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Clean Diesel Technologies Evolve

Clean diesel technologies are paving the way for a more renewable and efficient transportation sector. But first, what is clean diesel? What does the term mean? Decades ago, the term “clean diesel” referred to diesel fuel free of water or other contaminants that could negatively impact powertrain performance. Now, that definition has changed.

The use of the word “clean” in fuel applications today refers to a technology that is also “green,” or more environmentally friendly. Gone are the days of stacks belching out black soot. While a lot of this is marketing, there is some truth to the terminology. To start, clean diesel fuel contains 97% less sulfur than old varieties and represents the new standard for on- and off-highway diesel engine variants. These changes came as a direct result of the federal emissions regulations standard change that went into effect in 2000.

The benefits of ultra-low sulfur diesel fuels, when combined with other advanced technologies such as electronic controls, common rail fuel injection, turbocharging, and reconfigured combustion chambers, can be quite significant. Today’s diesel engines are now cleaner and quieter but are also more powerful than previous variants.

Diesel engines also enjoy the ability to run a range of renewable fuels and specific blends. This allows them to become a potential backbone of green engine technology adoption across the U.S. transportation sector, much as they already have been in Europe. The most popular varieties are being adopted right here in the United States.

What’s in a Name?

Currently, most diesel engines are compatible with 100% diesel fuel or renewable diesel. Depending on the manufacturer and warranty, 5% to 20% are bio or renewable diesel fuels. As ASTM standards evolve, compliance with the renewable standard will pave the way for new clean diesel fuels to enter the market.

For some, the different varieties can lead to confusion. Biodiesel and renewable diesel terminology are different things. Although the terms “bio” and “renewable” can be applied to diesel fuel in referring to them as “clean diesel” fuels, they are not one in the same. While biodiesel seems to get more media attention, it is markedly different from renewable diesel.

The main difference lies in how the fuels are produced. They both have different production methods, emission levels, and combustion efficiencies. In some cases, they can also be differentiated by their varying performance factors. The key differentiating factor of biodiesel is that it is generally offered in blends. Whether it be vegetable oils, animal fats or recycled restaurant grease, these are all referred to as biodiesel.

Biodiesels physical properties are similar to petroleum diesel, but it burns cleaner. Biodiesel also meets biomass-based requirements set by the federal Renewable Fuel Standard. This standard requires that transportation fuel sold in the United States must contain a minimum volume of renewable fuels. In pure form, without a blend, biodiesel is referred to as B100. B20 refers to a 20% blend of “neat” diesel and a biodegradable mix. Most biodiesel manufacturers utilize B20 blends in production.

Renewable diesel, on the other hand, is a fuel derived from biomass that meets the requirements established by the Clean Air Act, but also conforms to petroleum clean diesel specifications. The primary selling point for renewable diesel is that it can be used “as is,” with no blending requirement. Even more, it is compatible with current diesel fueling infrastructure.

While biodiesel has some limitations where cold weather operation is concerned, renewable diesel suffers little-to-no performance or efficiency issues when the mercury drops. It has a high combustion quality that puts it on part with conventional diesel. Both diesel and biodiesel also contain certain aromatics and particulate impurities that leave the possibility for contamination and problems with fuel injectors and diesel particulate filters.

Since renewable diesel contains nearly zero impurities, it burns much cleaner than diesel and even biodiesel. It produces less soot, which is less taxing on aftermarket fuel treatment systems, and is easier on critical engine components since it leaves far less deposits. With demand for renewable diesel outstripping supply, however, the door is open for greater adoption of biodiesel. Either way, OEMs and transportation companies stand to benefit.

Who is Using Clean Diesel?

Clean diesel engines, emission systems, and associated technologies account for approximately 30% of all heavy-duty commercial motor vehicles on the road today. Over the past 5 years, fleets have been adopting these technologies at a breakneck speed, according to a recent report by the Diesel Technology Forum. The increase is significant, as the 2017 clean diesel reading was only 27.5%.

This represents an interesting change, as clean diesel variants used to be the mainstays of European fleets. As fuel efficiency measures and the price of diesel has fluctuated, fleets are finding an increased value proposition in turning to clean diesel, and the numbers are quite impressive.

Nearly 3 million heavy-duty diesel big rigs between model years 2011 and 2016 on the roads in the United States are now being powered by the latest in clean diesel technology. What does that translate into where fuel savings are concerned? Nearly 4.2 billion gallons of fuel and a reduction in carbon dioxide of 43 million tons represent significant improvements. Furthermore, nearly 21 million tons of NOx and 1.2 million tons of particulate matter were reduced over the same period.

When looked at from a holistic perspective, the numbers are quite impressive. Newer generation of clean diesel trucks emit 99% less NOx and put out 98% less particulate matter than older generations of the same vehicles. The clean air benefits of this change cannot be understated.

Since diesel overwhelmingly dominates the heavy-truck sector, clean diesel technologies were poised for a big outbreak. Clean diesel is also rapidly becoming the go-to technology for medium-duty vehicles. Thus, the transition to this technology has been rapid and ongoing. And which states are adopting clean diesel technologies the fastest? Surprisingly, Indiana comes in first, with a clean diesel adoption rate of 51%. California, long known for some of the toughest fuel and environmental regulations in the nation, surprisingly comes in 46th place with a 25% adoption rate.

To break these numbers down further, if the Golden State were to reach the same level of clean diesel adoption as Indiana, that move alone would eliminate another 200,000 tons of NOx and 11,000 tons of particulate matter from the air. This would represent one of the strongest “green” statements the state could make.

Not only does transitioning to clean diesel represent good news for pollution and environmental policy, it represents significant fuel savings for transportation companies who make the switch. Clean diesel technologies are also making a big splash with no renewable fuel variants that could save fleets big money on fuel costs.

Clean Diesel from Yeast?

The subheading may seem strange, but they do say the truth can be stranger than fiction. Engineers at the Massachusetts Institute of Technology have announced a significant breakthrough in the production of renewable diesel fuel. So, what is all the hype about? The breakthrough surrounds a hyper-efficient version of yeast as its main fuel source.

The novel new technique involved researchers essentially reprogramming a strain of yeast to more efficiently convert sugars into fats, otherwise known as lipids. Once the conversion has taken place, the lipids can be used to create high-density fuels, such as clean diesel. It is well-known in the scientific community that yeast already converts sugars into fatty oils, but the natural process is slow and inefficient, so researchers zeroed in on a way to make the process far more economically viable for use in fuel production.

The researchers set out on modifying the metabolic pathways of certain type of yeast. Doing so allowed the yeast to complete the fatty acid conversion with 30% more efficiency than normal. The result? Scientists were able to produce the same amount of fatty oils as before, but with a third less sugar than would be required using unmodified yeast.

The result of this research is to use cheap crops – such as sugar cane or corn – to produce high-density fuels at far lower costs. Using something as simple and cost-effective as corn starch, researchers can use yeast to reduce production costs. To produce a specific amount of fuel, far less glucose will be required during processing.

Even more promising, researchers have announced that follow-up experiments have gotten the efficiency number up to a whopping 75% efficiency. They hope to follow that up by finding where the additional 25% can be gained, which would be a significant advancement. But where does this potential ‘fuel yeast’ stack up when compared to other biofuels?

Current renewable fuels, such as ethanol, are appropriate for use in passenger vehicles, but because of their low energy density, they are less suitable for use in commercial motor vehicles. Cooking oil has been used as a renewable source of clean diesel, but producing it is not scalable and is cost-prohibitive. Could we one day see high-efficiency yeast biproducts in the tanks of a big rig? The way research is headed, that answer is likely yes.

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