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Diesel And Hydrogen: The Present-Day Solution For Reducing Emissions

Written By, Mike McGlothlin


As America and much of the rest of the world continues the march toward zero-emission vehicles, it’s clear something will have to be done to meet emission regulations between now and whenever that is achieved. Though it’s a formidable alternative to internal combustion engines (ICEs), battery electric vehicle (BEV) technology still has a lot to prove in terms of range capability and charging availability, and adequate BEV infrastructure may not even be in place until the year 2035. So what can be done in the interim? For many engine manufacturers and engineering firms alike, hydrogen—as in internal combustion diesel engines that benefit from hydrogen injection—provides an immediate path toward decarbonization and reducing emissions.

This month, we’re covering everything you need to know about hydrogen-fueled diesel engines, from why they’re a good idea to how existing diesels can be retrofitted to burn it. Then, we’ll detail the different types of hydrogen-fueled internal combustion engines (ICEs), followed by a discussion on this technology’s shortcomings. Finally, we’ll divulge what Cummins has been working on. Hint: this OEM is knee-deep in hydrogen technology, and even plans to bring 6.7L and X15-based hydrogen-burning engine production online in 2027. Below, you’ll find that combining hydrogen technology with proven diesel engine platforms is the logical “next step” for reducing emissions and reducing the worldwide carbon footprint in the near term.

Mixing Hydrogen With Diesel Fuel

It’s been documented since the 1970s that injecting small amounts of hydrogen into an internal combustion diesel engine (ICE) makes the engine run cleaner, produce more power and return better fuel efficiency. Surprising to some, diesel engines respond very well to small amounts of hydrogen being used. Hydrogen easily mixes with air when introduced on the intake stroke. This is called enrichment, or induction of hydrogen (as hydrogen cannot be directly injected in-cylinder in a diesel engine due to its auto-ignition temperature being much higher than that of diesel). After that, the hydrogen helps optimize the combustion process during the power stroke. More on the enhanced burn hydrogen provides in a bit.

Why Hydrogen Makes Sense

Before getting into the full list of benefits associated with dual fuel (diesel/hydrogen) ICEs, it’s important to note how cost-effective hydrogen conversions are. In medium-duty and especially heavy-duty truck applications, it’s more affordable for companies to convert their existing fleets (or a portion of their fleets) to hydrogen rather than purchase brand-new vehicles. If a company’s existing diesel-powered fleet is running perfectly fine, converting them to burn hydrogen in addition to their native diesel is not only more feasible, but the smarter choice. This way, the majority of the problems associated with these vehicles can continue be diagnosed and repaired by the same mechanics who were already familiar with the original, diesel-only platform.

Reduced Greenhouse Gas Emissions

Bringing hydrogen into the mix in a diesel engine reduces emissions significantly. Inparticular, hydrogen eliminates the majority of the most commonly found greenhouse gas emissions: carbon dioxide (CO2) and nitrous oxide. In fact, some dual-fuel hydrogen retrofit systems have proven capable of dropping an engine’s carbon dioxide output by more than 85-percent. And, depending on the type of hydrogen used, CO2 emissions can be completely eliminated. Hydrogen-fed engines are known to produce nitrogen oxides (NOx), but if the hydrogen is properly stratified, NOx can be reduced by a significant margin. Aside from that, diesel/hydrogen ICEs will continue to feature the common, NOx-curbing aftertreatment systems we’re all familiar with, such as EGR and SCR.

No Tailpipe Emissions, More MPG

Particulate matter (PM) is drastically reduced with diesel-hydrogen ICEs. This is because hydrogen fuels don’t produce particulate matter (nor carbon monoxide or volatile organic compounds). And, as previously stated, if the hydrogen is properly stratified nitrogen oxides (NOx) can even be reduced (although not eliminated). On top of that, the way hydrogen interacts and works with diesel fuel leads to a laudable improvement in fuel economy. In many applications, a hydrogen conversion has yielded fuel efficiency increases of 25-percent or more.

What Combustion Looks Like

Hydrogen-diesel hybrids work by injecting a small amount of hydrogen into the engine’s intake air stream, prior to the air entering the cylinder (combustion chamber). Injecting hydrogen here disperses it within the intake charge. Immediately following the diesel injection event, the hydrogen begins to burn as well. And because hydrogen burns approximately 10 times quicker than diesel fuel, the hydrogen ignites the diesel fuel throughout the entire mix of air, which results in a more complete burn of the fuel. By accelerating the diesel fuel’s burn rate, you get more work out of the combustion event, and much less energy is wasted.

How A Hydrogen-Diesel ICE System Works

In chemistry class, you learned that water is made up of two gases: hydrogen and oxygen (i.e. H2O). Here, you’re learning that when water is exposed to electrical voltage, these two gases can be separated. This is known as electrolysis. The electrolysis component can be powered by the vehicle’s electrical system (usually connected to the alternator). In the Hy-Drive Technologies system for example, small amounts of hydrogen and oxygen are generated when the ICE is running. Both the hydrogen and oxygen are pressurized and then injected into the engine’s intake stream, downwind of the turbocharger. While the added oxygen has no positive or negative effect, the hydrogen helps extract more energy out of the same amount of diesel fuel.

Advantages Beyond Emissions Reduction & Fuel Efficiency Increases

The benefits of a hydrogen-diesel ICE don’t end with reduced GHG, PM and NOx, or substantial fuel savings—and one of them is key for fleet owners. By running cleaner (i.e. producing less CO2, NOx and especially particulate matter, among other pollutants), the internal combustion engine the system is based on lives longer. Fewer contaminants created during combustion makes for cleaner, healthier engine oil. This means purer lubrication for bearings, bearing surfaces, and ensures optimum cooling. It also means less buildup of carbon, soot, and grime on intake ports, valves, and even pistons.

How Hydrogen-Diesel ICE Retrofit Systems Work

Outfitting an internal combustion diesel engine with hydrogen injection isn’t as complicated as it might seem, and much of this is due to so many companies embracing the technology in recent years. By creating what essentially amounts to a bolt-on kit, a plethora of systems are available. You already know that a hydrogen-diesel hybrid system is going to work in conjunction with the original diesel engine, its original injection system, and the added hydrogen injection system. However, the ability to electronically control the hydrogen injection process is perhaps the most important piece of the puzzle. Hydrogen injection has to be precisely controlled and regulated.

What Stays The Same, And What Changes

During a hydrogen retrofit, the diesel engine’s block, rotating assembly, and the rest of its lower (short block) internals remain unchanged. Above that, things are different. A hydrogen injector will have to be present within the engine’s intake tract (again, post compressor side of the turbocharger in turbodiesel engines) and a spark plug to initiate combustion. Other key components include a hydrogen generator, H2 flow meter, high and low-pressure regulators, bubbler tank, control module, appropriate wiring and of course the storage tank(s), if required.

Hydrogen ICEs Vs. FCEVs

Before we go any further, there are different types of hydrogen-fueled applications co-existing within the same realm of the automotive world. There are diesel-hydrogen ICEs (what we’re primarily discussing in this article) and hydrogen fuel cells (pictured), also known as fuel cell hydrogen electric vehicles (or FCEVs). FCEVs convert chemical energy from hydrogen and oxygen into electrical energy (namely for electric drive motors). FCEVs are particularly attractive when taking refuel time and driving range into account. When compared to a battery electric vehicle (BEV), an FCEV can typically be refueled in five minutes or less, along with traveling further.

Diesel-Hydrogen ICEs Can Still Run Solely On Diesel Fuel

Although both hydrogen ICEs and FCEVs can power vehicles using hydrogen as fuel, fuel cell applications are cost-prohibitive in comparison. Whereas fuel cell vehicles would require a completely new vehicle fleet for most transport and freight companies, converting existing diesel vehicles to dual-fuel, hydrogen ICEs calls for significantly less investment. Another benefit of operating hydrogen ICEs is that, when (or if) no availability to refuel with hydrogen exists the engine can still be run solely on diesel fuel. This isn’t an environmentally friendly talking point, but it is a reality that helps sell the idea of hydrogen ICEs to fleet owners (i.e. the vehicle isn’t disabled due to the inability to refuel its hydrogen tank).

Diesel-Hydrogen ICEs Are Ideal In Heavy-Duty Applications

Internal combustion diesel engines typically operate at their most efficient when placed under load. This is why hydrogen ICE conversions work so well on diesels—especially those used in long-haul trucks where moving 80,000 pounds or more is the order of the day. In direct contrast, FCEVs peak in efficiency when operating at lower workloads. This is part of the reason FCEVs are often said to be the better choice in passenger cars and light-duty trucks but is precisely why this isn’t the case in the heavy-duty segment.

HYDI’s Simple, Affordable Hydrogen Solution

HYDI, an Australian-based company, has developed a comprehensive hydrogen injection system for diesel engines that does not store hydrogen. The company’s on-demand system produces its own hydrogen by way of electrolysis, receiving power from the alternator to split distilled water into hydrogen and oxygen. Impressively, the HYDI system only requires roughly 2 liters for every 70 hours of engine use. That’s right, no hydrogen distributor required. Further placing its system on the cutting-edge of modern-age, hydrogen technology is the fact that the unit utilizes Bluetooth applications to display the system’s operation status in real-time right from the comfort of your Android phone or tablet.

HYDI’s On-Demand System Is Efficient, Clean, And Low Maintenance

Paired with a traditional diesel ICE, from 6 liters to 40 liters in displacement, HYDI’s hydrogen system cuts tailpipe emissions in a compelling way. Particulate matter (PM) pollutants have shown to be reduced by as much as 80-percent, although PM reductions range from 25 to 80-percent depending on your specific engine and application. Carbon monoxide (CO) emissions are typically reduced between seven and 25-percent, while fuel efficiency can increase as much as 14-percent. As mentioned above, the biggest selling point with HYDI’s system is that it eliminates the need to store hydrogen. This makes finding a refueling station, having onboard storage tanks, and dealing with the safety risks associated with handling hydrogen a non-issue.

Cummins’ New Hydrogen Engines

When it comes to engine manufacturers getting in on the hydrogen game, Cummins has arguably led the charge for years. The Columbus, Indiana-based juggernaut is adapting many of its engines—and even creating brand-new ones—to run on hydrogen. Embracing hydrogen technology wholeheartedly, Cummins has developed two hydrogen-fueled engines, both of which are set to begin full production in 2027. Cummins was even directly involved in powering the world’s first hydrogen fuel cell commercial maritime vessel, so the company is no stranger to alternative fuel technology. ICE, FCEV and even the BEV acronyms reside in Cummins’ extensive portfolio.

The B6.7H And X15H

Both of Cummins’ new hydrogen engines, the B6.7H and the X15H, are based on existing short block platforms. Using familiar engine architectures not only simplifies production, but it makes them easier to sell. One of the biggest factors in the appeal of diesel-hydrogen ICEs is that the engine is still an engine. It still sounds and runs like an engine and is repaired in much the same way. Only the fuel delivery is different. This familiarity makes adapting to diesel-hydrogen technology a more comfortable transition for many fleet owners.

Hitting The Highway In 2027

With production set to go full steam ahead in 2027, it’s clear that Cummins expects its X15H (which is based off the current X15) to power various Class 8 truck makes and models. Keeping things on-highway, we could see the B6.7H debut in plenty of medium-duty truck applications—and, who knows, maybe even in future versions of Ram heavy-duty pickups… As we mentioned above, these new engines will be business as usual below the head gasket. Above the deck of the block however, Cummins will outfit each engine with what it calls its fuel-agnostic arrangement for burning hydrogen.

Why Diesel-Hydrogen ICEs—And Why Now?

Use of its fuel-agnostic system in conjunction with the proven X15 and 6.7L rotating assemblies will allow Cummins to tackle the tall order of reducing GHG emissions this decade, rather than developing a completely new engine platform that would likely delay the company’s ability to immediately begin reducing its carbon footprint and reducing emissions. Of course, Cummins’ hydrogen internal combustion engines integrate into their respective trucks just like the engines of old—which is another big selling point for fleet owners. Quick refueling, long range, ease-of-integration with existing transmissions and drivelines, and lower initial costs than battery electric are the icing on the cake.

The H2-ICE Truck Concept

Testing of Cummins’ new B6.7H platform has been underway for more than a year now. A proof-of-concept installation, coined the H2-ICE truck concept, has been run in a Germany-based, Mercedes-Benz Atego 4x2 truck with great results. It’s powered by a Cummins B6.7H that turns out 290 hp and roughly 885 lb-ft of torque, and is expected to provide truck applications in the 10-to-26-ton gross vehicle weight (GVW) range the potential to achieve 500 kilometers of range. One of the biggest perks associated with the 6.7L-based engine is its compatibility with transmission, drivelines, and cooling packages that are already on the market.

Twice The Range Of Battery Electric

The H2-ICE truck concept earns its exceptional range thanks to being equipped with dual hydrogen storage tanks. The tanks are reinforced with carbon fiber for maximum weight savings yet optimum strength and safety. For this class of truck, a 500 km range is vastly higher than what a BEV would provide, with battery electric-powered medium duty trucks capable of achieving roughly half that, at least at the present time. Cummins designed the advanced fuel control module the B6.7H uses, and the system boasts a single unit that combines the hydrogen fuel refill point, fuel filtration and fuel distribution system, contributing to reducing emissions.

The X15H Lowdown

For Class 8 applications, Cummins made sure the X15H was close to matching what the current, advanced diesel X15 engine produces for horsepower and torque. At present, Cummins expects the X15H to make 530 hp and more than 1,900 lb-ft of torque (2600 Nm). In this category of truck, where cross-country hauling is the name of the game, 1,000 km of range (or more) is the target. So far, Werner Enterprises, one of the largest transportation and logistics companies in the United States, has signed on to receive 500 X15H engines for its Class 8 fleet. Werner’s fleet consists of 10,000 tractors in all, but a 500-tractor test pool should give the $2.7 billion company plenty of data to either convince or talk them out of adding additional diesel-hydrogen ICEs to its fleet.

What About Storage?

In diesel-hydrogen ICEs that require onboard storage (as a gas) at high-pressure, there is more concern than just safety, and that would be storage density. The higher the pressure, the more hydrogen you can cram into the holding tanks—and the farther you can travel between refueling. While some hydrogen is stored at 350 bar, 700 bar is more common and obviously offers longer range. On the subject of Cummins, its heavy-duty hydrogen engines (which will store hydrogen at 700 bar) are estimated to boast driving ranges of 500 miles or more in most fleet operations.

Where Hydrogen Makes The Most Sense

So with all the talk of electrification and BEV technology these days, why are we spending time discussing hydrogen? Because there are a myriad of applications where electrification isn’t viable, or even possible, as a means of propulsion. Be it due to range, environmental factors (i.e. cold-weather susceptibility) or time to refuel, hydrogen technology makes more sense in the marine, agriculture and construction sectors. Off-highway applications such as mining equipment, where hydrogen is oftentimes already piped into the work site, is another arena where either diesel-hydrogen ICEs or FCEVs make better practical sense and are significant for reducing emissions.

Hydrogen’s Biggest Challenges

As we alluded to earlier (and aside from the HYDI hydrogen system we mentioned), onboard storage is a drawback of hydrogen technology. And while we’ve shown that it works in commercial applications, the same can’t be said for the passenger car or light truck market. For this reason, don’t expect hydrogen to catch on as BEV technology has in recent years. Another major turnoff for hydrogen is its lack of infrastructure. Unlike diesel pumps, and the fact that you can easily access electricity to charge a BEV, hydrogen can’t be topped off at the local gas station. Aside from California, few other states in the U.S. have hydrogen refueling stations available to the general public.

The Possibilities Are Endless With Hydrogen

According to the U.S. Environmental Protection Agency, vehicle transportation accounts for 28-percent of all greenhouse gas emissions. Hence the reason the agency has expended so many resources on regulating this economic sector in recent decades. Cummins is (once again) here to help—and it thinks hydrogen could play a huge role in reducing GHG and reducing emissions. According to them, if every medium and heavy-duty truck in the U.S. transportation sector was converted to clean hydrogen it would eliminate roughly 25-percent of all greenhouse gas emissions. That’s huge, and it could be done in the near-term.

Additional Benefits Of Hydrogen

In the sea of all the zero-emissions, full-electrification talk we hear today, it’s worth noting that hydrogen is a great, low-emission alternative to lithium batteries. Whether BEV proponents know it or not, competition for lithium-producing resources will become fierce in coming years, and a struggle for control over those resources may ensue. Lithium supply shortages could wreak havoc on the BEV segment if demand multiplies as projected. Companies that have diversified and are invested in multiple technologies, such as advanced diesel, hydrogen, CNG, propane and battery electric, are prepared for anything the future throws at them.



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