Clean Diesel Technology

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Clean Diesel Technology

Clean diesel is an emerging technology that has many long-term benefits to offer if it is utilized accordingly. A detailed account of the pros and cons of clean diesel, the differences between clean diesel and regular diesel, the current state of this technology in the US, the Diesel Emissions Reduction Act (DERA), and the implementation of the technology in the US has been provided below.

Pros and Cons of Clean Diesel

As with anything, where clean diesel has its benefits, it also has its trade-offs. A few advantages and disadvantages of clean diesel technology have been outlined below.

Advantages of Clean Diesel

Cleaner Fuel

Advanced Engines

  • Reducing the sulfur content of diesel has enabled the design of newer and more advanced diesel engines. These engines paired with advanced emission control systems also help in controlling emissions. These engines, and emission control systems, cannot be operated on fuels that have high sulfur content.
  • Diesel engines can also be run on advanced biofuels, e.g. biodiesel, that have the potential to reduce the emission of greenhouse gases by 50%.

Emissions Control

  • Clean diesel fuel also reduces emissions of nitrogen compounds by up to 50%.
  • This reduction in the emission of nitrogenous compounds is achieved through the use of advanced exhaust emission control systems.
  • This technology also reduces particulate emissions by 90%.

Fuel Efficiency

  • Diesel fuels have some of the highest energy density, i.e. the ability to store energy per unit of fuel.
  • Diesel fuels have higher energy density than gasoline, CNG (Compressed Natural Gas), and LNG (Liquefied Natural Gas).
  • Diesel fuels are so efficient that even the alternative versions of diesel, i.e. biodiesel and renewable diesel fuels, have higher energy density as compared to many other fuels.

Disadvantages of Clean Diesel

NOx Emissions

  • Diesel fuels, unlike gasoline, are made up of a wide variety of hydrocarbons. It is essentially crude oil that is extracted from the ground with very little refining. The variety of hydrocarbons produce different types of emissions, including sulfur and nitrogen compounds.
  • Although sulfur emissions are well-controlled using the emission control systems in diesel-powered vehicles, the NOx emissions (NO2, NO3, etc.) are unpredictable and hard to control.
  • NOx emissions cause several health issues and even fewer diesel vehicles as compared to gasoline vehicles can cause problems for people living in such cities.
  • With all of the above in mind, research is being done on making diesel fuels less harmful and it might emerge as the most economical as well as energy-efficient fuel once engineers have figured out how to get the most energy out of diesel without producing the harmful byproducts.

Water Accumulation

  • Since diesel runs longer, it is also stored longer. This causes water buildup in diesel storage tanks, which is virtually unmanageable due to its nature.
  • Water can cause oxidative degradation of the diesel fuel inside the storage tanks. It can also cause injector blowouts as well as microbial growth.

Lubricity and Cold Flow

  • ULSD (Ultra-Low Sulfur Diesel) is prepared using very low amounts of sulfur. With the plummeting sulfur levels, diesel fuels can exhibit other issues.
  • These issues include lower lubricity, or the decrease in the ability of the fuel to provide lubrication, and inadequate cold flow properties.

Clean Diesel Vs. Regular Diesel

Clean diesel is the modified form of regular diesel and solves many problems associated with regular diesel. A few major differences between the two have been identified below.

Sulfur Levels

  • Clean diesel has very low sulfur levels. As per EPA regulations, clean diesel must have sulfur levels of 15 ppm or lower.
  • Traditional diesel has higher sulfur levels, up to 500 ppm. It has 97% more sulfur as compared to clean diesel.


  • Sulfur is one of the most important factors when it comes to pollution caused by diesel fuels. This makes clean diesel much less harmful in terms of its impact on the environment.
  • Regular diesel fuels can produce unburned hydrocarbons, carbon monoxide, nitrogen oxides, and particulate matters on top of the additional sulfur pollutants that clean diesel eliminates.

Physical Properties

  • A few years earlier, gasoline vehicles were so much better than diesel vehicles due to a variety of reasons including exhaust odor, poor performance, engine noise, and cold start difficulties associated with regular diesel fuels.
  • Nowadays, clean diesel is being used in advanced diesel engines and diesel vehicles seem to be identical to gasoline vehicles. In fact, diesel vehicles provide more power and fuel economy.

Health Risks

  • Clean diesel comes with the promise of reduced health risks as compared to regular diesel. Although it is better than regular diesel, there are still issues that need to be addressed and research is being conducted to make it even safer. Clean diesel has also been said to have the potential to reduce carbon dioxide emissions as compared to gasoline.
  • Regular diesel poses serious health risks as compared to clean diesel because of the increased emissions. Diesel produces very fine particles upon burning, which can get into the lungs and even into the bloodstream.

Soot Production

  • Clean diesel is said to produce considerably less amount of soot as compared to regular diesel. It should be noted though, that clean diesel requires the use of specific fuel systems to be effective.
  • Regular diesel, when used in conventional engines, "produces a fuel-rich, sooty flame".

Clean Diesel Technology in the US

  • The regulations for diesel vehicles in the US have become 'progressively stringent' over the years.
  • Clean air guidelines in the US have forced diesel to become cleaner than ever before it could be used in diesel engines throughout the country.
  • Although the infamous dieselgate scandal impacted the diesel vehicle market in the US and also enraged customers, the diesel vehicle market saw a 9% increase in sales in 2018.
  • With the increase in sales, automakers have also started to roll out new models, especially the most famous vehicle in the US, i.e. full-size pickup trucks.
  • Several manufacturers are currently offering clean diesel vehicles in the country and many more are in the pipeline. Manufacturers that are currently offering clean diesel models include Chevrolet, Ford, GMC, Jaguar, Jeep, Land Rover, Mazda, Mercedes, Nissan, and RAM.

Diesel Emissions Reduction Act (DERA)

  • The Diesel Emissions Reduction Act is part of the Energy Policy Act of 2005. The act was introduced in 2010 and authorized funding for projects that aim to reduce emissions caused by existing diesel engines. The bill authorized $100 million per annum from 2012-2016.
  • As per the act, "Seventy percent of the DERA appropriation is to be used for national competitive grants and rebates to fund projects that use EPA or California Air Resources Board (CARB) verified or certified diesel emission reduction technologies."
  • The rest of the DERA appropriation, i.e. 30%, "is allocated to the states and territories to fund programs for diesel emissions reduction projects. Base funding is distributed to states and territories using a formula based on overall participation. Additional incentive funding is available to states and territories that provide matching funds."
  • The objective of the DERA is to improve air quality and protect human health through the reduction of harmful emissions caused by diesel engines. The act authorizes national grants, tribal grants, schoolbus rebates, and state grants.

Implementation of Clean Diesel Technology in the US

  • The implementation of clean diesel technology in the US will primarily be phased out through the implementation of regulations. Several regulations and bills have been passed for the implementation and promotion of clean diesel technology in the US, including the NCDC (National Clean Diesel Campaign), the DERA, and others.
  • The US EPA (Environmental Protection Agency) maintains a list of technologies that have been approved. The list also provides the percentage reduction of emissions for each technology. The list can be found here.
  • Diesel engines are at the core of US transportation and many other industries, including construction, highways and roads, etc.
  • While diesel engines are widely used in the country, they also pollute the environment impacting the environment and human health.
  • Diesel engines cause pollution including "large amounts of nitrogen oxides, particulate matter and air toxics, which contribute to serious public health problems, including asthma, lung cancer and various other cardiac and respiratory diseases. These problems result in thousands of premature deaths, millions of lost work days, and numerous other negative health and economic outcomes every year."
  • As many as 11 million diesel engines in the country did not meed EPA's emissions standards back in 2009.
  • The EPA also launched the Recovery Act Program with the aim of reducing emissions from diesel engines through reduction strategies that ensure job preservation and/or creation.
  • In line with these goals, the EPA established NCDC (National Clean Diesel Campaign). The goal of NCDC is "to accelerate emission reductions from older diesel engines to provide more immediate air quality benefits and improve public health."
  • A detailed account of the priorities of the Recovery Act Program and the NCDC can be found here.