Why Don’t Diesel Engines Sell in The USA?

Diesel engines are superior to gas engines in a few critical ways:

1. Diesel engines are more efficient due to the thermodynamic benefits of their higher compression ratios
2. They’re much more durable – diesel engines commonly run 2-3 times longer than a comparable gas engine
3. They put out more torque for any given RPM than a similarly sized gas engine, meaning that a tiny little diesel engine can power a small car very efficiently (Ford’s euro-spec Fiesta diesel gets 60+ mpg with a 1.6L motor)

Point #1 and #3 are very important, as they are the main reasons that diesels are so popular around the world. In Europe, for example, about 50% of the vehicles (be they tiny little commuter cars or big trucks) are powered by diesel. Considering that the average cost of fuel in most Western European countries ranges between $6-8 per gallon (1.27-1.72 euros per liter), the fuel economy benefits of diesel engines make them a very popular option.

Yet in the United States, diesel vehicles are barely 5% of the market. Why? What is it about diesels that people in the USA dislike?

The answer? Emissions rules, the “carbon penalty,” and a myriad of other smaller issues keeps diesels from selling. What follows is an attempt to explain – comprehensively – why diesels don’t (and probably won’t ever) sell at any substantial volumes in the USA.

Emissions Rules Handicap Diesels

The Carbon Monoxide Conundrum

Emissions regulations are particularly harsh when applied to diesel engines. By nature of their fuel and their combustion cycle, diesels generate two types of emissions that gas motors don’t really generate (at least not in the same quantities):

1. Nitrous oxides (NO1,NO2, and NO3, commonly abbreviated as NOx), which are more likely to form in the higher temperatures of the diesel combustion cycle
2. Particulate matter, also known as soot

Particulates and NOx are admittedly bad for the environment (and probably our lungs too), but it’s debatable that particulates and NOx are substantially “worse” than carbon monoxide (CO), which gas motors pump out in significant volumes. Carbon monoxide is dangerous because, if it’s inhaled, it competes with oxygen in the bloodstream. If inhaled in large enough quantities, carbon monoxide is fatal.

Soot and NOx aren’t any picnic either. Not only are they unpleasant, they have long-term health effects and can even cause lung cancer. Yet for some reason, US emissions rules allow for much more carbon monoxide than NOx or particulates.

The California Air Resources Board (CARB) mandates that  ultra-low emissions vehicle phase 2 (ULEV II) regulations allow passenger cars to pump out 2.1 grams of carbon monoxide per mile (pdf, see page 3). NOx and particulates? 0.08 grams per mile…combined!

The point? There’s no denying that emissions are bad. The question is, why are diesel engine emissions so much worse in the eyes of US regulators? Carbon monoxide can kill people, but it isn’t as heavily regulated as soot and NOx. Go figure.

Diesels Need More Emissions Equipment to Meet Stricter Rules, So They Cost More

The most recent emissions regulations from CARB have forced diesel vehicle manufacturers to install a complicated system that either a) traps NOx and soot or b) treats the exhaust gases with a chemical known as urea before they’re expelled into the atmosphere, essentially eliminating NOx and soot from the exhaust stream. Additionally, most diesels also use some sort of EGR system to reduce NOx emissions, further reducing engine efficiency.

This video from Detroit Diesel has a nice little segment that explains how these new clean diesel systems work (starting at 1:16 and ending at about 2mins elapsed).

As you can imagine, all this fancy emissions equipment isn’t free. Here’s a table that shows how the cost of a diesel F250 has increased over the years, adjusted for inflation:

*Price includes automatic transmission option, since that is now included in the package in 2012

After adjusting for inflation, the cost of a diesel engine in a big truck has increased at least 12% – and I say at least because there’s a good chance that the cost of the automatic transmission (which is included in all the numbers) hasn’t increased at the same rate as the entire package.

If we look at the 2003 VW Golf TDI option price (about $1200) and compare that to the option price of a diesel engine on the 2012 model ($4,000, give or take, as a straight figure isn’t available from VW), we’re seeing that the cost of emissions systems on diesel cars are at least as expensive as big trucks, if not more – perhaps as much as $2500.

The Diesel “Carbon Penalty”

Let’s set aside the increased cost and complexity of modern diesel exhaust systems and focus on the future. The EPA’s proposed 2025 vehicle emissions rules would mandate that all engines reduce their CO2 emissions by about 32%, resulting in a fleet-wide target of 203 grams of CO2/mile driven for light trucks, and 144 grams of CO2/mile for cars.

Yet three of the cleanest, most efficient diesel cars on the market today are far above those goals:

All three of these cars put out more than twice the amount of CO2 per mile that will be allowed under the new regulations. As for trucks, the EPA doesn’t provide official estimates…but 500 grams of CO2 per mile seems pretty realistic (if not low). This means that today’s diesel cars and trucks emit 2-3 times the amount of CO2 per mile that the government wants them to by 2025.

While critics argue that making gasoline and diesel engines meet the same CO2 regulations is inherently fair, the deck is stacked in gasoline’s favor. For starters, gasoline contains less carbon. Burning a gallon of pure gasoline generates about 19.6 lbs of CO2. Yet vehicles driven in the US don’t run on “pure” gasoline – they run on a blend that’s at least 10% ethanol. Since ethanol is supposedly “carbon neutral,” a gallon of gas really only generates 17.7 lbs of CO2 as far as the EPA is concerned.

Compare that 17.7 lbs of CO2 generated per gallon of gas to 22.4 lbs of CO2 generated per gallon of diesel. Diesel has a higher energy density than gasoline – which no doubt helps to make diesels more fuel efficient – but unlike gasoline, it’s not “cut” with ethanol. The bottom line here is that a diesel vehicle has to be 21% more efficient than a similar gas engine to meet the same emissions regulations. This is the “carbon penalty.”

To put this in real world terms, a 2025 version of the Toyota Prius will need to achieve a 62 mpg combined fuel economy rating (20% better than today) to meet the CO2 standard. But a 2025 version of VW’s Jetta TDI (currently rated at 34mpg combined) will need to average nearly 71 mpg to meet the same standard!

If the CO2 per mile targets were decreased for diesel vehicles to account for the carbon penalty, the rules would be a lot closer to fair.

Refineries, Taxes, and More

In addition to mystifying rules that encourage carbon monoxide pollution, expensive emissions systems, and the carbon penalty, there are a myriad of smaller reasons that diesel vehicles don’t sell very well in the US.

US Refinery Fuel Mix – Oil refineries break down a barrel of crude oil into components based on a pre-determined ratio. This ratio will vary from one refinery to the next, but a sample breakdown might look like this:

Once a refinery decides on a specific “mix,” they build their refinery system to produce that mix indefinitely. The only way to alter the mix is to re-design and/or rebuild the refinery, and that is expensive. As a result, U.S. refineries turn out just barely enough diesel to meet market demand. In years when consumer demand for diesel has increased (such as 2008), diesel prices skyrocketed relative to gasoline prices.

Refineries won’t re-align their systems to produce more diesel until consumer demand increases, but consumer demand for diesel likely won’t increase until refineries adjust their production. It’s a catch-22, and it means that diesel prices will rise as consumers buy more diesel vehicles…but consumers won’t buy more diesels if the price of diesel fuel increases.

Fuel Taxes – According to a 2008 congressional report, diesel tax rates are about 50% higher than gasoline taxes (roughly $0.75 per gallon, depending on locality).

Higher Up-Front Vehicle Costs – Adding a diesel engine to a vehicle will increase the total vehicle cost by about 15% (give or take). While this higher up-front cost is frequently earned back in terms of both increased fuel efficiency and increased longevity, some consumers aren’t willing or able to make the higher investment.

Fuel Availability – Depending on the fuel stations in your community, fueling your diesel might not be convenient. Many consumers aren’t interested in buying a diesel vehicle if it means going out of their way to fill-up.

If you add it all up, it’s clear that the deck is stacked against diesels. While it’s unlikely we’ll see Toyota debut a diesel Tundra (only rumors persist that one is undergoing testing in Texas), diesel versions of the Chevy Colorado and Dodge Ram are gaining steam. The question is, how will these trucks survive the 2025 emissions rules? Will they be discontinued when the rules get too strict, or will their manufacturers just bite the bullet and pay the penalty?

Time will tell.