Charged Ignition (Diesel) Engines

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Instead of compressing the air/fuel mixture to high temperatures and pressures as is done in gasoline engines, diesel engines operate by compressing air alone. Because there is no fuel present, air can be heated to pressures and temperatures well over the ignition temperature of fuel without concern for engine knock. Unlike gasoline engines, diesels require no carburetors or spark plugs. Instead, tiny droplets of diesel fuel are injected directly into the cylinder, where they mix and react with already heated air and burn (Figure 1). Since injection times are relatively long, the piston travels an appreciable distance before fuel is cut off, keeping the pressure in the cylinder nearly constant.

Figure 1 Four-stroke Otto Rotary Engines.
Figure 1 Four-stroke Otto Rotary Engines.

Generally speaking, diesels are less efficient than gasoline engines with similar compression ratios. However, because diesels are designed to operate at higher compression ratios than spark-ignition engines (20-22 compared to 8-9 for spark ignition engines), they have higher efficiencies (~40% compared to ~30% for the petrol engines). Their main drawbacks are that they are bulkier, emit more, have a higher capital cost, and accelerate more slowly. These characteristics make diesels particularly attractive in stationary applications and for buses and large trucks. Because of the stricter air pollution standards, diesels are less common in the United States than Europe. New technological inventions are underway that makes diesels cleaner, and thus sales of diesels are likely to increase in the US in the near future.


(1) Toossi Reza, "Energy and the Environment:Sources, technologies, and impacts", Verve Publishers, 2005

Further Reading

Tillman, D., Fuels of Opportunity: Characteristics and Uses In Combustion Systems, Academic Press, 2004.

Sorensen, K., Hydrogen and Fuel Cells: Emerging Technologies and Applications, Academic Press, 2005.

Dhameia, S., Electric Vehicle Battery Systems, Academic Press, 2001.

Hussain, I., Electric and Hybrid Vehicles: Design Fundamentals, CRC Press, LLC. 2003.

Jefferson, C.M., and Barnard, R. H., Hybrid Vehicle Propulsion, WIT Press, 2002.

Spelberg, D. The Hydrogen Energy Transition: Moving Toward the Post Petroleum Age in Transportation, Academic Press, 2004.

Fuel, Direct Science Elsevier Publishing Company, Fuel focuses on primary research work in the science and technology of fuel and energy fuel science.

Transportation Research Part C: Emerging Technologies, Direct Science Elsevier Publishing Company; this journal focuses on scholarly research on development, application, and implications in the fields of transportation, control systems, and telecommunications, among others.

Fuel Cells Bulletin, Direct Science Elsevier Publishing Company, Fuel Cells Bulletin is the leading source of technical and business news for the fuel cells sector.

International Journal of Hydrogen Energy, Direct Science Elsevier Publishing Company, Quarterly journal covering various aspects of hydrogen energy, including production, storage, transmission, and utilization, as well as economical and environmental aspects.

External Links

US Department of Transportation (

US Department of Energy (

US Environmental Protection Agency (

National Energy Renewable Laboratory Hybrid Electric &Fuel Cell Vehicles (

FreedomCar (