What is Clean Diesel?

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About Clean Diesel

About Advanced Diesel Technology

Diesel is the world's most efficient internal combustion engine

Diesel is the world's most efficient internal combustion engine. It has greater energy density and provides more power and fuel efficiency than alternatives such as gasoline, compressed natural gas or liquefied natural gas.

Diesel engines have dramatically evolved since their invention nearly 150 years ago. Today’s advanced diesel technology is a three-part system that includes engines with optimized components, controls, design, and combustion strategies; ultra-low sulfur diesel fuels and/or low-carbon renewable biodiesel fuels as well as state-of-the-art emissions control technology that taken together, virtually eliminate emissions from diesel engines.

Advanced diesel’s proven energy efficiency, and ability to use renewable fuels, position it as a key technology to help achieve cleaner air and lower greenhouse gas emissions for a sustainable environment.

How does a diesel engine work?

Diesels are known as compression ignition engines. How the engine burns fuel is the main difference between gasoline and diesel engines. Gasoline engines ignite fuel with spark plugs. Diesels ignite fuel with compression instead. Inside a diesel engine, the combustion of air and fuel takes place under pressure. Heat is created by compressing the air-fuel mixture so intensely that it spontaneously combusts, releasing energy. That energy is transmitted to powering the vehicle’s wheels, the piston's motion and creating mechanical energy.

Why is diesel technology so fuel efficient?

Advanced diesel is fuel efficient because of a combination of the energy-rich properties of the fuel and the completeness of its combustion which creates more useful mechanical energy than other fuels. Ultra-low sulfur diesel fuel (ULSD) is a petroleum-based fuel with the highest energy density among transportation fuels; about 10-12% more energy (btu’s) per gallon than gasoline. The U.S. Energy Information Administration states that few transportation fuels surpass the energy density of diesel. Even advanced biofuels including biodiesel and renewable diesel have energy densities far superior than other alternatives.

Energy Density Graph

Advanced Engines

Advanced diesel engine designs are highly optimized to achieve maximum power, performance and fuel efficiency while minimizing and controlling the formation of emissions. This is accomplished through unique combustion chamber configuration, and specialized coatings of metal engine components such as bearings, pistons, and crankshafts.

Computer controlled engine management systems precisely control and optimize each combustion event on a real time basis through managing precisely controlled multiple high-pressure fuel injection events, and variable geometry turbochargers. Cylinder deactivation, hybridization, electrification of some components, as well as other strategies are also emerging aspects of advanced diesel engine design.

Effective Emissions Control

Advanced diesel engines minimize the production of emissions through efficient combustion. Controlling remaining emissions involves a series of strategies including particulate filters, oxidation catalysts, selective catalytic reduction (SCR) systems and catalysts.


Ultra-low sulfur diesel fuel (ULSD) containing 97% less sulfur than previous generations of diesel is the standard diesel fuel for both on-highway and off-highway diesel engines in the United States and a growing number of countries around the world.

Advanced renewable low-carbon biodiesel fuels are a further asset to advanced diesel technology. Use of these biodiesel fuels in new and existing diesel engines can lower greenhouse gas and other emissions by 20 to 80% compared to conventional petroleum diesel, depending on feedstocks.


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