The Reduction Of Green House Gases Environmental Sciences Essay

Introduction

The provision of a sustainable environment to the next generations is a matter of global interest which is growing the last years. The reduction of Green House Gases (GHG) emissions, the conscious use and efficient allocation of non-renewable energy resources are worldwide goals. One of the greatest projects takes place in road transport. The transportation sector is responsible for the 13.1% of GHG emissions worldwide, two thirds of which are contributed from road transport [1]. Apart from the CO2, many other gases are emitted such as NOx, PM10, CO, HC which contribute to air pollution [2] [3]. As far as energy is concerned, 90% of the transport sector is powered by derivatives of oil [4], which is not unlimited and whose price is highly dependent on regions with unstable political conditions [5]. In the context of the project, new technologies are applied. One of these is the development and production of hybrid and electric cars in excess to conventional cars.

Hybrids are vehicles which use two different sources for propulsion. The most common combination is Internal Combustion Engine (ICE) and Electric Motor (EM) (gasoline and electricity respectively). One classification is made depending on which is the main engine: mild-uses the electric motor as an assist to the ICE, Full- both systems can work either as main or as assist of the other, Plug in – uses the electric motor as main and the ICE as a back-up. Another classification can be done according to the structure of the drivetrain: series, parallel, series-parallel hybrids [6]. This report focuses on mild parallel hybrid cars which comprise the most popular choice of the market [citation]. Their advantages and disadvantages over the conventional and electric vehicles will be reported below. The comparison is made in the following fields: energy, economic, environment and performance.

Energy

Less fuel consumption is one great advantage of hybrid cars over the conventional cars. They use the electric motor in low speeds, instead of the ICE, which is more efficient (conversion of chemical energy from batteries to electricity has 25% losses whereas energy from gasoline to ICEs leads to 80% losses) [7]. What is more, hybrid’s ICE is downsized due to the existence of the EM. Electric Vehicles which use only batteries to store the energy are the most fuel efficient of all the vehicles as shown in Table 1. Hybrid and electric vehicles also achieve better fuel consumption as they combine features as regenerative braking (the kinetic energy during braking, is converted to electricity and charges the batteries – in conventional vehicles, energy losses from braking can reach up to 46% of all tractive losses) and start n stop systems (no wasted energy while engine idling or standby) [8].

However, the fuel consumption is highly dependent on the driving conditions. Driving in highways results in more or less the same consumption for hybrid and conventional cars whereas urban cycle gives a big difference [9]. The third column of table 1 is based on 45% highway and 55% city driving which is an average driving pattern.

Economic

As far as prices are concerned, hybrid cars are more expensive than the conventional but cheaper than the electric ones. This happens because of the high cost of batteries [10] [11] [12] and rare materials used for electric motors (dysprosium, neodymium) [13]. Although maintenance of hybrid and electric cars is not so often as of conventional cars, must be done by professionals due to complexity of electric circuits. The cost of purchasing each car with the same specifications is shown in table 1. In the fifth column of the table, the total cost per year is shown, including the capital cost of the car, the cost of fuel, VAT, and costs of maintenance [4].

However, the difference in cost can be compensated by the incentives that some governments give for obtaining a green car such as subsidies, free parking, discounted fees on toll gates and travelling through congestion zones free of charge. Finally, surveys show that plug-in hybrids and battery cars can achieve an extra revenue by improving the reliability and reducing the costs of the electric system (Vehicle-to-grid) [14].

Table 1. Fuel consumption, total cost of purchase and total cost of ownership per year

Type of car

Environment

In order to measure the environmental impact of these cars, it is not enough to measure the GHG emissions that have during their normal operation. A Life Cycle Assessment (LCA) must be done in order to take into account every aspect of producing and using the car. An LCA consists of the fuel life cycle and the vehicle life cycle. Fuel life cycle has two parts· Well to Tank emissions, which cover the production, transport of primary fuel and production, distribution of final fuel· Tank to Wheel, which is the use of fuel in the vehicle. Vehicle life cycle includes the extraction of vehicle raw materials, the manufacturing and assembly of different components, the service and repair of the cars, and also the disposal of the whole vehicle after the end of its lifetime.

This kind of assessment is very important, because hybrid cars are known to have lower emissions than the conventional in terms of fuel usage (TTW). The construction of the main parts of the vehicles emits almost the same amount of GHG. However, the construction and disposal of hybrid’s batteries (and electric’s too) is a procedure with great CO2eq emissions [16].

Another key element is that electric cars are vehicles with zero tailpipe emissions (TTW). However the electricity used for charging the batteries, has CO2eq emissions which are dependent on the energy production unit so the electric’s car carbon footprint varies (zero for renewables, but a great amount for coal or other units) [17]. All these data are presented in Table 2.

Table 2. WTT, TTW, WTW, Vehicle life cycle and total emissions from different cars in ()

Vehicle

WTT()

TTW(

WTW)

Vehicle life cycle

(

Total emissions )

Conventional petrol

140

Hybrid

112

Electric

Units are in gCO2eqkm-1 and includes all GHG emissions

Data for WTT,TTW,WTW taken from ref [4]

Vehicle life cycle data taken from ref [4] and converted to 14000km/year, 10 years lifetime.

It is obvious that hybrid cars have an advantage over the conventional cars as far as GHG emissions are concerned. This advantage increases with the increase of degree of hybridization (full-hybrids, plug-in hybrids).

Performance

Hybrid cars show comparable values of acceleration with the conventional despite the existence of two drive trains and the weight of batteries [18]. However electric cars have the fastest acceleration because power is immediately available without the need of increasing in engine revolutions. On the other hand, the driving range of a fully electric car is much shorter than the conventional vehicles and it is highly dependent on the battery technology and capacity [19]. Hybrid and especially full and plug-in hybrids have similar driving range and in some cases even longer due to the better fuel consumption that they achieve. Finally, the big charging time of batteries in electric and plug-in hybrid cars comprises a drawback which has not been solved until now [citation].

Conclusion

Concluding, it is clear that the green cars contribute positively in the reduction of GHG emissions. Better fuel economy, lower carbon footprint and similar performance to the conventional cars, are some characteristics which combined with financial incentives, make the hybrid cars a very attractive option for the consumers. Nonetheless, there are great potential improvements and further development to be done. Reducing the weight and increasing the capacity of the batteries are two of the major challenges for the future. Within the next few years, when “clean” technology will have become more mature and hence cost-effective , it is expected a large invasion of green cars.

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