Turbocharged Diesel Engine DOC Bypass for Face Plugging
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Solution Overview
Problem
In turbocharged diesel engines, the diesel oxidation catalyst (DOC) often fails to reach its 'light off' temperature, especially at cold starts and light loads, leading to face plugging due to entrained exhaust matter, which affects the operation of the after-treatment system.
Innovation Solution
A portion of the exhaust from the exhaust manifold is diverted directly to the DOC, bypassing the turbocharger, increasing heat energy input and promoting early 'light off' and maintaining temperature, potentially avoiding the need for a separate heater, with control mechanisms like the EGR valve or bypass control valves to manage the bypass flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If all exhaust flows through the turbocharger turbine, then the turbocharger can provide boost pressure for engine operation, but the exhaust temperature reaching the DOC is insufficient to achieve light off temperature, especially at light loads and low speeds
Solution Approach 1:
The exhaust flow is segmented into two separate paths: one path directs exhaust through the turbocharger turbine to maintain boost pressure, while the other path directs a portion of exhaust directly to the DOC to ensure sufficient temperature for light off. This segmentation resolves the contradiction by allowing each path to fulfill its specific function without compromising the other.
Solution Approach 2:
A bypass passage acts as an intermediary channel that allows a portion of the exhaust to bypass the turbocharger turbine and flow directly to the DOC. This intermediary path enables hot exhaust gases to reach the DOC without being cooled by the turbine, while the main exhaust flow still passes through the turbocharger to maintain engine boost pressure.
2Temperature
If a separate heater is installed to achieve DOC light off temperature, then the DOC can reach light off temperature reliably, but the device complexity and cost increase
Solution Approach 1:
The exhaust system itself is utilized to provide the heating function. By routing a portion of the hot exhaust directly to the DOC, the system uses its own thermal energy to achieve light off temperature, eliminating the need for external heaters or additional heating devices. This self-service approach reduces system complexity while maintaining reliable temperature achievement.
Solution Approach 2:
The exhaust gas flow serves multiple functions simultaneously: it provides boost pressure through the turbocharger, performs after-treatment in the DOC, and naturally heats the DOC to light off temperature through the bypass path. This multi-functionality eliminates the need for separate heating components, reducing overall system complexity.
3Productivity
If the DOC is positioned downstream of the turbocharger turbine, then the exhaust flow can be efficiently utilized for boost pressure, but the temperature of exhaust reaching the DOC is reduced, leading to face plugging by entrained matter
Solution Approach 1:
The exhaust flow is divided into two segments: one segment flows through the turbocharger turbine for efficient boost pressure generation, while the other segment flows directly to the DOC via a bypass passage to maintain high temperature and prevent face plugging. This segmentation allows both productivity and reliability requirements to be satisfied simultaneously.
Solution Approach 2:
The bypass passage is designed to deliver hot exhaust to the DOC before the exhaust would otherwise be cooled by the turbocharger turbine. This preliminary action of heating the DOC with fresh hot exhaust prevents the accumulation of entrained matter that would cause face plugging, ensuring reliable DOC operation from the start.
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 ensures earlier attainment and maintenance of the 'light off' temperature, reducing the likelihood of face plugging in the DOC, thereby enhancing the operation and efficiency of the exhaust after-treatment system.
Implementation Method 1
the heat energy input to the DOC is increased over the heat input to the DOC without the bypass. The resulting temperature increase promotes early 'light off' for a cold engine
Data Source
AI summary
A turbocharged engine (20, 20′, 20″, 20′″) counteracts plugging of a diesel oxidation catalyst (DOC 48) by causing a first portion of exhaust from one or more exhaust manifolds (26, 28) to enter the DOC after having passed through the turbocharger (30), and causing a second portion of the exhaust (HEG) to enter the DOC without passing through the turbocharger.