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An entrepreneur coach named Dan Sullivan encourages his clients to ask a question that goes like this: “It’s three years from today, and you are looking back with great satisfaction. What has happened for you to feel this way?” I’ve got an answer: Diesel engines are no longer made. It may take longer than three years, so let’s say it’ll take 10 and in doing so, declare the 2020s, DIESEL’S LAST DECADE.

Not long ago, I wrote an article entitled “The Path to Zero” where I laid out five beliefs that can propel us toward a low carbon future. Among them, was this: “The path to zero [carbon] means we should replace more bad, while we add more good, to the energy grid…” and went on to explain that carbon isn’t the only problem we’re facing. When I published that idea, I had diesel on my mind, so my declaration of independence from diesel isn’t a new thought, but the time has come to make it public –– and the idea is gaining momentum.

A Few Surprising Facts

Rudolf Diesel, the German engineer who invented the eponymous engine in 1893 held a dim view of external combustion steam engines because they wasted a lot of energy. His internal combustion design compressed air inside a cylinder until it was so hot, it would ignite a fuel, which would drive a piston and in turn, rotate a crankshaft. Interestingly, his first energy source of choice was peanut oil, but he also experimented with crude oil-derived diesel fuel, which over time, became the standard energy source. About 85% of diesel fuel’s mass is carbon, and when burned, you might assume by its exhaust, a great deal of carbon gets thrown into the atmosphere. That’s not totally wrong, but the CO2 emissions from diesel are actually slightly lower than for gasoline (73.25 g/MJ vs. 73.38 g/MJ), and aren’t nearly offensive as, say, kerosene or coal.

Diesel is also a relatively dense fuel. It burns hot and as a result, delivers more miles per gallon than comparable gas-powered engines. It’s this efficiency that explains the engine’s popularity for long-haul, heavy freight transportation including trucks, ships, buses and trains.

I recap this bit of history because it’s important to know how we got to this point. Diesel’s invention paved the way for massive productivity improvements in everything from agriculture to zinc mining. At the same time, we do well to remember that Mr. Diesel was an inventor, and inventors are driven to create new and better things for the world. We can do the same, and we should because…

Diesel is Big

The Energy Information Administration (EIA) says consumption of diesel fuel by the U.S. transportation sector in 2019 was about 47.2 billion gallons. This amount accounted for 15% of total U.S. petroleum consumption and, on an energy content basis, for about 23% of total energy consumption by the transportation sector. That squares up with the fact that more than 890,000 heavy duty diesel engines were produced in the United States in 2017 alone. We can make a good guess that with a service life of about 7 years, about 6.3 million diesel engines are operating today. That makes the presence of diesel big in our midst and worthy of a serious conversation about its end-days.

Diesel is Dirty

The World Health Organization has labeled diesel emissions carcinogenic. The reason? Exhaust from diesel engines is full of criteria pollutants –– on the order of six to 10 times higher than from gasoline engines. Of the six criteria pollutants defined by the Clean Air Act, diesel exhaust bellows out four:

  • Carbon monoxide (CO) – exposure to elevated CO may result in reduced oxygen to the heart;
  • Nitrogen dioxide (NOx) – diesel engines are responsible for 85% of all NOx emissions from mobile sources, and NOx is a big contributor to smog;
  • Sulfur dioxide (SOx) – another big smog contributor and an acid rain accelerant; and
  • Particulate matter (PM) – the black soot you see coming out of the exhaust pipe containing microscopic solids or liquid droplets are so small they can be inhaled, resulting in negative impacts to your heart and lungs.

Smog, acid rain, soil and water pollution, heart and lung disease, respiratory damage and even premature death are all connected to criteria pollutant exposure – and not just in the U.S. The European Environment Agency found that nitrogen dioxide (NO2) from diesel fumes had caused around 71,000 premature deaths across the continent in a single year.

It’s worth reminding ourselves that even “renewable diesel” made from waste cooking oil, is still diesel –– the exhaust emissions don’t change. Even the popular TV guys, the Diesel Brothers, who, by the way, were sued and subsequently fined $850,000 for “significant, repeated and ongoing violations of federal law” for rolling coal, can’t make diesel any less dirty.

Momentum is in the Marketplace

Diesel’s Last Decade is already in motion:

  • Two years ago, Volvo pledged it would never again launch a new car with a diesel engine;
  • BMW is ending production of two of its popular diesel engines;
  • Last year, Daimler’s head of Trucks North America said the beginning of the end is here for the internal-combustion truck engine; and
  • Public policy is making its move as well. This past June, the California Air Resources Board (CARB) unanimously voted to require truck manufacturers to begin the transition from diesel to zero-emission trucks in 2024. CARB says trucks are to blame for 70% of the smog-causing pollution and 80% of carcinogenic diesel soot in the state.

And now, the Department of Energy (DoE) is joining the parade. DoE’s Energy Vehicle Technologies Office recently released $9,017,921 to fund six propane-fueled transportation research projects. Why?

With propane, particulate matter emissions are virtually zero when used in modern engines. With a simple three-way catalyst, propane reduces NOx in engines by 95% compared to best-in-class diesel counterparts. Our best propane-powered engines certified to the ultra-low NOx standard of .02 operate at half that rate through a full duty cycle, even in stop-and-go applications like delivery trucks or school buses.

Propane puts us on a positive path toward a low carbon future because it is chemically cleaner than other fuels.

Let’s Go to School

Here’s just one thing we could do to make the 2020s the last decade for diesel: Convert all the school buses in the country from diesel to propane. The savings in fuel and maintenance costs alone would be enough to hire 23,000 new school teachers, but there’s more:

  • Propane-powered school buses produce up to 22% fewer greenhouse gas emissions, 24% fewer nitrogen oxide (NOx) emissions and 44% fewer sulfur oxide (SOx) emissions compared to gasoline-fueled school buses.
  • Propane-powered school buses using new low-nitrogen oxide (NOx) engines produce 95% fewer NOx emissions than comparable diesel-fueled school buses and 88% fewer NOx emissions than comparable gasoline-fueled school buses.

Accelerating Diesel’s Demise

Forbes published an article asking whether or not diesel was on its deathbed. At that time, the author concluded the outlook was cloudy. It’s ironic, really, as Rudolph Diesel’s own death was shrouded in cloudy controversy worthy of a made-for-TV special, but honestly, the clouds have lifted and we can see clearly ahead.

In propane and propane engines, we have the clean fuel and technology necessary to very affordably (unlike electric or hydrogen alternatives) accelerate diesel’s demise without requiring any compromises in power, range or performance. Rudolph Diesel –– the engineer, consummate inventor and continuous improver of machines –– would tell us it is the right thing to do.

For more comparative facts about diesel vs. propane, please visit

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About the Author

Tucker Perkins, President and CEO

Tucker is an engineer, entrepreneur, business leader, speaker and is now the president and chief executive officer of the Propane Education & Research Council. He has worked in the propane industry nearly his entire professional career, having served as the director of business development for Inergy, chief executive officer of Premier Propane, and the chief operating officer of Columbia Propane, a unit of the Columbia Energy Group. Tucker is also the former chairman of a PERC advisory committee on engine fuel matters and is active with the National Propane Gas Association and the Virginia Propane Gas Association.