Citroën will unveil its new C4 Cactus AIRFLOW 2L concept at the Paris Motor Show. With the C4 Cactus AIRFLOW 2L concept, Citroën is demonstrating fuel consumption of 2l/100 km (118 mpg US) through the use of optimized design with a 20% improvement in aerodynamics; lower rolling resistance (Tall&Narrow) tires; efforts to use lighter parts and thus reduce overall vehicle weight by 100 kg; and the implementation of Hybrid Air technology, which cuts fuel consumption by 30%.

The C4 Cactus AIRFLOW 2L project was conducted as part of the “2l/100 km vehicle” program set up by the Plateforme de la Filière Automobile, an industry group. The objective was to deliver practical solutions to reduce the impact of vehicle running costs, on household expenditure and to reduce the eco-footprint of car travel.

Citroën decided to develop this project on the basis of its new model, C4 Cactus. The production C4 Cactus already ships with a range of features designed to reduce fuel consumption. With the C4 Cactus AIRFLOW 2L concept, Citroën went further.

Hybrid Air. With its latest-generation small engines meeting the future Euro 6 standard, the production Citroën C4 Cactus already ranks among the best in its segment with CO₂ emissions from 82 g/km and fuel consumption starting at just 3.1 l/100 km (76 mpg US).

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 at the 2013 Geneva Motor Show on the Citroën C3, this technology combines a range of proven sub-systems and technologies: a 3-cylinder PureTech gasoline 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 optimize energy efficiency. Three operating modes are available:

• Air power (zero emissions) in which the compressed air motor replaces the gasoline combustion engine;
• Gasoline power, using only the combustion engine; and
• Hybrid 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 positioned at the rear of the vehicle.

The PureTech 82 engine, already available on the production model, has been optimized for this new hybrid drivetrain.

Friction losses, which account for 20% of the power consumed by the engine, have been reduced in several ways: 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 on the C4 Cactus AIRFLOW 2L concept reduces fuel consumption by 30% and contributes significantly to achieving a vehicle of 2l/100 km while approaching the PureTech 110 in terms of dynamic performance.

Body style optimized for aerodynamic performance. The unique design of the Citroën C4 Cactus associates flowing lines with strong graphic features, each one highlighting a function (protection with the Airbumps and wheel arches; transporting objects with the roof arches; light with the glazed panoramic sunroof). On the C4 Cactus AIRFLOW 2L, some styling features have been modified and others created in order to optimize vehicle aerodynamics.

Variable-geometry styling parts:

• The new front bumper features three controlled air intakes the openings of which are continuously adjusted in accordance with vehicle use, both for engine cooling and for airflow.
• Mobile side deflectors have been added behind the quarter-window to effectively guide the air flow around the vehicle.
• The wheels feature mobile shutters activated and controlled by centrifugal force.

Fixed-geometry styling parts:

• The tires selected to equip the vehicle are of the new-generation 19″ Tall&Narrow type. Their design and “ultra ultra” low rolling resistance characteristics improve both energy efficiency and aerodynamics. Their large diameter also contributes to comfort since they are better able to soak up bumps and dips in the road surface.
• The wheel arches feature an “Air Curtain”. Small aerodynamic slats on either end of the front bumper channel the airflow and smooth it out along the wheels.
• The spoiler has been lengthened and an air extractor added on the rear bumper in order to effectively channel the airflow around the C4 Cactus AIRFLOW 2L and reduce the turbulence that can increase drag.
• The conventional door mirrors have been replaced by smaller, slimmer rearview cameras to reduce impact on air flow.
• The vehicle substructure has been entirely streamlined. The air flows smoothly, unhampered by the sub-systems positioned under the car.
• LED light modules at front and rear replace the existing lights. Consuming little power, they save energy and thus fuel.

These changes can be recognized by their color and by the materials used. The color orange identifies all the aerodynamic features and underlines the high-tech character of the C4 Cactus AIRFLOW 2L concept.

Lighter weight. The production C4 Cactus is already 200 kg (441 lbs) lighter than the Citroën C4, and the C4 Cactus AIRFLOW 2L concept shaves off a further 100 kg (220 lbs), including the drivetrain. These efforts have therefore reduced the weight of the concept by 11% compared with the production vehicle.

Efforts to reduce the weight of structural parts on the C4 Cactus AIRFLOW 2L concept entailed the use of new materials in the body substructure:

• aluminium, in particular, for the upper cowl panel, inner side members and rear floor pan;
• high-yield steels for the front side rails and heel board; and
• composite materials for the front floor.

This multi-material substructure made it necessary to develop special assembly techniques never used before in the automotive industry. Composite structural parts are a promising field of exploration and will certainly be essential to efforts 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, Citroën noted.

Beyond structural parts, extensive studies were conducted on all vehicle parts to reduce the weight of the C4 Cactus AIRFLOW 2L concept. Emphasis was placed on lightweight, high-performance materials:

• Carbon-based composite materials were 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 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 surrounding features.
• Aluminium is used for the engine cradle. The bonnet specifications were the same as for the production C4 Cactus, which already used aluminium.

Owing to their significantly lower bulk density (around 2,700 kg/m³ for aluminium and around 1,200 kg/m³ for carbon compared with 7,800 kg/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 of the exhaust line and thus reduce weight.
• 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 ultraviolet filtering capability.
• Carbon fibres on the Airbumps to make the material lighter while maintaining its technical properties