Physics Behind Electric Cars

Research suggests that driving an electric car that is charged at night is the equivalent of spending ~75 cents per gallon of gasoline, thereby combatting the issue of higher gas prices. These vehicles make use of the national grid in order to amass electricity. Additionally, these vehicles could actually deliver energy into the grid. Cars parked in busy downtown areas would not only be feeding the grid, they would also be reserving energy for efficient local transportation. Maintenance and serving costs for electric vehicles are lower and there are fewer moving parts.

When first marketed the cost of the electric vehicle battery was prohibitive. However, advances in the technology plus increased demand have caused the prices to drop. Cost-effectiveness and care for the environment has caused consumer and manufacturers to transition from traditional gas-powered engines to the Plug-in Hybrid Electric Vehicle (PHEV) as well as to look farther into the future toward the all-electric vehicle. In order to understand the viability of alternatives to gas powered vehicles an examination of the various power basics is required (Larminie and Lowry 17).

Chemical energy in cars refers to the power that derives from gas fuels. Typical internal combustion engines use the Otto-cycle to convert heat from fuel into work. In order to produce power from the chemical energy in fuel vehicles use a combustion engine. Piston motion in response to combustion produces work and each cylinder has a piston. The piston movements are called strokes. Thus, in a common small four-stroke engine is one in which the piston makes four distinctive strokes: intake, compression, power, and exhaust thereby completing one cycle. The piston movement eventually causes pressure higher than atmospheric pressure and the exhaust gases exit the cylinder. Then those gases are forced out.

A fraction of the energy supplied by fuel is the net chemical energy released. The stoichiometric air-fuel ratio divided by the actual air-fuel ratio determines combustion efficiency. The stoichiometric is the relationship of relative quantities of substances taking part in a reaction or forming a compound, i.e. oxidation. As the mixture becomes richer than stoichiometric the efficiency decreases due to air restriction.

The kinetic energy that makes the engine operate an electric vehicle derives from the conversion of electrical stored energy into kinetic energy. The thrust derives from the road via the vehicle’s tires. The friction between the road and tires produces momentum. In converting energy delivered into kinetic energy approximately twenty-five percent of the energy in gas fuel reaches the vehicles wheels. Seventy-five percent of the gas fuel is expelled as exhaust or via the cooling system. Seventy-five percent fuel waste via combustion engines compared to the conversion loss of approximately twenty percent of the energy stored in an electric vehicle. Electric motors convert eighty percent of their stored energy into operation (Fariaa, Mouraa, Delgadoa, and Almeidaa 7).

The electric energy that is used to propel PHEVs or all-electric vehicles is a result of a couple of systems. When a gas-powered engine is connected to an electric motor, the electric motor powers the wheels. Torque from the gas-powered motors produces electric energy that is amassed in the battery. In this way, the gas-powered engine operates at a higher rate of efficiency. This combination prevents the vehicle from being charge-dependent. These vehicles are referred to as self-sustaining because they do not rely solely on electric input. Charge-dependent vehicles release lower emissions and therefore are very useful in local and short-range driving in cities with chargers because the vehicles can be re-charged easily. The self-sustaining version is useful locally and in long distance, long duration driving (Franke, Neumann, Bühler, Cocron, and Krems 1).

Physicist Barry Parker uses chaos theory to enlighten readers about everything from local driving habits to the principles of electricity and magnetism. Additionally, he makes predictions about how future cars will operate. Self-sustaining electric vehicles use large capacity generators and charge-dependent electric vehicles use high capacity batteries. The laws of physics cap the uppermost limits on the efficiency of the engines. Therefore, the electric motor is the most efficient. When an engine converts heat derived from fuel into work to propel the vehicle the second law of thermodynamics restricts the amount of heat that converts into work. Electric energy is not subject to this equation (23).

The impediment to the use of electric-only vehicles is range (Franke, Neumann, Bühler, Cocron, and Krems 8). Batteries store only so much energy. The feasibility of electric-only vehicles becomes better when there is a self-sustaining component to the vehicle. Manufacturers have averted the issue of battery life by focusing on the making of Plug-in Hybrid Electric Vehicle (PHEV) and Extended Range Electric Vehicles. In these engines fuel operates at high efficiency. In other developments physicists are researching compounds in hopes of finding a viable solution to such question as can waste heat itself be converted into electric energy (Kever 1).

Businesses and scientists were first to begin studying the viability of electric vehicles, particularly in daily local transportation. Additionally, commercial developers now offer after-market conversion kits that change hybrid vehicles into plug-in hybrids. Finally, the large automakers have joined the initiative and already offer a variety of PHEVs and all electric vehicles.

Works Cited

Fariaa, Ricardo, Mouraa, Pedro, Delgadoa, Joaquim, Almeidaa, Anibal T. A sustainability assessment of electric vehicles as a personal mobility system. University of Coimbra, Dept. of Electrical and Computer Engineering, 3030-290 Coimbra, Portugal. (2012).

Franke, Thomas, Isabel Neumann, Franziska Bühler, Peter Cocron, and Josef F. Krems. "Experiencing Range in an Electric Vehicle: Understanding Psychological Barriers." Applied Psychology. 61.3 (2012): 368-391

Kever, Jeannie. Research Creates New Opportunities from Waste Heat. University of Houston. (2013).

Larminie, James, and John Lowry. Electric Vehicle Technology Explained. Hoboken: John Wiley & Sons, 2012.

Parker, Barry R. The Isaac Newton School of Driving: Physics and Your Car. Baltimore, MD: Johns Hopkins University Press, 2003.