Diesel Engine NH3 Sensor Control for Low-Pressure EGR
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Solution Overview
Problem
In diesel engines, high levels of ammonia (NH3) can be recirculated during low-pressure exhaust gas recirculation, leading to undesired emissions and increased urea consumption, especially when the SCR-combined diesel particulate filter is hot or under real driving conditions.
Innovation Solution
Measuring the NH3 concentration downstream of the SCR-combined diesel particulate filter and adjusting the low-pressure exhaust gas recirculation rate accordingly, while also using NH3 and NOx sensors to control urea dosing and optimize urea consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If low-pressure exhaust gas recirculation is performed with the exhaust gas recirculation conduit branching off downstream of the SCR-combined diesel particulate filter, then CO2 reduction is improved, but ammonia recirculation occurs leading to undesired emissions and elevated urea consumption
Solution Approach 1:
The system uses NH3 sensors to continuously monitor ammonia concentration in the exhaust gas downstream of the SCR-combined diesel particulate filter. Based on these measurements, the control unit dynamically adjusts the exhaust gas recirculation rate to maintain optimal operation. This feedback mechanism prevents excessive ammonia recirculation while preserving CO2 reduction benefits.
Solution Approach 2:
The system dynamically changes the exhaust gas recirculation rate parameter based on measured NH3 concentration levels. When ammonia levels are high, the recirculation rate is reduced or suspended. When ammonia levels are low, recirculation is permitted to continue, thereby optimizing both emissions reduction and urea consumption under varying operating conditions.
2Loss of energy
If high low-pressure exhaust gas recirculation rate is used, then CO2 reduction is improved, but ammonia recirculation increases leading to elevated urea consumption
Solution Approach 1:
NH3 sensors provide continuous feedback on ammonia concentration levels. The control unit uses this information to adjust the exhaust gas recirculation rate, preventing situations where high recirculation rates would cause excessive ammonia recirculation and urea consumption. This ensures urea is consumed efficiently only when needed for NOx reduction.
Solution Approach 2:
The system dynamically adjusts the exhaust gas recirculation rate parameter based on real-time NH3 measurements. By changing this parameter according to actual ammonia levels, the system optimizes the balance between CO2 reduction and urea consumption, avoiding unnecessary urea usage while maintaining emissions control effectiveness.
3Device complexity
If NH3 concentration is not monitored, then system complexity is reduced, but precise control of exhaust gas recirculation cannot be achieved
Solution Approach 1:
NH3 sensors are installed in the exhaust gas stream downstream of the SCR-combined diesel particulate filter to provide continuous concentration measurements. This feedback information enables precise control of the exhaust gas recirculation rate, ensuring optimal emissions control and urea consumption while justifying the added system complexity through significant performance benefits.
Solution Approach 2:
The system replaces mechanical or indirect control methods with sensor-based electronic measurement and control. NH3 sensors provide direct, precise measurement of ammonia concentration, enabling sophisticated electronic control of the exhaust gas recirculation system, which is more precise and adaptable than traditional mechanical 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
This approach allows for precise control of exhaust gas recirculation, reducing unwanted emissions and minimizing urea consumption by adjusting recirculation rates based on NH3 levels, thereby optimizing engine performance.
Implementation Method 1
In the case of appropriate combination with a diesel particulate filter/appropriate integration the diesel particulate filter may comprise an SCR coating for example. In the method of selective catalytic reduction (SCR) an aqueous urea solution is continuously injected into the exhaust gas stream to reduce nitrogen oxides and form carbon dioxide and ammonia by hydrolysis. Ammonia reacts with the nitrogen oxides in the exhaust gas over the SCR catalyst/SCR-combined diesel particulate filter to afford elemental nitrogen N2 and water.
Implementation Method 2
an aqueous urea solution is continuously injected into the exhaust gas stream to reduce nitrogen oxides and form carbon dioxide and ammonia by hydrolysis
Implementation Method 3
the exhaust gas systems of diesel engines increasingly employ a diesel particulate filter having an integrated SCR catalyst (SDPF). An SCR catalyst is a catalyst which performs a selective catalytic reduction. In the case of appropriate combination with a diesel particulate filter/appropriate integration the diesel particulate filter may comprise an SCR coating for example.
Implementation Method 4
Such SCR-combined diesel particulate filters are employed ever more often, in particular in combination with a downstream SCR catalyst in order to reduce emissions both during the warm-up phase of the engine and during low-load operation (town driving) and high-load operation (motorway driving).
Data Source
AI summary
Various embodiments include a method of operating a diesel engine having an exhaust tract and an SCR-combined diesel particulate filter in the exhaust tract, wherein an aqueous urea solution is introduced into the exhaust tract, and an exhaust gas recirculation apparatus having an exhaust gas recirculation conduit branching off downstream of the SCR-combined diesel particulate filter for performing a low-pressure exhaust gas recirculation comprising: measuring an NH3 concentration in exhaust gas downstream of the SCR-combined diesel particulate filter; and upon exceeding a threshold value of the measured NH3 concentration, reducing the low-pressure exhaust gas recirculation rate based at least in part on the measured NH3 concentration.