Caner Bektas
Comm106
Fall2012
Automobiles with Less Carbon Dioxide Emission Every day millions of people drive their cars in order to go their jobs or schools or because of any other reason. Unquestionably, automobile makes our lives easier and that is the reason why automobile is considered as one of the most important inventions. However, as the automobiles make easier our lives they also damage the environment. The carbon dioxide emission is one of the major harmful effects caused by vehicles operated by conventional combustion engines. So it is obvious that there is still room for improvement and major thing that must be done is reducing harmful effects of carbon dioxide emission on environment. The most significant reason why carbon dioxide emission is high for conventional combustion engine is the dependence on oil for fuels used in that type of engine. Especially in the big cities which have large populations, harmful effects are more significant because in those cities there is a traffic jam which is caused by large number of cars. As the technology improves rapidly, researchers and scientists are focusing on finding a solution which is beneficial for car producers as well as environment. Most significant goal is replacement of automobiles used widely today with energy efficient vehicle which leads to reduction in carbon dioxide emission that causes urban air pollution, climate change and dependence on imported oil. The air pollution caused by different types of automobiles is showed in the following Figure [1].

Researchers that aimed increasing energy efficiency while decreasing carbon dioxide emission focused on the operation systems of automobiles powered by diesel or gasoline. They came with an idea indicating that the operation systems of automobiles can be replaced by two different operation systems working together and switching according to the condition of automobile. In order to achieve this goal, the method of using two different operation systems have been tried in hybrid cars in which a parallel direct electric drive train with motor is added to the conventional combustion engine [2]. Actually, hybrid drive trains are separated into two types according to the structural properties. On the one hand in series hybrid drive trains, the electricity is generated by internal combustion engine but the wheels are not powered directly. On the other hand, unlike the series hybrid drive trains, parallel hybrid trains have small electric motor and internal combustion engine which power the wheels directly as well as generating electricity [3]. For the hybrid cars, the electrical storage system is the key point since its power and life are the most decisive factor for the cost of the overall system [4]. In order to determine how well an electricity storage device is, four factors should be considered. These factors are cost per unit (€), lifetime (h), specific power (kW kg-1), and specific energy (kWh kg-1) [3]. The second approach about the operation system is changing the system entirely and used a new method to power the engine, namely the electricity. Electricity based engines are used to manufacture the electric cars. The propulsion system of an electric car consists of three major parts which are connected up by heavy wires and cables. These three major parts are electric motor, the battery, and the controller that has the transistor responsible for power delivery from the battery to the motor [5]. Even though electric cars have no carbon dioxide emission, they are totally electric so they are charged by plugging in and the distance that electric cars can go depends on the range of the charge [6]. Although car manufacturers know how to produce fast and comfortable electric cars, the range of the charge is the biggest obstacle for car producers. If the life of the battery which is charged by plugging in will be extended, the electric cars can be the most efficient solution to the air pollution caused by carbon dioxide emission produced by conventional combustion engines [7]. Another thing what previous researchers have focused on is dependence on oil for fuel, so they have came with an idea which indicates that alternative sources can be selected and used in order to run the automobile engines. This idea leads to production of another type of vehicle which is named as fuel cell powered vehicles. Fuel cell-powered engines use different fuels as a source of hydrogen which will come from fossil fuels by reforming natural gas or gasoline. The chemical energy of hydrogen is converted into the electricity by fuel cell powered engines. Mostly, methanol and gasoline are used as a source of hydrogen. Although methanol and gasoline emit small amounts of toxins caused by reformation, this amount of toxins are a lot lower than the amount of toxins emitted by internal combustion engines [8]. Obviously, using fuel cell powered system can reduce the harmfull efects on environment since hydrogen is the ultimate clean fuel and the products that came out from the combination of hydrogen with air are only heat, water and small amount of oxides of Nitrogen [9]. Nevertheless, hydrogen-based technologies such as fuel cell powered engines are expected to become availible in approximately 20 years and concern about air pollution caused by high level carbon dioxide emission becomes major issue for researchers. They come up with an ideal solution based on clean and renewable sources as alternatives for diesel and gasoline based engines. Some minor modifications on internal combustion engines enable to use natural gas as a clean alternative fuel [10]. Air that can exist in two forms compressed gas form and cryogenic liquid also considered as an alternative source for fuel. The compressed air vehicle enables same efficiency as battery electric vehicle and at the same time it promises high maturity with complete zero emission [11]. The principle of compressed air power system is simple. In order to produce work which drives the car the pressure potential must be released and this pressure potential is released by compressed air expanded through an expander. For the liquid air engines, there are some cycles used in thermodynamics and the most frequently observed one is Rankine cycle. The pressure of the liquid stored in the a tank is converted into the working pressure in the liquid state. Heat exchanger is used to vaporise and heat the liquid in order to drive an expander which can be either single stage or multistage. The efficiency of the engine can be increased by using multi-stage expander, since inter-heating occurs between stages [11]. Both working principles are shown in Figure (a) and (b) [11].

In my opinion, the trend which is focused on improving or changing the operating system is more likely to be successful in the future. Although the solutions found through following the second trend are more realistic, they are less efficient than that of first trend. In order to achieve zero emission, the efficiency of the engine must be hundred percent. However, the Cournot cycle which is scientifically considered as the most efficient thermodynamic cycle proves that it is impossible to gain hundred percents efficiency from any engine. In that case it is more reasonable to follow the first pattern in order to solve the problem. There are two patterns used to modify operating systems. First pattern is modifying conventional combustion engine by adding a parallel direct electric drive train with motor while the second pattern is replacing conventional combustion engine with an electric motor powered by a battery. Although the second pattern would be a good solution, there is a gap that lies in battery. Three major problems appear when the battery is considered. First problem is the cost of the battery which also increases the price of the car and the second one is time required for recharging [7]. In economics, the quantity demanded must be balanced with quantity supplied in order to reach an economic equilibrium. Therefore, battery must be mass produced in order to decrease the price. However, if people do not demand electric cars, manufacturers will not produce in large amounts. In my opinion, in order to increase demand of electric cars the range that car can go without charging must be extended while the time required for recharging must be shortened. If this goal will be achieved by researchers, the demand of electric cars would increase which causes a significant drop in price. Besides this, since the price of battery will decrease, the car users will be able to have more than one battery. But this method will be successful if and only if charging stations where robotic devices are used to change the battery are built. Another opportunity which may encourage people to drive electric cars is levying tax on batteries and as drivers change their battery at the station they give the empty one to the station and get the tax which is paid before. Actually, this tax will be like deposit. Consequently, it is obvious that the automobiles powered by conventional combustion engine damage the environment by high level carbon dioxide emission. Researchers focused on two different trends that are based on operating system and source of power. For each trend, two patterns were followed and according to my evaluations from these four approaches the most efficient one is operating system powered by electricity. Unfortunately, there is a gap which is the battery in that case must be filled. In order to encourage people for using electric cars, the level of price is key point and price would decrease if and only if the demand will increase. Therefore the demand for electric cars can be increased only by fixing the lack of batteries used in electric cars.

References:
1. Thomas, C.E., Fuel cell and battery electric vehicles compared. International Journal of Hydrogen Energy, 2009. 34(15): p. 6005-6020.
2. Deutch, N.D.a.J., Hybrid Cars Now, Fuel Cell Cars Later. Science, 2004. 305: p. 974-976.
3. Oscar P.R. van Vliet, T.K., Wim C. Turkenburg, André P.C. Faaij, Techno-economic comparison of series hybrid, plug-in hybrid, fuel cell and regular cars. Journal of Power Sources, 2010. 195(19): p. 6570-6585.
4. Otmar Bitsche, G.G., Systems for hybrid cars. Journal of Power Sources, 2004. 127(1-2): p. 8-15.
5. Anonymous, Electric cars. Metal Bulletin Monthly, 2009(464): p. 38-39.
6. wiseGEEK.
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8. Singer, S., It's not easy being green. Machine Design, 1998. 70(14): p. 1.
9. Siuru, B., FUEL-CELL POWERED VEHICLES. Electronics Now, 1998. 69(5).
10. S. ABDULLAH, W.H.K., M. KHAMAS, Y. ALI, EMISSION ANALYSIS OF A COMPRESSED NATURAL GAS DIRECT INJECTION ENGINE WITH A HOMOGENOUS MIXTURE. International Journal of Automotive Technology, 2011. 12: p. 29-38.
11. Haisheng Chena, Y.D., Yongliang Li, Xinjing Zhanga, Chunqing Tan, Air fuelled zero emission road transportation: A comparative study. Applied Energy, 2011. 88(1): p. 337-342.