Constant Volume SCR Injection for NOx Reduction
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Solution Overview
Problem
Fixed interval, variable amount selective catalytic reduction (SCR) systems for internal combustion engines face inaccuracies in reductant dosing, excessive reductant deposit formation, and increased complexity due to continuous spraying, leading to inefficiencies and higher costs.
Innovation Solution
Implementing a system with multiple reductant injectors that deliver constant volume pulses of reductant at variable time intervals based on NOx content, using a controller to adjust the timing and prevent reductant deposits and films by spreading the reductant over a larger area or alternating between injectors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single reductant injector continuously sprays reductant into the exhaust component, then the reductant is delivered continuously to treat NOx, but localized cold spots form on the component wall where reductant contacts the component, inhibiting reductant breakdown into ammonia
Solution Approach 1:
The patent divides the continuous spray into multiple discrete injection events distributed over time. Instead of one continuous injection stream creating localized cold spots, the system uses multiple smaller injection events that spread the reductant delivery across different locations and times, allowing the component surface to recover heat between injections and preventing persistent cold spots that inhibit ammonia formation
Solution Approach 2:
The patent implements periodic injection events rather than continuous spraying. The controller is configured to inject reductant at multiple discrete time intervals, creating a periodic injection pattern. This periodic action allows the exhaust component surface to return to higher temperatures between injection events, preventing the formation of persistent cold spots while still maintaining continuous NOx treatment through the cumulative effect of multiple injection events
2Adaptability or versatility
If a fixed interval, variable amount SCR system is used, then the system can adapt to different engine operating conditions, but the system requires sophisticated controllers, high cost DEF pumps, and more complicated and less robust injectors
Solution Approach 1:
The patent inverts the conventional approach by using a constant volume injector with fixed injection amount rather than a variable volume injector. Instead of varying the injection amount continuously to adapt to engine conditions, the system uses a fixed injection volume and varies the injection timing. This inversion simplifies the injector design, eliminating the need for sophisticated variable volume control mechanisms while maintaining adaptability through timing control
Solution Approach 2:
The patent extracts the complex variable volume control functionality from the injector and relocates it to the controller's timing management. By using a simple constant volume injector that delivers a fixed amount per event, the system removes the complexity of variable volume metering from the injector hardware, placing the adaptation logic in software timing control instead
3Productivity
If excess DEF is dosed into the exhaust stream under lower than normal exhaust gas temperatures, then more NOx can be treated, but excess DEF forms deposits or film on the exhaust gas components
Solution Approach 1:
The patent uses periodic injection events spaced apart in time to prevent deposit formation. Between injection events, the exhaust gas temperature has time to rise and evaporate any condensed DEF, preventing the formation of persistent deposits and films. This periodic action allows the system to dose adequate amounts of reductant for NOx treatment while giving the surface time to clear between doses
Solution Approach 2:
The patent incorporates preliminary heating of the exhaust component surface before reductant injection. By ensuring the surface is sufficiently hot before each injection event, the system prevents premature condensation and deposition of the reductant. This preliminary thermal preparation ensures that when reductant is injected, it vaporizes quickly and completely, preventing deposit formation
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 reduces errors in reductant dosing, minimizes deposit formation, lowers system complexity and costs, and enhances NOx reduction efficiency while maintaining accurate control over NOx treatment.
Implementation Method 1
a pump in fluid communication with the tank, a valve in fluid communication with the pump, and an injector in fluid communication with the valve
Implementation Method 2
When the urea is heated by the exhaust gases, the urea breaks down into ammonia
Implementation Method 3
the urea breaks down into ammonia, which reacts with NOx to form water and nitrogen thereby reducing NOx emissions
Data Source
AI summary
Various embodiments relate to a selective catalytic reduction system for treating exhaust gases of an internal combustion engine. The system includes an inlet section that receives exhaust gases from the engine. The system includes a tank storing diesel exhaust fluid (“DEF”), a pump, a valve, and an injector each in fluid communication with each other. The injector is coupled to the inlet exhaust pipe and configured to inject DEF into the exhaust gases flowing through the inlet exhaust pipe in a plurality of pulses. Each of the plurality of pulses injects a constant volume of DEF into the inlet exhaust pipe. The system further includes a controller configured to operate the pump and the valve such that a time interval between successive constant volume pulses of the plurality of pulses is varied based on a variable oxides of nitrogen content of the exhaust gases.