporarily adjusts the LP-EGR ratio to maintain operation within safe limits while achieving emission reduction goals.
Solution Approach 2:
The patent changes the physical parameters of the EGR system by temporarily adjusting the LP-EGR ratio rather than maintaining a fixed total EGR rate. This parameter adjustment allows the system to respond to varying operating conditions, preventing compressor surge and after-treatment parameter exceedance while still reducing NOx emissions through optimized EGR distribution between HP-EGR and LP-EGR pathways.
2Adaptability or versatility
If the operating range is extended to cover new homologation cycles (WLTP, RDE), then adaptability is improved, but operating limits (temperature, space velocity, pressure ratio) are frequently exceeded
Solution Approach 1:
The patent implements a feedback control mechanism that continuously verifies compressor parameters (pressure ratio, inlet humidity, outlet temperature) and after-treatment parameters (exhaust gas temperature, space velocity at LNT inlet). Based on this feedback, the system temporarily adjusts the LP-EGR ratio to ensure operation remains within optimal parameter ranges even when operating in extended ranges required by new homologation cycles like WLTP and RDE.
3Manufacturing precision
If the LP-EGR ratio is increased to optimize after-treatment parameters, then space velocity and temperature control are improved, but compressor inlet humidity and outlet temperature limits may be exceeded
Solution Approach 1:
The patent dynamically adjusts the LP-EGR ratio based on real-time verification of multiple parameters including compressor pressure ratio, inlet humidity, and outlet temperature. This dynamic control allows the system to optimize after-treatment parameters (space velocity and temperature at LNT inlet) while simultaneously preventing compressor parameter exceedance, adapting the EGR distribution in response to changing operating conditions.
Data Source
AI summary
A method of controlling an exhaust gas recirculation system of an internal combustion engine is disclosed. The engine includes a compressor, an intake manifold, an after-treatment system, a low pressure EGR system and a high pressure EGR system. The method temporarily adjusts a low pressure EGR ratio, keeping constant a total EGR rate, after verifying at least one among compressor parameters, after-treatment system parameters or intake manifold parameter.