Efficiency Improvements in new engines and equipment, accelerating fleet turnover and increased use of low-carbon renewable biofuels are key opportunities to reduce GHG emissions in the transportation sector.
Diesel is the most energy-efficient internal combustion engine and is the prime mover for key sectors of the global economy. New diesel engines now achieve near-zero emissions with increasing fuel efficiency and lower CO2 emissions, and further improvements are now on the horizon. Both new and existing engines and are capable of utilizing low-carbon renewable biofuels. Taken together, these elements make diesel technology part of the solution to reducing GHG emissions.
Driven by the desire to address climate change and reduce emissions as well as advancements in new technologies, alternatives to diesel technology are emerging in some sectors. Electric-powered vehicles and equipment that run on hydrogen are being developed. While some of these alternatives may hold promise, none of the technologies that seek to replace diesel can deliver in the near term the unique combination of attributes that position diesel as the technology of choice in so many sectors of the economy. Experts predict that in the commercial trucking sector for example, that diesel will continue to be the technology powering the majority of commercial vehicles in 2040 and perhaps beyond.
Emerging technologies are constrained by the lack of available fueling infrastructure and the much higher cost of infrastructure as well as vehicle acquisition. Similarly, further reductions in allowable emissions from diesel engines will increase costs, but also make the technology more efficient and even nearer-to-zero emissions. Ultimately all fuels and technologies have tradeoffs, and all will have some role in helping meet the climate challenge.
Given the longer timeframe and considerable uncertainties of emerging technologies seeking to replace diesel, to ensure progress in reducing greenhouse gas emissions in the near term, continued innovation and investment in diesel engines is essential to achieving domestic and international climate change objectives.
Advanced diesel engines – through efficiency and performance gains -- are contributing toward reducing emissions today, and there are several opportunities to further reduce GHG emissions from diesel engines and equipment in the transportation sector.
Accelerating turnover to Advanced Technology Diesel: Trucking Industry
Diesel fuel is the technology of choice for the global trucking industry. Thanks to its unique combination of energy density of the fuel and performance of the engine in why diesel powers 76% of commercial vehicles on the road today.
Much like cars, fuel economy standards are now required of the large variety of commercial vehicles from heavy-duty pickups to vocational trucks like cement mixers and utility trucks to full-size Class 8 tractor-trailer type trucks. These standards, adopted jointly by the U.S. Department of Transportation and the U.S. Environmental Protection Agency, require increasing improvements in fuel efficiency of commercial vehicles. The first phase of those rules became effective in 2014 while the second and more stringent fuel economy standard was implemented in 2021. For a new typical Class 8 long haul tractor-trailer-size truck, these new requirements will result in about a 25% improvement in fuel economy.
To meet these requirements, a variety of technologies will be used to make these vehicles more efficient and reduce greenhouse gas emissions, while also maintaining near zero emissions performance for criteria emissions particulate matter and oxides of nitrogen.
The new generation of diesel-powered commercial vehicles has already contributed substantially to a better environment. Between 2007 and 2030, these technologies will save 1.5 billion tons of carbon dioxide emissions and save 150 billion gallons of fuel compared to previous generations. These benefits are equivalent to removing all cars, pickup trucks and SUVs on the road for a year and half or making them all zero-emission vehicles.
While new generation advanced technology diesel trucks now make up about half of all registered commercial vehicles, the other half of the existing fleet is of an older generation of technology, relatively higher in greenhouse gas and other emissions. The opportunity to accelerate the turnover in the existing fleet is considerable and would bring immediate clean air and climate benefits.
Construction, agriculture, power generation, marine, rail, and other industrial sectors:
The off-road sector of diesel engines is considerably a larger and much more diverse population of engines and equipment than the commercial truck sector. Off road engines and equipment complete many different kinds of tasks and have many different duty cycles, power demands and other considerations.
Since 2014, new machines, engines and equipment are of the newest and most advanced generation of diesel technology, that is more fuel efficient and has lower emissions of nitrogen oxides and particulate matter.
Compared to older generations of technology, it would take about 23 new backhoes or farm tractors to equal the emissions of one older backhoe or tractor.
Reducing GHG emissions in the off-road sectors is occurring through replacement of older engines and equipment with new technology diesel engines. Both construction and agricultural sectors also are deploying advance connected and smart technologies that utilize global positioning satellites (GPS) and proprietary connected jobsite technologies that communicate, monitor and control equipment operations to optimize the efficiency of each project or task.
Smart farming technologies enable farmers to reduce fuel consumption and optimize tractor settings to coordinate and reduce time and activities in the field. Precision planting, automated machine guidance and powered implements are just a few of the examples of strategies to reduce GHG emissions in the farm sector.
In the construction sector, precision machine guidance and connected worksites and technologies that monitor and reduce idle time all contribute to lower fuel consumption and fewer GHG emissions.
All off road engines and equipment are also suitable for using advanced biofuels such as biodiesel and renewable diesel, based on manufacturer recommendations.
Utilizing Biodiesel and Renewable Diesel Fuel
Diesel engines of all kinds are capable of operating on a variety of advanced biofuels. These low-carbon renewable fuels deliver significant reductions in greenhouse gas emissions, and are considered advanced biofuels by the U.S. EPA, capable of reducing greenhouse gas emissions by at least 50%.
In 2020, the United States produced 3 billion gallons of biobased diesel fuel. Two types of biofuels available for diesel engines, both generally produced from the same feedstocks – waste residues derived from soybeans and animal fats; known as biodiesel and renewable diesel fuel Most modern diesel engines are capable of operating on blends of biodiesel up to 20%, known as B20 (20% biodiesel and 80% petroleum diesel). The differences in the fuels are based on how they are processed and the properties of the finished products.
Renewable diesel fuel, sometimes known as HVO or hydrogenated vegetable oil is derived from the same feedstocks as biodiesel but is refined using a different chemical process to generate a fuel that meets the same engineering specification as petroleum diesel fuel. This means that renewable diesel fuel may be used as a 100% substitute to petroleum-based diesel fuel, or in any blend combination. California is the leading consumer of biodiesel and renewable diesel fuel consuming almost one out of every four gallons of the fuel supplied in the United States. In 2020, the California Air Resources Board found that these fuels generated the greatest reduction in transportation emissions among all the many fuel and technology types. Since 2011, biodiesel and renewable diesel fuel eliminated more than 32 million tons of carbon dioxide (43%). This compares to only 10 million tons (13%) of carbon dioxide eliminated from the use of battery electric vehicles.
Fleets across the country seeking to lower their carbon footprint are switching to these biobased fuels and realizing significant benefits without incurring significant costs required for infrastructure and new vehicles of other alternative fuels. The San Francisco Municipal Transportation Authority has been using renewable diesel fuel in its fleet of over 600 buses to reduce carbon dioxide emissions by over 10,000 tons. Florida Power and Light uses biodiesel in its fleet of over 3,900 utility vehicles to reduce carbon dioxide emissions by 6,700 tons.
Black Carbon Reduction
While carbon dioxide is the most abundant greenhouse gas, there are other greenhouse gas forming compounds known as short lived climate pollutants (SLCP). One of these pollutants is black carbon and it is upwards of 900 times more potent than carbon dioxide. Unlike carbon dioxide, eliminating man made emissions of black carbon is relatively easy. Black carbon, also known as soot, is generated by the incomplete combustion of fuels including contributions from forest fires, charcoal stoves and also diesel engines. Soot is emitted and rises in the atmosphere where it deposits on polar ice. The black particles trap solar heat and contribute to melting polar ice.
Eliminating sources of black carbon emissions is very cost effective and many countries across the globe are adopting cleaner fuel standards and tighter regulations on tailpipe emissions that will nearly eliminate diesel’s contribution to black carbon emissions. Since 2007, all highway vehicles have achieved near-zero emissions for particulate matter, a 97% reduction from previous levels. Similar performance is now in place for off road engines and equipment since 2014.
The US has been a success in developing and deploying technologies like particulate filters that are projected to reduce black carbon emissions by 91% between 2005 and 2030. Clean diesel technologies that control black carbon emissions will be an important strategy to meet ambitious climate goals as more countries adopt cleaner diesel fuel standards and tailpipe emissions regulations.