Close-Coupled Three-Way Catalyst for Diesel NOx Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Compression-ignition engines face challenges in reducing NOx emissions due to the remote location of SCR devices, which leads to heat loss and inefficient warm-up, resulting in higher NOx emissions during cold starts and low-load conditions, especially with modern diesel engines that are fuel-efficient.
Innovation Solution
A close-coupled three-way catalyst device is integrated upstream of the SCR device, with an engine control unit that monitors SCR device temperature and adjusts the air-fuel mixture from lean to stoichiometric or rich operation when the SCR device temperature drops below a threshold, preventing uncontrolled NOx emissions and ensuring the three-way catalyst maintains sufficient temperature for effective NOx conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the SCR device is located remotely from the engine, then it can be properly positioned for urea injection and mixing, but heat loss occurs and the SCR device takes longer to reach operating temperature
Solution Approach 1:
The exhaust after-treatment system is divided into two separate functional segments: a close-coupled three-way catalyst device positioned near the engine for rapid warm-up and NOx reduction, and a remotely positioned SCR device for high-temperature NOx conversion. This segmentation allows each device to operate in its optimal temperature range and location, resolving the contradiction between remote positioning for urea injection and maintaining temperature.
2Use of energy by moving object
If the engine operates with lean air/fuel mixture, then fuel economy is improved, but NOx emissions increase when SCR device is cold
Solution Approach 1:
The engine control unit continuously monitors the temperature of the SCR device and dynamically adjusts the air/fuel mixture ratio based on this feedback. When the SCR device temperature is below the threshold, the control unit enriches the mixture to reduce NOx emissions; when the temperature is sufficient, it returns to lean operation for optimal fuel economy. This feedback-based control resolves the contradiction between fuel economy and NOx emissions control.
3Object-generated harmful factors
If a three-way catalyst device is added in close-coupled position, then NOx reduction during cold phases is improved, but device complexity increases
Solution Approach 1:
The close-coupled three-way catalyst device is designed to perform multiple functions: oxidizing CO and hydrocarbons, reducing NOx during cold operation, and protecting the downstream SCR device from thermal shock. By consolidating these functions into a single multi-functional component, the system achieves improved NOx control during cold phases while minimizing the increase in overall device 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
This approach significantly reduces total tailpipe NOx emissions by ensuring the three-way catalyst operates effectively during acceleration phases and low-load conditions, while maintaining overall lower CO2 emissions compared to conventional systems with heat-up strategies.
Implementation Method 1
a three-way catalyst device and an SCR device, the three-way catalyst device being arranged upstream the SCR device
Implementation Method 2
Selective catalytic reduction (SCR) can be used to reduce the NOx, wherein a gaseous or liquid reductant (most commonly ammonia or urea) is added to the exhaust gas stream and is adsorbed onto a catalyst. The reductant reacts with NOx in the exhaust gas to form H2O (water vapour) and N2 (nitrogen gas).
Implementation Method 3
the engine has to be controlled to operate stoichiometrically, i.e. so that the amount of oxygen supplied to the combustion chamber corresponds to that required for complete combustion of the amount of fuel supplied
Data Source
AI summary
A compression-ignition engine (10) comprises an exhaust system (16) with an exhaust gas after-treatment assembly, the after-treatment assembly comprising a three-way catalyst device (30) and an SCR device (34), the three-way catalyst device being arranged upstream the SCR device in close-coupled position with respect to the engine. An engine control unit (47) is provided for controlling operation of the engine. The engine control unit is configured to monitor the temperature of the SCR device and to control the engine to change over from an operation with a lean air/fuel mixture to an operation with a stoichiometric or a rich air/fuel mixture in response to the temperature of the SCR device dropping below a temperature threshold.