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