2014 Citroen C4 Cactus 2L AIRFLOW Brings 141-MPG Via Active Aero and Compressed Air Hybrid

C4 Airflow gif23It must be aero concept day in Paris today, as the C4 2L AIRFLOW is also joined by the new Renault Eolab concept with an ultra-svelte EV design.

This C4 2L Cactus AIRFLOW is a highly modified Hybrid Air concept cased on the new C4 Cactus production crossover. The most eye-catching tech is the active aero shutters up front and in the wheels, but the 141-mpg truth is more complicated.

In fact, the active aero additions can, at most, drop the fuel consumption by perhaps 10 percent. The rest of the gain comes from the PSA compressed-air hybrid system that packs air into twin trunk canisters under braking. The Hybrid Air solution slowly lets this pressurized air out to power the battery hybrid technology.

While promising in concept, the Hybrid Air solution is widely considered to be vaporware within the car industry. That is: something too good to be true. Aka fake technology.

2014 Citroen C4 Cactus 2L AIRFLOW

C4 Airflow gif





  • 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.2014 Citroen C4 Cactus 2L AIRFLOW 23 2014 Citroen C4 Cactus 2L AIRFLOW 22 2014 Citroen C4 Cactus 2L AIRFLOW 21 2014 Citroen C4 Cactus 2L AIRFLOW 20 2014 Citroen C4 Cactus 2L AIRFLOW 19 2014 Citroen C4 Cactus 2L AIRFLOW 18 2014 Citroen C4 Cactus 2L AIRFLOW 17 2014 Citroen C4 Cactus 2L AIRFLOW 16 2014 Citroen C4 Cactus 2L AIRFLOW 15 2014 Citroen C4 Cactus 2L AIRFLOW 142014 Citroen C4 Cactus 2L AIRFLOW 2

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 force2014 Citroen C4 Cactus 2L AIRFLOW 13 2014 Citroen C4 Cactus 2L AIRFLOW 12 2014 Citroen C4 Cactus 2L AIRFLOW 11 2014 Citroen C4 Cactus 2L AIRFLOW 10 2014 Citroen C4 Cactus 2L AIRFLOW 7 2014 Citroen C4 Cactus 2L AIRFLOW 6 2014 Citroen C4 Cactus 2L AIRFLOW 5 2014 Citroen C4 Cactus 2L AIRFLOW 4

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 properties2014 Citroen C4 Cactus 2L AIRFLOW 3 2014 Citroen C4 Cactus 2L AIRFLOW 1 2014 Citroen C4 Cactus 2L AIRFLOW 30 2014 Citroen C4 Cactus 2L AIRFLOW 29 2014 Citroen C4 Cactus 2L AIRFLOW 28 2014 Citroen C4 Cactus 2L AIRFLOW 9 2014 Citroen C4 Cactus 2L AIRFLOW 8 2014 Citroen C4 Cactus 2L AIRFLOW 27 2014 Citroen C4 Cactus 2L AIRFLOW 26 2014 Citroen C4 Cactus 2L AIRFLOW 25 2014 Citroen C4 Cactus 2L AIRFLOW 24

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.


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

 C4 Airflow gif23 C4 Airflow gif

About The Author

Tom Burkart is the founder and managing editor of Car-Revs-Daily.com, an innovative and rapidly expanding automotive news magazine. He holds a Journalism JBA degree from the University of Wisconsin - Madison. Tom currently resides in Charleston, South Carolina with his two amazing dogs, Drake and Tank. Mr. Burkart is available for all questions and concerns by email Tom(at)car-revs-daily.com.