Race on the track dreaming the road: XAM, the 120 km/l urban concept

eXtreme Automotive Mobility or, in other words, XAM. This is the name of ours Urban Concept, designed and built in 2011 that in May 2015 will blow out its fifth candle, reaching one lustrum of activity. As the name suggests XAM is a very particular vehicle, in fact it has been designed to join, in conformity with the rules of the competition, features of urban vehicles and innovative solutions with the aim of reaching the best result in race, i.e. the best fuel efficiency. For this reason XAM is for sure the vehicle, among the participants to Shell Eco-marathon (SEM), that is closer to a real city car and, as many box visitors suggest, probably the best-looking one.

XAM in action on the track at the Shell Eco-marathon 2014

Let us take a closer look. First of all XAM, as IDRA, takes part to Shell Eco-marathon. But, unlike the prototype presented last week on this blog, it competes in Alternative Fuels Urban Concept category, i.e. hybrid vehicles fueled with second generation bio-ethanol (E100). This category has been introduced to induce Shell Eco-marathon Teams to design and put on the track vehicles more similar to the ones that we see every day in our cities. In fact the race format too reflects this will to get closer the competition to what happens on the roads. So the competing vehicles must run the 1.6117 km long street circuit for a total of 10 laps, at the end of which must execute a start & stop procedure, as it was a traffic light. This distance must be covered in a maximum of 39 minutes, i.e. with an average speed of 25 km/h, that represents a typical value of average speed in the downtown of a big city.

The track surrounding the Ahoy Arena (Rotterdam, Nederland)

where is run the Shell Eco-marathon

From the technical point of view XAM is a parallel hybrid vehicle (Plug-in Hybrid Electric Vehicle), i.e. it has an electric engine that takes charge of the acceleration phase, while a 50cc Honda scooter adapted internal combustion engine is dedicated to the maintenance of the cruise speed and to the regeneration of supercaps. This latters aren’t conventional batteries but capacitors with very high capacitance. This because, despite of the apparent drawback of having very little discharge time, they have a higher specific power with respect to a traditional battery stack and minimum recharge time, fundamental during the race as for the regulation the accumulators must have the same state of charge at the beginning and at the end of the run, for this reason having little recharge time means less work by the engine and, obviously, better fuel efficiency. The two engines are coupled to the same fixed transmission ratio transmission, designed and optimized as a whole in the Team. By the way, the most critical component for the performance in the competition, i.e. the fuel efficiency, is the thermal engine for its relatively low efficiency. A standard thermal engine has an efficiency (the ratio between the useful energy output and the energy spent for the operation) around 30 % indeed, while an electric motor is between 85% and 90% of efficiency.

For this reason is fundamental to optimize every aspect of XAM’s bio-ethanol engine, done through experimental test on both fuel efficiency and ECU mapping on our Engine Test Bench in the Dipartimento di Energia’s Lab by the Powertrain area Members of Team H2politO. This tests give the data for the dimensioning of intake and exhaust too.

For the optimization of the powertrain in the 2013/2014 campaign XAM has been object of a complete revolution in its “heart”. In fact the older 35 cm3 Honda engine, adapted from a mower, has been substituted by the actual unit: a 50 cm3 engine coming from the Honda Vision scooter, tuned to be mounted on the test bench and on the car and to improve its performance during the race.
Moreover XAM is equipped with special Michelin tires, capable of a very low rolling resistance coefficient, a very important contribution to the breakdown of the consumption.

In May 2014 we had some problems and malfunctions but we made a satisfying result: 120 km/l and new fuel efficiency record for XAM on the street circuit of Rotterdam. But the new engine didn’t performed at its whole potential, Team’s will to improve is huge and we hope that, with the new updates for the 2015 season we’ll go far and we hope that the dreamed 200 km/l achievement would be attained.