Low Pressure EGR Humidity Control via Lambda Sensor Feedback
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Solution Overview
Problem
Low Pressure EGR systems in turbocharged Diesel engines cause high relative humidity in the air path, leading to water condensation and potential damage to components like the compressor and charge air cooler, necessitating a method to estimate and regulate humidity without adding complexity or using additional sensors.
Innovation Solution
A method that calculates specific and relative humidity in the intake line using existing sensors like the lambda sensor, estimating ambient humidity, and adjusting exhaust gas flow to maintain humidity below saturation points, utilizing the Electronic Control Unit to regulate the ratio of exhaust gas flow between High Pressure and Low Pressure EGR conduits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a Low Pressure EGR conduit is added to reduce NOx emission, then the NOx emission is reduced, but the relative humidity in the air path increases causing water condensation and component damage
Solution Approach 1:
The system calculates relative humidity in the intake line by measuring O2 concentration in the exhaust line with a lambda sensor, determining specific humidity in the exhaust line, and using this information to estimate the mixing ratio of fresh air and exhaust gas. The ECU continuously monitors and adjusts the EGR valve to maintain humidity below saturation points, preventing water condensation while preserving the NOx reduction benefit.
Solution Approach 2:
The system changes the control parameter from simple exhaust gas flow rate to a composite parameter that includes relative humidity calculation. By calculating specific humidity in the exhaust line as a function of O2 concentration and determining the mixing ratio of fresh air and exhaust gas, the system adjusts the EGR valve to maintain optimal humidity levels, preventing condensation while preserving NOx reduction.
2Reliability
If the relative humidity in the air path is monitored and controlled, then water condensation and component damage are prevented, but the device complexity increases due to additional sensors and control systems
Solution Approach 1:
The system uses existing sensors already present in the engine management system, particularly the lambda sensor for measuring O2 concentration in the exhaust line. The ECU leverages its existing computational capabilities to calculate specific humidity and estimate relative humidity without requiring additional dedicated humidity sensors, thus preventing water condensation while avoiding increased hardware complexity.
Solution Approach 2:
The existing lambda sensor and ECU are made multi-functional by using them not only for their primary functions (combustion control and emissions management) but also for calculating exhaust gas humidity. This approach enables humidity monitoring and control without adding dedicated sensors or control systems, preventing water condensation while maintaining system simplicity.
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 provides a reliable estimate and regulation of relative humidity, protecting engine components from water condensation and corrosion without unnecessary costs or complexity, ensuring safe operating conditions across various engine operating conditions.
Implementation Method 1
calculating specific humidity in the exhaust line, as a function of the O2 concentration in said exhaust line
Implementation Method 2
an EGR cooler for cooling the exhaust gas before mixing it with the induction air
Implementation Method 3
an intercooler, also called a charge air cooler, located in the intake line downstream the compressor, for cooling the air stream before it reaches the intake manifold
Implementation Method 4
the air path components in the portion comprising the compressor and the charge air cooler can experience a high value of relative humidity that may even lead to water condensation in the form of water droplets
Data Source
AI summary
A method is provided for estimating the relative humidity in an intake line of an internal combustion engine provided with an intake manifold connected to the intake line, an exhaust line, and a Low Pressure EGR (LPE) conduit which fluidly connects the exhaust line to a connecting point of said intake line. The method includes, but is not limited to calculating specific humidity in the exhaust line, as a function of the O2 concentration in said exhaust line; determining ambient specific humidity; calculating specific humidity in a portion of the intake line comprised between said connecting point and said intake manifold, as a function of a flow of external air entering into said intake line, a flow of exhaust gases coming from said Low Pressure EGR (LPE) conduit, the specific humidity in said exhaust line and the ambient specific humidity; calculating the relative humidity in said portion of the intake line, as a function of the specific humidity thereof.