Ok so I have read about BMW's Turbosteamer and I think it's a good idea. However, I'm pretty sure that they could have done better. Popular Science says that it "reclaims more than 80 percent of the heat lost from the engine’s exhaust and cooling systems", but there is still a lot more heat untapped. If a typical gasoline ICE is 25% efficient, that means about 75% of the energy is wasted in heat. Assuming the 1.8L I-4 cylinder BMW used for their turbosteamer was the 113HP N46, hypothetically if all of the waste energy was harnessed that engine could make 452HP. The Turbosteamer, on the other hand, only brings that engine up to 126HP. So here is how I think heat recovery could be improved.
Wikipedia says that steam piston engines (like the one used in the Turbosteamer) "are very inefficient which is why there are no longer any steam locomotives in commercial use". First off, I would make the steam engine a steam turbine, which can be up to 90% efficient if run at a constant speed. For those of you who might wonder why BMW didn't use a steam turbine, it is because there wasn't enough room in the engine bay for a steam turbine and the CVT that would be needed to connect it to the engine. In fact, there wasn't even enough room for the piston-driven Turbosteamer and an Inline-6, which is why they used an Inline-4. Second, since (as I already pointed out) there wouldn't be enough room for a steam turbine and CVT hooked up to the crankshaft, I would use it to generate electricity. The car would be a hybrid and the electricity would recharge the batteries. That would mean that up to 90% of waste heat would be recovered and used to power an electric motor. While BMW's system allows the engine to work less hard since the steam is generating power, a hybrid would allow the motor to shut off completely in many circumstances. And while BMWs system might increase HP by 13, A proper sized electric motor (like the kind used in the Lexus GS450h) can generate almost 200HP. By taking into consideration that the Lexus GS450h's gasoline engine makes 292HP and it has a combined peak HP of 339, that means that the gasoline engine is boosted 47HP. If that were the case on BMW's N46, it could have made 160HP, far from 452 but still 34 more than the measly 126HP the Turbosteamer allowed it to make. That's a lot, considering we're talking about free power.-- acurafan07, Mar 04 2007 Popular Science http://www.popsci.c...004eecbccdrcrd.htmlPopular Science article [acurafan07, Mar 04 2007] Wikipedia http://en.wikipedia...i/Engine_efficiencyWhere I get the engine efficiency facts [acurafan07, Mar 04 2007] Wikipedia #2 http://en.wikipedia...peration_and_DesignThis is where I found the 90% thing (20-90% depending on the setup) [acurafan07, Mar 04 2007] Exhaust-driven turbine alternators http://www.greencar...igers_exhaust_.htmlProbably could be converted to a steam turbine alternator semi-easily [acurafan07, Mar 26 2007] Hmmmm.. First off, the wikipedia article clearly states that "This article or section is in need of attention from an expert on the subject". Read this as there are no references, and some of the subject matter is a wee bit suspect.
Second, where did you get the 90% efficiency of a steam turbine bit from? I admit I didn't spend a great deal of time on the wiki article, but I did look for that figure and got nothing.
I think we all wish steam turbines were that efficient. From memory, they're at around 50%, for large high-efficiency installations. You may have read about specific efficiencies, which are a totally different matter, and are calculated as efficiency of a turbine section as compared to it's theoretical limit. Gross eficiencies are well below that.
Hey, nothing wrong with a steam turbine hybrid (maybe better off using something other than steam), but 90% is a bit of a reach.-- Custardguts, Mar 04 2007 Like [Custardguts], I'm not too sure about the numbers, but the idea is a good one. Even if you axed the hybrid part and simply ran your car's alternator with a steam (or ethanol, like the BMW's low temp loop) turbine, there would surely be some gain somewhere. Find me a junkyard steam turbine, and I'll see if I can hook it up to the alternator on my car.-- Hunter79764, Mar 04 2007 And as a side note, you might want to try to find sites other than Wikipedia to back up claims on efficiency ratings and power outputs and such. As reliable as it is on some stuff, it's still written by regular folk who may or may not have any clue what they're talking about. It's like citing the HB for a research paper.-- Hunter79764, Mar 04 2007 [Hunter], you're right, I just use the wiki because I can't find a better site and the numbers are just for the sake of argument. As to the steam turbine, I'll be sure to visit ebay a few times. But (and I'll find a link), I also recall visiting a website that sold exhaust-driven turbine alternators. I'm sure that you could convert one of those to steam with little-to-no modification.-- acurafan07, Mar 04 2007 //It's like citing the HB for a research paper.// We're not supposed to?-- MaxwellBuchanan, Mar 04 2007 I suppose you could try it, but I think you'll end up with a [marked-for-failure] if you do.-- Hunter79764, Mar 05 2007 47 HP is not "almost 200 HP".-- BJS, Mar 05 2007 The actual motor in the GS450h makes a peak of 200HP, It just works out that when the electric motor and gasoline engines are combined, the peak HP of the gasoline engine and the peak HP of the electric motor doesn't match up since they occur at different RPMS, meaning that you cannot simply calculate combined peak HP just by adding the two.-- acurafan07, Mar 05 2007 Why even combine peak horsepower then?-- BJS, Mar 05 2007 To give a rough estimate.-- acurafan07, Mar 06 2007 Just for the sake of argument, did you take into account the losses caused by converting the steam turbine's power into electricty, pumping that into a battery, converting it back into motive force, etc?
I'm no expert, but those may be significant in your final determination of overall efficiency.-- ye_river_xiv, Jul 04 2009 random, halfbakery