Citroen C4 Cactus Airflow 2L brings the fuel-sipping funk [w/video]

Fri, 03 Oct 2014

Full disclosure: I love the Citroën C4 Cactus. Really, I just love French automakers. Kudos to them for flexing their design muscles, creating products that compete in the mass market while not looking like anything else on the road. This C4 Cactus, for example – it's a small hatchback that's about the same size as a Ford Focus, designed to take on small crossovers like the (also weird) Nissan Juke and Renault Captur. But it looks radical, what with its funky Airbump door trim (think of it as aerodynamic, protective Braille), extensive and imaginative color palette, and decidedly weird styling. It's just plain cool.

This specific C4 Cactus, however, takes things a step further with a massive focus on emissions and fuel economy. Much like the Peugeot 208 with which it shares a powertrain, the Cactus 2L Airflow uses PSA Peugeot Citroën's Hybrid Air powertrain, comprised of a three-cylinder PureTech gasoline engine and a compressed air storage unit. There are three different operating modes for the Hybrid Air system, including "air power," where the compressed air motor runs things, "petrol power," which is pretty self-explanatory, and "combined power," where the combustion engine works with the compressed air system to move things along.

The end result? A five-door hatch that weighs just 2,100 pounds (you know, lighter than a Mazda Miata) and is capable of getting 141 miles per gallon on the European cycle, or two liters per 100 kilometers (that's why it's got "2L" in its name). And it's all wrapped in colorful, textured, uniquely French package. Sign me up.

C4 CACTUS AIRFLOW 2L CONCEPT: JUST 2 LITRES/100 KM (OVER 141 MPG)

Citroën C4 Cactus AIRFLOW 2L concept to be unveiled at the Paris Motor Show
Concept achieves fuel economy of over 141mpg (2l/100km)
Optimised design on C4 Cactus AIRFLOW 2L results in 20% improvement in aerodynamics
PureTech 82 engine with Hybrid Air technology reduces fuel consumption by 30%
Lightweight, high-performance materials used, including carbon fibre, aluminium, high-yield steels, composite materials & translucent polycarbonate
Concept is 100kg lighter than production Citroën C4 Cactus

Faced with environmental requirements and economic pressures, many customers today see fuel consumption as a key concern. As a result, Citroën is applying its creativity and technology to a new challenge with the C4 Cactus AIRFLOW 2L concept, which will be unveiled at the Paris Motor Show.

A laboratory for new ideas, the C4 Cactus AIRFLOW 2L is packed with advanced technologies that illustrate the ambition and ability of the brand to develop innovative responses to the automotive challenges of the present and the future.

With the C4 Cactus AIRFLOW 2L concept, Citroën delivers breakthrough fuel consumption of 2l/100 km (over 141mpg), using:

optimised design with a 20% improvement in aerodynamics
lower rolling resistance "tall & narrow" tyres
lighter parts to reduce overall vehicle weight by 100kg
Hybrid Air technology, which cuts fuel consumption by 30%
The birth of the C4 Cactus AIRFLOW 2L concept

The C4 Cactus AIRFLOW 2L project was undertaken as part of the "2l/100 km vehicle" programme set up by the Plateforme de la Filière Automobile industry group in France. The objective is to reduce the impact of vehicle running costs on household expenditure and to reduce the eco-footprint of car travel.

Citroën decided to progress this project using its newest model, the C4 Cactus. With this vehicle, the brand has made a commitment to bring customers more of what really matters today: more design, more comfort and more useful technology, combined with an affordable cost of ownership. More than any other vehicle, the C4 Cactus lends itself to this ambitious exercise – to develop a very low consumption, high-tech concept that is both efficient and attractive.

The Citroën C4 Cactus AIRFLOW 2L Concept

With its smooth design lines, efficient engines and technologies selected to reduce vehicle weight, the production Citroën C4 Cactus already boasts a range of features designed to reduce fuel consumption.

With the C4 Cactus AIRFLOW 2L concept, Citroën is taking this approach even further.

1. A body optimised for aerodynamic performance

On the C4 Cactus AIRFLOW 2L, some styling features have been modified and others created in order to optimise vehicle aerodynamics.

Variable-geometry components:

The new front bumper features three air intakes that continuously adjust in accordance with vehicle use, both for engine cooling and to regulate air flow
Mobile side deflectors have been added to effectively guide the air flow around the vehicle
The wheels feature mobile shutters activated and controlled by centrifugal force
Fixed-geometry components:

New generation 19-inch "ultra ultra" low rolling resistance "tall & narrow" tyres. Their design improves both energy efficiency and aerodynamics. The large diameter also means they are better able to soak up bumps and dips in the road surface
The wheel arches feature an "Air Curtain". This is achieved with small aerodynamic slats on either end of the front bumper to channel the air along the wheels
The spoiler has been lengthened and an air extractor has been added on the rear bumper in order to reduce the turbulence that can increase drag
The conventional door mirrors have been replaced by smaller, slimmer rearview cameras to reduce the impact on air flow
The vehicle sub-structure has been entirely streamlined so the air flows smoothly underneath the car
LED light modules at the front and rear replace the existing lights. Consuming little power, these new modules save energy and benefit fuel economy
The changes can be identified by the colour of the components and by the materials used. The colour orange identifies all the aerodynamic features and underlines the high-tech character of the C4 Cactus AIRFLOW 2L concept.

The changes reflect how styling and design can contribute to vehicle aerodynamics, reducing vehicle drag for an overall improvement of 20% in terms of aerodynamic performance compared with the production model.

2. Innovative materials for lighter weight

The production C4 Cactus is already 200kg lighter than the Citroën C4 hatchback, yet the C4 Cactus AIRFLOW 2L concept shaves off a further 100kg. This means Citroën's designers have reduced the weight of the concept by 11% compared with the production vehicle.

To achieve this, the brand has reduced the weight of many structural components, with the body sub-structure featuring new materials:

Aluminium, for the upper cowl panel, inner side members and rear floor pan
High-yield steels, for the front side rails and heel board
Composite materials for the front of the vehicle floor
These new materials are structural and help to soak up energy in the event of an impact. They also meet the highest standards in terms of mechanical strength.

This multi-material sub-structure made it necessary to develop special assembly techniques never used before in the automotive industry. Composite structural parts are a promising development area and will be essential to make cars lighter in the future. The large-scale production of these parts is one of the high-tech, industrial challenges to be addressed by the automotive sector.

Looking beyond the structural components, extensive studies were conducted on all vehicle parts to reduce weight.

Emphasis was placed on lightweight, high-performance materials:

Carbon-based composite materials have been used for the suspension springs, tailgate, rear bench, side panels, roof, roof cross-members, wings and doors. On the lower side sill, wheel arches and the lower part of the front bumper, the "textured" look of the carbon brings out the matt appearance of these parts, providing an attractive contrast with the pearlescent appearance of the surrounding features
Aluminium is used for the engine cradle. The bonnet specification is the same as for the production C4 Cactus, which already uses aluminium
Owing to their significantly lower bulk and density (around 2,700kg/m3 for aluminium and around 1,200 kg/m3 for carbon, compared with 7,800kg/m3 for steel), these materials contribute significantly to reducing overall vehicle weight
Given that every gram is important, Citroën also decided to use:

New processes to reduce the thickness of the tubes and cups in the exhaust system
Translucent polycarbonate, for the panoramic sunroof. This material is even lighter than multi-layer glass, but has the same properties in terms of thermal and acoustic insulation and ultra-violet filtering capability
Carbon fibre on the Airbump® panels to make the material lighter, while maintaining its technical properties
Hybrid Air technology for breakthrough fuel consumption

With the brand's latest-generation Euro 6 engines, the production C4 Cactus already ranks among the best in its segment with CO2 emissions from 82g/km and fuel consumption starting at just 91.1mpg.

The C4 Cactus AIRFLOW 2L concept goes even further by adopting the Hybrid Air drivetrain. Presented by the PSA Peugeot Citroën Group in January 2013, and featured on a Citroën C3 at the 2013 Geneva Motor Show, this technology combines a range of proven sub-systems and technologies. This includes a 3-cylinder PureTech petrol engine, a compressed air energy storage unit, a hydraulic pump/motor unit and an automatic transmission with an epicyclic gear train. An intelligent electronic management system manages input from the driver to optimise energy efficiency.

Three operating modes are available:

Air power (zero emissions) where the compressed air motor takes over from the petrol engine
Petrol power, using only the combustion engine
Combined power, drawing upon both the combustion engine and the compressed air
On the C4 Cactus AIRFLOW 2L concept, the two compressed air storage tanks are made of composite materials and are positioned at the rear of the vehicle.

The PureTech 82 engine, already available on the production model, has been optimised for this new hybrid drivetrain. Friction losses, which account for 20% of the power consumed by the engine, have been reduced in several ways. This includes using a Diamond-like carbon coating, making moving parts lighter and using bearings to guide rotating parts. Further improvements were made by adopting new polymer pads and using very low viscosity oil. Combined with efforts to optimise combustion, overall engine efficiency has been improved by 5%.

Combining the PureTech 82 engine with Hybrid Air technology for this concept reduces fuel consumption by 30% and contributes significantly to achieving a vehicle capable of 2l/100 km, while approaching the PureTech 110 in terms of dynamic performance.

C4 Cactus AIRFLOW 2L concept, just 2l/100 km

All these advanced technologies together deliver consumption of 2l/100 km. It could therefore be possible, in the medium term, for a production vehicle such as C4 Cactus to reach this target.

TECHNICAL CHARACTERISTICS:

Unladen weight: 865kg

Length: 4,156mm

Width: 1,729mm

Height: 1,487mm (to be confirmed)

CdA: improvement around 20%

Hybrid Air drivetrain mated to the PureTech 82 S&S engine

Tyres: Michelin 155/70/R19

By Steven J. Ewing