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Energy: Turbine Electric Hybrids

It is entirely possible for us to find alternative sources that will even out the market for our transportation fuels.  It’s even possible for us to make that fuel from sustainable sources.  But we would still be left with an incredible 140 billion gallons per year of gasoline, about 1,200 per household, consumed simply getting around.  Nevermind that at the end of the day most of us end up exactly where we started off.

Any drive to long-term sustainability has to include  conservation.  Even if we can make a tremendous amount of fuel from cropland we need energy for electricity and heat as well.  Consuming less will always be important, and as the price of fuel rises we are in fact using less of it all the time.  But to really drop our consumption we need new technology.  Fortunately, at least one is nearly ready for prime-time – the turbine electric hybrid.

The most advanced small turbine suitable for use in transportation, among other things, come from Capstone company.  They are called “microturbines” because they are as small as 30kW (40 hp).  With only one moving part, an electric generator is built right into the system.

The main advantage of the Capstone system is that it operates at very high temperatures and pressures, giving it 36% efficiency at full throttle.  That’s better than double what can ever be obtained by a conventional “Otto Cycle” piston engine.

The conventional car engine was first made practical in the 1880s, and despite some major improvements it remains very similar.  It’s a big block of steel with heavy pistons that have to stop and change momentum twice per engine revolution.  Between those inefficiencies and the limit set by temperature at which the metal melts, they can never get better than 16% efficiency.

What makes this microturbine technology possible is not just the ingenious Capstone design, but the advance of ceramic technology in the last 20 years.

Why hasn’t this powerplant been more widely implemented already?  The Chrysler corporation worked very hard on a turbine powered car in the 1960s, even before advanced ceramics.  The main problem is that a turbine is very slow to get up to speed, requiring it to remain at high idle even when sitting at a stoplight.  The trade-off was always incredibly sluggish acceleration in city traffic or fuel consumption that showed no benefit for the more expensive technology at all.  It was eventually abandoned.

With the advance of hybrid electric systems, however, the problem is solved.  Batteries can store enough electricity to drive electric motors as the turbine brings itself up to speed gradually, replenishing the charge.  The turbine electric engine needed two very new techs before it became practical for road transportation.

In the last six years, many road-ready vehicles have been made from Capstone microturbines in a hybrid system.   The most prominent are the buses in New York, manufactured by DesignLine of New Zealand.  At 7 miles per gallon they hardly seem fuel efficient, but that’s double what any piston-powered hybrid has been able to reach.

Cars are a bit trickier, but the Whisper Eco-Logic from the UK has shown it is possible.  Achieving 80 miles per gallon in a decent sized minivan is no small achievement, especially given that this is the first generation.  The CMT-380 “supercar” was designed to impress in a different way, reaching 60 miles per hour from a dead stop in 3.9 seconds – but still gets 45 MPG in turbine-only mode.

The improvements from a turbine electric hybrid are a doubling of fuel economy, considerably lower weight (about 500 pounds in a car) and dramatically lower maintenance.  Cost will certainly be higher, but given that these have never been mass it is unclear exactly how much more expensive the system will be.  Given the 1,200 gallons of gasoline per household per year, however, the potential savings from double the mileage is on the order of $2,400 per year, offsetting additional costs.

Given that the average over the entire US is still a shade over 20 miles per gallon as more efficient cars are still working their way into the system, our ever decreasing gasoline addiction has nowhere to go but down.  Turbine electric hybrids have the potential to dramatically improve that trend.  This technology, or really basket of technologies, is still being developed but we can expect it to be a major part of our transportation future.  The best source of energy is not renewables, but not consuming it in the first place.

The 130 year old piston based technology that we all rely on to get around may soon be obsolete.  What it will take, like all three of the proven techs discussed here, is a bit more development and investment.  And that’s what we will talk about next.

12 thoughts on “Energy: Turbine Electric Hybrids

  1. Again, wow. This is very informative! Buses only get 3.5 MPG? What does an LRT get? (I know its hard to compare). The average fuel economy is only 20? We can conserve a lot if that is where we are starting from. If this is what gets us there I am impressed but 36% efficiency does not sound all that great to me. How is that measured, what does it really mean?

    • So many questions! 🙂 Yes, buses are terrible, but passenger*miles per gallon makes it work out. Still not great at best. I have been told that streetcars/LRT are about 4X as efficient, but the calculation is long and I have not verified what went into it.
      36-40% is an upper limit for turning force from heat in all practical senses. Your basic powerplant gets around that as well, so doing it on a small scale is quite impressive. It’s a measure of the work out as energy divided by the heat in as energy, so it’s a very real number. In all these systems a man named Carnot figured out these limits long ago, and it’s all based on the temperature difference they operate under. The formula for the max possible efficiency is (Temp(hot) – Temp(cold)) / Temp(hot) , where the temp is all in absolute terms (ie, right now we are at about 293K, or 20C).

  2. Very good. I sorta thought hybrids were a bridge that took a long time for payback (recouping extra costs) but with the turbine that may change. I imagine gasoline would still be the fuel. Now if the average household drives so many miles in its vicinity (the typical usage is work/school/market/kid’s sports) is this still the best bet? I imagine this turbine would be absolutely great for long distance fleets. If you can answer any of these questions so much the better and thanks again for a very good article

    • Thanks. This still may be a bridge, but it’s nearly drop-in today and the potential savings are pretty large. They can burn a wide variety of fuels, but gasoline is one of them (as is diesel!). Yes, this is best for long-distance fleets and so on, but I didn’t get into trucking – or trains, which already use something like this and have for about 50 years.

  3. 80MPG wounds like a 4 times improvement over where we are now. I imagine you are being conservative, but the potential is incredible. So why isn’t Ford/GM/Chrysler jumping all over this?

    • Yes, being conservative. I think we can reasonably expect that if this was all fully implemented the 140B gallons of gasoline would be down below 50B, or a savings around 2/3. There are still a lot of gas-guzzlers on the road, for sure!
      Ford is working on cars like this, and UK Ford sponsored the Whisper Eco-Logic (it’s a Ford platform!). Don’t know about the other two, but they are aware of it. I think Ford will be the first ones to the market, which could be before 2016.

    • Unless battery tech changes dramatically, the weight needed to carry enough energy for any decent range is massive. Chemical fuels being burned is still the best source for a range on the order of 300 miles, which is what we’re used to. Good question, tho. I’m highlighting techs that are proven and can be dropped-in to our existing world without a ton of fuss, but there are always out-of-the-box ones that you never know how they’ll play!

  4. This is fascinating. Back in the late 60s as a memeber of the 3M Sports Car Club, I worked in the Timing & Scoring booth at Donnybrook (now BIR) and there was a single appearance by the Howmet Turbine Can-Am racecar [http://tinyurl.com/7s32ukc ]. Spooky quiet & fast, it didn’t finish the race due a non-engine-related problem. Ultimately, the SCCA & USAC banned turbines altogether after their successes (especially) in Indy-car racing. Imagine how much sooner the devlopment of turbine auto powerplants might have been if they’d not been banned.

  5. This is an interesting idea–the Capstone turbines have been around, but their use in vehicles is something new to me.
    However, it is not correct to suggest that these turbines are twice as efficient as reciprocating engines. (“Efficiency” is often vaguely defined, but here I think we mean the percentage of the heat energy available by burning the fuel that actually appear as mechanical power on an output shaft.)
    The efficiency of a heat engine ultimately depends on the difference between the hot and cold ends of the cycle. Whether the engine is rotary or reciprocating does not, fundamentally, matter. Some large reciprocating ship diesel engines are over fifty percent efficient. Smaller engines can be in the forties.
    But: What has made turbines work in aircraft and power stations, but not vehicles, is that their efficiency drops off more quickly at lower loads than recip engines. Vehicles, especially cars, run at low load factors most of the time, only occasionally needing full-power for acceleration or hill climbing. This is what killed the Chrysler and other turbine car and truck projects–along with high costs. Turbines are typically ten times as expensive per horsepower as recips. As another example, the US Abrams “main battle tank” is turbine powered, while almost all its foreign counterparts are diesel powered. So it has a high power to weight ratio but burns around twice as much fuel. Take a look at the Pentagon fuel budget sometime!
    Seems to me that the hybrid concept, where the engine can (maybe) be either off or running at full power, could be a way around this.

    But lets face it–the problems with high fuel consumption in the US are cultural, not technical. Just go out on the road and look at what people are driving, and most of the time they are alone and not hauling anything.

    • A point of clarification: The M1 Abrams’ turbine is multi-fuel, it can burn diesel, kerosene, any grade of motor gasoline, and kerosene based jet fuel, JP-8. JP-8 is the standard fuel for US Army tactical vehicles today. They do this for logistical simplification.

  6. Pingback: Energy: Implementation | Barataria – The work of Erik Hare

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