Exhaust Gas Purification System for Diesel Engine Emission Control
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Solution Overview
Problem
Existing exhaust gas purification systems for diesel engines face challenges in maintaining catalyst activation temperatures, efficiently removing NOx at varying temperatures and flow rates, and reducing the frequency of forced regeneration of diesel particulate filters, which increases CO2 emissions and can lead to turbine corrosion from sulfur oxides.
Innovation Solution
An exhaust gas purification method that includes a previous-stage oxidation catalyst, an ammonia-based solution feeder, a diesel particulate filter, and a NOx selective reduction catalyst in a specific order, with hydrocarbon injection to raise exhaust gas temperature for continuous regeneration and positioning the ammonia-based solution feeder close to the engine to enhance ammonia production and NOx removal, while converting sulfur oxides into calcium sulfate to reduce corrosion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple exhaust gas purification devices are mounted to remove hazardous substances, then removal effectiveness is improved, but device size and thermal capacity increase, making it difficult to ensure catalyst activation temperatures
Solution Approach 1:
The exhaust gas purification system is divided into multiple functional stages: a first oxidation catalyst for CO and HC removal, a diesel particulate filter for PM removal, and a second oxidation catalyst for final purification. This segmentation allows each component to be optimized for its specific function while maintaining overall system effectiveness and managing thermal loads.
Solution Approach 2:
The first oxidation catalyst is positioned upstream of the diesel particulate filter to perform preliminary oxidation of CO and hydrocarbons before the exhaust enters the DPF. This preliminary action reduces the thermal burden on subsequent components and ensures the DPF receives exhaust gas with lower contaminant loads, facilitating easier catalyst activation.
2Reliability
If engine combustion is improved to reduce PM and NOx discharge, then emission control is enhanced, but exhaust gas temperature decreases by 30-50°C or greater
Solution Approach 1:
The system compensates for the temperature decrease caused by improved combustion by using oxidation catalysts that can activate at lower temperatures. The first oxidation catalyst is designed to effectively remove CO and HC at the reduced exhaust temperatures, maintaining emission control effectiveness without requiring high temperature operation.
3Productivity
If urea water injection distance to SCR device is increased to improve dispersion and decomposition, then urea decomposition efficiency is improved, but device size increases
Solution Approach 1:
The urea injection function is extracted from the traditional SCR device configuration and integrated into the exhaust gas flow path before the diesel particulate filter. Urea solution is injected into the exhaust stream at a location where it can effectively disperse and decompose into ammonia, which then participates in NOx reduction reactions. This extraction allows for shorter injection distance while maintaining decomposition efficiency.
Solution Approach 2:
The exhaust gas purification system performs multiple functions: CO oxidation, HC oxidation, PM filtration, and NOx reduction. By integrating urea injection into the existing exhaust flow path rather than requiring a separate, distant SCR device, the system achieves multi-functionality in a compact arrangement, improving space utilization while maintaining all required emission control functions.
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 configuration improves NOx removal rates across a wide temperature and flow range, decreases the frequency and CO2 emissions associated with forced regeneration, and suppresses turbine corrosion by converting sulfur oxides into non-corrosive calcium sulfate.
Implementation Method 1
an oxidation catalyst, a urea injection device, a diesel particulate filter device, a NOx selective reduction catalyst converter, and an oxidation catalyst are disposed in an exhaust passage
Implementation Method 2
a urea decomposition catalyst is supported in the diesel particulate filter device
Implementation Method 3
a NOx selective reduction catalyst converter
Data Source
Figure 1
Figure 2
Figure 3
AI summary
An exhaust gas purification system (1, 1A) for removing particulate matters and nitrogen oxides in the exhaust gas (G) of an internal combustion engine (10) is formed by disposing a previous-stage oxidation catalyst device (21), an ammonia-based solution feeder (24), a DPF device (22), a turbine (14) of a turbocharger, and a NOx selective reduction catalyst device (SCR device) (23) in the exhaust system of the internal combustion engine (10) in this order from an exhaust port side. With the suitable arrangement of the exhaust gas purification units, the NH3 production rate is improved to improve the NOx removal rate; the temperature of the DPF device is kept high to increase the time and frequency of continuous regeneration, thus decreasing the frequency of forced regeneration of the DPF device and the amount of discharge of CO2 produced during the forced regeneration; and also corrosion of the turbine of the turbocharger by SOx is suppressed.