Science and Technology

Chennai start-up makes gas turbine-battery combo for trucks

M Ramesh | Updated on April 25, 2021

Paves the way for plying heavy-duty vehicles powered by electricity

Batteries onboard electric trucks have to be bulky (5-7 tonnes!) because they need to carry enough power to drive the vehicle over long distances. Their size and weight affect the economics of the operations.

It’d be a lot better if we could produce electricity onboard the vehicle rather than carry it in a battery. This is what a fuel cell does. But fuel cells are, at least till the foreseeable future, extremely expensive.

A Chennai-based, IIT-Madras-incubated start-up, Aerostrovilos, has come up with a novel solution for this: Mount a micro gas turbine on the vehicle to produce electricity. After all, gas turbines have been used for decades for electricity generation — why not use them to drive trucks?

Aerostrovilos has developed a ‘turbine electric vehicle’ or TEV, which is halfway between a regular truck and a battery-driven one. It features a 60-kW gas turbine-generator, and a small battery to take in the power and supply it in a regulated manner to the motors that drive the vehicle. The ‘fuel tank-GT-battery-motor’ configuration is unique and weighs less than a tonne.

Aerostrovilos CEO Rohit Grover tells Quantum that the company is close to testing the prototype.

Challenges

Sounds simple, but it is easier said than done. First, gas turbines don’t come cheap, and the smaller ones are even costlier for the power they produce. You can make the turbines cheaper by using lower grade materials — such as stainless steel instead of ‘aero grade’ materials — but then you would also need to lower the flame temperature inside the turbines to be able to withstand the heat. (By the way, the lower the temperature the less the nitrous oxide produced)

Second, it doesn’t make sense to waste the heat of the exhaust from the gas turbines. The Aerostrovilos team devised a ‘recuperator’ that acts as a heat exchanger, with the help of their mentor, Satya Chakravarthy, professor of aerospace engineering at IIT-Madras and convenor of the multi-institute research lab National Centre for Combustion Research and Development. Air that enters the gas turbine first picks up heat from the exhaust inside the recuperator.

There were also other challenges, such as ‘combustion instability’, or non-even burning, tackling which means ensuring uniform delivery of fuel and air to the flame zone. This, an area of active study the world over, is currently being addressed by running the air and fuel through circular channels. NASA Glenn Research Centre calls it the ‘swirl-venturi lean direct induction’. Chakravarthy and his colleague TM Muruganandam have improved upon that by inventing a system of hexagonal channels — they have a patent for this ‘swirl-mesh’ technology. Aerostrovilos adopted this technology, and the result is a compact gas turbine — a one-metre box that can be mounted onto a truck.

Grover points out that while a fuel cell system can produce power only with hydrogen, Aerostrovilos’s TEV can run on any fuel, including hydrogen. Until such time as alternatives to diesel (such as DME, methanol, ethanol, hydrogen) become easily available, the vehicle can run on diesel.

Grover says a TEV can be bought for ₹55 lakh, which is almost double the price of a comparable diesel truck. But the TEVs are more fuel-efficient — can run 5.5 km on a litre of diesel, compared with 3.5 km of a conventional truck. The additional cost, he says, will be offset within three years if the vehicle runs 90,000 km a year. The TEV also has a significantly longer life of 12 lakh km compared with 8 lakh km for a regular, IC engine-powered diesel truck.

Chakravarthy explains that the role of the battery is to act as a buffer — take in power from the gas turbine and supply only what the motors need at any point during the journey.

Will the TEV be a game changer? We will know after the prototype gathers data.

Published on April 25, 2021

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