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Re: Whaaat??
analyst   8/28/2012 11:02:32 AM

It would seem to me that, aside from your personal finances, one should consider the effect of a higher efficiency auto and truck fleet on the country. In 1973, when the Arab world decided to impose an oil embargo on us, it was simply devastating.

Since then, increasing CAFE standards have made us far less susceptable by dramatic changes to the price of oil -- the price of crude first hit $100 a barrel in February of 2008 -- but it is a still a major factor that takes dollars out of the pockets of consumers, and therefore acts to hold the economy back.

When we hit 54 MPG average efficiency, and this will take more than a few years, our cars will be roughly twice as fuel efficient than they are now. And the effect of price shocks, of which we have no control, will be roughly half as harmful.

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Re: CAFE loop holes
analyst   8/28/2012 10:52:36 AM

For what it is worth, naturalgas.org says that combined cycle natural gas plants can achieve efficiencies up to 60% and microturbines with new waste heat recovery techniques can achieve energy efficiencies of up to 80 percent.

It would appear obvious that maximum energy conversion can be achieved by multiple heat conversion loops, with each one using a different working fluid (and therefore phase transition temperature) or working fluids operating at different pressures so as to manipulate the phase transition temperature. (For example, one steam loop operating at 1520 Torr, another at 760 and a third at 380 Torr.) 

I assume that this is the sort of thing going on in the 80% efficient microturbine cited above.

According to what I have read, gas powered generators, by virtue of the limited amount of material subject to the working temperature, can afford to use more expensive turbines, such as those made of ceramic, and therefore operate with input temperature of 900-1400°C. 

Let's compare 4 cases:

1. TH and TC  = 1000°C and 32°C   (90°F)
    theoretical efficiency = 1 - (305/1273) = 76%

2. TH and TC  = 1400°C and 32°C   (90°F)
    theoretical efficiency = 1 - (305/1673) = 82%

3. TH and TC  = 1000°C and 15°C
     [Utilizing a deep lake as the heat sink.]

    theoretical efficiency = 1 - (288/1273) = 77%

4. TH and TC  = 1400°C and 15°C
    theoretical efficiency = 1 - (288/1673) = 83%


From which I conclude that if gas plants are not getting higher efficiency than that available from an internal combustion engine, they are probably planning to upgrade.

Again, based on what I have read, coal powered plants are a different matter, simply because a larger amount of material is involved in the turbine, necessitating the use of less heat tolerant materials like steel.

I would really like to see a reference that shows where internal combustion engines, specifically those used in cars and trucks, are getting 40% efficiency. Facts are good!


A post word: Given the success of the fracking industry, it would appear to me that there is an irresistible force towards the shutting down of coal powered electrical generators and the starting up of natural gas powered electrical generation.

I think that solar gets closer to cost parity every year, and when it becomes as cost effective as natural gas, then we will have an even more attractive option for running EVs.

Lastly, I never intended to advocate EVs as "the" solution. I stand by the decision on a 54 MPG standard for a bunch of reasons but I don't know when Lithium Ion (or the Holy Grail, Lithium Air) battery packs will get down to the $5k range. Until then, I think EVs will remain rare.

My own interest in EVs is largely motivated with the idea of replacing a $50 fillup with a $5 recharge, but we will see how that works out.


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Re: Whaaat??
Noswad   8/28/2012 9:09:07 AM
I prefer to drive a fuel economical car with very basic add ons. These cars are cheaper than the "Expeditions" etc... So, I term them the "$11,000" car. The reason we have to send troops to the oil rich countries is to protect these people that want their excess. Such as the big gas guzzling luxury vehicle just to drive around in. Why do we need video players, zone comfort systems, heated seats, etc... in a car or truck just to get from point A to point B.

Safety enhancements are worth the cost. Since people have to drive 80 miles an hour and can't be patient enough to drive safely then we have to compensate for these too. I am guilty of it myself.

But the auto industry is a business and will build and offer what most people demand. There is nothing wrong with wanting just some basic transportation with the expensive luxury items that drive up the basic cost of a basic vehicle.

Yes, I do know when someone is LYING. It happens everyday. They are called politicians and analyst.

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Save newcomers some time
akwaman   8/28/2012 8:50:52 AM
After reading and participating in this discussion, I realized I could save new readers some time.  Save a big chunk of your day and don't waste time reading the stuff by Totally_Lost, the name says it all.  I wish I could get back the part of my life involved in reading those posts, 99% of it misinformed trash.  Proven wrong over and over, Totally_Lost just moves on to another useless and misinformed point(?), if you can call it that.  I think I found the problem with EV technology advancement, when Totally_Lost says "I've been doing electric motor EV design for a few years now".  High points of this discussion are from <analyst> and <bwilson4web>.

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Re: Smaller is better
naperlou   8/28/2012 8:39:29 AM
An alternative to raising taxes at the pump is to drill here (and I do not include Canada for this purpose).  The price of oil from the Middle East includes "royalties", or taxes, paid to those governments.  By drilling in the USA, we get that tax revenue at the wellhead.  Overall, the consumer's cost is no higher.  In addition, unfriendly governments have less to use to destabalize the world. 

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Re: CAFE loop holes
Kevin   8/27/2012 9:58:35 PM
Sorry to stay on my soapbox!

Analyst -

one thing I forgot to answer:  Yes, if today all power plants were combined-cycle natural gas power plants, my 2.5X "reality adjustment" for the EPA's EV MPGe would be much less....and EV's would indeed be very green.  But...as I mentioned, these plants are new, rare, and expensive for now.  

My comments are based on TODAY'S grid average power sources.  see this wonderfully informational chart:  www.llnl.gov/news/newsreleases/2010/images/energy-flow-annotated.pdf

William K:

Here's some supplemental reading on ammonia as a fuel.  Note that it can be absorbed at very high density into inexpensive magnesium chloride powder...mitigating risk of a large accidental venting of ammonia.  Also, ammonia is lighter than air, so rises rather quickly (as opposed to, say, propane, that dangerously fills basements and low areas).  

Note that ammonia can be burned as a fuel in today's internal combustion engines (with some modifications, of course), with essentially zero emissions.  The octane rating is very high, which support high compression ratios – improving engine efficiency further.

It can also be used in fuel cells in the future, when that technology is ready. 

And lastly - did you know that today's fertilizer is nearly 100% made from natural gas feedstock?  If we converted to a solar-synthesized ammonia fuel, it could be used directly as a fertilizer or as a feedstock to make other kinds of fertilizer.






and definitely read this: 


sorry if I'm somewhat obsessive on this stuff...but hopefully you'll see that my data is correct and based on non-biased factual study.  There is SO MUCH hype and distortion out there on energy topics and EV's!


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Re: CAFE loop holes
Kevin   8/27/2012 9:43:41 PM

Thanks for your (very civil and intelligent) response.  I've actually studied these things, and also understand Carnot efficiency, etc.  The facts are a bit surprising!

The Prius atkinson-cycle engine (this type of engine gets higher efficiency but lower power for a given displacement by expanding the gasses more) is 38% efficient, and Toyota is working on a 42+% version.  Car engines passed the 25% mark a long time ago (big V-8's)...but EV people keep dragging that old figure out.  www.green.autoblog.com/2011/04/24/toyota-targets-45-thermal-efficiency-for-engines-in-next-gen-hy/

The average coal power plant in the USA has an efficiency of ~33% (http://en.wikipedia.org/wiki/Fossil-fuel_power_station ) with the best coal plants approaching 40%.  The latest high-tech combined-cycle natural gas power plants can get up to 56-60%, However, there are only a few of these and they are  expensive because they are essentially two power plants in one (a gas-turbine generator with a steam-turbine system run off of the waste heat of the first).  FYI - in case you google around: Power plant efficiencies are published in a strange way - they don't talk about "efficiency", they use "heat rate".  Efficiency = 3412 / HEATRATE, where HEATRATE is in BTU/KWh.  

There are several reasons why an internal combustion engine can get such high efficiency vs. most power plants:  

1.  The peak temperatures are actually VERY high, but last only a short time, then falls as the gas expands.  I think peak temp can be over 1800°C.  (someone can perhaps confirm this?) 

2. The cylinder sees a an average temperature much lower, due to #1 above, but also due to the other 3 cycles (of the 4 engine cycles) being much lower temperature.  This is how melting is avoided, along with water cooling of course.

3.  Power plants run their boiler and turbine in a steady-state condition.  The temperature is much lower than the peak temp in an ICE.  I think they usually run around 600°-700°C.  

4.  Power plants recoup some efficiency with tricks like "multiple reheat" where the steam is reheated between successive steam turbine stages.  Even with this, 40% eff. is doing well.

So...without being too rigorous about it - a combined cycle power plant can get, say, 34% efficiency from the gas turbines (implying waste heat of 66% of the combustion input heat), then a steam turbine system converts 38% of this 66% to work, giving an additional 25% net conversion of heat to work - summing to 59% total efficiency.  These plants must burn natural gas, because of course gas turbines can't easily burn coal.  see:  http://www.power-hitachi.com/products/gtp/h25h15/ebook/book124/H25-H15_12p_0421.pdf

So why don't we just make power plants all "natural gas burning diesel engines"?  Well....we could, but efficiency would only be about 40% and there would be many moving parts to wear out an maintain and the engines would be HUGE (costly).  For a power plant, the high power density and simplicity & reliability of turbines is a much better choice.

Fortunately, the invention of fracking is now producing a bonanza of cheaper and cleaner natural gas, so hopefully in the short-term we will see many more combined-cycle power plants....until we can develop better solar power and solar-synfuels.





William K.
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Re: CAFE loop holes
William K.   8/27/2012 8:25:11 PM
Kevin, Good respose, no doubt. Except that big power plants are a lot more efficient than automotive engines.

The part I liked best is the concept of a solar-produced Amonnia type fuel. The challenge would be on the emissions end of the deal, and if you think living downwind of a gas station is bad, immagine living near an amonnia filling station. Of course, possibly the solar powered fermentaion of municiple sewerage would work, producing useful quantities of methane while getting rid of waste. It would need to be solar powered because adding energy to almost anything takes power.

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Re: CAFE loop holes
analyst   8/27/2012 8:11:57 PM

I only have one small disagreement with you. You say this: "and those power plants, on average, are not much more efficient than the best car engines."

Huh? All heat engines should be Carnot efficiency limited. You will recall that at the limit, the efficiency of heat engines can approach but never exceed n= 1 - (TC/ TH).

Obviously, internal combusion engines have a much more limited difference between TC and TH than that available in a power plant. The power plant can both generate hotter TH and colder Tc. For example, the power plant likely uses a river or other body of water for cooling.

In any case, thermal efficiency for an internal combustion engine is approximately 25% and that of a coal power plant might be 40% and that of a gas powered plant can get to 60%.


If we assume the power to charge the EV is derived from a natural gas burning plant, which certainly seems the trend, then your calculations can be expected to be off by a factor of 60%/25% = 2.4. Which might very well mean that the EPA equivalent MPG calculations for EVs are correct and yours are the figures in error.

As I understand it, my community has just signed up to have 100% (it could be 50%, I don't recall clearly) of its electricity to come from renewable sources. That obviously makes the EV that much more attractive.

On the other hand... no one wants a EV that runs off of Nickle Metal Hydride, like those which I believe the Prius uses. If you get an EV, you are going to want the greater energy/mass, and therefore greater range of Lithium Ion batteries. And enough Lithium Ion batteries to drive your car are still quite expensive. Which is why I am not counting on buying one in the next couple years.

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Re: CAFE loop holes
Kevin   8/27/2012 7:49:51 PM
Wow - this article has brought out the zealots on both sides of the fence!  Many of these comments are so far off-in-the-weeds that they don't merit a response.  A more productive (engineering related) question is: Is the 54.5 MPG target reasonable and acheivable?  I have not read the document, but assume that this is the target for EPA COMBINED city/hwy ?

Let's take a sober look at what exists TODAY, to see what might be possible.  First, the Prius hybrid, at 51/48 MPG (city/hwy) is currently the high watermark in the USA, and has been for many years. Also, note that the Prius V and the Lexus CT hybrid have identical drivetrains and get only 44/40 and 43/40 MPG.  The larger Camry hybrid gets 43/39 and the upcoming ford fusion hybrid reportedly gets 47/44.  It is clear that hybrid technology is very advanced and in the "diminishing returns" zone...where ~50MPG is probably the avg. asymptote...and 54.5 seems very challenging, esp. if larger cars and trucks are included in the average.  Note that there are now MANY non-hybrid cars that get 29/40 MPG city/highway, and VW Jetta TDI gets 31/43.

Using my (not insignificant) knowledge of all the details that roll up into a car's efficiency, here are some factoids:  Hybridization (and start-stop systems) can dramatically help city MPG, but highway is only slightly improved, vs. a very efficient non-hybrid.  Also, a hybrid can have better acceleration than an equivalent highwayMPG car...due to the temporary electric boost.  Weight mainly affects city mpg, but has a small effect on highway.  Also, a hybrid system can compensate somewhat for a heavier car weight in city driving by regenerative braking. Aerodynamic drag affects mainly highway mpg, not city.

Now for EV's:  Electric motors can be very efficient (95%+),but that is not really the point.  The issue where EV zealots get lost in their comparisons with gas or diesel cars is that if you start with FUEL (the most fair comparison IMO), then you'll see that 70% of today's power comes from fossil fuels (coal & natural gas), and those power plants, on average, are not much more efficient than the best car engines.  Factor in a 7% powerline loss and ~20% battery charge/discharge & controller loss, and you'll find that with today's grid, EV's do NOT save a significant amount of total energy or fossil fuel.  They mainly just shift the fuel away from oil.  Also, the batteries add a lot of counterproductive weight and cost.  Some day, when the grid is primarily powered by renewables - EV's could be of great benefit (but not now).  Unfortunately, the EPA's MPGe calculation is deeply fraudulent.  34 KWh of electricity took approx. 70-85 KWh of fossil fuel to create.  In other words, if the Nissan Leaf's 100 MPGe were calculated honestly, one would divide by ~2.5 to get ~40 MPG.  To be fair, if  you live in Seattle, your power is 90%+ hydro, and EV's are therefore wonderfully green.  

However, back to the 54.5 MPG target - I think the government is relying on this EV distortion to acheive it.  It is technically incorrect, misleading, dishonest.  In short, the 54.5 goal can only be acheived with a massive number of EV's on the road, and calculating MPGe in the above incorrect way.

Regarding vectors for REAL future MPG improvement...I think drag reduction is really the main one left.  Lower weight helps...but mainly only for city mpg and even then mainly for non-hybrids.  Many cars are already using high strength steel to reduce weight...but going to carbon fiber is super-expensive and actually dangerous (poor impact strength), and would only help MPG a little.  So...the main trade-off will be smaller cars with super-aero shapes (which may not have especially appealing styling).  I think this, plus continued refinement of hybrid drives could probably <JUST BARELY> get us there...where the BEST cars are 60+MPG, and larger cars are ~45-50MPG...for an avg. of ~55MPG.  Avg. horsepower / performance will definitely be lower, however.

For good recreational reading - learn about the highest watermark yet - the Edison2 car which won the Automotive XPrize with over 100 MPG actual results:  http://www.edison2.com/   They won with a fuel-burning engine, but because no venture capital was available for this, their production car will be an EV.  Fortunately, their low weight and especially their super-low drag will benefit either type of drivetrain.  

Lastly, in my opinion, we should be putting much more effort into creating a renewable, solar-synthesized, low emission, domestically produced liquid (or gaseous) fuel to replace gasoline.  Ammonia fuel is probably the most practical (google: "the other hydrogen"). After that is accomplished - EV's are not necessary, nor are "oil wars", coal strip-mining, etc.  

Cheers!  Kevin

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