Idée Fixe [2]

In this second part, Steve Randle commences his treatise on how he would shape a credible modern-day successor to the original Citroën DS.

Image: adac

Steve Randle: “First and foremost, while this car would carry the history of its ancestors proudly, it must above all not be a ‘me too’ exercise. The questions have changed since the DS, and hence so too must the answers. An attempt to recreate the DS would be self-defeating by its own definition. We should pause to consider the vehicle from which Monsieur Macron will emerge before the waiting world. It most certainly is not a DS7 Crossback.”

Image: ©Driven to Write

 

Layout & exterior:  “In this respect, I would retain the long front / short rear overhang profile of the SM / C6 I’d wish for something elegant and unfussy – not swamped with details like so many current production designs. I would also retain the four door fastback shape of the C6, but would add a tailgate like the Audi A7. I’d like to see a narrow rear track with faired in wheels to reduce drag and make the car look distinctively Citroën and I’d really like the car to have a less masculine / aggressive personality than all other luxury cars currently on the market. It would also bear the Citroën name and double chevron clearly upon it..”

Image: ©Driven to Write

Propulsion:  “Front wheel drive is perfectly satisfactory, and part of Citroën’s DNA. An electric drivetrain will be necessary, but I don’t believe that using a battery pack to cover all the vehicle’s energy storage is the way forward. Certainly, with the alarming amount of CO2 generated in the production of a lithium ion battery pack, we want to keep this to a sensible minimum. I’m not interested in participating in the horsepower arms race either – that’s not what this vehicle is about – so traction isn’t really an issue.”

“Internal combustion engines are fraught with difficulty due to emissions problems which are inherent with intermittent combustion processes. I would prefer a gas turbine approach, but using a multi-stage axial flow device, as used in helicopters. With a twin or triple-shaft turbine, you can get the high compression ratios necessary for the circa-50% thermodynamic efficiency that’s required. You won’t get there with a radial flow device. This route makes the generator tiny as it will be running at such high speeds.”

“Overall, we would achieve a refined, efficient, clean, multiple fuel capable drivetrain. The cost of developing such a turbine was not huge (as quoted by Williams – the aerospace turbine people, rather than the F1 group), and very small in contrast with a typical IC emissions program. I hasten to add that my father Jim was working towards this with Jaguar and Volvo 20 years ago or so, and I’m shamelessly plagiarising him!”

Driven To Write: It might be useful at this point to expand a little on what a multi-stage axial flow device is, given that some of us may not be all that familiar with the world of aviation. How does it differ to what the Hybrid Kinetic Group are proposing for the concept they displayed with Pininfarina at Geneva for instance?

Steve Randle:  “We need something that develops a high compression (or more importantly, expansion) ratio to be efficient. The turbines developed using bits of turbocharger (like the HKG unit) are limited to about 4:1, and hence a thermal efficiency of about 18% at best. Modern turbodiesels are good for about 38% at peak torque. With multiple stages, you can get about 18:1 and around 50%. With an electric generator, we don’t concern ourselves with the fact that the power band is narrow and at high rotational speed.”

DTW: What would the turbine need by way of air intakes?

SR:  “The turbine needs cooling, and of course air for combustion. I don’t think we need big aggressive scoops however. I would prefer a smooth, elegant shape.”

DTW: Given that the turbine will be burning fossil fuel of some kind, what emissions would be likely and how would they be handled?

SR:  “Continuous combustion means very much less trouble with NOx, particulate and unburned HC. I’m hopeful that no after treatment would be needed, but we may need a catalyst. This could be combined as part of the combustion chamber’s body. I favour compressed natural gas as a fuel, though a turbine lends itself to running a wide variety of fuels. CNG can be derived from existing waste, and burning it is less damaging to the environment than letting methane escape directly into the atmosphere. Biofuels are essentially turning airborne CO2 into hydrocarbon using solar energy. Putting the CO2 back again simply closes the loop.”

DTW: Although you have stated a preference for front-drive, given the likely compactness of the turbine powertrain, is there any merit in a rear or mid-mounted layout?

SR:  “It’s down to what other use you can make of the space in front of the occupants. Whatever you put in front of the scuttle needs to be safe when it’s damaged (no fuel or batteries, which need to be well inside the wheelbase and as low as possible). The turbine, HVAC etc. are fine at the front, and also luggage of course.”

DTW: How many electric motors would you employ and where would you site them?

SR:  “I’m tempted to adopt front wheel drive out of reverence for the car’s heritage. There is sense to rear drive if we’re not going to use that space for something else, however. I’m going to reserve judgement for the time being, but putting the turbine and motors at the rear under the floor, and splitting the luggage to a space above and another under the bonnet has a certain appeal…”

DTW: Would any form of transmission be required and if so, what kind?

SR:  “The final transmission would probably be a gear reduction system to the drive motors, but with a single speed.”

Image: ©Driven to Write

Interior: “I would suggest ridding the car of leather and wood. There is no shortage of interesting natural fibres and materials, and I would like to see them used. I would also like to see some of the working systems of the car made to look good in their own right, rather than covered up with big lumps of expensive heavy plastic. How about a visible cooling & heating system? I’m not suggesting going as far as the Pompidou Centre, but I’d like to explore the possibilities. The turbine should be similarly shown off – either under the bonnet or under the boot floor, depending on its size. As you move upwards through hi-fi equipment, it becomes more confidently minimalist – not festooned with gimmickry as many cars now seem to be. I would seek to adopt this approach to appeal to a customer who would sooner drive the car rather than program it.”

In part three, Steve Randle concludes his proposal for a truly modern haut de gamme Citroën.
Styling renders: Richard Herriott.

©Driven to Write. All rights reserved.

Author: Eóin Doyle

Founding Editor. [Dis]content Provider.

8 thoughts on “Idée Fixe [2]”

    1. Wool nylon mix: the XM had it and it is durable and comfortable. I’d choose a brand like Kvadrat and make it a selling point. “The new Citroen DX: no ****ing leather.”

  1. Thanks for this article! I can find some very interesting ideas in here.

    I especially like the part about the interior. The DS was proudly showing modern materials of its time and the shapes that could be achieved using them; so should the new car. The idea of showing things instead of hiding all technical functionality appeals very much to my purist and engineering sense; hard to tell if it wouldn’t put off a larger audience.

    The thoughts about the drive system are interesting and seem credible to me. I like the idea of not carrying around hundreds of kilograms of batteries, as long as they are still sufficient to cover 20 or 40 kms of locally emission free driving through a city, for example. And why not combine them with a solar roof for another kilometre or two?

    One question remains: what about the suspension? I’m looking forward to part three.

  2. The powertrain suggested by Steve sounds intriguing. It seems lots of talented engineers have worked on such a concept for decades, so is this just a theoretically sound concept lacking real world feasibility or so complex a design that it’s been lacking the funding and/or support to be turned into a reality?

    1. My impression is that the automotive industry of our days is very good in developing and refining well-known concepts that can be produced in masses with standard components. Bringing new technologies to the market is a different story altogether. Risk-aversion doesn’t help here.

      I’m working in a different industry, and I have seen several projects dealing with new technologies. Many of them fail, others take a long time and lots of resources to finally succeed — and, above all, an ownership who is willing to fund this, who isn’t short-sighted and too dependent of the stock markets.

      From a technological viewpoint I can’t comment, my insights in this field are far too limited.

  3. It would be wonderful to see this come to life as a concept – there is a rich vein of thinking here which deserves to be taken further.

  4. As is common, a DTW article has led me off into a minor but enjoyable research project. I do like Richard’s drawings, and feel that smooth and rounded is the way to go. I have yet to see birds and fish sprout aero/fluid dynamic fillips like sculpted tail-light lenses proud of the body and various external excresences designed to lower their coefficient of drag. All these additions strike me as working only over limited speed ranges with perhaps deleterious effects at others that no one admits to. A porpoise looks pretty smooth to me, as does a diving falcon. There is roughened skin for boundary layer friction reduction on porpoises, which among other things fish scales are also theorized to be for. Looking at the frazzled grilles with holes and pockets and flanks sculpted for light reflection and maybe a sporty little wing out back that cars have, and you think, yes, there goes man thinking he’s smarter than nature. Then you see a new Civic hatchback and realize that some people are just plain bonkers anyway, while the Type R people should be locked up immediately for their own safety.

    I suppose if one is coming up with a clean sheet car, then designing one with a power source nobody has really perfected yet for automotive use is one way to start. Gas turbines, whether pure jet or turbofan are not very efficient when scaled down. Clearances and low volume to surface area tend to cause fluid friction problems. If one is to obtain an 18 to one compression ratio by multiple compression stages, then the compressor blades need to be extremely close to their casings to avoid reverse flow at their tips, equivalent to loss of compression and efficiency. There is no equivalent loss in a poppet valve cylinder. The size problem means that a one thou clearance compressor blade to casing on a three or four inch diameter unit is a big percentage compared to a couple of thou clearance on a 12 inch or larger unit. A four inch to twelve inch compressor offers approximately a 9 to1 difference in surface area and mass volume flow. In commercial aviation engines, compressor to casing clearances are so minute that differential heating during warm up can cause blade tip scuffing with the case. That’s why, despite modelling, actual suck-it-and-see development work is still required to avoid such mechanical mishappenstance. Expensive.

    Then there is the situation that in a hybrid car, the engine does not run continuously. The start up phase is generally an engine’s most “dirty” operating regime until revs and temperatures stabilize. New petrol piston engines generally now have no exhaust manifold – all that collection is performed in the cylinder head. Then the exhaust is routed to a turbo then a catalyst then EGR recirculation. Running a turbine with continuous combustion, like an IC but at higher temperatures to maximize efficiency, leads to excess NOx generation. Diesels are “turned down” from what they could achieve for this very reason by using massive exhaust gas recirculation to cool combustion, minimizing NOx. The ways to avoid excess hydrocarbon, unburnt fuel, on startup have pretty much been perfected on petrol engines, not diesel, which is probably why Toyota stays with them on their hybrid cars, and they have engines up to 40% efficiency or slightly more at optimum rpm for hybrid use, just as other companies and researchers have accomplished.

    I looked at the small turbines from Bladon (Isle of Man) and Capstone Turbine Corp (California) that Jaguar and Whisper respectively use(d). We’re looking at 30% efficiency in the real world, and the Capstone, a 30kW unit, costs 20,000 GBP. Hmm.

    There is a research project on a small turbofan engine for driving an alternator, with tantalizingly few details, but very disappointing efficiency, which is not its main goals, which are small size and big power:

    http://www.metisdesign.com/multidisciplinary-systems/propulsion-systems.html

    Using advanced CFD like Achates do, or like Delphi are doing to get a 45% efficiency IC petrol engine, or in other words refining existing piston engines seems to make more sense to me than striking off into new horizons with another gas turbine gambit. There would be development expenses aplenty without designing a new engine as well. The DS used a prewar four pot after all. The advances were in system controls and suspension and aero.

    However, I am in no way the last word on the subject. Far from it, and welcome corrections in my possibly wayward thinking and personal observations. I just like to look at things and see if they make sense or not, according to the what engineering logic is still left at my ready disposal brain-wise at three score years and ten.

    By the way, I’m not sure if the following website is known to others here, but the Society of Automotive Engineers summary pages list most of what automotive companies trumpet about their latest products or research to other people in the industry:

    http://articles.sae.org/automotive/browse/

    If you do go there, note that VW is touting their new B high efficiency version of the 2.0 litre petrol turbo. It’s fitted as standard over here in the new Tiguan, and doesn’t seem much cop so far as Car and Driver are concerned. So it’s buyer beware when you read those engineering puff-piece articles, but you get a pleasant dose of the latest news if you like a bit of a ponder.

  5. I would like to suggest a sense of haute couture in draping the car. There has always been a sense of a very refined extreme simplicity over the DS. It’s like a little black dress, tailor cut in silk, just draped over the cars caisson chassis, then neatly tucked and streched over the car. And with openings for doors and such scissor cut with extreme thought only in the right places.

    Except for the front under valance panel, there really are no unneccessary panels anywhere on the DS, there are no filler panels at all. The car consists of a chassis superstructure with a roof, foor doors, foor wings, a boot and a hood bolted to it and nothing else. Just look at the way the hood, front wing, and front door meet each other in one single line, the thought and beauty of it is unmatched in car history, no one ever managed to match that anywhere.

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