Looking to solve the problem of range anxiety in electric vehicles, many companies have started exploring the business model of recharging electric batteries in automotive vehicles with a parallel turbine engine driving a generator – coined under the term ‘micro-turbine range extender’ (or MTRE). As seen in the turbine-powered car programs initiated in the 50s and 60s, issues with low efficiencies, slow throttle response, and capital cost of the powertrain rendered all of these programs futile shortly after their inception. However, the revolution of electric vehicles and hybrid technologies has allowed this technology to resurface from a different direction. With battery-driven electric motors designated as the main driver, these cars are equipped with a technology that has both energy efficient low-end torque as well as groundbreaking throttle response and many of the former drawbacks during its initial iterations are solved using an electric drivetrain. 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 can be seen below in Figure 1.
One application within commercial vehicles that has benefitted from this technology utilizes a MTRE system developed by Wrightspeed. The specific application lies within retrofitting refuse trucks with this electric powertrain in order to help them save an estimated $35,000 a year on fuel and maintenance costs. In such heavy-duty applications, it is obvious that the potential for fuel cost and maintenance savings is much higher due to the large fuel burning needed for these vehicles as well as the harsh drive cycle a refuse truck goes through. The question in the expansion of this technology generally comes in two forms: What makes the micro-gas turbine range extender a better alternative than a normal ICE hybrid option? – and – What is the viability of scaling this for consumer vehicles given the capital cost of the drivetrain?
Micro-Turbine Range Extender vs. ICE Hybrids
It is true that modern diesel engines have achieved efficiencies higher than 40% on a frequent basis, which is greater than those of micro-turbine engine units. However, the power-to-weight ratio of gas turbine units significantly beat that of a piston engine, which allows for a lighter-weight engine within the hybrid. Another large factor is related to the combustor and overall combustion process on a micro-gas turbine unit. Unlike a piston engine, the gas turbine unit uses a continuous combustion process, which not only allows for a plethora of fluids to be used, but also results in significantly lower emissions in comparison. Without the need for after treatment methods, a micro-gas turbine unit has far lower emissions than even the most carefully treated and engineered ICEs on the market. Furthermore, a micro gas turbine allows differing fluid operation, so fuels such as diesel, CNG, LNG, and landfill gases can be utilized in the combustion process. Finally, considering only one moving part in this GTU, the rotor train, a micro-turbine arrangement enjoys the benefits of extremely low maintenance, less upkeep, and quieter operation.
Scaling for Consumer Vehicles
In order to find such technology in a fleet of future commercial vehicles, MTREs must achieve a price point that remains attractive to the consumer from a capital investment standpoint. A company in the UK, Delta Motorsport, has revealed their version of a Micro Turbine Range Extender, which supports a 15kW engine at an aimed price point of less than 1,000 pounds per unit (~$1300 USD). Supercar manufacturers such as British company Ariel Motor Co. as well as Chinese company Techrules have begun to explore these technologies in their new HIPERCAR and Ren models respectively. These proof-of-concepts vehicles are certainly the start of what could eventually scale into a high-production MTRE-supported car. With time, practice, and volume, this rapidly evolving technology of the Micro-Turbine Range Extender could prove to make a serious impact on the uprising of consumer hybrid-electric vehicles as they enter the market.