Improved performance and efficiency using Variable geometry turbines
How to have your cake and eat it too
To satisfy increasing strict regulations and meet the demands of a vastly dynamic consumer basis, automotive engineers are challenged to solve a complex relationship between efficiency and performance. Instead of alternative fuel sources or hybridization, some automotive engineers have decided to continue developing and evolving standard internal combustion gasoline engines to power their vehicles. This redesign has proven challenging, given that a standard Otto Cycle engine is largely inefficient by design. Engineers are tasked with finding the optimal balance between various factors to meet stakeholder requirement and needs in an evolving market. Implementing smaller volume engines equipped with variable geometry turbochargers has been a successful route in achieving a balance between efficiency, power, affordability, and reliability in passenger automobiles.
A variable geometry turbocharger (VGT) is a successor to a fixed geometry turbocharger (FGT). While fundamentally identical, the VGT differs by offering the ability to maintain optimal velocity of air through the turbine by adjusting the cross-sectional area of the inlet. A key aspect in turbocharge sizing is the area over radius (A/R). A small A/R turbocharger delivers more power at low engine speeds but limits the overall volume of air to the engine, limiting the power delivery at high engine speeds. A large A/R turbocharger delivers more power at higher engine speeds but exhibits low velocity airflow at lower engine speeds due to the high cross-sectional, resulting in lower power at low engine speeds. A dynamometer graph below from Garrettmotion.com shows the difference between an A/R of 0.83 and 1.01 on the same engine.
VGT systems can adjustment the cross-sectional area of the housing creating a variable A/R based on load and demand. A properly tuned control system on a VGT system offers a large band of efficiency of the turbocharger, which is typically very small on a FGT system. VGT systems remove the negative aspects of choosing a fixed low or high A/R ratio turbocharger, while maintaining the positive aspects of each ratio. When implemented with goals of energy conservation, a fully optimized VGT system can offer the same power and performance using less fuel. When implemented on a VGT system with goals of performance, more power can be achieved for the same fuel consumption.
Stakeholders
Stakeholders for a VGT system vary greatly dependent on intent and relationship. While these innovations would seemingly only interest automotive enthusiasts, the benefits of this design are not solely performance driven. Provided this design can yield both performance and economy-based improvements to vehicles, stakeholders can extend to those interested in more fuel-efficient vehicles and those who desire alternative driving experiences. This design is also used heavily with large commercial diesel-powered equipment, provided a more consistent deliver of power throughout the engine speed band and offering more power for the same fuel consumption.
Although providing improvements to power and efficiency, the increased mechanical complexity, and advanced controls logic necessary to properly operate the system will result in negative reception to some of the consumer population who desire simple operation and lower maintenance costs associated with standard large displacement engines without forced induction. Small moving parts reside within the harsh environment of the turbocharger housing and are susceptible to malfunction, especially when utilizing exhaust gas recirculation into the system. Some consumers would prefer to exchange power and efficiency of a VGT engine to avoid the potential failure and associated repair expense that can occur in such a system. When considering this application commercial vehicles, a simpler and less efficient option would be preferred to reduce maintenance costs, increase maintenance intervals, and minimize equipment downtime.
Relation to Concept from INCOSE SE Handbook
The development of VGT systems showcase various concepts related to the INCOSE SE Handbook. Modeling and simulation methods were used by design engineers during initial research and development stages to determine design and potential benefits of the improvement of VGT over FGT. Expanding from the simulation portion indicates the need for specialty engineering, specifically reliability engineering, for this application. Due to the harsh environment that the small adjustable parts of the VGT system reside, reliability engineering analysis is required to determine methods for ensuring long system life without catastrophic failure or too frequent of maintenance intervals for the system. Producing a device that is affordable is another concept from INCOSE that this device would require. While offering increases to efficiency and performance, the cost for such advantages must be practical to both the manufacturer and the consumer to justify the design and implementation. A final concept ties the lifecycle of a system into the reliability aspect of the system. Automotive vehicles are engineered to last between 200,000 and 300,000 miles (CarandDriver), so the lifecycle of the VGT must align with the full or predicted fraction expected lifetime of the vehicle, as to not engineer a device that requires overly frequent replacement, rendering the potential savings of the innovation void due to an inability to maintain longevity.
Utilization of SE Principles
The history of turbochargers on engines has spanned decades and detailed various modifications and improvements since its inception. The first patent for a turbocharger was filed in 1905, but the first turbocharger on a passenger vehicle did not occur until the 1960s. Although it was old technology, the following 60 years yielded significant development and refinement to this system as design engineers achieved excellence through continually improve upon fundamental designs with innovate technology. While being an undeniably optimal addition to internal combustion engines in theory, turbochargers from the 1960s into the 1980s were largely inefficient and unreliable. Design engineers continued to improve on the design of turbochargers and eventually developed VGT systems in the early 1990s, showcasing System Engineering principles of continuous improvement. While the addition of turbochargers onto internal combustion engines was a continuous improvement of the engine, the development of VGT technology showcases principles of continuous improvement and the perfection principle.
References
INCOSE. (2015). INCOSE Systems Engineering Handbook: A Guide for System Life Cycle Processes and Activities. 4th Edition Wiley.
pg 180–181, pg 211–213, pg 226–228,
Garrettmotion. (2019) Turbo Tech: The Difference An A/R makes going from 0.83 to 1.01 with a GTX3076R Gen II Turbo
https://www.garrettmotion.com/news/newsroom/article/turbo-tech-how-to-turbo-and-the-difference-an-a-r-makes-for-optimizing-your-turbo-system/
Mitsubishi Turbocharger.(2020.) A History of turbocharging
https://www.turbocharger.mtee.eu/a-history-of-turbocharging/
Variable Geometry Turbochargers. (2016). Hannu Jääskeläinen https://dieselnet.com/tech/air_turbo_vgt.php
The Basics of Variable Geometry Turbochargers. (2020). https://turboturbos.com/blogs/news/the-basics-of-variable-geometry-turbochargers
Car and Driver. How Many Miles Does a Car Last? Carhttps://www.caranddriver.com/research/a32758625/how-many-miles-does-a-car-last/
