DTU Roadrunners 2013: Full-on optimization.
In the 2012 edition of Shell Eco-marathon, the Danish team DTU Roadrunners and their ethanol powered Urban Concept car Dynamo won their class of the competition for the fourth time in row, with an average fuel consumption equivalent to 611 km/l if driving on ordinary petrol. This year the team and Dynamo are back to attempt to improve on last year’s result and push the limits of an ethanol powered car even further. The journey towards this year’s Eco-marathon has been both long and interesting, stressful and rewarding. This year’s version of the eco car Dynamo has been made lighter, more efficient and is the first DTU eco car to be constructed using 3D-printed parts. Instead of trying to design a completely new and innovative car, the team decided to focus on evolution rather than revolution. Last year’s design proved its worth in the 2012 edition of Shell Eco-marathon, but nevertheless, the team knew that the car still had some areas which could be improved on. Five focus areas were lined out for the new car:
- Improve engine control and performance
- Develop a carbon fiber monocoque
- Development of carbon fiber rims
- Develop a KERS-system (Kinetic Energy Recovery System)
- Development of transmission
Improving engine control and performance
Between the 2012 and 2013 Eco Marathon, the team has worked intensely on improving its engine performance. Amongst the improvements is a completely new and redesigned crankshaft housing, a new clutch system and a new cylinder liner. The crankshaft housing has been redesigned to be a lighter, more compact construction, which has allowed the team to mount the engine lower in the car and closer to the cockpit. The redesigned crankshaft housing has also allowed the team to relocate the engine starter motor to a new position and fit a Bendix drive to the starter motor, in order to completely isolate the starter motor from the drive line when it is not in use. This means that less mechanical energy is wasted on overcoming friction within the driveline, and that the engine needs less power to drive the car forward. The result of the reduced resistance in the driveline is improved fuel consumption and engine performance due to the reduced mechanical loss. The repositioning of the engine also means that the team has been able to design a Kinetic Energy Recovery System, also referred to as KERS, to recover energy while breaking.
The recovered energy can then be used to assist the engine in powering the car during the next acceleration phase. During breaking, the KERS-system is charged by engaging a PMDC motor (Permanent Magnet Direct Current) to one of the rear wheels with an electromagnetic clutch. This charges a number of super capacitors with electrical energy, while slowing the car down due to the inertia of the rotor inside the electric motor. When activated, the super capacitors discharge their electrical energy, turning the PMDC motor into a drive motor, capable of powering its own rear axle. Once the super capacitors have released their energy, the PMDC motor is disengaged, and remains inactive until the car needs to brake again. Through this process, almost half of the kinetic energy lost while braking, is recovered and used again. The gathered energy is used to propel the car at the beginning of each lap from a standstill. This has a favorable effect on the overall fuel efficiency of the car, since quite a lot of mechanical energy is lost in the engine and clutch when accelerating the car from a standstill.
This year, the car has been fitted with an all new carbon fiber monocoque. The new monocoque is a combination of a full carbon fiber chassis and the bottom half of the car’s outer shell. This eases the assembly of the car, and it saves weight, as the monocoque can be tailor-made for its purpose instead of having to be assembled from two separate pieces. The monocoque has been constructed with the purpose of facilitating engine mounting without any kind of support structure. On last year’s DTU eco car, the Dynamo 8.0, which achieved a fuel consumption equivalent to 611 km/l on one liter of ordinary petrol, the engine was supported by an aluminum frame. This year, the team has been able to use special adhesive and mounting brackets from the company Click Bond, which has made it possible to mount the engine directly onto the bottom of the carbon fiber monocoque. This again saves weight and has allowed the team to better place the engine within the engine bay.
The weight reduction following the new monocoque and crank shaft housing is around 30 kg, resulting in a total weight of just above 100 kg for Dynamo 9.0.
One step further
The goal for the team attending this year’s Eco-marathon is to improve on last year’s record in order to prove that DTU Roadrunners are at the very forefront of energy efficient mobility. Last years’ world record set by DTU Roadrunners was equivalent to an average fuel consumption of 611 km/l and the team expects to exceed last year’s record by approximately 10 %, which should result in a fuel consumption equivalent to around 700 km/l.