Diesels Aren't Bad

I dug a little deeper, I have an article from 1976 that reviews Golf Diesel for European market in that article is a quote:
"Problems will only be with nitrogen oxides (NOx), which in the diesel exhaust are more than allow, for example, the strictest US regulations for the coming year"
https://www.avto-magazin.si/media/upload/Test/volkswagen/golf-diesel.pdf

NOx in the diesel cars was the problem from the very beginning, they solved it just enough to get through emissions, this may have a little to do with real world emissions. But the biggest problem older diesels have that gets them banned from the cities is PM, no one want's to have cars on the road that emit visible smelly smoke.

Europe has a specific problem, average car on the road is near to 10 years old, and a 10 year old diesel may not even have DPF, because EURO 4 standard didn't require it. There are many cars like that on the road, no one gives a damm about diesel or petrol from the 80s or 90s because those cars are a rarity, but 2000-2009 (Pre EURO5) diesel cars are a BIG problem in Europe. Share of diesel cars in Europe is more than 50%, so this is the big problem.

 

We visited northern Italy in the early 1990's and I was astonished at how bad the auto pollution was. It was pretty darn disgusting. I really hope they have better emissions controls these days! However, from your post it still seems like it may be a problem.

For the record, I owned a Honda Civic VX here in the USA back in the early 1990s. It got fantastic gas mileage ( up to mid 50's MPG ). In fact, this is a reason I was skeptical of hybrids for so long ( I'm not anymore though ). However, the VX was infamous for NOx emissions. It was also very light and lacked many of the safety components of vehicles today. It also had a manual transmission.

As for emissions control...regardless of what some folks say today about the EPA ( I'll leave it at that so as to not be political ) , it is essential for clean air and water. People tend to have extremely short memories. Just google 'Pre EPA smog', etc...and see what I mean.

Here is an example...I hope it isn't too political.

What Cities Looked Like Before the EPA - CityLab

 

Mind you they were able to lower the NOx emissions to acceptable levels simply by slightly retarding the timing. Not even enough to make a noticeable difference in fuel economy. And this was done at a the same compression ratio of 23:1! By 1985 they were still able to meet the requirements at that compression ratio. In the late 80's things started changing over to direct diesel injection and the compression ratio was lowered considerably, which also lowers NOx. And this was all that was needed back then to meet emissions clear up through the early 1990's.

On the other hand, all gasoline engines in the US back in 1976 all needed EGR valves to meet the requirements. Many by that time had very retarded timing and lower compression ratios, enough to make their fuel mileage numbers drop compared to previous years. Many vehicles also had other NOx reducing emissions equipment besides EGR valves, such as those valves that slowly allowed vacuum advance to come on or that increased the RPM when the engine was idling if it reached certain temperatures. And carburetors were much more complex in an attempt to get better air/fuel ratios over a broader range of speed and load. By 1976, VW even had to make electronic por fuel injection standard across all their air-cooled vehicles to meet the requirements in the USA.

But jump back 5 years from before 1976 and gasoline cars had none of those emissions equipment and were producing much more NOx emissions. And take those EGR valves and such off those 1976 cars and then compare their emissions to diesel back then. In the beginning diesel produced less NOx. I remember reading about this back then in World Book Encyclopedia. I wish I still had access to some of those old articles that lauded diesel for producing less NOx, besides other emissions. Saying that diesel produced more NOx from the beginning simply isn't true.

Now don't get me wrong. Those emission on both diesel and gasoline needed to be cleaned up. And there's still plenty of cleaning to do. Hopefully some day soon we'll all be driving electric cars that run off of solar power.

 

Here's a graphic copied from a Johnson-Matthey brochure from many years ago. Engine-out NOx emissions (i.e., "No catalyst") of petrol are about twice as much as diesel:





Also, the graphic on the following web page suggests NOx emissions from petrol without catalyst are about three times as high as diesel:

Vehicle Emissions | Air Pollution | City Diesel | LPG | CNG

 

Diesels today are at a disadvantage in terms of NOx in relation to gasoline because the composition of their exhaust means the 3-way catalytic converter doesn't work as well as it does in a gas car. They need to use a NOx trap to catch any peak amounts in the emissions, and release it slowly after for the cat to handle, or use SCR that adds a nitrogen source to the exhaust. Many are doing both.

This is a young technology in comparison to NOx emission controls for gasoline. We will likely see some big improvements to it in the coming years.

The first Insight made heavy use of lean burn, and had a NOx trap. Such may become common on gas cars has fuel economy and carbon emission regulations become stricter.