NOx Slip Detection via Differential Sensor Analysis
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Solution Overview
Problem
Existing exhaust systems for internal combustion engines, particularly diesel engines, face challenges in accurately detecting ammonia (NH3) slip due to varying engine conditions, which affects the efficiency of urea dosing for NOx reduction, leading to unutilized NH3 passing through catalysts.
Innovation Solution
A method involving an exhaust system with upstream and downstream NOx sensors, a urea injector, and an engine control unit, where predetermined doses of NH3 are administered to calculate the NOx to NH3 ratio by measuring NOx levels before and after a catalyst, using a lookup table to determine the relative ratio, potentially with additional catalysts and temperature sensors for improved accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If NH3 slip detection is implemented using traditional NH3 sensors, then detection accuracy is improved, but system cost and complexity increase
Solution Approach 1:
The patent uses NOx sensors as intermediary devices to indirectly detect NH3 slip. By measuring NOx levels upstream and downstream of the catalyst and analyzing the difference, the system infers NH3 slip without requiring direct NH3 sensing. This intermediary approach maintains detection capability while avoiding the complexity and cost of dedicated NH3 sensors.
Solution Approach 2:
The invention creates a virtual representation of NH3 slip detection by using existing NOx sensor data. Instead of physically installing NH3 sensors, the system copies the detection function through computational analysis of NOx measurements, using lookup tables and algorithms to translate NOx differential readings into NH3 slip information.
2Productivity
If accurate NH3 slip detection is achieved, then urea dosing optimization is improved, but system cost increases due to requiring additional sensors
Solution Approach 1:
The patent makes existing NOx sensors perform multiple functions: their primary function of monitoring NOx emissions is enhanced with a secondary function of detecting NH3 slip. By analyzing the differential readings between upstream and downstream NOx sensors, the system extracts additional information about catalyst efficiency and NH3 slip without requiring dedicated sensors for each function.
Solution Approach 2:
The existing sensor infrastructure serves itself by providing dual functionality. The NOx sensors already installed in the exhaust system automatically provide data for both emissions monitoring and NH3 slip detection, eliminating the need for additional sensing components and reducing overall system cost.
3Difficulty of detecting and measuring
If larger NH3 doses are used for detection, then signal detection ease is improved, but NH3 consumption increases
Solution Approach 1:
The system uses periodic pulse dosing of NH3 rather than continuous dosing. By administering controlled pulses of NH3 and measuring the transient response of the catalyst through differential NOx sensing, the system achieves sufficient signal strength for detection while minimizing total NH3 consumption. The periodic nature allows the system to accumulate detection data over time with minimal substance input.
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 method allows for efficient detection of NH3 slip and optimized urea dosing, reducing NOx levels and pollutant output while minimizing system complexity and cost by utilizing existing sensors, thereby enhancing the chemical efficiency and reducing pollutant emissions.
Implementation Method 1
a chemical reaction in the catalysts causes the decomposition of NOx, NH3 (ammonia) and water, in reaction with catalytic coatings in a catalyst convert NOx into Nitrogen and water
Implementation Method 2
a chemical reaction in the catalysts causes the decomposition of NOx, NH3 (ammonia) and water
Implementation Method 3
Measuring a first NOx level at the upstream NOx sensor; Measuring a second NOx level at the downstream NOx sensor
Data Source
Figure 1
AI summary
There is described a method for calculating the relative ratios of NH3 and NOx in exhaust gases to detect NH3 slip using NOx sensors.