Two-Stage Parallel-Flow Turbocharger Compressor for High EGR Efficiency
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Solution Overview
Problem
High levels of exhaust gas recirculation (EGR) in diesel engines lead to increased pumping loss and reduced engine efficiency due to negative pumping work, which is exacerbated by the mismatch in compressor and turbine sizes required for optimal efficiency, making it difficult to maintain acceptable turbine efficiency and transient response.
Innovation Solution
A single-shaft turbocharger architecture featuring two parallel-flow first-stage centrifugal compressors in series with a single second-stage centrifugal compressor and a one-stage turbine, where the compressors and turbine are fixedly mounted on the same shaft, allowing for high volumetric flow and pressure ratio requirements while maintaining high turbine efficiency through a unique two-stage compressor arrangement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If high levels of EGR are driven through the engine, then NOx reduction is improved, but negative pumping work increases and engine efficiency deteriorates
Solution Approach 1:
The compressor is divided into two independent stages (first-stage compressor and second-stage compressor) that can operate at different speeds, allowing each stage to be optimized for its specific function while working together to reduce the overall pumping work penalty
Solution Approach 2:
The turbocharger system incorporates variable geometry mechanisms including variable turbine vane area and variable compressor vane area that can dynamically adjust to changing operating conditions, optimizing the pressure gradient and reducing negative pumping work across different EGR rates
2Quantity of substance
If compressor size is increased to handle high EGR flow, then EGR capacity is improved, but turbine efficiency deteriorates due to speed mismatch
Solution Approach 1:
The compression system is segmented into two stages with different impeller designs and operating characteristics. The first-stage compressor handles the bulk EGR flow at lower speeds, while the second-stage compressor operates at higher speeds to provide the necessary pressure ratio, allowing the turbine to operate efficiently without being oversized
Solution Approach 2:
The system changes the operating parameters of the compressors by using two different speeds rather than forcing a single speed to handle all requirements. This allows the turbine to operate at its optimal speed range while still achieving the required total compression for high EGR rates
3Device complexity
If single-stage compressor is used, then device complexity is reduced, but ability to maintain turbine efficiency at high EGR rates deteriorates
Solution Approach 1:
The compression function is segmented into two stages with independent speed optimization, where the first-stage compressor and second-stage compressor can rotate at different speeds to maintain turbine efficiency while handling high EGR flows that would be impossible with a single-stage design
4Speed
If turbine size is reduced to improve transient response, then responsiveness is improved, but turbine efficiency deteriorates due to operating at too slow speed
Solution Approach 1:
The variable turbine vane mechanism dynamically adjusts the effective turbine area to optimize the turbine's operating speed and efficiency across different load conditions, allowing a smaller turbine to maintain high efficiency while responding quickly to transient changes
Solution Approach 2:
The system changes the turbine's effective operating parameters by varying the vane area, which allows the turbine to operate at optimal speeds for efficiency even when physically smaller in size, thereby maintaining both transient response and efficiency
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 enables efficient operation at high EGR levels by ensuring the turbine can operate at a higher speed for improved efficiency and responsiveness, reducing the negative pumping work and maintaining acceptable engine performance.
Implementation Method 1
two parallel-flow first-stage centrifugal compressors in series with a single second-stage centrifugal compressor
Implementation Method 2
a one-stage turbine arranged to drive both the first- and second-stage centrifugal compressors
Data Source
Figure 1
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AI summary
A single-shaft exhaust gas-driven turbocharger includes two parallel-flow first-stage centrifugal compressors in series with a single second-stage centrifugal compressor, and a one-stage turbine arranged to drive both the first- and second-stage centrifugal compressors via a single shaft on which the compressors and turbine are fixedly mounted. The compressor housing defines from one to a plurality of circumferentially spaced inlet ducts for the second wheel of the first stage, and from one to a plurality of circumferentially spaced interstage ducts leading from a vaneless diffuser of the first stage into the inlet of the second stage.