The Effects of Hybrid Electric Vehicles to Internal Combustion Engines

The internal combustion engine has dominated the car and light-truck market for over 100 years. Although remarkable improvements have been made over the past 30 years to reduce air pollutants to nearly zero and to almost double vehicle efficiency, increasing concerns about global warming and energy security are pushing vehicles toward even greater efficiency. Adding a high power electric motor and electric storage capacity to an internal combustion engine offers significant fuel savings. The engine can be shut off at idle to avoid wasting fuel, the motor can be driven in reverse when braking to capture energy that would otherwise be lost, and the boost from the electric motor allows use of a smaller, more efficient, engine. In the long term, the electrical power from the motor can be used to replace existing mechanical accessory drives with more efficient electrical devices, as well as to provide power for additional features desired by customers. Against these benefits must be weighed the additional complexity and costs of the hybrid electric power system.

In the early days of the automobile, around the turn of the 20th century, there was spirited competition between vehicles powered by electricity and by internal combustion engines. The internal combustion engine won primarily because of the high amount of energy in liquid fuels, which allows vehicles to travel farther without refueling than is possible on an electric charge. Ten gallons of gasoline weighs only about 28 kg (62 lb), but contains about 330 kWh (kilowatt- hours) of energy (1.1million Btu). By comparison, a modern lead-acid battery weighing the same 28 kg provides only about 1.1 kWh. This overwhelming energy advantage of liquid fuel has ensured the dominance of the internal combustion engine for the past 100 years, despite its relatively low efficiency.

Problems with the use of internal combustion engines and fossil fuels are well documented, including low efficiency, air pollution, fossil fuel use, energy security, dependence on foreign oil suppliers, lead poisoning, and leaking storage tanks. To combat these problems, many alternatives to the gasoline internal combustion engine have been proposed over the years, such as steam power, turbine engines, electric vehicles, and the use of alternative fuels such as methanol, ethanol, compressed natural gas, and propane. The latest contender is the fuel cell, powered by hydrogen. However, so far, the internal combustion engine has won over all proposed alternatives. It has accomplished this because the incremental advantages of switching to another propulsion system have been less than the cost of switching to an entirely new infrastructure. In addition, every time the internal combustion engine has been challenged, it has responded with enough improvement to keep the alternative off the market. For example, with the development of modern computer controls and catalysts, air pollutants have been reduced to levels undreamed of even 10 years ago. Fuel efficiency has also increased greatly due to advances in technology. The average car today achieves almost twice the fuel economy of the average car 30 years ago, in addition to accelerating much faster. However, even with the efficiency increases, the average efficiency of a gasoline internal combustion engine in typical in-use operation is still only about 15%. The other 85% is lost to engine heat, heated exhaust gases, aerodynamic drag, tire rolling resistance, driveline losses, and braking.

Adding an electric motor and energy storage to the internal combustion engine can significantly improve efficiency in a variety of ways, depending on how the system is designed: Engines are least efficient when operating at low loads. The electric motor can be used to supply part or all of the propulsion energy at low speeds and loads, minimizing engine use under inefficient conditions. The electric motor can assist the engine during acceleration. This allows use of a smaller engine without any loss in overall performance. For a given load, smaller engines have better efficiency, due to lower frictional and heat losses The high power electric motor allows rapid engine restarts. This allows the engine to be shut off at idle and avoids fuel consumption while the vehicle is stopped. The electric motor can be used to capture regenerative braking energy. This is done by using the vehicle’s inertia to drive the electric motor in reverse while the vehicle is slowing down, thus creating free electric energy. The additional electric power from the motor/ generator can be used to replace mechanical and hydraulic devices and pumps with more efficient electric versions.

The advantages of hybrid systems have long been recognized. The first hybrid vehicle was built in 1898 and several manufacturers sold hybrid vehicles in the early 1900s. However, hybrid vehicles technology also have significant problems. They require two propulsion systems, which take up room, add weight, and greatly increase the cost. Another problem is that careful coordination of the operation of the engine and the motor is necessary to achieve much of the efficiency benefits and to avoid drivability problems. This was not possible with mechanical controls, and the production of hybrid vehicles did not survive continued development of the internal combustion engine in the early 1900s.

Renewed interest in hybrid vehicles has coincided with development of computer controls and improved batteries, combined with increasing concerns about the contribution of carbon dioxide emissions to global warming. Sophisticated computer controls allow maximum efficiency benefits while providing smooth, seamless coordination of the two propulsion systems. Advanced batteries, such as those made with nickel–metal hydride (NiMH), provide higher energy density and much longer cycle life, which is important to customer acceptance of hybrid vehicle technology. Hybrid vehicles offer a way to reduce fuel use significantly, with corresponding reductions in global warming gases and fuel cost to consumers, plus modest reductions in criteria air pollutants. The primary concern with hybrid systems remains the cost of the additional components.