Powering the Blue-Collar Vehicle

Few of us would disagree that Greenhouse Gases (GHGs) are having a measurable, negative effect on our biosphere, and there is urgency in addressing this.  Number one on the list is CO_2, which according to the EPA comprises more than 75 percent of U.S. GHGs. The combustion of fossil fuels are the largest source of CO₂ emissions. According to the Visual Capitalist, CO₂ emission sources in the U.S. are roughly divided into quarters:  transportation, electricity, industry, and other (including agriculture and residential).

The pervasive use of fossil fuels has resulted in policymakers challenging the science and engineering communities to address our base energy supply.

This article speaks to powering transportation and its impact on GHGs (25 percent of U.S.CO₂ emissions).  Within the transport sector, 58 percent is light-duty and all but approximately 8 percent (aviation) are traditionally motivated by Internal Combustion Engines (ICE).

Last year in August, the U.S. Inflation Reduction Act, which heavily incentivizes battery-powered transportation, was signed into law.  Battery technology primarily targets light-duty vehicles, the 58 percentile of GHG emissions mentioned above, yet batteries are not applicable when higher power and rapid energy reconstitution are demanded (the remaining 34%). Agriculture equipment, semi-trucks, heavy construction equipment are such examples. In these sectors, batteries won’t work because the power demand is high and today’s batteries expend energy rapidly, and energy reconstitution is relatively slow. These hard-to-abate sectors by necessity require alternate means of power and fueling options. Vehicular energy demand and reconstitution dictates the application of select energy sources for America’s heavy-duty vehicles.

This subject of powering commercial truck and off-highway transportation is publicly debated, and regulations are being promulgated from Washington as you read this article.  The Final Renewable Fuels Standards Rule was released on the 21^st of June, action from the EPA on the Diesel Emissions Reduction Actis expected in August, and the Greenhouse Gas Emissions Standards for Heavy-Duty Vehicles – Phase 3 will likely be released before the end of 2023.  All these compliance laws and regulations target the U.S. working class vehicle fleet. No doubt, the impact of this legislative salvo extends beyond heavy-duty vehicles with notable implications for our nation’s GDP.

This blue-collar vehicle sector has been termed “hard to abate”because of the concerns over making power with minimal GHG emissions. One can imagine how the alphabet soup of compliance laws creates a difficult business environment where OEM strategies are difficult to maintain, and flexibility must be exercised.  In other words, capital must be metered, portfolios diverse and investors a bit twitchy.

Success in development of engines for these blue-collarapplicationsis about customer satisfaction while complying with U.S. GHG legislation.  Furthermore, if batteries are not applicable for this hard-to-abate sector today, then the two remaining viable energy sources are the fuel cell and the ICE. The right power mix for these sectors is business critical.   While OEM strategies are normally cloaked in secrecy, we can gain insight into how development is evolving from the public comments from two notable engine/vehicle producers, namely, Cummins Inc. and JCB Inc.    

Jim Nebergall, General Manager of the Hydrogen Engine Business at Cummins Inc., stated last year that

“Hydrogen engines and hydrogen fuel cells offer complementary use cases. Internal combustion engines tend to be most efficient under high load—which is to say, when they work harder. FCEVs [Fuel Cell Electric Vehicles], in contrast, are most efficient at lower loads.”

In a May 2023 article written by Guy Youngs and published by OEM Off Highway, Youngs references JCB’s experience, stating

“One can imagine how the alphabet soup of compliance laws creates a difficult business environment where OEM strategies are difficult to maintain, and flexibility must be exercised.”

“Initially, JCB had designed an excavator that used a hydrogen fuel cell. But after extensive testing, JCB decided fuel cell technology was not the best option for their customers at this time, and they decided to move toward a hydrogen-combustion solution.”

Later, Youngs concludes, “FCEVs and HICEs do not compete with one another... Ultimately, it’s not a matter of which technology is better, but rather which is more suitable to an end user’s conditions, applications and needs.

Note that both these OEMs are leaning on the same carbon-free energy source and the ICE for their future applications in these working-class vehicle sectors.  Fortunately, the EPA accommodates H₂-ICE as a zero GHG option in the Phase 3 proposed draft.  Finally, hydrogen is very attractive, as it offersabundant fuel for millennia.

Although H₂appears to be a panacea fuel solving GHG emissions, it presents a double-edge sword called combustion flame speed. The high combustion flame speed of hydrogen is the friend of both the Diesel (Compression Ignition) and Otto (Spark Ignited) cycles.   

Significant improvements in efficiency can theoretically be realized if we can harness flame speed and induce a near constant volume pressure rise in the Otto cycle. Furthermore, Westport Fuel Systems’ David Mumford reported that with a HPDI fuel system, 51.5% efficiency was achieved with a late injection Diesel cycle (H2 Technology Expo Houston, June 28, 2023). 

On the other hand, hydrogen’s flame-speed produces an astonishing amount of heat-release over a short amount of time, and a combustion pressure rise approaching engine-knock accelerations. 

There are a couple more hydrogen combustion characteristics that are risky to ignore.  The lower flammability limit of hydrogen allows the combustion wave to propagate near enough to the cylinder wall to combust the lubricant. 

Also, after hydrogen combustion, the in-cylinder environment is void of ions (unlike gasoline) and the ignition system builds a capacitive charge waiting to pre-ignite the next air/fuel mixture as it enters the combustion chamber. Sometimes called “ghost sparking,” this produces negative work and can potentially damage engine components.

Finally, regardless of fuel type, combustion charge air contains 78 percent N₂, and NOx is produced.  This criteria pollutant is a precursor to ozone, acid rain, and is regulated. Abatement technologies exist to address NOx beyond 2027 regulations.

The hydrogen combustion characteristics may seem daunting, but not as daunting as producing a battery to drive working-class vehicles.  The industrial engine developer must tackle these concerns, or their engines will not go to market.  Fortunately, early engine testing has identified these concerns and viable solutions are emerging.

Stronger piston materials and designs, durable self-lubricating ring coatings, ignition systems designed to mitigate ghost sparking, and exhaust after treatment systems designed to function directly after start-up are currently under test or in production and ready for hydrogen fuel applications.  Full functionality of hydrogen fuel is challenging but only requires special design considerations (not a technological perturbation). H₂-ICE seems to occupy that functional “sweet spot,” meeting emissions regulations while also meeting customer demands.  It is critical that OEMs find suppliers who enable them to achieve their goal of employing hydrogen in the blue-collar vehicle.

In addition to the cited references, the author wishes to thank Tenneco technology experts Dmitri Konson, Dr. Steffen Hoppe, Dr. Frank Doernenburg, and Dr. Volker Scherer.