Strict standards have been placed upon the auto industry. By 2025 automobile makers must meet the 54.5 gallons per mile standard set forth by the US government. In order to stay competitive against many foreign auto makers, major car manufacturers have come up with new technology to help save fuel.

The first technology to create fuel efficient cars is clean diesel. “Ultra low sulphur diesel fuel has been refined so that its sulphur content is 15 parts per million (ppm) or less. This is 97 percent cleaner than the standard highway-use diesel fuel sold in the US, which contains an average of 500 ppm of sulphur.” ULSD has been the standard for cars in Europe for many years now.

The next technology that has helped improve gas mileage is direct injection.  Direct injection improves fuel efficiency and will generally yield more power when compared with a port-injected engine of similar displacement and design. 

A third technology used is turbochargers. Although turbochargers do not make the engine more efficient, it allows for smaller engines to produce more power by sucking clean air into a pressurized turbine with two fans. A turbocharged engine is more powerful and efficient than a  regular engine because the turbine forces more air, and proportionately more fuel, into the combustion chamber than atmospheric pressure alone.

These three technologies have contributed to the reduction of carbon emission and higher gas mileage. Newer forms of fuel efficient technology are created each year. For example, hybrid cars and hydrogen powered cars. The forms of technology above have the led to the creation of these newer types.

Sources:

http://auto.howstuffworks.com/fuel-efficiency/alternative-fuels/how-clean-diesel-fuel-works1.htm

http://www.hotrod.com/techarticles/engine/hrdp_0909_direct_injection_guide/

http://auto.howstuffworks.com/turbo.htm