Week 2 Challenge

Vehicle electrification is one of the strategies with higher potential for increasing the

efficiency of vehicle powertrains, reducing the dependency on dwindling fossil fuel

sources and meeting stringent emissions targets set by policy makers. Despite all the

theoretical assessments and manufacturer’s claimed efficiency and emissions records of

current vehicles, there is a lack of data concerning real life comparisons of Electric

Vehicles (EV) against Internal Combustion Engine (ICE) cars.

A test program comparing the energy consumption of an EV and a diesel powered (ICE)

car was carried out.

Both short (at levelled ground and 6% up-hill) and long distance tests were performed for

several fixed vehicle speeds. Measurements enabling the assessment of average energy

consumption, required power and energy suplied were performed for both vehicles.

Results indicate that in terms of vehicle use (Tank-to-Wheel perspective) the electric

powertrain is significantly more energy efficient than the Diesel powertrain, although the

difference between the two is less pronounced for higher power events.

Energy and Environmental Concerns and Policies

The expansion of car traffic in the last decades has been arising serious environmental

concerns over the increase of greenhouse gas (GHG) emissions, urban air pollution and

dependence on dwindling fossil fuel reserves. The oil crises of the seventies, along with the

concerns over the volatility of oil prices and the security of fuel supply from politically

unstable countries has further spurred the quest for increased energy efficiency and low

emission alternatives to conventional fossil fuel-based powertrains [1][2].

Several national and international agreements and policies have been put forth in order to

place even more stringent limits on fuel consumption and/or CO2 emissions of vehicles. Such

was the pioneering Kyoto Protocol at the global level or the Corporate Average Fuel

Economy (CAFE) regulations in the US [3]. In the European Union voluntary emissions

agreements celebrated between the European Commission and institutions like the European

Automobile Manufacturers Association (ACEA) were later followed by mandatory

regulations on emission performance standards for new passenger cars [4].

Increasing the Energy Efficiency of Conventional Powertrains

A first approach for decreasing vehicle emissions is by increasing the efficiency of the

Internal Combustion Engine (ICE). Engine downsizing and turbo-charging are strategies that

have proved to be effective in this respect [5]. Also the strategy of overexpansion studied by

the group, especially if combined with variable compression ratio and variable valve timing,

has a good efficiency potential, as efficiencies higher than those typical of ICEs may be

obtained with a gasoline engine over a broad portion of the engine map [6][7]. There are also

the strategies which increase the efficiency of the powertrain by harvesting some of the

thermal energy normally wasted through the tailpipe of vehicles and converting it into

electricity to reduce alternator use. This can be done namely with Organic Rankine Cycle

(ORC) turbines or Seebeck effect thermoelectric generators. The authors has been working in

some of these promising technologies [8][9] but they still need to be further developed before

they become mature for vehicle use.

Despite the promising advances in fuel economy technologies it is expected that the

automotive market will grow steadily in the next decades, mainly because of increasing

standards of living in rapidly developing economies, such as South Eastern Asia and South

America. So, between 2000 and 2050 it is expected that the population will grow 1.7 times,

but the number of cars is expected to increase even more (3.6 times) [10]. So, it seems that

the sole increase of conventional powertrain efficiency will not be sufficient by itself to meet

the current medium to long term emission and efficiency goals. Alternatives not relying

exclusively on the combustion of fossil fuels need to be considered.

Improving Efficiency through Vehicle Electrification

An increasingly higher degree of vehicle electrification (also called vehicle

hybridization) is one of the options which seems logical to take in order to meet theaforementioned targets and diversify energy sources. Electrified vehicles are more efficient

than ICE ones namely under urban traffic since they have no idling losses, no unefficient

clutching at starts (they have good low end torque) and they can recover a portion of the

braking energy through regenerative braking [1]. In fact, hybridization has been quite an

effective way of some sports vehicle brands to meet emission standards without sacrificing

the performance figures of their vehicles. For instance, the soon-to–be-sold flagship model of

Porsche, the 918 Spyder, will be a plug-in hybrid capable of a combined power of 652 kW

(887 hp), attaining 0-100 km/h in under 2.8 s. However, its New European Driving Cycle

(NEDC) consumption has been rated at only 3.3 L/100 km with CO2 emissions of just 79gm)Km