Diesel technology continues to evolve to meet the demands of today and tomorrow for efficient, clean and reliable power across wide sectors of the global economy.
An energy transition is underway.
Fueled by new efforts to reduce greenhouse gas (GHG) emissions, the development of emerging technologies such as batteries and fuel cells will play an increasing role in the future in the transportation and possibly other sectors of the economy. Some of these emerging technologies may replace diesel in some applications, while diesel will continue to be the dominant technology for the foreseeable future in others.
From government sources to international consulting firms, authorities agree that internal combustion engines - both gasoline and diesel - will continue to be important for many decades into the future to ensure continued progress on meeting society’s greatest challenges - achieving cleaner air and reducing GHG emissions - as other emerging technologies are yet to reach commercial availability at scale and with still unknown impacts from the global pandemic.
Diesel technology continues to evolve to meet the demands of today and tomorrow for efficient, clean and reliable power across wide sectors of the global economy. Four key strategies will define the future of diesel: reducing emissions even closer to zero, improving energy efficiency, increasing use of low carbon renewable biofuels and hybridization.
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Emissions Closer to Zero
Diesel remains the dominant technology in long-haul trucking, powering 97 percent of Class 8 big-rig trucks in the United States. Cleaner diesel fuel, advanced engines and effective emissions control make up the new generation of advanced technology diesel and work together to achieve near zero emissions for fine particles and smog forming compounds like oxides of nitrogen (NOx).
A growing percentage of diesel-powered commercial trucks rely on the newest-generation diesel technologies, which deliver near-zero emissions performance while using less fuel. Consider that today, more than 43 percent of commercial Class 3-8 vehicles are of this newest-generation technology (2011 and newer model years).
Diesel’s proven energy efficiency and ability to use renewable fuels position it as a key technology to achieve cleaner air, lower GHG emissions and eliminate black carbon (a short-lived climate pollutant), which are necessary to buy important atmospheric time as longer term strategies to deliver zero-emissions solutions become available. This new generation of diesel technology is here now, ready and available today to deliver significant climate and clean air benefits.
In 2020 new emissions standards were adopted by California establishing lower levels of NOx and particulate matter starting in 2027. A similar new national standard is expected to be proposed in 2021 by the U.S. Environmental Protection Agency (U.S. EPA). Taken together, these will even further reduce emissions from new technology diesel engines to even nearer to zero levels.
Increasing Energy Efficiency
Today, diesel is the technology of choice for commercial vehicles and the goods movement sector. The U.S. EPA and National Highway Traffic Safety Administration (NHTSA) estimate that the Commercial Vehicle Fuel Economy and Greenhouse Gas Reduction Standards Phase 1 rules saved 270 million tons of CO2 and 530 million barrels of oil between 2014 and 2018, and that the Phase 2 rules will save another 1 billion tons of CO2 and nearly 2 billion barrels of oil between 2021 and 2027. Research commissioned by the Diesel Technology Forum confirms that the majority of these significant societal benefits will be delivered by more efficient new technology diesel trucks.
Since 2011, the more than 4.9 million new-generation commercial diesel trucks have already delivered reductions of greenhouse gases (carbon dioxide-CO2). The use of new-generation diesel trucks has also removed more than 18 million tons of nitrogen oxides (NOx) and 126 million tons of CO2, compared to previous generations.
Much like technologies developed to meet the model year 2010 emissions standard for commercial vehicles, off-road engine and equipment manufacturers have coupled fourth-generation near-zero emissions control technology (“Tier 4”) with substantial fuel savings strategies including advanced engine designs, more efficient hydraulic systems, telematics, boosts in work productivity from connectivity and hybridization. Taken together, today’s generation of construction equipment delivers both fuel savings and fewer GHG emissions along with clean air benefits to many communities.
Expanded Use of Renewable Fuels
Advanced diesel engines and biodiesel and renewable diesel are key strategies in the effort to meet the climate challenge. High-quality biofuels are available, affordable, proven and, because they are suitable for both new and existing vehicles, they deliver substantial near-term reductions in GHG and other emissions across wide sectors of the economy that rely substantially on diesel engines today and will well into the future.
Originally designed to operate on peanut oil, the diesel engine patented by Rudolf Diesel over a century ago has evolved dramatically. Today, ultra-low sulfur diesel fuel powers most diesel engines around the world, but diesel engines of all kinds have an inherent capability to utilize renewable biofuels.
Most heavy-duty diesel engines, like those in commercial vehicles, are capable of operating on blends of biodiesel up to 20 percent (B20). Some diesel engines in fleet applications are approved to operate on higher blend levels. Renewable diesel fuel is produced to meet the same engineering standard as petroleum diesel fuel and can be used as a 100 percent replacement fuel to petroleum.
Both biodiesel and renewable diesel fuel are derived from waste agricultural feedstocks. Oil derived from soybeans and corn and waste animal fats make up the largest feedstock for these fuels, according to the U.S. Energy Information Administration. As long as we produce soy for animal feed and other uses, producers of biodiesel and renewable diesel fuel will have access to feedstocks.
While expectations are high for zero-emission trucks, using advanced biofuels - renewable diesel fuel and biodiesel - in all existing diesel engines is an often-overlooked immediate term strategy to reduce carbon.
Both biodiesel and renewable diesel fuel are considered advanced biofuels by U.S. EPA, defined as reducing GHG emissions by at least 50 percent. Renewable diesel fuel is capable of reducing GHG emissions upwards of 80 percent. The use of these fuels is already generating large GHG reduction benefits with the least cost compared to other alternatives.
Relative to petroleum diesel fuel, the consumption of these advanced biofuels is relatively small but growing. As of May 2020, 147 million gallons of biodiesel was consumed. This compares to 4.5 billion gallons of ULSD petroleum diesel fuel consumed during the same period. While the price of biodiesel varies across the country, the Department of Energy in its most recent alternative fuel report, estimates the biodiesel (B20) is sold at about a $0.13/gallon discount to petroleum diesel fuel.
The consumption of renewable diesel is much smaller and currently used primarily by fleets and focused in a few states and regions that incentivize low carbon transportation fuels.
The U.S. Renewable Fuel Standard (RFS) mandates the use of certain biofuels blended into petroleum-based diesel and gasoline in an effort to grow domestically sourced fuel with the capability of reducing greenhouse gas emissions. Nationwide, the Renewable Fuel Standard requires the use of biofuels, including biodiesel and renewable diesel fuel. Separately, California and Oregon have adopted policies that require the gradual reduction in the carbon content of transportation fuels sold in the state through a Low Carbon Fuel Standard.
Biodiesel and renewable diesel fuel are already generating the greatest reduction in GHG emissions in the transportation sector. In California, these benefits exceed those from the electrification of cars, trucks and buses by almost 4:1.
Compared to the investments required for a switch to all-electric vehicles or other alternative fuels, the switch to biodiesel and renewable diesel is comparatively easy and comes at a low cost, with no need to invest in new trucks, engines or refueling or recharging stations. These fuels may be distributed in existing fuel infrastructure and may be used in existing diesel engines. Their benefits can be realized immediately across entire fleets of vehicles, rather than only in newly acquired vehicles dependent on new infrastructure. Biodiesel and renewable diesel fuels can be stored, used, pumped and handled virtually the same way as petroleum diesel products.
Hybridization Where it Makes Sense
Expanded use of hybrid technology is another aspect of the continuous improvement of diesel engines and another strategy to further save fuel, and lower GHG and other emissions from internal combustion engines (ICE) across all applications.
Hybridization is technology that captures wasted energy, storing and applying it to useful work and will be a greater player in the future in selected applications. The elements of hybrid systems - electric motors, controllers and energy storage systems - work in close integration with the internal combustion engine and conventional transmissions to use energy from both sources to propel the vehicle or machine or operate accessories with overall less energy consumed than an engine alone.
Are hybrid systems a consideration for all vehicles or machines? No. The key considerations for whether or not hybridization makes sense are how a vehicle or machine is used, whether its duty cycle or work patterns are good candidates for capturing wasted energy and applying it to the machine’s useful work, and the cost factors and competing technologies.
There are essentially three types of hybrid systems, parallel, series and mild.
Available for well over a decade, hybrid systems, have been most popular and incorporated into public transit buses, where they are mated with a downsized diesel engine. The stop and go driving cycle of a transit bus is ideal for hybrid technology, while also saving on brake maintenance, a major expense for transit agencies. Public transit agencies in Washington, DC, San Francisco, New York and other major metropolitan areas all have diesel hybrid electric buses in their fleet.
For trucks, medium to large sized large box trucks hauling heavier loads, but typically shorter driving range than a longer haul tractor trailer, are the application of the most interest. However, consideration of hybrid technology is waning in these segments as greater interest in all electric and fuel cell technologies emerge. Hybridization may still be a strategy for complying with increasingly stringent greenhouse gas emissions for commercial vehicles in some applications.
Cummins recently introduced its electric hybrid PowerDrive utility truck, a Kenworth T370 that is a versatile hybrid system, offering both parallel and series capabilities, and features the ability to switch in real time between two hybrid and two pure electric modes, optimizing the powertrain for the best fuel economics in any driving situation.
Beyond commercial trucks, off-road equipment makers are working on innovative ways to develop reliable, efficient, cost-effective alternatives to traditional pure diesel-powered drivetrain systems and have commercial products available on the market today.
One of the first was Caterpillar’s D7E, a hybrid drive dozer that debuted in 2009. This track-type tractor utilized an electric drive system, whereby the diesel engine operates in a fuel-efficient steady state mode generating electricity that in turn drives electric motors for machine propulsion and hydraulic systems, delivering up to 30 percent more fuel efficiency and 10 percent more production and material moved per hour. The latest D7E model continues to provide outstanding fuel efficiency, along with some new performance-enhancing features.
Wheel loaders are often used to move and load bulky loose materials like stone and gravel, mulch and other materials. These units have repetitive motion in the cycle, and a range of manufacturers have various hybrid options available, including Caterpillar, CNH, Deere and Volvo.
John Deere was among the first to introduce electric drive technology in off-highway equipment, as it produced the 644K hybrid loader in 2013 and the 944K hybrid loader in 2015. Hybrid-electrics drive smoothly and efficiently recapture energy to slow the loader when the operator lets off the accelerator. This lessens the load on the engine and reduces fuel consumption by as much as 25 percent, along with quieter operation.
Achieving a 50 percent reduction in fuel consumption and 35 percent fewer greenhouse gas emissions is a key reason why hybrid technology is making inroads into construction equipment. Volvo CE’s concept LX1 wheel loader, now in test service in California with Waste Management, has exceeded expectations, including demonstrating that it is able to do the work of a wheel loader the next size up.
CNH Industrial – its FPT and Steyr tractor divisions - has developed a concept farm tractor without a conventional transmission where the tractor’s diesel engine serves entirely as a generator operating in the optimum steady state efficiency mode, powering electric motors to drive each of the wheels and power take off points. Fuel savings for the concept is reported at 10 percent.
Beyond the construction site, hybrid systems are also featured in the marine and rail sectors.
Marine vessels like workboats, tugs and pushers, require tremendous horsepower to maneuver ocean freighters and tow heavy barges. Caterpillar and boat-builder Sanmar teamed up for a new hydraulic hybrid propulsion system that, compared to traditional tugs, will dramatically reduce fuel consumption and carbon emissions as well as through life maintenance costs. Given the propensity for tugboats to work in waters near populated coastlines and in big city ports, the ability of this technology to mitigate climate change in a meaningful and measurable way is both promising and exciting.
Yanmar has a hybrid application in a new propulsion system that outrivals conventional propulsion engines in efficiency and functionality, using the diesel engine to power shipboard generators that supply electrical power to motors that drive propulsion systems and separately power electrical loads of the boat.
Cummins offers marine diesel electric solutions in a wide range of marine vessel applications, as does MTU and Rolls-Royce Power Systems with its fully integrated marine hybrid diesel electric systems that launched in 2020.
Beyond large engines in marine applications, hybrid drive systems also now extend to rail applications. MTU hybrid power packs allow for diesel or diesel electric train operation enabling flexibility particularly in Europe where some portions of passenger rail are electrified, but many still rely on diesel power. These settings, where a combination of diesel and electric power are available to train operators, position both hybrid and conventional diesel-only settings to be utilized for maximum efficient train operation.
As is evidenced here, the diesel engine is perfectly suited for hybridization in a growing number of applications, be it on the road, in the water, on the rails, in the fields or on the jobsites of the future. The expanded use of hybrid technology is just one way that diesel engines will play a continued key role to save fuel, and lower greenhouse gas and other emissions across all applications.