Preheating Oxidation Catalyst Layout for Low-Temperature SCR Warm-Up
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Solution Overview
Problem
Conventional SCR systems struggle to effectively convert NOx at low temperatures, leading to higher NOx emissions during cold starts due to insufficient catalytic conversion efficiency, which is exacerbated by low exhaust gas temperatures.
Innovation Solution
Incorporation of a preheating oxidation catalyst upstream of the SCR system to combust hydrocarbons and increase exhaust gas temperature to an optimal level for efficient NOx conversion, using a controller to manage hydrocarbon insertion and optionally a heater for additional temperature control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the SCR system operates at low temperatures during cold starts, then the system can start immediately without preheating, but the catalytic conversion efficiency of NOx is reduced
Solution Approach 1:
The patent applies preliminary action by introducing a preheating oxidation catalyst upstream of the SCR system that activates before the SCR system reaches its optimal operating temperature. This preheating catalyst oxidizes hydrocarbons in the exhaust gas to generate heat, raising the exhaust gas temperature to a level that enables the SCR system to operate efficiently from the start, thereby resolving the contradiction between immediate cold start capability and catalytic conversion efficiency.
2Temperature
If hydrocarbons are inserted into the preheating oxidation catalyst to increase exhaust gas temperature, then the SCR system reaches optimal temperature faster, but CO2 emissions increase
Solution Approach 1:
The patent applies parameter changes by carefully controlling the amount and timing of hydrocarbon insertion into the preheating oxidation catalyst. The controller adjusts hydrocarbon dosing parameters based on exhaust gas temperature, engine operating conditions, and SCR system temperature requirements. This controlled approach ensures sufficient temperature increase for efficient NOx conversion while minimizing excessive CO2 generation, thus resolving the contradiction between warming the exhaust gas and reducing CO2 emissions.
3Reliability
If a preheating oxidation catalyst is added upstream of the SCR system, then NOx conversion efficiency improves during transient phases, but device complexity increases
Solution Approach 1:
The patent applies universality by designing the preheating oxidation catalyst to serve multiple functions: it preheats the exhaust gas for the SCR system, oxidizes hydrocarbons to reduce emissions, and can operate independently or in conjunction with the SCR system during various operating conditions. This multi-functionality justifies the added device complexity by providing multiple benefits from a single component, thereby resolving the contradiction between improved NOx conversion efficiency and increased system complexity.
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
Achieves ultra-low NOx emissions and faster SCR system warm-up with reduced CO2 emissions by ensuring the SCR system operates at optimal temperatures during transient phases, enhancing catalytic conversion efficiency.
Implementation Method 1
The preheating oxidation catalyst is configured to catalyze combustion of the inserted hydrocarbons so as to increase the temperature of the exhaust gas to be above the threshold temperature
Implementation Method 2
The preheating oxidation catalyst is configured to catalyze combustion of the inserted hydrocarbons so as to increase the temperature of the exhaust gas
Data Source
AI summary
An aftertreatment system for treating exhaust gas includes: an exhaust conduit configured to receive the exhaust gas; a preheating oxidation catalyst disposed in the exhaust conduit; a primary oxidation catalyst disposed in the exhaust conduit downstream of the preheating oxidation catalyst; a selective catalytic reduction system disposed in the exhaust conduit downstream of the primary oxidation catalyst; and a controller configured to: determine a temperature of the exhaust gas at an inlet of the selective catalytic reduction system, and in response to the temperature of the exhaust gas at the inlet of the selective catalytic reduction system being below a threshold temperature, cause hydrocarbons to be provided to the preheating oxidation catalyst or to the exhaust conduit at a location upstream of the preheating oxidation catalyst. The preheating oxidation catalyst catalyzes combustion of the hydrocarbons so as to increase the temperature of the exhaust gas to above the threshold temperature.