What is Clean Diesel?

Share This Page


Meeting Clean Air Goals

Diesel continues to serve as an efficient fuel source with near zero emissions helping to provide clean air benefits to communities here at home and around the globe. Thanks to decades of collaboration between regulators and industry, a new generation of diesel technology is now delivering even more clean air benefits to communities around the country.

Diesel has long been known for delivering power and performance along with fuel efficiency. More people and goods can be moved and more work performed with a gallon of diesel fuel than any other transportation fuel around. This explains why diesel engines power over 95 percent of heavy-duty vehicles and are nearly ubiquitous in construction, agriculture, mining, locomotives and other off-road applications. In fact, more and more consumers are taking noticing of the performance and efficiency offered by a growing number of diesel cars, SUVs and pickups. Today, diesel continues to deliver these attributes along with near zero emissions helping to provide clean air benefits to communities here at home and around the globe. Thanks to decades of collaboration between regulators and industry, a new generation of diesel technology is now delivering even more clean air benefits to communities around the country. 

The latest generation of clean diesel engines that power vehicles and equipment delivers near zero emission along with climate benefits owing to enhanced fuel savings. These benefits are further enhanced when considering the diesel powertrain’s capability to operate on blends of first generation biodiesel and second generation renewable diesel.

New Technology Diesel Engines: Building on a Strong Tradition of Low Emissions for Heavy-Duty Commercial Vehicles

While new technology diesel engines deliver impressive emission reductions, the latest technologies developed to meet or beat the latest emissions requirements are just one chapter in the clean diesel story. Whether it is heavy-duty commercial vehicles or off-road equipment, new technology diesel engines are the latest point in a downward trend for tailpipe emissions.

Commercial Vehicles


For commercial vehicles, comprising everything from large pickups to even larger Class 8 tractors, the latest strict emissions standards established for model year 2007 and the stricter model year 2010 result in near zero emissions of particulate matter and oxides of nitrogen, an ozone forming compound.

Meeting and Beating the Standard

Recent research estimates that heavy-duty diesel engines actually beat these emissions requirements handily. The Advanced Collaborative Emissions Study found that heavy-duty diesel engines manufactured to meet the model year 2010 emissions standard demonstrate that these engines deliver NOx emissions 60 percent below the standard and particulate matter emissions 90 percent below the standard.

The population of these clean diesel vehicles in service today are delivering substantial clean air benefits.  According to research commissioned by the Diesel Technology Forum, heavy-duty diesel commercial vehicles powered by an engine that meets or beats the model year 2010 standard has resulted in a reduction of 1.5 million tons of NOx between 2010 and 2014 while vehicles powered by engines that meet or beat the 2007 standard have reduce emissions of particulate matter by 40,000 tons since 2007.

While these clean diesel vehicles are generating substantial clean air benefits, roughly one-in-five heavy-duty vehicles on the road today is powered by an engine that meets or beats the strict model year 2010 standard. Clearly, even more substantial savings can be realized if more of these clean vehicles enter into service. In fact, air quality regulators in the Los Angeles area estimate that NOx emissions attributable to diesel-powered commercial vehicles in the South Coast basin could fall by 70 percent if all commercial vehicles in the region were powered by one of these engines.

How Clean is Clean?

The reduction of NOx emissions from these vehicles is equivalent to the entire NOx and PM emissions from 128 million passenger vehicles emitted over 15 months.  Put another way, NOx emissions from these heavy-duty vehicles is equivalent to the entire NOx emissions from 154 coal power plants.

In California, that keeps close emissions inventory data, NOx emission from large pickups to even bigger Class 8 tractors have fallen by 54 percent between 2015 and 2005 and PM emissions have fallen by 66 percent over the same time frame. 

Next Up: Off-Road Equipment

Today, diesel engines and fuel power over 95 percent of commercial vehicles yet they also power a similar share of off-road equipment from construction, agricultural, warehouse and mining equipment, locomotive and marine engines and mobile and stationary generators. Technology developed to meet strict emissions standards for commercial vehicles are have also been deployed in of off-road equipment. In 2014, most off-road equipment had to meet the latest emissions standards known as the Tier 4 standards. As of 2015, most large engines typically found in locomotives, marine applications and industrial engines must meet these standards. Relative to the first generation of emission standards for this equipment, emissions have been reduced anywhere from 86 percent to 96 percent for both NOx and PM thanks to the deployment of clean diesel technology. 

Much like technologies developed to meet the model year 2010 emission standard for commercial vehicles, off-road engine and equipment manufacturers have coupled near-zero emission technology with substantial fuel savings capabilities.  Many of these fuel savings capabilities involve advanced engine designs but also more efficient hydraulic systems, telematics and even hybridization.  This equipment will deliver clean air benefits to many communities as more of these Tier 4 engines, and the equipment powered by them, enter into service. 




Clean Diesel Cars Deliver Air Quality Benefits Along with Substantial Fuel Savings

Clean diesel technologies developed to meet the clean air challenge by heavy-duty vehicles and off-road equipment are now also found in diesel cars, SUVs and pickups. While diesel passenger vehicles are held to the same emission standard as gasoline vehicles, the diesel option delivers substantial fuel savings and greenhouse gas reduction benefits. Since 2005, the banner year for the reintroduction of diesel into the passenger vehicle market in the U.S., diesel vehicles have saved 36 million barrels of crude oil and 9.7 million tons of carbon emissions as of 2014. Meanwhile, the number of models of diesel cars, SUVs and pickups has almost tripled growing from 11 in 2005 to 29 as of 2014. With more consumer choices available in the market today, and many more expected in the future, diesel-powered vehicles are expected to make up about 7 percent of the passenger vehicle market by 2020 and are expected to save another 9 million tons of CO2 emissions. One of the benefits of the diesel platform is its proven capability for continued improvement. This long tradition of continued improvement is expected to keep diesel as a technology to meet the forthcoming Tier 3 emissions standard for passenger vehicles beginning in 2017.


Policy Overview

Hot Issues

"I don’t have concerns
with diesel technology in general"

When asked during the Congressional hearings on the VW situation about its random vehicle audit of all light-duty diesel, Chris Gundler, U.S. EPA Director of the Office of Transportation & Air Quality, replied:

“I don’t have concerns with diesel technology in general. I don’t expect to find widespread problems but we are going to be taking a very close look.”

See More

Sign up for diesel direct

weekly analysis & commentary from the diesel technology forum