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Forum » Eco Car Forums » Tech Log

Turbine vs ICE for Range Extended EV's

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Written on: 28. 07. 08 [22:13]
ecoadmin Administrator Topic creator registered since: 20.07.2007 Posts: 368	GM built some years ago the EV1 Serial Turbine Hybrid which was using an Auxiliary Power Unit (APU) connected to a high-speed permanent-magnet AC generator. On wikipedia it says: "The program demonstrated the technical feasibility of such drivetrain, but concluded that commercial viability was out of reach at that time." http://en.wikipedia.org/wiki/General_Motors_EV1#EV1_series_hybrid Could someone explain me in more detail why this option was dropped? I see two reasons: a) Efficiency - a turbine is not as efficient as a combustion engine b) Higher production costs Any other ideas? ecocarforum.com - Green Car Network Community for sustainable transport
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Written on: 01. 08. 08 [16:03]
Lensman registered since: 31.05.2008 Posts: 77	ecoadmin wrote: Could someone explain me in more detail why this option was dropped? I see two reasons: a) Efficiency - a turbine is not as efficient as a combustion engine b) Higher production costs Not sure what you mean by "a turbine is not as efficient as a combustion engine". A gas turbine uses combustion, and it can be considerably more efficient than a piston-driven engine, which loses much of its power in friction and in fighting the inertia of the pistons. Every time it has to stop the piston from moving in one direction and push it in the other, it loses energy. Since a turbine just spins, there's much less loss of energy that way. But of course turbines have other disadvantages, or we'd all be driving turbine-powered cars. I'd *guess* that the reason it wasn't considered commercially viable is the same reason hybrids weren't competitive until very recently. Putting two separate engines into a car, along with a *very* expensive battery pack, makes it hard for a hybrid to compete economically with a gasser. It's only because the price of gas (petrol) has shot up so far that hybrids are now considered competitive.
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Written on: 03. 08. 08 [20:06]
ecoadmin Administrator Topic creator registered since: 20.07.2007 Posts: 368	Lensman wrote: Not sure what you mean by "a turbine is not as efficient as a combustion engine". A gas turbine uses combustion, and it can be considerably more efficient than a piston-driven engine, which loses much of its power in friction and in fighting the inertia of the pistons. ...it should have read 'Internal Combustion Engine'. Please excuse my imprecise writing. I fully agree with your points that a turbine can be more efficient for the given reasons. But the way I see it, this can only be said for applications in the aviation industry. Why? The fuel to power ratio is not as good as on internal combustion engines. On airplanes size and weight of the engine is a very important factor. That characteristic outweighs the attribute of the lower fuel to power ratio. The superior weight to power ratio has a significant impact on overall efficiency, because weight determines airframe lift requirements. Bodies increase in drag as a proportion relative to size. The small physical profile has an impact on drag which is a significant factor in aircraft power requirements. Those reasons make the turbine a preferred application in aviation applications. The above factors have less impact on automobile mechanicals. The added expense of turbine technology does make the ICE to the number one choice. ecocarforum.com - Green Car Network Community for sustainable transport
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Written on: 04. 08. 08 [03:23]
Lensman registered since: 31.05.2008 Posts: 77	Well, as usual, searching Wikipedia is useful. From their article on "gas turbine", specifically the "Gas Turbines in Vehicles" section: http://en.wikipedia.org/wiki/Gas_turbine#Gas_turbines_in_vehicles - - - - - - - - - - It is worth noting that a key advantage of jets and turboprops for aeroplane propulsion - their superior performance at high altitude compared to piston engines, particularly naturally-aspirated ones - is irrelevant in automobile applications. Their power-to-weight advantage is far less important. Gas turbines offer a high-powered engine in a very small and light package. However, they are not as responsive and efficient as small piston engines over the wide range of RPMs and powers needed in vehicle applications. In hybrids, gas turbines reduce the responsiveness problem, and the emergence of the continuously variable transmission may also help alleviate this. A recent idea is the 'Multi-Pressure' turbine proposed by Robin Mackay of Agile Turbines. This concept is expected to provide three different power level ranges - each of them exhibiting high efficiency and low emission levels. The engine has two compressor spindles and an intercooler. By a system of three-way valves, it can be operated with both 'wings' in super atmospheric pressure mode (high power) or one 'wing' super atmospheric and the other sub atmospheric (cruising power) or both 'wings' in sub atmospheric mode (idling). Since there is no change in direction or speed of gas flow at transition from one power level to another (only mass flow changes) transition is almost instantaneous - thus overcoming the slow throttle response characteristic of gas turbines in land vehicle applications. Turbines have historically been more expensive to produce than piston engines, though this is partly because piston engines have been mass-produced in huge quantities for decades, while small gas turbine engines are rarities; but turbines are mass produced in the closely related form of the turbocharger. - - - - - - - - - Of course, reading one Wikipedia article doesn't make me an expert but it would appear that, in addition to the problems mentioned above, turbines are more prone to breakdown than traditional piston engines.
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Written on: 13. 08. 08 [20:54]
insight registered since: 26.04.2008 Posts: 10	Other problems with turbines is the volumn of intake and exhaust that has to be dealt with plus the heat of the exhaust and noise.They are just not suitable for road cars but ideal 30,000 ft up. I realize the noise and heat can be tamed at the expense of bulky add-ons but there is no getting around the volumn of air and fuel going through the thing. This characteristic is perfect for efficiently pushing an aircraft at high speeds through the air but not as a captive powerplant driving a generator or CVT in a car,very inefficient use or in other words the wrong engine for the job. Re: The EVI serial hybrid Turbine...I would bet it was not built for economy of running but to just prove the concept or for PR reasons.In todays climate it would be a non starter. Insight [This article was edited 2 times, at last 13.08.2008 at 21:03.]
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