Micro-turbines for Extending Electric Car Range

[:en]The concept of using gas turbines to power a car is not new. In fact, for many decades now, various car manufacturers have experimented with the idea of using either axial or radial gas turbines as the main propulsion of concept vehicles. In the 50’s and 60’s it was Fiat and Chrysler who introduced such concept cars. In those cases, the gas turbine was directly powering the wheels for propulsion. Toyota followed the same concept in the 80’s (Figure 1) [2]. Their concept car utilized a radial turbine in order to propel the vehicle using an advanced electronically controlled transmission system.

Figure 1
Figure 1: Toyota GTV engine [3].
The main advantage of a gas turbine compared with conventional reciprocating (or even rotary) car engines is the fact that it has a much higher power-to-weight ratio. This means that for the same engine weight, a gas turbine is able to deliver much higher power output. This is why aviation was one of the biggest adopters of this technology.

In  recent years, there has been significant interest from both traditional and new car manufacturers to investigate, again, the use of micro-turbines in cars. This time, not as the sole means of propulsion but rather as a power source for extending the range of their primarily electrically driven powertrains. The electrification of cars solves some key challenges in adopting turbines as a power source on such vehicles. The main reasons that former efforts failed to establish themselves in the market had to do with the cost and usability of the solution. Turbines were much more expensive then, however, in the modern era of 3D printing and advanced materials, turbines have a very promising value case to make, especially considering the fact that we can easily design them to work with a vast variety of “clean” fuels, in contrast to traditional internal combustion engines. Usability on the other hand, was greatly hindered by the fact that gas turbines cannot govern their power output as quickly as a typical reciprocating engine. Hence, when directly coupled with the drivetrain, despite any advanced transmission systems, the driver could not have the immediate response accustomed by conventional car engines.

Figure 2: AxSTREAM™ Platform for Radial Turbine Design.

The electrification of car propulsion solves that problem by acting as a “buffer” between the power demand from the driver and power delivery from the propulsion system. In addition, manufacturers can now optimize their gas turbines to work within “optimal” conditions, while charging the battery pack or supplying additional power to the electric power train. The engineers must consider how to design a turbine that will create the optimal amount of power for the operating ranges.  With high efficiency targets, the proper experience and resources are required to create high-efficiency turbines that can achieve these targets (see Figure 2). The turbine-engine, instead of operating as the main driver, will now only operate at its most efficient power output mode and work to simply drive electricity through the generator, recharging the vehicle’s battery packs.  Acting as an isolated thermo-mechanical system, a micro-turbine range extender can be designed and optimized without having to worry about the varying duty cycles and idling that is inherent in the vehicle’s drivetrain. The thermodynamic model of a typical micro-turbine range extender is depicted in Figure 3.

Figure 3: Thermodynamic formulation of a Micro-Turbine Range Extender model in AxCYCLE™
Hybrid Kinetic micro-turbine hybrid powertrain
Figure 4: Hybrid Kinetic micro-turbine hybrid powertrain [1].
In the last few years, Jaguar has produced a concept car that combines all the aforementioned benefits from a micro-turbine, integrated into a hybrid powertrain that has high performance while being fuel efficient and environmental-friendly. Another company that is currently developing such a car is Hybrid Kinetic (Figure 4). They are also working on a powertrain solution that employs a micro-turbine a fraction of the size compared to a typical car engine, which is able to give impressive range performance with minimal environmental footprint.

Jaguar C-X75 using micro-turbine as range extender
Figure 5: Jaguar C-X75 using micro-turbine as range extender [4].
Interested in learning about how AxCYCLE™ and AxSTREAM®  can help improve your electric car range and operational efficiency? Contact us to schedule a demo!



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