How would you like to have a car which gets better than 50 miles per gallon? Such cars exist, and are actually rather common in Europe. Why aren’t they sold here? They are essentially illegal, thanks to some very tight regulation. They are diesels, and as such run in Europe on a fuel which by law includes 15% minimum biofuel, a renewable resource.
But efficient engines like this run at higher temperatures and pressures, meaning they essentially burn a little nitrogen and thus produce more Nitrous Oxide, or NOx.
This is at the heart of the infamous Volkswagen “cheating scandal”, which was indeed a terrible moment. But now that Chevrolet’s small diesels may be guilty of the same thing, it’s worth talking about.
It’s a completely different fuel. But better.
Diesel engines have never been popular in the US for a lot of reasons. Historically, they were nasty brutes that were nowhere near smooth enough to be considered for cars. They are heavier, louder, and to top it all off need a different fuel altogether. The advantages, found in better low end torque and efficiency, were always good for large trucks – but despite a few tries, never passenger cars.
That has all changed with some sophisticated engineering. Many things have been perfected in recent years, most notably reliable turbochargers and precise computer controlled fuel injection. The end result is an engine smooth and comfortable enough for a car. The additional cost has been offset by rock-steady reliability and a general trend by consumers to favor cars which last 250,000 miles and more.
In Europe, road fuel has always been much more expensive. There are many reasons for this, most notably the complete lack of desire to subsidize roads with other taxes, particularly property taxes. Cars are required to pay their own way in Europe, a far cry from the roughly 50% subsidy that is typical in the US. Other taxes to support transit are indeed on top of that, but the cost of roads dominates the heavy European tax bill per liter.
On top of this, fewer refineries operating less efficiently and other challenges add a lot to the cost for simple motoring fuel. The net result is a tab typically three times what it is in the US.
The VW TDI engine. It looks the same, but it’s a precisely engineer marvel.
This has fueled, pun intended, the need for higher efficiency cars. The main driving force, pun still intended, is consumer choice.
To meet this need for greater efficiency, European engineers have indeed developed cars which routine get mileage 2-3 times better than in the US. The development of high mileage diesels has been critical to this effort. Such engines run in a very different cycle than a gasoline engine with much higher heat and pressure. This is absolutely critical because there is simply no other way to have a higher efficiency engine in a car.
That process, however, converts some small amount of nitrogen to poisonous Nitrous Oxides or NOx. It can’t be avoided. And that’s where the US standards become strange.
In the US, a car is not permitted to emit more than 0.2g of NOx per mile. In Europe, the standard is 0.8g per mile. How were these standards set? It’s completely unclear, but clarity is critical understanding where it came from.
The Diesel Cycle is different from the Otto Cycle of a gasoline engine.
Urban smog has two major components. They are unburned fuel, or hydrocarbons, which generate the grey haze you may see over a city. NOx is a brown haze and it creates acid rain in the form of nitric acid. It’s not as bad as sulfuric acid, now greatly reduced in our fuels by regulation, but it’s still not good.
Why is the US standard set lower? My hunch is that brown smog is more of a problem for us, particularly in the big bowl that defines Los Angeles. Certainly, with more cars running as a primary means of transportation, the net total of all NOx coming out is going to be higher.
But it’s still unclear why our standard is set so low that high efficiency diesels are essentially banned from the US. Truck diesels, for example, have to meet a standard of 2.0g per mile, which is ten times higher.
This is why Volkswagen cheated so horribly at their emissions testing for the US market. Their behavior was reprehensible all around and involved a massive conspiracy among thousands of people who actively destroyed documents and clearly knew what they were doing was wrong. But it was the only way that high efficiency cars could come to the US at all.
Chrysler, which makes a lot of small truck diesels, appears to have done something similar. It’s not forgivable behavior but it is understandable. Innovation in a key area leading to lower Carbon Dioxide emissions, lower consumer cost, and a real shot at energy independence has been stopped.
Should we have such a low NOx standard? I have no idea why it is set as low as it is, to be honest. But that is what stands between American consumers and truly efficient cars. And there is no way around it. It’s one of those many little things that we, as a people, should be talking about but aren’t.
Barataria - The work of Erik Hare 
Erik: The articles you cite here are full of errors and anti-government nonsense. It is true that diesels tend to have higher thermal efficiency than spark-ignition engines, but at the cost of higher NOx and particulate emissions, even with the latest in NOx abatement and particle traps. There is now, because of this, a considerable reaction against diesel vehicles in Europe. “The mayors of Paris, Madrid, Athens and Mexico City announced plans on Friday to take diesel cars and vans off their roads by 2025.” (https://www.theguardian.com/environment/2016/dec/02/four-of-worlds-biggest-cities-to-ban-diesel-cars-from-their-centres) The real causes of low mileage in the US are larger, heavier vehicles, low fuel costs, failure to connect registration fees with vehicle weight, cultural issues, and the fact that US diesel typically costs more than motor gasoline, the opposite of the rest of the world. (Just drive around in Minnesota and see the pickup trucks with one person in them…..) Also, diesel has on the order of a 14 percent higher energy content by volume that gasoline. If you want villains to blame, blame the oilers and the auto industry, which spends megabucks on marketing campaigns to get people to buy oversized and overpowered vehicles….I’m not arguing that there’s no place for diesel, obviously there is. But the efficiency advantage seems to grow less with time, as spark-ignition engines get more sophisticated.
I can buy that I don’t have the best info. And I can see why the NOx, which can’t be fixed, might be a reason to ban diesels. In fact, I really don’t know why either the EU or US have the standards they do.
What I can tell you is that in my nearly constant search for alternative technologies that might be interesting, as I don’t think Lithium batteries are really the future, I always run into the standard for efficiency as being these diesels.
My search includes the previously mentioned turbine electric hybrid and even magneto hydrodynamic plasma generators – both of which are interesting and both of which create a lot of NOx as they run very hot. And both are not yet ready to challenge these high mileage diesels.
So I’m always ready to listen to arguments on how we balance the priorities for cleaner cars. This is one area that I really don’t get, to be honest.
What’s really wrong with the US? Gasoline is too cheap and roads are heavily subsidized. That’s about it to me. But if we fix that consumers will want higher mileage cars right away, as they did when gasoline was over $4 a gallon two years ago. And they will demand these cars.
Then what?
Diesels are totally the way to go and the lack of them in the US is ridiculous. If this is why we don’t have them it needs to be changed. I am sure there is some environmental reason why people don’t like them but is’nt there some technology to take care of that? I would want to know more before I back less regulation.
I do believe that these cars are at least a useful interim technology. The ability to use biodiesel is a big benefit to me. BUT – I completely agree that the regulation we have now is a bit of a mystery and I do want to know a lot more myself. I can tell you that there is really no fix for the NOx emissions – you either live with it or you ban it.
CNG engines have the thermodynamic-efficiency benefits of higher compression ratio as in diesels, but with cleaner emmissions including much less NOx. A technology in use in europe and SE asia, but did not catch on in the US due to lack of infrastructure and ultra cheap conventional motor fuels in recent years.
I am not a fan of CNG because of the amount of energy necessary to compress and ship it. Propane, liquifying under pressure, interest me more. BUt in general the move to a natural gas economy is interesting give the number or biofuel and other renewable sources for it which can come online in their own time. I wrote about this some time ago. So I’m willing to keep an eye on it, for sure.
My understanding is incomplete, but the basic advantage of spark-ignition engines is that they mostly operate at stoichiometric air/fuel ratios under closed-loop control. Diesels, on the other hand, run with full air supply all the time, with only the fuel limited, so their air/fuel ratios are variable but usually excess air, which makes NOx control by reduction difficult. I am less clear on why higher particulate emissions seem to be inherent to the Diesel cycle. Either CNG or ethanol can use higher compression ratios, benefiting efficiency but tending to increase NOx. Interesting times in transportation……
OK. That would be great if it comes into being. Sounds like primarily a computer control issue, meaning we have everything in place to implement it.
Just keep paying attention. It’s your money their after – or is it your mind?