A jet engine for a hybrid vehicle generator set seems at first a little extreme. But is it? The scale for jet turbines for outside observers is the huge engine hanging from the wings of airliners. That’s a little deceptive, as those jet’s turbine engines are much smaller than what’s visible. The power turbine inside is turning the big slave turbine that is so visible. The slave turbine is really a very high-speed propeller. The mass of pulled and forced air bypasses the smaller power turbine inside.
Inside is a much smaller turbine engine. These engines have seen immense improvements since the early days when the easy to recognize torpedo shape was common. Those engines worked by exhausting a hot high-speed gas flow. But a lot of energy is wasted in heat. Much energy could be recovered by mechanically connecting to the rotating shaft.
Even so, jet turbines we recognize are big. From natural gas turbines powering utility size generation sets to ship-sized turbines these are massive power engines. But little ones have been built. Some of you can remember the Chrysler automotive turbine model in the 1960s. Small turbines have come a very long way since.
A consortium led by the UK’s micro gas turbine company Bladon Jets with Jaguar Land Rover and leading electrical machine company SR Drives, has secured investment from the UK’s Technology Strategy Board to develop an Ultra Lightweight Range Extender (ULRE) for next-generation electric vehicles. That’s Brit speak for a hybrid vehicle generator set. The allure is – turbines are very tolerant about the fuel they can use.
The consortium’s objective is to produce the world’s first commercially viable – and environmentally friendly – gas-turbine generator specifically for automotive applications. Their ULRE will incorporate the Bladon Jets’ patented axial-flow gas turbine engine coupled to a high-speed generator using SR Drives’ proprietary switched-reluctance technology. Engineers at Jaguar Land Rover will oversee the design of the ULRE’s packaging and integration into vehicles.
The advantages in Bladon’s claim for small external combustion gas turbine engines are they’re more efficient, less polluting and lower cost than internal combustion reciprocating engines. Add to that gas turbine engines will run on just about any type of fuel including natural gas and bio-fuels. Turbines are not dependent on specific fuels, external combustion allows a wide range for fuel choice. Rigged for liquid fuel, a turbine could use ethanol up to heavy diesel. It’s fuel accessibility risk reducer as well.
Bladon’s specific choice in turbines is to use axial flow instead of radial flow. An axial flow turbine uses more fans to compress close to the axial shaft. That allows very high compression. A radial flow uses less fan compression with the compression increase coming from a squeeze between the extended shaft body and the outer wall. Radial flow is much less costly to build, but axial flow is much more efficient.
Bladon may have answered some of the radial build advantage with a new process to manufacture the blades and hubs. Bladon is doing a full bladed hub and blades in one piece. That allows the machining to be quite precise and the singular casting is stress free at lower mass. No more assembled blades to the hubs. Plus engineering adaptations are easily accommodated in manufacturing. The surprise is Bladon is now at 75mm (just under 3 inch) rotor diameter. Now one can see the hybrid vehicle potential.
Turbine engines while expensive, might finally be cost comparable to internal combustion. The turbine won’t need the water-cooling system components, or catalytic converters and much of the emission equipment. The fuel system will be simpler; the total number of parts will be greatly reduced as well as the total weight. They warm up in just seconds saving cold start inefficiency.
The Bladon route to hybrid vehicle generation sets might just work if the costs can be driven low enough. Turbines are high-speed precision engines. Fed clean air they should last a very long time with very little attention. Keep in mind, compared to sophisticated piston engines the 5% effect applies to size, weight, part count and power output. An effective turbine HEV generator set isn’t going to be very big or heavy.
It’s all about cost. The materials are not cheap, but what power and rotational speed requirements would be needed isn’t discussed yet. Bladon has a patented technology to reduce manufacturing costs and claims they can address material from the lower cost to the most expensive. One just has to assume, the Bladon team must have the numbers to make the effort, and if they do, series hybrid designs with turbine generator sets might just really take off.
It’s very encouraging. The ability to catch an emergency fill from the cooking oil in the kitchen, or a simple kerosene fill up or ethanol or whatever might be cheapest is an alluring feature that should support the Bladon effort for quite some time.