Low Temperature Reductant Dosing in Diesel Exhaust Systems
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Solution Overview
Problem
Existing diesel exhaust systems face challenges in managing reductant dosing at low temperature operating conditions, leading to reductant buildup and excessive NOx emissions, as continuous reductant injection is ineffective and discontinuous injection fails to meet emission limits.
Innovation Solution
A system and method that modulates the flow rate of reductant in the exhaust aftertreatment system using a controller to determine the quantity and duration of reductant injection based on temperature and flow rate sensors, employing pulsed injections and adjusting the dosing cycle dynamically in response to mid-bed SCR catalyst temperature, exhaust flow rate, and other conditions to optimize NOx reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If reductant is injected at a continuous rate during low temperature operating conditions, then NOx emissions are reduced, but reductant buildup and reductant slip occur
Solution Approach 1:
The system implements periodic pulsed injections of reductant instead of continuous injection during low temperature operation. The controller delivers reductant in a series of pulses with specific duty cycles, where the total quantity over the dosing cycle equals what would be injected continuously, but distributed in intermittent bursts that prevent buildup while maintaining NOx reduction effectiveness.
Solution Approach 2:
The dosing system dynamically adjusts the pulsed injection parameters (pulse width, frequency, duty cycle) based on real-time temperature measurements from the mid-bed SCR catalyst temperature sensor. As temperature varies during low temperature operation, the controller modifies the pulsed dosing characteristics to optimize both NOx reduction and prevent reductant accumulation.
2Quantity of substance
If reductant is not injected at low operating conditions, then reductant buildup is prevented, but NOx emissions exceed required limitations
Solution Approach 1:
By using periodic pulsed injections rather than continuous injection, the system prevents reductant buildup through the intermittent delivery pattern while still providing sufficient total reductant quantity over each dosing cycle to maintain NOx emissions below regulatory limits.
Solution Approach 2:
The system changes the dosing parameter from continuous flow to pulsed flow with specific duty cycles. This parameter change allows the same total reductant quantity to be delivered in a manner that prevents accumulation in the exhaust stream, while the timing and distribution of pulses ensure adequate NOx reduction throughout the low temperature operating period.
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 effectively reduces NOx emissions by optimizing reductant injection patterns, preventing reductant buildup, and ensuring compliance with emission limits even at low temperature conditions, thereby enhancing the performance of diesel exhaust systems.
Implementation Method 1
SCR systems typically include a reductant storage tank connected to a doser that injects reductant into the exhaust stream to reduce NOx emissions
Data Source
AI summary
System, apparatus, and methods are disclosed for reductant dosing in an exhaust aftertreatment system. A dynamic flow rate and injection duration of a reductant injected from a reductant dosing system to the exhaust aftertreatment system is controlled in response to a dosing command when the exhaust system is operating in a low temperature operating condition.