I'm really surprised the Europe big car manufacturers spent so much effort on small Diesel engines instead of Turbo gasoline engines. My theory is the fact that having a majority of Diesel vehicles in Europe lowers their oil consumption vs Gasoline engines, hence, lowers their CO2 production but with the extremely negative fact of increased local smog.
Diesel was always popular due to high fuel efficiency. Since diesel also has lower CO2 emissions they really took of in the 90s. However, gas engines are catching up in both areas.
Diesel has a much lower tax than gasoline per liter. The car manufacturers just serve the higher demand for diesel cars, because it is cheaper to operate monthly.
There's at least few EU countries where Diesel is much more expensive than petrol at the moment. People like diesels because it's actually hard to get huge fuel consumption with those, while if you're not particularly careful any turbo petrol will drink fuel quickly. I had a 1.6dCi Qashqai and that car would not burn more than 10L/100km, no matter what I did or how aggressively I drove. Zero chance. I also have a 1.2TSI petrol Polo, and you can easily make it use 20L/100km if you drive it like a maniac - you have to be actively careful to keep it in the 6-7L/100km range, while the 1.6dCi would easily do 5L/100km without really thinking about it.
Wow, I have a Seat with the same 1.2 engine and is really really hard for me to surpass the 8L/100.
Maybe driving very fast can get you over these numbers but driving in the legal limit of most countries won't make you burn that much fuel!
It has absolutely nothing to do with driving above the speed limit -as a matter of fact driving at a completely legal 120km/h won't use anywhere near as much fuel because you are travelling pretty fast and not accelerating anymore, so the consumption will be decent.
But try accelerating from every stop in the city all the way to the redline, pedal to the floor, but never going above 50km/h - you would never go above the speed limit, but the tank would disappear in no time at all. I'm certain that if I tried I could burn the entire 50L tank of the Polo in ~250km, by just keeping it in high revs and accelerating hard(as hard as you can in a 90bhp Polo anyway) and frequently. The injectors will happily keep feeding the engine more and more fuel as you do this, while diesel common rail systems have almost a hard limit of how much fuel they can inject - no matter what you do you won't go above certain values.
Diesel emissions standards are lower in Europe than in US. So that makes diesels easier to produce and sell in Europe.
I believe, as you said, diesels also have lower CO2 emissions per mile than gasoline engines. The problem is the increased SOx and NOx emissions as well as soot emissions that contribute to smog.
In theory, Diesel engines should have much lower smog than gas engines because Diesel engines require excess oxygen rather than stoichiometric ammounts like in gas engines. The problem is that diesel fuel doesn’t vaporize nearly as well as gasoline, so you end of with tiny droplets of diesel in the engine rather than pure vapor. So even though there is excess oxygen, the O2 can’t get to the inside of the droplets and the engine heat basically cooks them into soot.
Perhaps but car manufacturers will point fingers at higher sulfur content in lower-graded diesel. Other issues like fuel filters and water traps performing sub-optimally (due to age or lack of replacement/maintenance) can introduce contaminants that further exacerbate the situation, surely there are sensors for this.
Diesel is not really "less refined" it is a different distillate of crude oil, and contains heavier molecules. I think major contributor to its worse atomization is it's higher viscosity and lower vapor pressure at room temperature. It just evaporates a lot less readily. If you've never handled gas and diesel, diesel feels a lot oilier and if you soak a rag with diesel vs gas, the gas will evaporate a lot sooner.
> I believe, as you said, diesels also have lower CO2 emissions per mile than gasoline engines.
There was a massive push following the Kyoto Treaty to reduce CO2 emissions. From 1996, when separate emissions standards for diesel/gasoline engines were introduced in the EU, diesels initially were allowed less than half the emissions of gasoline engines, though since 2005 it's been exactly half. Combined with this, many countries moved vehicle taxation to being based on CO2 emissions of the vehicle, providing a financial incentive for diesel powered cars.
As for the cause of the various emissions: NO_x emissions are mostly a function of combustion temperature, AFAIK, whereas PM is indeed caused by incomplete combustion.
Small turbodiesels were way ahead of small gasoline engines for decades in fuel economy, power, and so forth. Diesel, which uses direct injection and compression ignition, has always been a natural fit with turbocharging, which makes them intrinsically suited to the paradigm of a small engine for efficiency with a turbo for power. They also intrinsically have great low-end torque, which complements the top-end power of turbos.
Turbo gasoline engines were hard to make well, I gather mostly due to predetonation. Gasoline engines historically use manifold injection and spark ignition, which limits compression ratios. However, with advances in technology, particularly in engine computers & sensors, small turbo gas engines have recently become far more competitive.
So, basically, from the vantage point of 2018 turbodiesels might seem like a questionable choice- but ten or twenty years ago, good small turbocharged gasoline engines mostly didn't exist.
This is my understanding as well. Highly advanced knock and temperature sensors, high pressure gasoline direct injection, turbochargers, and high compression ratios in gasoline engines are a relatively new combination. Gasoline engines have seen huge leaps in efficiency in the past decade.
>Germany’s automotive regulator KBA found five unapproved software functions in Daimler’s Euro 6 diesel engines, affecting as many as 1 million vehicles in Germany, Bild am Sonntag reported Sunday.
And then,
>“We don’t see any evidence that Daimler was designing software to deliberately cheat on emission testing,” said Arndt Ellinghorst, an analyst with Evercore ISI in London.
If it's not a defeat device like the VW scandal, then what specifically is the prohibited function causing the recall? The article doesn't really explain what the device or function in question is.
One way to reconcile these seemingly contradictory statements is the following.
The actual programmer & designer of the software is the supplier of the engine control units (ECUs), in most cases Bosch. The software that they supply actually already contains these cheating routines. These routines are delivered as a part of the software packages, and can be turned on/off with some flags.
It is up to the auto company how to set these flags.
Source: Close relatives working in the car industry.
So is the issue that those routines are supported regardless of the configuration, or that they were delivered in a way that the routines can still be used?
This very ambiguity makes it easy for both sides to just shift the blame to the other side in case this whole collusion gets discovered – which you can now nicely see in the wild. In the best case scenario for both companies, both just get away with it this way.
Taking this a step further, presumably an honest vendor only need flash a new firmware at the dealer to the ECU with the unused cheating codeblocks removed, while a secretly cheating vendor is suddenly trapped.
Which is reasonable, for a narrow definition of reasonable.
The emissions standards don't apply on a world-wide basis. Maybe they should. But disabling them for markets which don't require them, and gaining fuel efficiency, is at least not fraudulent behavior.
I know you didn't insinuate that, but I would like to point out that there's nothing wrong with detecting test conditions, per se.
It might have safety implications (e.g. deactivating airbags so they don't fire because of implausible-on-the-road vehicle states), or even enable certain tests in the first place (perhaps by disabling traction control systems confused by vastly differing speeds per axle).
Using them in order to cheat, however, is clearly not nice at all.
Speaking as a German, and as someone who has worked in the automotive industry, I'd really like for manufacturers to be punished hard on this.
The amount of complacency and disdain for regulations on the part of the manufacturers is disappointing, and the collusion by the German government distasteful.
It might even be a good thing to remove dead code -- what isn't there can't possibly cause trouble.
But it complicates product management: instead of a single binary and a bunch of feature flags, you now have a bunch of binary versions; and the number of permutations can get quite large quite quickly.
The cheating code is probably necessary. There are dozens of higher emission modes that an engine may go into to prevent damage in certain situations. E.g. low ambient pressure, high coolant temperature, slow wastegate response...
According the a German news site one of these functions can be used to disable some kind of filter system which causes higher nitrogen oxide emissions.
The last rumoured explanation what they did was that they disable the emission control system when the AdBlue (carbamide) tank fill level drops under 10%. According to the EU laws a diesel car isn't allowed to start if the AdBlue is empty so they didn't use it anymore, so it never gets empty...
Got to love those European values, talk big about the Paris accord and climate change while making billions raping the environment through deception. Looking forward to Trump hammering Germany with tariffs and fines for once again deliberately violating US emissions laws. I'd be willing to bet he knew this was coming based on all his talk about EU tariffs against American cars last week.
The most vexing part of this is how long it took for others to notice. Did no competitor try to legitimately meet emissions requirements, fail, and immediately turn to Dalimer/VW to see how they "met" those requirements?
If the answer is collusion, then that only raises more questions on what else they could all be working to sweep under the rug.
Mazda announced in 2012 that it was going to introduce the Mazda 6 diesel in the US, but kept delaying due to having trouble getting it to meet US and California emissions standards. It has only now figured out a way to meet emissions standards without overly compromising performance, and is releasing a diesel vehicle in the US (the CX-5) now, after a 6 year wait.
Well, if you look at the third-party emissions tests from normal city driving, emissions of basically all brands are many times above the limit. They were just smart enough not to sell in the US.
But really the bigger question is: surely if this was somehow fixable by a software ECU update, they would have done so? Defeat devices are an old game in the car industry. But as long as those recalls consist of merely software updates, it's clear they are just preparing the next, even bigger con while apologizing for the current one, and EU governments are happy to look the other way.
It's relatively simple. If you have AdBlue, you pretty much eliminate NOx. PM2.5 should be fix-able with either filters or driving the engine iirc more lean, to incentivize full combustion. That might increase the use of AdBlue required, but I am not sure.
If I were driving, I'd look for a car that, based on my own testing (e.g., during a test drive at the dealer), measures sane emissions and drinks AdBlue. But for all I know, such a car does not exist. I really wish they make them take all the dirty cars from the streets, mandating a retrofit AdBlue system to allow them back onto the street. With an allowance for those that have an AdBlue system already to measure at a test drive, i.e., with a probe shoved up the tailpipe, and the mechanic/owner driving a loop around the block or so, maybe with some mandatory measuring for the first 100km after installation or so, and if the car at any point during this fails the standards, don't allow it back on the road. The effect from this would be that teaching the car to cheat would be next to impossible, especially if you could mandate another test e.g. at any point between 10000 and 15000km, as best fits the owner schedule. While it should be possible to engineer a cheat for this, it would be hard to conceal as an accidental bug, which would be what they'd have to make it look like to avoid potential criminal liability (they could certainly create suitable criminal statutes along with the testing requirements, and make sure these hit those that actually do it, along with everyone up the chain. Make it conspiracy or so, and catch all at once. Some prosecutor would have a lot of fun.)
It's beyond belief that Toyota's research division hasn't both tried to build clean-and-efficient small diesels, and taken apart the european ones. They just didn't put them into production.
For politicians, this was a very convenient non-tarif barrier. Since Toyota wasn't making such engines, you can help VW without attracting WTO fines. And you look good on TV talking about euro technology. And, of course, striking a strong pose about CO2 also looks great on TV.
> The most vexing part of this is how long it took for others to notice.
This has been an open secret for years. Anyone who wanted to know, easily could.
Perhaps not the existence of "defeat devices", but open disdain for and cavalier circumvention of the rules by all manufacturers.
> Did no competitor try to legitimately meet emissions requirements
Probably.
German manufacturers openly share products for comparison with their competitors (realising they can't avoid it anyway). I think it's a safe bet that everyone knows what everyone else is doing.
US companies are too big/corrupt to make good decisions.
European cars are all style. Expensive, non-reliable, hard to fix.
Not sure what the solution is, everyone else is a low quality copycat(Tesla/Kia/Chinese car companies).
Not to say any cars are bad, but the companies are awful. A car is entirely dependent on the engineering team behind it, you can only hope that a company set things up to be successful.
I know this is not really your point, but what do you mean the US manufacturers are corrupt? From where I'm standing, it looks like European autos have that problem more than the US does.
Just as interesting as the charge that US auto companies are all corrupt - how are European cars unreliable? German cars especially are amongst, if not the most reliable in the world, no? Bear in mind I'm not a petrol head so this is my perception.
The make/model matters more than company. An f150 is wayyy better than anything else ford makes. Its really uncomparable. As another note, the Chevy Sonic was designed in Germany and is probably the worst car GM made in recent memory.
But yes, German cars are known to be a pain to own due to problems and the difficulty to fix them.
European cars are considered unreliable in the US because they're generally high-end models with newer tech (and more of it), and that kind of stuff tends to break and be expensive to fix.
From a mechanical standpoint, they're not particularly unreliable, but again, parts can be pricier (particularly in the US).
The way I view it is that Japanese cars are built with extreme precision in high volume to exactly the right tolerances. They tend to be very consistent and reliable and parts are cheap due to volume. However, if things DO fail, it's generally because they're just slightly underbuilt and built to a pricepoint. German cars tend to be overbuilt from a mechanical standpoint (heavier/sturdier parts) but that doesn't mean they're more reliable as a finished product.
Hmm, the Prius is ~20yrs old, I suppose you could claim it wasn't innovative, just an incremental improvement, but you could say that about adding turbo- and superchargers to normal IC engines, and all of them increase efficiency. All-electric cars seem innovative to me? They offer a simpler, cleaner, lower-maintenance vehicle which is adequate for day-to-day uses.
Nissan has been leading electric vehicle commercialization for a couple decades now. They made and sold the first commercial li-ion pure electric cars in the US in the '90s, and hundreds of thousands of Nissan Leafs around the world. They're also largely responsible for the largest electric car fast-charging network in the world, the CHAdeMO standard, which has over 18000 public charging points in 51 countries on 5 continents. They've replicated their supply chain and production facilities for in-house EV battery packs, electric motors and EV vehicle production on 3 continents now (JP, US, EU). And their Nissan ProPilot driver assistance system, that can self-drive on well-marked roads today, promises door-to-destination self-driving by 2020.
As clarification, every company has 'innovated', but its obvious the differences between Japanese companies and the rest of the industry.
That is a very large scale 'car' innovation. At the component level, they are using the same stuff as decades ago. Maybe that is okay, but other companies dont do this.
Gasoline engines are getting better and better. Have you seen some of Mazda's latest engine innovations? Emissions have been improving rapidly, and fuel economy has been improving too (unfortunately these gains have been hidden by increasing size and curb weight)
Yes and yes, I believe. American regulations on emissions have been tightening, which (as one of the largest markets) drives requirements. Also, Mazda is one of the smaller fish, so they have to innovate to stay competitive.
Diesel engines should be banned entirely. The collective effects on human health are catastrophic, even when compared to gasoline.
You will find a lot of Europeans, particularly Germans, who still believe in the "efficiency" and "cleanness" of diesel engines, but this is really just a residual effect of VW's extensive marketing campaign during their turbodiesel "glory days" - before they got caught lying about it. VW really caused crimes against humanity that we're still paying for.
There is no such thing as "clean" diesel and there never will be.
Evidence for this? They product more soot and smog, but less CO2. For certain driving characteristics they are MUCH better than gas. (E.g. heavy trucks that require larger amounts of torque)
Googling for numbers, many sources quote these EU tests which everyone's cheating on. Out in the real world it sounds like switching Petrol -> Diesel saves maybe 20-30% CO2, and emits 10-20x the NOx.
The paper I linked "sampled ... 56% of all passenger cars sold in Europe in 2016". So they all have this stuff, right?
Maybe next year's models will actually use it fully, and become clean. I'm not holding my breath though, it seems like a political problem. And if they do use it fully, in the real world, will they still be more CO2 efficient, and by how much? After all, the efficiency measure is the major incentive for all this cheating.
AdBlue is usually made from natural gas, so one has to figure the CO2 it takes into it. It should be able to use less diesel fuel, but I don't know if the reduction there is worth the increase in AdBlue use. The hotter the engine burns, which in this case should mean the higher the compression/inlet pressure is, the higher the efficiency, as well as the NOx levels generated. The impact of particle filters on engine efficiency is not know to me.
There's also increasing evidence that the kind of particulates that the newer diesel engines emit are actually worse for humans that the older ones.
The particles are smaller size and seem to cross the blood-brain barrier as well as penetrating further into the lungs.
I would say that it just simply isn't clear which one is actually better right now, but there are some concerning signs around diesel engines right now.
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[ 2.9 ms ] story [ 201 ms ] threadBut try accelerating from every stop in the city all the way to the redline, pedal to the floor, but never going above 50km/h - you would never go above the speed limit, but the tank would disappear in no time at all. I'm certain that if I tried I could burn the entire 50L tank of the Polo in ~250km, by just keeping it in high revs and accelerating hard(as hard as you can in a 90bhp Polo anyway) and frequently. The injectors will happily keep feeding the engine more and more fuel as you do this, while diesel common rail systems have almost a hard limit of how much fuel they can inject - no matter what you do you won't go above certain values.
maybe in a frictionless vacuum!
At high speeds the force you have to exert to counter wind resistance is less than what you need to gently accelerate when going slowly.
I believe, as you said, diesels also have lower CO2 emissions per mile than gasoline engines. The problem is the increased SOx and NOx emissions as well as soot emissions that contribute to smog.
In theory, Diesel engines should have much lower smog than gas engines because Diesel engines require excess oxygen rather than stoichiometric ammounts like in gas engines. The problem is that diesel fuel doesn’t vaporize nearly as well as gasoline, so you end of with tiny droplets of diesel in the engine rather than pure vapor. So even though there is excess oxygen, the O2 can’t get to the inside of the droplets and the engine heat basically cooks them into soot.
There was a massive push following the Kyoto Treaty to reduce CO2 emissions. From 1996, when separate emissions standards for diesel/gasoline engines were introduced in the EU, diesels initially were allowed less than half the emissions of gasoline engines, though since 2005 it's been exactly half. Combined with this, many countries moved vehicle taxation to being based on CO2 emissions of the vehicle, providing a financial incentive for diesel powered cars.
As for the cause of the various emissions: NO_x emissions are mostly a function of combustion temperature, AFAIK, whereas PM is indeed caused by incomplete combustion.
Turbo gasoline engines were hard to make well, I gather mostly due to predetonation. Gasoline engines historically use manifold injection and spark ignition, which limits compression ratios. However, with advances in technology, particularly in engine computers & sensors, small turbo gas engines have recently become far more competitive.
So, basically, from the vantage point of 2018 turbodiesels might seem like a questionable choice- but ten or twenty years ago, good small turbocharged gasoline engines mostly didn't exist.
This gives you an efficiency advantage right off the bat.
And then,
>“We don’t see any evidence that Daimler was designing software to deliberately cheat on emission testing,” said Arndt Ellinghorst, an analyst with Evercore ISI in London.
If it's not a defeat device like the VW scandal, then what specifically is the prohibited function causing the recall? The article doesn't really explain what the device or function in question is.
The actual programmer & designer of the software is the supplier of the engine control units (ECUs), in most cases Bosch. The software that they supply actually already contains these cheating routines. These routines are delivered as a part of the software packages, and can be turned on/off with some flags.
It is up to the auto company how to set these flags.
Source: Close relatives working in the car industry.
This very ambiguity makes it easy for both sides to just shift the blame to the other side in case this whole collusion gets discovered – which you can now nicely see in the wild. In the best case scenario for both companies, both just get away with it this way.
https://en.m.wikipedia.org/wiki/Plausible_deniability
Obviously, no parts supplier would integrate these functions in the first place if nobody asked for it...
The emissions standards don't apply on a world-wide basis. Maybe they should. But disabling them for markets which don't require them, and gaining fuel efficiency, is at least not fraudulent behavior.
It might have safety implications (e.g. deactivating airbags so they don't fire because of implausible-on-the-road vehicle states), or even enable certain tests in the first place (perhaps by disabling traction control systems confused by vastly differing speeds per axle).
Using them in order to cheat, however, is clearly not nice at all.
Speaking as a German, and as someone who has worked in the automotive industry, I'd really like for manufacturers to be punished hard on this.
The amount of complacency and disdain for regulations on the part of the manufacturers is disappointing, and the collusion by the German government distasteful.
It might even be a good thing to remove dead code -- what isn't there can't possibly cause trouble.
But it complicates product management: instead of a single binary and a bunch of feature flags, you now have a bunch of binary versions; and the number of permutations can get quite large quite quickly.
If the answer is collusion, then that only raises more questions on what else they could all be working to sweep under the rug.
But really the bigger question is: surely if this was somehow fixable by a software ECU update, they would have done so? Defeat devices are an old game in the car industry. But as long as those recalls consist of merely software updates, it's clear they are just preparing the next, even bigger con while apologizing for the current one, and EU governments are happy to look the other way.
If I were driving, I'd look for a car that, based on my own testing (e.g., during a test drive at the dealer), measures sane emissions and drinks AdBlue. But for all I know, such a car does not exist. I really wish they make them take all the dirty cars from the streets, mandating a retrofit AdBlue system to allow them back onto the street. With an allowance for those that have an AdBlue system already to measure at a test drive, i.e., with a probe shoved up the tailpipe, and the mechanic/owner driving a loop around the block or so, maybe with some mandatory measuring for the first 100km after installation or so, and if the car at any point during this fails the standards, don't allow it back on the road. The effect from this would be that teaching the car to cheat would be next to impossible, especially if you could mandate another test e.g. at any point between 10000 and 15000km, as best fits the owner schedule. While it should be possible to engineer a cheat for this, it would be hard to conceal as an accidental bug, which would be what they'd have to make it look like to avoid potential criminal liability (they could certainly create suitable criminal statutes along with the testing requirements, and make sure these hit those that actually do it, along with everyone up the chain. Make it conspiracy or so, and catch all at once. Some prosecutor would have a lot of fun.)
They are (apparently) entering a (high emission) engine protection mode at a time that is not allowed.
It isn't impossible that their excuse, they read the requirements differently, really was in good faith.
It's beyond belief that Toyota's research division hasn't both tried to build clean-and-efficient small diesels, and taken apart the european ones. They just didn't put them into production.
For politicians, this was a very convenient non-tarif barrier. Since Toyota wasn't making such engines, you can help VW without attracting WTO fines. And you look good on TV talking about euro technology. And, of course, striking a strong pose about CO2 also looks great on TV.
This has been an open secret for years. Anyone who wanted to know, easily could.
Perhaps not the existence of "defeat devices", but open disdain for and cavalier circumvention of the rules by all manufacturers.
> Did no competitor try to legitimately meet emissions requirements
Probably. German manufacturers openly share products for comparison with their competitors (realising they can't avoid it anyway). I think it's a safe bet that everyone knows what everyone else is doing.
Japan hasnt innovated in 30 years.
US companies are too big/corrupt to make good decisions.
European cars are all style. Expensive, non-reliable, hard to fix.
Not sure what the solution is, everyone else is a low quality copycat(Tesla/Kia/Chinese car companies).
Not to say any cars are bad, but the companies are awful. A car is entirely dependent on the engineering team behind it, you can only hope that a company set things up to be successful.
Unions exploiting the company. Sales people getting special favors.
It seems sick.
But yes, German cars are known to be a pain to own due to problems and the difficulty to fix them.
From a mechanical standpoint, they're not particularly unreliable, but again, parts can be pricier (particularly in the US).
The way I view it is that Japanese cars are built with extreme precision in high volume to exactly the right tolerances. They tend to be very consistent and reliable and parts are cheap due to volume. However, if things DO fail, it's generally because they're just slightly underbuilt and built to a pricepoint. German cars tend to be overbuilt from a mechanical standpoint (heavier/sturdier parts) but that doesn't mean they're more reliable as a finished product.
Nissan has been leading electric vehicle commercialization for a couple decades now. They made and sold the first commercial li-ion pure electric cars in the US in the '90s, and hundreds of thousands of Nissan Leafs around the world. They're also largely responsible for the largest electric car fast-charging network in the world, the CHAdeMO standard, which has over 18000 public charging points in 51 countries on 5 continents. They've replicated their supply chain and production facilities for in-house EV battery packs, electric motors and EV vehicle production on 3 continents now (JP, US, EU). And their Nissan ProPilot driver assistance system, that can self-drive on well-marked roads today, promises door-to-destination self-driving by 2020.
That is a very large scale 'car' innovation. At the component level, they are using the same stuff as decades ago. Maybe that is okay, but other companies dont do this.
Just in case, soon to hit the market (hopefully) Mazda's HCCI/SCCI new engine:
https://www.extremetech.com/extreme/253842-mazdas-2019-effic...
You will find a lot of Europeans, particularly Germans, who still believe in the "efficiency" and "cleanness" of diesel engines, but this is really just a residual effect of VW's extensive marketing campaign during their turbodiesel "glory days" - before they got caught lying about it. VW really caused crimes against humanity that we're still paying for.
There is no such thing as "clean" diesel and there never will be.
News articles are easily found as well:
https://www.theguardian.com/environment/2017/may/15/diesel-e... http://erj.ersjournals.com/content/17/4/733 https://www.theguardian.com/uk/2013/jan/27/diesel-engine-fum... etc etc
Diesel is significantly worse for human health than gasoline.
https://www.sciencedirect.com/science/article/pii/S004896971...
Maybe next year's models will actually use it fully, and become clean. I'm not holding my breath though, it seems like a political problem. And if they do use it fully, in the real world, will they still be more CO2 efficient, and by how much? After all, the efficiency measure is the major incentive for all this cheating.
The particles are smaller size and seem to cross the blood-brain barrier as well as penetrating further into the lungs.
I would say that it just simply isn't clear which one is actually better right now, but there are some concerning signs around diesel engines right now.