Jaguar's C-X75 concept, an electric coupe with a 780hp gas turbine electric engine wowed us last week. Jaguar now claims they might produce the car, but could those miraculous-sounding gas micro-turbines eventually happen?
At first sight, your impression of the powertrain through the rear window of the car is likely to be something akin to those silly gadgets in the James Bond films, gimmicky, with a super-futuristic appearance, but not much better than todays conventional real-world tech. Afterall, the lithium battery when fully charged carries the car for only 68 miles and relies on the turbine for an additional 500 miles. 68 miles may be enough for your commute and back if thats the only purpose of your car, but for someone to own a supercar like this, you're bound to be reguarly kicking into the back-up power provided by the gas-turbines. In fact, for the majority of the time, you're likely to be using gas as your fuel-source, and so why use a combustion engine to charge a battery to power an electric motor which will waste energy along this longer route than say running the car primarily through a gas engine and attaching an electric motor?
The electric motors are both 145kW, and at that power-level are likely to have an energy transfer efficiency greater than 90%. A gasolene combustion engine typically has an energy-transfer efficiency of around 20-30% with the majority of that energy becoming waste heat. The rules of physics dictate that the hotter an engine burns, the greater the efficiency, however the materials currently in use for creating our engines are incapable of withstanding the higher temperatures for a more efficient energy transfer ratio.
So what is the energy-efficiency like of the route Jaguar would take should this concept car's engine eventually reach mass-production? Jaguar being Jaguar, these turbines are no ordinary turbines, but are engineered by specialist firm Bladon jets, who have refined the technology to produce a much-smaller, super-efficient 'micro' gas turbine under a programme supported by the British government's Technology Strategy Board. Using the aviation industries advanced knowledge in creating jet-turbines , it allows for an engine that spins at 80,000 revs per minute, albeit sucking in consider volumes of air. While comparing the revs to a car-engine would be comparing apples and oranges, most car engines max out at 9,000 rpm.
This approach from using the twin micro-turbines are likely to extract as high a level of energy as possible from our fossil fuels today. The engine runs on many fuels which are more efficient than gasolene including diesel, biofuels, compressed natural gas, lpg, and possibly methane. With a high engine efficiency, and a 90% plus efficieny from the electric motors, this leads to a super efficient car which according to Jaguar can achieve 32 us mpg and only emits 28g/km of co2.
Jaguar says that the car could also run on a conventional petrol engine to power the motors, the same approach as that of GM's Chevy Volt. With the turbines though, there are fewer moving parts as turbines do not require oil lubrication or water cooling systems, though a lithium battery will be required.
At present, this technology is specialist, and patented,and its unlikely we'll see it become more common in the near future. Though the cars turbines may not seem so energy efficient at first glance, delving deeper shines the light as to why this concept is genius. While there will be many competiing green technogies such as hydrogen fuel-cell's and battery only electric engines, there are far too many limitations at present, and they are no where near as environment as at first glance. Lithium extraction for the far larger lithium batteries are likely to pollute the environment and perhaps even affect the lives of indigenious tribes akin to the movie Avatar.
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