Bjorn’s Corner: Why e in ePlane shall stand for environment, Part 14.

March 20, 2020, ©. Leeham News: In this week’s Corner, we continue our analysis of what it means for a regional airliner to go from Turbofan propulsion to Hybrid Electric propulsion. Last week, we looked at a Serial Hybrid. Now we analyze a Hybrid where the electric power applies in parallel with the gas turbine power.

Figure 1. Embraer’s E175-E2, a very efficient  88 seater jet. Source: Embraer.

How does a Parallel Hybrid compare with Turbofan propulsion

We use the Embraer 88-seat E175-E2 for our test of a Hybrid powerplant as last week, Figure 1. We could then see the Hybrid Electric propulsion had little chance to compensate for the effects of the added weight of the batteries needed in a Hybrid configuration.

The aircraft flies the complete mission with a minimum of 6t added weight (the weight of the batteries). The extra weight set back the efficiency of the mission with 9.3% and hybridization of the powerplant can’t regain such a loss.

This week, we look at a Parallel Hybrid to see if this changes the result. Figure 2 shows the differences between a Serial Hybrid, a Parallel Hybrid, and the default Turbofans.

Figure 2. Turbofan, Serial Hybrid and Parallel Hybrid as propulsion. Source: Leeham Co.

For a Turbofan, the gas turbine core drives the fan directly.  For the Serial Hybrid, an electrical motor drives the fan. Energy to the motor is feed in parallel from the battery and a gas turbine-driven generator.

The Parallel Hybrid we look at today couples the gas turbine and electric motor in parallel to the fan via a gearbox. The motor takes energy from the battery via an inverter.

The Parallel Hybrid is both simpler (no generator, the motor can work as a generator to charge the battery if needed) and more complex, as we need a gearbox to combine the power of the gas turbine and electric motor.

We would need a motor/generator of about 1,000kW to complement the 11,000kw the gas turbine shall develop (the engine core on an E175-E2 delivers about 12,000kW to the fan at takeoff power).

We now have a smaller motor and inverter and no generator, for a trade of a gearbox. This is a lighter configuration than a Serial Hybrid, but the elephant in the room remains. We still have a battery that weighs 6 tonnes when we want to trade 75kg of jet fuel consumption for grid battery power (if we don’t precharge the battery we gain nothing. In fact, we lose efficiency as the routing: core to the generator via the inverter to the battery and then later back through the inverter to motor causes us at least a 10% energy loss).

If we keep the assumption of equal weight for the Turbofan propulsion and the Parallel Hybrid (which still is the best case for the Hybrid), we keep the 9.3% deficiency in fuel for the trip for the Hybrid due to the added battery weight.

Would a 9% Parallel Hybrid (1000kW combined with 11,000kW) reduce the fuel consumption of the gas turbine? Yes, by the energy input from the battery but not from making the gas turbine smaller.

Making a gas turbine 9% smaller doesn’t change its specific fuel consumption (TSFC). The issue is smaller gas turbines run into a problem of increased relative tip clearances for compressors and turbines. The losses due to these clearances increase with a reduction in the size of the gas turbine (the axial stage dimensions get smaller and this makes the fit more tricky. This is why small gas turbines use less efficient radial stages for the smallest diameter compressor stages at the end of the high-pressure compressor). We would have a gas turbine with, at best, the same TSFC as the original core.

Any gain in efficiency comes from assistance with gas turbine transients from running the motor torque back trough the gearbox and using the motor as an engine starter. But these effects can’t compensate for the 9% losses caused by the added constant weight of the battery. Once again we have a Hybrid that increases the energy consumption compared to the aircraft it shall replace.

There is a deeper discussion if the precharge energy from the electric grid is generated more efficiently than our core power (it isn’t today) but we don’t have to go to any level of sophistication in this discussion. The evidence of fundamental efficiency problems with anything battery driven is too obvious.

Conclusion

Every time we try to go the route of increasing the efficiency of our airliners with energy from a battery, the weight of the battery kills the idea.

A Parallel Hybrid without the large battery is, in essence, the integrated Starter Generator I wrote about three Corners ago; it’s just a matter of how it’s coupled to the shafts of the Turbofan. And an integrated Starter Generator makes sense.

It shouldn’t replace or assist the power of the gas turbine at takeoff, climb or cruise, however. Because then our battery size increases, and everything capsizes.

So we can conclude;

  • Battery based Electric airliners don’t work
  • Hybrid Electric airliners don’t work
  • More Electric airliners work.

This thesis remains until our certifiable battery systems have at least a magnitude of improvement in their energy density.

37 Comments on “Bjorn’s Corner: Why e in ePlane shall stand for environment, Part 14.

  1. The conclusion is too general as it ignores the possibilities inherent in structural batteries, as I’ve commented on before. There is no chance of a near term structural battery based airliner but there is a longer term chance.

    • I know about structural batteries. Please explain to me how these change the equation.

      As I know them they don’t change the fundamental problem of the energy density of the battery chemistry and the structure + system needed around a battery system. We are not 30% or 50% off at the starting point. Right now we are 10,000% off with a certifiable battery system for an airliner. Please explain how you carve down this deficiency.

      The aim of this series is to kill the hype and bring the whole discussion to reality. Only then can we understand where we shall invest our money and resources to fix the environmental problems. Please give a plausible route to how such batteries can help.

      • For the obvious reason that if designers can replace a given mass of structural material with an identical mass of material that is both structural and energy storage you reduce the mass of material required to be dedicated solely to energy storage.

        It is very ealy days on structural battery technology, let alone how to design/integrate an air vehicle, but a couple of examples:
        a) in 2017, discussed in https://journals.sagepub.com/doi/full/10.1177/1045389X16679021, 102Wh/kg was achieved;
        b) this year, traditional CF layup methods have achieved 35Wh/kg, discussed in https://www.sciencedirect.com/science/article/pii/S240582971930916X

        I can’t see the correct mass to use for the E175 E2 so am hazarding a guess at 10t of CF for an airliner designed to similar CF % as an A350. At this very early level of 35Wh/kg disucussed in b), CF structural batteries would then look to something like 350kWh. Call it 1/3 of the storage discussed for the 6t 150Wh/kg additional battery in https://leehamnews.com/2020/03/13/bjorns-corner-why-e-in-eplane-shall-stand-for-environment-part-13/. With an evolution of today’s manufacturing processes. Take the a) route instead and you’ve matched the 6t add on battery.

        Of course, there there is insufficient detail to determine if switching to a structural battery as in b) would introduce structural volumetric inefficiencies, negative design limitations, maintenance issues, damage tolerance issues (also being addressed for structural energy storage in such as https://iopscience.iop.org/article/10.1088/2399-7532/ab686d), charging issues, ancillaries issues, safety issues etc. etc.., but the key point is that structural batteries do offer the opportunity to signifcantly accelerate development and the potential to make the additional mass of the (6t) battery discussed in pt13 unnecessary.

        • Thanks.
          These batteries use the skins in a CFRP sandwich to work both as the cell enclosure and as a loadbearing member for a structure. They, on the lab and cell level, exhibit density levels half to 1/3 of the ones I assume on a system level. On a system level, we could probably take away 30%-50% again. And then we haven’t looked at the load-bearing capability of the equivalent optimally used CFRP or the safety aspects of having the cells flex for every cycle of the aircraft. Non-structural batteries avoid movements in the cell as a high-performance Li-Ion cell is a miracle of tight tolerances to not have the components ever touch and start a fire.
          If this is a more intelligent and certifiable approach time will show. There will be an enormous amount of cycle and crash testing needed to declare such structures safe to use for aircraft structures. There is a long way until we see these batteries in prototypes with a pilot in them, let alone in airliners.

          • Another problem is that in airliners we already have structural energy storage (integral wing tanks) to a substantial degree. Structural batteries offer the biggest benefit where they can hide some of the weight increase from inferior specific energy by bearing some loads that previously required dedicated structure. This reduces structural dead weight by taking advantage of energy storage system mass for two tasks rather than one as previously (e.g. tank in a car), but again, to a significant extent that’s already the case in a modern airliner.

          • Remember the submarines have ‘unused space’ at the bottom of the tubular hull shape for battery storage.
            Taking a cue from that there is space under the cargo hold floor and perhaps the hold itself for battery storage- obviously best in larger planes but could even work with single bubble regional type jets who have baggage on main deck as there is ‘low ceiling space’ under the floor.
            You are only limited by issues with removing depleted batteries easily , but that applies to other ‘innovative’ locations as well.

          • I recall a couple of decades ago, being interested in EVs, looking for people to discuss them with. I had to drive, if I remember correctly, around an hour away to get to my nearest interested group and the group itself was so small it met in someone’s modest house. I would say there were less than 20 people there, maybe less than 10. It wasn’t many.

            At that time there were multiple small scale EV efforts from major car manufacturers, yet they were rudimentary. But there was pressure to develop battery technology and volume efficiencies coming from IT, and the waves of environmental pressure (from society and government) were becoming ever stronger.

            To me, now in air transport feels similar. The role of IT in providing pressure on energy density and energy storage design flexibility (to include structural) remains but the vast, concentrated demands of automotive have been added, with their clear applicability to aerospace.

            Automotive has also had an interest over the past couple of decades in making structures much more complex, such that whereas a body shop of old knew it was dealing with the same steel and same gauge on most structures now has to deal with multiple gauges and/or materials across single structures, let alone whole vehicle. It is beyond many. So the general pressure on structures has been safety but it has also benefitted OEMs in driving MRO back towards them and their dealers. My hunch is that, absent the success of iStream or similar, the auto sector will see structural energy storage as a similar MRO driver, strengthening the development of them.

            I’m not foolish enough to predict timeframes and clearly we are early stages with structral energy storage (or multi-function materials of any sort) but I would be surprised if, in another couple of decades, we do not have air transport at smaller sizes not incorporating structural energy storage in a significant part of their mass.

        • Woody,

          I’m not against your thoughts and certainly not against progress and research. We only progress when people think out of the box. What I have problems with is the craze around electric planes and even more, telling the world it will fix the environmental problems.

          – Firstly, it kind of agrees air transport is a major part of the environmental problem “but hey” we will fix it in 10 to 20 years. Both those statements are wrong, and the electrical craze thus puts people’s attention on the wrong things. Greta was right in getting the world’s attention to our big problem but wrong in sailing across the Atlantic. It puts the focus on the wrong issue in our environmental fight and gives the blatant problem areas media and attention shadow while the World focuses on:

          1. A minimal problem area (go back to the first articles to where I showed the problem and the causes).
          2. With no real fix other than alternative fuels (which get very little attention as it’s not sexy like electric).

          – Secondly, it steals investment money, entrepreneurship, and resources away from more sensible approaches. We have 200+ projects that will all fail. There is a likely backlash from all these failures and other areas that could have made real progress with the money got starved.

          • I don’t think things are as clear cut as that.

            Is air transport a major part of the problem? No, if considering solely in the context of % of overall emissions. There are other valid ways to consider it though. A paper published just this month (https://www.leeds.ac.uk/news/article/4562/shining_a_light_on_international_energy_inequality) addresses the inequality of energy usage dependent on wealth and as part of this looks at travel generally and references air travel. This is a single study and I feel it is always important to appreciate the motivations (confirmation bias etc) of those involved in such a case (and in this case the author declares herself on her twitter feed to be an ecosocialist) and so maybe qualify results, but the findings are that the richest 10% are responsible for more than half of global travel energy consumption. Flying is the dominant travel energy consumption for anyone doing multiple trips per year. So, at a time when we are all being asked or required to reduce our CO2 emissions and these emissions are proportional to energy usage, the morality/ethics of allowing such an inequality to continue will be widely questioned. Air travel can be seem as a symptom of inequality and inequality may be seen as something that could or should be addressed.

            Regarding Greta’s actions, well, lots of people need or choose saints.

            Regarding alternative fuels or the new ventures in the final paragraph, traction is the key. Without it the sound money won’t flow. The ballooning of money in the world looking for somewhere to make a strong return since 2008 means there it too much money sloshing around and I don’t see any problem with very wealthy individuals ill advised making investments in electric air vehicle projects that will never reach decent traction, let alone market or beyond. There is more than enough money to enable sufficient to find its way to the projects that will succeed, either wholly by coming to market or partially by generating useful IPR, demonstrating what doesn’t work (technically, business model, whatever) and the like that can then feed into the next round of developments.

            My personal opinion is that the multiple project 199 fail, 1 succeeds North American approach is significantly the better approach to developing electric air vehicles than the put it all in 1 or 2 baskets centrally governmentally decided European (in general) approach. The latter approach can be better where standards need to be developed (GSM comes to mind) or where the foundations and lower levels already exist (eg in starting Airbus), but it is ill suited to the current phase of electric air vehicle development.

            More br

  2. These experiments are a waste of effort , until the battery technology is FAR better than it presently is . Even then , hydrocarbon-generated grid-energy usage negates most environmental gains . This is made worse by environmental destruction/ pollution caused by mining component materials , and disposing of toxic used components/materials . The “greenest” approach is increase the efficiency of air-industry practices and components , maintaining a beginning-to-end global perspective on environmental gains , and their consequences .
    *Air-transport requires extreme energy-densities , and that means fuel .
    D.H.

    • The only real large scale experiment being done by Airbus/Rolls Royce with a 4 engine Bae 146 is to have 1 completely electric driven fan and to massively upgrade the rear APU to power the batteries.

      “One Lycoming ALF502 turbofans replaced by a Siemens/RR 2 MW (2,700 hp) electric motor, adapted by Rolls-Royce and powered by its AE2100 turboshaft,[replacing APU] controlled and integrated by Airbus with a 2 t (4,400 lb) battery.”
      https://en.wikipedia.org/wiki/Airbus_E-Fan_X

      Rolls Royce had bought out the Siemens electric propulsion branch in 2019 and has through its naval propulsion unit experience with larger electric power generation aspects of turbofans
      Its not flown yet but will give large scale actual experience, but Im sure the engineers have done calculations and modelling along the lines suggested by Bjorn and have realistic goals.

      • There is a saying in English “To cut of ones own nose to spite the face” it refers to an angry over reaction leading to self harm. I think this can be applied to all of those that want directors to work without remuneration, employees to be jailed for making a mistake within the context of a flawed system, directors (who represent the shareholders) to be vicariously jailed, big corporations to go bankrupt. We know the know how will rot and atrophy and the competitors that spring up may not be from the USA and may not care about US FAA certification. The directors may be second rate as the talent seeks to avoid risk and either off shores or works in media. Its time to learn from mistakes, a few folks need to move on, its not time to cut of ones nose.

      • Depends what you mean by ‘large scale’. The Airbus program looks fairly big. In reverse chronological order:
        1 There is the BAe 146 based E-Fan X, which has not yet flown.
        But the following are all Airbus related, although e-Fusion was Siemens/Rolls-Royce.
        2 There is the E-Fan 1.0 and 1.1 which had 2 EDF. E-Fan 1.1 was the first electric aircraft to cross the channel. (Pipersal would have been first but was strong armed by Airbus through Siemens who claimed safety issue)
        3 Siemens e-Fusion flew in a Hungarian Magnus. Now of course Rolls Royce owned.
        4 There is the Vanhana “EVTOL” that has flown
        5 There is the CityAirbus “EVTOL” still in development
        6 There is the e-Genious sailplane
        7 There is the CriCri Electric

        The Siemens technology was impressive and Siemens has sold of some jewels to Rolls Royce.

        Siemens has developed a tiny inverter of highest power density for electric and hybrid-electric aircraft. It took its first flight on a Magnus eFusion electric test plane. The Siemens inverter “SD104” uses silicon-carbide semiconductors and has a micro channel cooling plate. The power electronics fits in a box of 47mm*94mm*141mm and weighs only 900g while and delivers a maximum of 104kVA of propulsive power

        So 0.9kg inverter powering essentially a 100kW motor. Standard Silicon fails at between 150-200C an this limits heat transfer. Silicon carbide transistors can operate at nearly 500C. The microchannel heatsink is impressive as well.

        It looks like electric flight is cost effective for self launching sailplanes (loved for its lack of noise) which typically provide 3-4 launches and safety and first trainers which operate at less than 70NM range.

        There are also some Airbus drone deliver projects targeted at medical deliveries and deliveries of supplies to the crews of merchant ships.

  3. Using the gas turbine at max efficiency only to charge the batteries and during T-O/climb makes for an engine running at its best TSFC of 0.2-0.3 instead of cruise 0.5 TSFC when you let the batteries power the fan. Once batteries are starting to be depleted during cruise you decend to thicker air and run the engine at max power again at max efficiency while climbing. You can then make a trade off between battery capacity and number of recharges while looking atthe Brequet equation and design for optimal L/D, a bit like the NASA-Boeing Sugar Volt. At each recharge you burn JET-A reducing the mass. Some Hybrid cars makes the similar process charging the batteries at max engine efficiency power output.

    • If you listen to Elon Musk his strategy is similar to yours. For electric flight seems to be:
      1 Use vertical take-off and landing to eliminate large wings subsonic wings, flaps and undercarriage and then associated weight and drag.
      2 Fly the aircraft to a very high cruising altitude where parasitic drag is negligible and only induced drag has an effect (induced drag is small component). This is of course possible since electric battery propulsion does not need air to maintain power.

      (Note Turbofans, with BPR of 3.3 work efficiently to Mach 2.7 and therefore Electric Ducted Fans work to effectively to about Mach 2,7)

      Musk has spoken of 400 watt hours/kg as being ‘compelling’ for electric flight. Using that energy density, assuming a 70% mass fraction for the battery and assuming 50% of the energy will be used to achieve cruising altitude at 66% efficiency suggests Musk is looking at a cruising altitude of around 30,000m.
      At 30,000m / 100,000ft the air density will only be about 1.5% as much. Hence parasitic drag will be 1.5%. Concord had a supersonic lift to drag ratio of 7 but I imagine the wings on such a supersonic transcontinental aircraft would be smaller than concord and that there would be savings from using thrust vectoring and gimbaling for control.

      A hybrid makes sense from the point of view of providing for the large reserves required for emergency hold, divert, head winds, as a safety during take-off and to provide for climb to an efficient altitude (which is your idea).

      Once at such an altitude (30,000m) there would be an enormous glide range.

      • Elon M. is a complex person but not an engineer of dutch Kidelberger, Kelly Johnson, Mel Bobo calibre, but he looks for those and hire them to develop his visions.

        Flying supersonic is hard to do with good fuel efficiency still as you move to the altitudes you mention the speed of sound V²= raa*R*T/M (raa is adiabatic constant, M is molecular weight of gas) as you fly at 100 000′ and higher, local M 0.9 is a quite fast speed over ground. Check the amazing story of the Airbus Perlan II glider project.
        You have to solve other problem but in theory you can use the thin and cold air “way up there” and glide for a good distance even if you have a glide ratio at those altitudes of only 30-45 compared with the best gliders at lower atitudes.

        • The North American XB70A Valkyrie had the extraordinary supersonic lift to drag ratio of 23.45 at Mach 2.39.
          http://www.ingaero.uniroma1.it/users/ingaero/joomla/attachments/683_filippone.pdf

          This is 3.3 times greater than Concord and is attributed to the compression lift of the fold down wing tips which reduce induced drag 30%. I suspect it’s high cruising altitude is the other.

          A 1 kg electric aircraft moving at Mach 2.4 (680 m/sec) with 0.4N thrust would have a power requirement of 275 Watts, say 400 watts allowing for EDF inefficiency. Certainly a current battery at 50% mass fraction could provide that power level for 20 minutes.

          I suspect at even higher altitude the L/D would improve further.

          • My idea was that you could get a speed over ground much higher than M1 by flying at subsonic indicated Mach speed at much higher altitudes due to temp and density being much lower. Not having to worry about supersonic flight problems, still there are lots of other problems cruising at +100 000′, radiation levels is one of them and decompression decent another. There are many more great aeronautical designers during history:
            Willgoose and Mead of PWA, Hooker of Bristol/RR, Hawker, Mitchell, Mikoyan, Schmued, Anselm Franz…

    • Tad,
      the article you reference correctly states you need higher compressor/turbine efficiencies to go with a higher T4. If you only raise T4 with the same compressor/turbine efficiencies you run the engine off the peak thermal efficiency spot. Doing the core smaller hits the compressor/turbine efficiencies as I described above, so raising the T4 in isolation doesn’t buy you the result you want. A smaller core has a problem with compressor/turbine efficiencies, thus it, everything else being equal, does not give you a lower TSFC.

      • It depends how you do it. The constant pressure lines in the h-s diagram diverges as you go up in temperature, i.e. you can extract more work for the same pressure difference across the turbine as you increase inlet temperature, Today most air entering the combustor is for cooling and tailor the temp distribution into the nozzle guide vanes and T1 blades. The less cooling air the higher the efficiency up to a limit. Trails with ceramic (Ceramic Matrix Composites) burner liners, NGV’s, shrouds and even HPT blades can make a step change in Turbine inlet temperature and make reduced turbine cooling air flows possible.

  4. Bjorn’s argument is rock-solid. Yet, it won’t stop the green dreams of climate alarmists, and it won’t stop industry to try to placate them with pie-in-the-sky promises and concepts.

    Meanwhile, almost no one dares to question to foundation of the climate alarm. Are we really certain that trace gas CO2 (0.04% of atmosphere) is the main climate driver? What about water vapor?

    How do we explain climate cycles before industrial age? How do we explain the last ice age that ended only 11 000 years ago? Why is no attention being paid to the Milankovitch Cycles?

    https://www.youtube.com/watch?v=4GUcn07enz4

    • same old.
      Water vapor is an amplifier and not a causal climate effector.
      solid | liquid | gaseous water are in thermal balance.
      Change the temp and the balance changes.
      solid (ant)arctic water aka “ice” is (was) a strong thermal buffer.
      Polar icecap vanishing is quite the danger sign.

      Minimal upward changes in temperature provide for large increases in water vapor content and thus massively increased energy transfer in the atmosphere.
      ( strongly driven by evaporation/condensation energy exchange.)

      At the moment CO2 content does not match the climate we have ( i.e. it will further change strongly to warmer. )
      Look back in time for the climate conditions fitting to current CO2 levels.

  5. Ive been a proponent of carbon neutral e-fuel or PtL fuels and I agree with Bjorn’s examples and assessments but I think there is a niche case the electric aircraft will be more efficient in energy usage over very short distances, under about 70NM. They will still be bigger aircraft.

    We have to get this argument clear because there are huge numbers of members of the public who are expecting or demanding electric battery aircraft and we don’t want to be railroaded into this counter productive nonsense.

    Consider an electric aircraft with a battery mass fraction of 33.3%, Payload of 33.3% and structural weight of 33.3% of MTOW. Assume motor and battery charging efficiency is 90% overall.

    A gas turbine version of this aircraft would require only 15th as much fuel assuming an thermal efficiency of 33.3% versus 90% efficiency for the electric motor and one would only need 2.4% as much weight of fuel as the electric requires batteries. The gas turbine version can thus be 2/3rd the size and weight and will only require 1.6% weight of fuel as the EV will require batteries.

    This fuel however carries 45 x more energy than a battery, even if only 1/3rd is extractable, making it equal to the energy content of batteries with a mass fraction of 72%.

    The efficiency of production of an e-fuel is 65% best case though the numbers become meaningless when one starts using thermochemical and photochemical reactions that bypass electrical conversion.

    So in very short ranges, the energy usage is better in the electric aircraft. The range is about 50-100 NM or less.

    it all depends on the source of the electricity for charging (wind, nuclear or combined cycle gas turbine) or the source of the energy for the fuel (e-fuel made from electricity obtained from renewable or nuclear or wind or sequestered and the losses.

    At very short ranges the batteries weight becomes less significant.

    It’s worth looking at the Pipersal Panthera which comes in Conventional, Hybrid and all Electric.
    https://en.wikipedia.org/wiki/Pipistrel_Panthera

    1 The hybrid and all electric carry only 2 instead of 4 passengers to make room for the batteries.
    2 The hybrid has half the range (700NM) compared to the conventional piston engine aircraft which has a range of 1200NM.
    3 The electric has 1/5th the range of the piston engine aircraft ie 250NM instead of 1200

    I would assume if range requirement were halved the Panthera might be able to carry 4 passengers 100NM. in other words 10 landings and takeoffs to travel the same distance.

  6. Will this interesting series of articles also look at ‘conventional ‘ ways of reducing the carbon footprint of aircraft?
    In reality these articles really show that present battery technology just isn’t ready yet.And won’t be for a while.
    But clearly there are things that can be done and some that already have been such as lighter construction materials and geared fans etc.
    How much more can be done whilst we wait for high density batteries?
    Blended ‘green’ bio-fuel ( 20%?) some tests have been run I believe
    Laminar flow wings? Perhaps that could save a further 10-20% ( but I don’t know).
    The key I believe is to show the world that the industry is doing its upmost.

    • What you mention are kind of global improvements.
      they touch all the drive concepts evenly.
      you need to look at technology that is exclusively applicable to a green propulsion concept.

      • And nuclear, which in the case of molten salt thermal neutron breeder is renewable. Nuclear is the only energy that will work if the climappocalypse were true unless you are a sort of sentimental medievalist who see expensive, poverty inducing energy as good way to reduce demand and population. Its being called the dark green-left by some. Electricity in Germany is a luxurious EU0.36 in nuclear rich France EU0.18. Germany can not afford the decarbonisation of its industry eg through the use of hydrogen to smelt iron. It will on present policies decarbonise by slowly deindustrialising.

        • I am rather relieved that you are an observer/oppinion holder and not a natural lawmaker.

          In the case of Germany you see quite a bit of renewables in the energy mix.
          ( I would have kept the nuclear plants and taken down more older (brown) coal power stations.

          On occasion I do wonder who finances all the green nimby acolytes. The US ?

          • In most cases these are “top down” movements funded and organised from above to appear grass roots. It became very apparent due to citizen journalists has subsequently been a big reason of the heavy social media crackdowns. Antifa, Green-Left, ISIS even the Russian revolution was organised, funded, seeded and fertilised from above. Both “sides” have been co-opted of course but certainly no strong grass roots movements exist in the west, they’re ruthlessly interdicted, coopted and crushed.

            The nuclear industry spurred on by Government funding and military interests made a fundamental mistake in pursuing a water based technology that the original American Inventor said was unsafe for reactors over 60MW due to the difficulty in natural cooling above that size and the expansion of water into superheated steam when there are failures in the vessel. The industry has been safe nevertheless.

            Decarbonising steal production requires cheap hydrogen when that comes, then removing the 4.2% of emissions that comes from steal is easy. The 5% of emissions from cement calcination production can be halved and that portion that comes from the lime itself can be collected and converted into liquid fuels. The electricity from nuclear can be used to split hydrogen and the low grade waste heat can be used to release the water and CO2 captured from the air by amine pellets to make the fuel we need for aircraft, ships and tractors. Electricity for electrical cars likewise. Ammonium nitrate can be made the same way. These things can be done with “renewables” but the calculations done with a spreadsheet yield horrifically expensive results, mainly because the plant needed will only be utilised 40% of the time.

            Maybe we’ll seem some 50% efficient cheap solar cell and a cheap battery, or similar, that both lasts 50 years but I rather doubt it.

        • William,wind and solar ( in the US) are now cheaper than coal and any new nuclear.This is also certainly the case in the UK.In holland there have recently been wind farm contracts with zero CFD’ ( i.e. The builder will take the risk of selling his electricity at the current market price whatever that may be).I don’t think it can the case in Germany as they recently announced the opening of a new brown coal mine.
          But the price of solar and wind continues to drop.I guess it all depends country by country for the efficiency of these two ‘natural’ energy sources.

          • The “cheap” wind/solar quoted to us by the publicity departments and CEO of “green” energy suppliers is essentially deliberately misleading, sorry 😐 to say. The price quoted is the “levelled cost of production” or NPV which is the average cost of production based on all cost: capital costs, running costs, maintenance, interest, wages etc.

            Sounds fair doesn’t it? It isn’t because no network costs.

            Producers of peaking power get paid at least twice as much as renewable suppliers. That’s because the solar & wind isn’t worth as much because it isn’t there when needed and can be knocked out pretty fast by cloud banks and becalmed. If there is a surge in demand or a fault in a transmission line it can’t despatch the 20MW/second power increase till a fault is cleared. Also the bulk of costs are now in the distribution network and its switchgear, harmonic filters and power factor equipment. Adding Tesla batteries to the grid does provide the power needed to stabilise the network, as was done in South Australia, hopefully till Generators start but it is not really storing renewable energy as stabilising the network for a few minutes against the messy surge prone power introduced by renewables. Thermal Turbines have something called “spinning reserve”. Transmission lines have been massively increased in capacity to try and balance out the power surges coming from different regions of renewable.

            This work on transmission lines and as well as peaking backup plants is why electricity is so expensive in so called green energy countries such as Germany. A luxury causing real suffering to the elderly and less fortunate.

            Ireland last year produced 12% of its energy from renewables but saved only 3% in CO2 emissions, that’s due to the inefficiency of peaking plants. I keep saying to my green friends we’d be better of just replacing our thermal power stations with long to build combined cycle power stations, for now, but instead we get wind turbines and peaking power stations and a worse result.

            For each unit of energy invested in solar you get 7 back. For wind it’s about 14. For gas combined cycle 60, for thorium thermal neutron nuclear 250,000.

            I don’t want to completely reject it, there are going to be improvements but the technology is far from ready.

            If we made e-fuels they be much more expensive if based on wind/solar since the plant would run only 45% of the time.

    • For range min min fuel you get into mass, glide ratio, flight speed and engine sfc.
      You might get another 10% reduction with super slender wings and flutter fly-by-wire supression.
      Reducing mass by going to more advanced material than Carbon Fiber reinforced structures like boron fiber in ceramic matrix materials and others is not that easy, engine fuel burn is maily a funcion of burner pressure and fan size and as you get over 70:1 pressure ratio you need active cooling of the compressor air as you get too hot combusion gases generation a pletoria of chemcial reaction and plasma giving problems. Fan size on UDF’s are around 140″ and up and give up to another 10% fuel burn reduction. So the GE9X and RR Ultrafan are getting close to what present jet engines can achive. Their next evolution would be counter rotating fans that might be unducted and cooling the compressor air thru the HPC/IPC’s putting that heat into the fuel.
      It might be easier to grow trees and algea in salt water ponds in deserts and make bio fuel from it and use GE9X and Ultrafan derivatives for 30-40 more years.
      75 years from now we might have solved the gravitation and can have anti-gravity machines for lift and a small thruster for form drag.

      • supercritical carbon dioxide (sCO2) closed cycle brayton cycle engines can achieve 47% efficiency at only 600C. They are 1/7th the size of steam turbines of similar power. They are likely to take over from steam turbines in combined cycle power plants. I’ve seen an 9 year old analysis that says that a turbofan with a second sCO2 cycle like this would have 3% more efficiency in consideration of increase weight, drag and lost jet thrust. Things have moved on: sCO2 cycles have improved , microchannel heat exchangers developed and geared turbofans are established. These engines are likely to be extraordinary used on their own. Pollution control would give exceptional opportunities.

  7. The gearbox is not a given. ( except you want basic GTF functionality. slow fan with high rpm turbine.)
    you can run BLDC type generator/motor “thingies directly on the spool shafts.
    this would allow to boost LP spool from battery and or HP spool, you can balance power between LP and HP spools i.e. improve on “impendance matching” without lossy bleed.
    … and a range of other option combos.

  8. Some great points being made imho.I hope Bjorn can do one section on conventional ( and commercially possible) ways that that 3 axis aircraft ( wings engines fuel materials etc) can be improved to increase overall environmental efficiency ( and by how much).

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