EGR Rate Measurement via Turbine Mass Flow Difference
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Solution Overview
Problem
Current methods for measuring and controlling the EGR rate in combustion engines face challenges such as accuracy issues, time delays, and sensor deterioration due to aggressive environments, particularly with soot deposits, which affect the precision and reliability of NOx emission control.
Innovation Solution
The method determines the EGR rate using pressure and temperature sensors by calculating the difference between the total exhaust gas mass flow across the cylinders and the turbine mass flow, employing models based on pressure sensors and temperature readings, and utilizing an adaptation algorithm to improve accuracy and account for changes in flow resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If direct EGR mass flow measurement devices are used, then measurement accuracy is improved, but sensor deterioration due to soot deposits and aggressive environment occurs
Solution Approach 1:
The patent uses an intermediary calculation approach based on the turbine mass flow and total exhaust gas mass flow difference, rather than direct measurement in the aggressive EGR environment. This intermediary method avoids placing sensors directly in the soot-laden EGR stream, thereby maintaining measurement accuracy without exposing sensors to deteriorating conditions.
Solution Approach 2:
The patent replaces direct mechanical/EGR-flow-based measurement systems with a calculation-based system using turbine parameters. By substituting direct measurement with indirect calculation using turbine mass flow data, the system achieves accurate EGR measurement without the reliability issues of direct sensing in harsh environments.
2Device complexity
If fresh air mass flow measurement is used, then device complexity is reduced, but measurement accuracy deteriorates due to error amplification
Solution Approach 1:
The patent introduces an intermediary measurement point at the turbine, where mass flow is measured under more stable conditions. This intermediary measurement avoids the error amplification problem of subtracting large fresh air flow from total flow, as the turbine measurement provides a more reliable baseline for calculating EGR mass flow.
3Ease of operation
If oxygen sensors are used for EGR rate measurement, then direct EGR rate calculation is enabled, but measurement accuracy is insufficient especially at low EGR rates
Solution Approach 1:
The patent replaces oxygen sensor-based chemical measurement with a mass flow calculation approach based on turbine parameters. This substitution provides more accurate EGR rate calculation, particularly at low EGR rates where oxygen sensors struggle, while still enabling direct EGR rate determination through the mass flow difference method.
4Measurement precision
If pressure drop measurement over EGR line is used, then EGR mass flow can be obtained, but measurement stability deteriorates due to changing flow resistance
Solution Approach 1:
The patent performs preliminary measurement of mass flow at the turbine before the EGR flow returns to the engine. By measuring at this upstream point and calculating EGR flow as the difference between total exhaust and turbine flow, the system avoids the stability issues of downstream pressure drop measurements where flow resistance characteristics change over time due to soot accumulation.
Data Source
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AI summary
The present invention provides for a method and apparatus for measuring and controlling the EGR rate in a combustion engine system, comprising an EGR cooler, an EGR valve and a turbine, and determining the EGR mass flow (dmEGR) from the difference between the total exhaust gas mass flow (dmTot) across the engine cylinders, and the turbine mass flow (dmTurb) across the turbine.