Powering The Blue-Collar Vehicle

Few of us would disagree that greenhouse gases (GHGs) have a measurable, negative effect on our biosphere, and there is urgency in addressing this. Number one on the list is CO2, which, according to the EPA, comprises more than 75 percent of U.S. GHGs. The combustion of fossil fuels is 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 made policymakers challenge the science and engineering communities to address our base energy supply.

This article discusses powering transportation and its impact on GHGs (25 percent of U.S. CO2 emissions). Of this 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, and heavy construction equipment are such examples. In these sectors, batteries won’t work because the power demand is high; 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 dictate the application of select energy sources for America’s heavy-duty vehicles.

This subject of powering commercial trucks 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 June 21, action from the EPA on the Diesel Emissions Reduction Act is expected in August, and the Greenhouse Gas Emissions Standards for HeavyDuty 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 developing engines for these blue-collar applications is 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 critical to business. 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, "Hydrogen engines and hydrogen fuel cells offer complementary use cases. Internal combustion engines tend to be most efficient under high load— that is when they work harder. In contrast, Fuel Cell vehicles (FCEVs) are most efficient at lower loads.”

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

“One can imagine how the alphabet soup of compliance laws creates a difficult business environment in which 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, 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 which is more suitable for an end user’s conditions, applications, and needs.

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

Although H2 appears to be a panacea fuel for solving GHG emissions, it presents a double-edged sword called combustion flame speed. The high combustion flame speed of hydrogen is a friend of both the Diesel (Compression Ignition) and Otto (Spark Ignition) cycles.

Significant efficiency improvements can theoretically be realized if we can harness the flame speed and induce a nearconstant volume pressure rise in the Otto cycle. Furthermore, Westport Fuel Systems’ David Mumford reported that with an 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 combustion pressure rises approaching engine-knock accelerations.

"Stronger piston materials and designs, durable self-lubricating ring coatings, ignition systems designed to mitigate ghost sparking, and exhaust aftertreatment systems designed to function directly after startup are currently under test or in production and ready for hydrogen fuel applications"

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 that waits 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 and 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 workingclass 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 selflubricating 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. The 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 and customer demands. OEMS must find suppliers who enable them to achieve their goal of employing hydrotgen in blue-collar vehicles.

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.