Green Car Congress  
Home Topics Archives About Contact  RSS Headlines

« NSF awarding $81M to 16 sites for new National Nanotechnology Coordinated Infrastructure (NNCI) | Main | Volkswagen of America debuts 2016 Passat; 38 mpg highway from the 1.8 TSI »

Print this post

Background on the 2.0L diesel engines at the core of the Volkswagen emissions testing debacle

21 September 2015

Last Friday, the US Environmental Protection Agency (EPA) and California Air Resources Board (ARB) charged that Volkswagen (Jetta, Beetle, Golf, Passat) and Audi (A3) passenger cars equipped with 2.0-liter diesels in the US have used a software defeat device to cheat on the results of NOx testing, and thus have violated the US Clean Air Act. According to the charges, the software, when it detected regulatory testing on a dyno, ran a different, more emissions-stringent engine calibration to meet test requirements than when it detected regular use. (Earlier post.) As a result, real-world NOx emissions increased by a factor of 10 to 40 times above the EPA compliant levels, depending on the drive cycle.

According to the charges, Volkswagen admitted to the software device. Both agencies have launched investigations; Volkswagen—which in addition to recall costs for the approximately 500,000 vehicles affected faces civil penalties and injunctive relief—says that it will fully cooperate and has launched its own external investigation; eager lawyers are ramping up for class action suits against the automaker; Volkswagen AG lost almost one-fifth of its market value on Monday; and some Volkswagen suppliers are also feeling a crunch.

The engines at the core of this evolving debacle began with a 2.0-liter unit introduced in the US in 2008 in the Jetta as Volkswagen’s first Tier 2 Bin 5/CA LEV II-compliant (i.e., able to be sold in all 50 states) diesel. (Earlier post). The new 2.0L TDI (EA189) featured a common rail injection system and was the first of a new generation of diesels from Volkswagen. The 2.0-liter with CR was based on the 1.9-liter TDI engine with the Unit Injector System (UIS) “pumpe düse”. The predecessor engine was one of the most frequently built diesel engines in the world and was widely used within the Volkswagen Group.

Volkswagen engineers redesigned a large number of the base engine components to improve acoustics, fuel consumption, and exhaust gas emissions. The conversion of the injection system to a common rail design was one of the major changes; the addition of a new lean NOx trap (LNT) to handle NOx emissions was another. (This is referred to as the Gen 1 aftertreatment design in the EPA/ARB documents.)

NOx (nitrogen oxides: nitric oxide and nitrogen dioxide) formation is a function of temperature. Nitrogen and oxygen gases in the air react during high temperature combustion and form NOx. Because diesels operate at higher temperatures than gasoline engines, NOx formation has always been an issue for diesels. While efforts continue to develop new combustion regimes to reduce engine-out NOxto acceptable levels, aftertreatment currently is still required.

Broadly, there have been two catalytic approaches used to reduce exhaust NOx: urea-based selective catalytic reduction (SCR) and lean NOx trap (LNT) catalysts.

  • The urea-SCR (urea=AdBlue) approach requires on-board storage of the reductant fluid which is introduced into the exhaust upstream of the SCR catalyst. It is then converted to ammonia which interacts with NOx on the SCR catalyst to form water and nitrogen.

  • LNT technology utilizes fuel from the vehicle and advanced engine controls to enable periodic operation of the engine at rich air-to-fuel ratios to produce oxygen-depleted exhaust suitable for reducing NOx stored on the LNT catalyst surface.

Volkswagen planned to use both. In 2007, as the automaker discussed introducing the Jetta with the new 2.0L diesel, it said that for car models of the Passat class and smaller, it was testing the new lean NOxOx trap catalytic converter (discontinuous). (Earlier post.) At λ of greater than 1, NOx was captured and stored; at λ less than 1, NOx was released and reduced. Ultra low-sulfur fuel was a necessity, and fuel consumption would increase as a result of catalytic converter regeneration. Larger and heavier models would feature Selective Catalytic Reduction (SCR) catalytic converter (continuous) with the use of AdBlue.

Combined EGR operation plays a role in NOxreduction as well. The new 2.0L engine featured high- and low-pressure exhaust gas recirculation (EGR) with a high-performance EGR cooler and a turbocharger with a low pressure EGR inlet nozzle. The 2.0L TDI continuously adjusted EGR operation depending on engine operating conditions and speed. No-load engine operation resulted in high amounts of High Pressure EGR application. With rising engine load and engine RPM, the recirculation of exhaust gases shifted to the Low Pressure EGR system to increase the recirculation rate to obtain optimal NOx reduction at middle and high engine loads. Particularly in the high engine loads, the cooled Low Pressure EGR provided an advantage over the High Pressure EGR system.

The emissions control subsystem included an oxidation catalytic converter; diesel particulate filter; the LNT and H2S catalytic converter.

All of this complexity was managed by software run by the electronic diesel control EDC17 from Bosch. The successor to EDC16, EDC17 had greater processing capability and a larger storage capacity than EDC16. It also offered the option of integrating control functions for future technologies.

Epa
Vehicles affected by the EPA NOV and CARB In-Compliance letter. Source: EPA. Click to enlarge.

Volkswagen vehicles affected by the agencies’ charges span model years 2009 to 2015, with three different aftertreatment system configurations (Gen 1, Gen 2 and Gen 3). Below, we’ll go into some detail outlining the complexity of NOx control for the Gen 1 system, and then go on to outline the broader hardware changes in Gens 2 and 3, without replicating the control complexity. The principles are the same, the details differ.

Gen1
Gen 1 exhaust system. Source: Volkswagen. Click to enlarge.

Gen 1 exhaust treatment. The diesel particulate filter and the oxidation catalyst are installed separately in a shared housing. The oxidation catalyst is located before the particulate filter in the direction of flow. The carrier material of the oxidation catalyst is metal, so the light-off temperature is reached quickly. This metal body has an aluminum oxide carrier coating, onto which platinum and palladium are vapor-deposited as catalyst for the hydrocarbons (HC) and the carbon monoxide (CO). The oxidation catalyst converts a large portion of the HC and CO into water vapor and carbon dioxide.

The diesel particulate filter consists of a honeycomb-shaped ceramic body made of aluminum titanide. The ceramic body is partitioned into a large number of small channels, which are alternately open and closed at the ends, resulting in inlet and outlet channels that are separated by filter walls. The filter walls are porous and coated with a carrier coating of aluminum oxide. Platinum, which acts as the catalyst, is vapor-deposited onto this carrier layer. As the soot-containing exhaust gas flows through the porous filter walls of the inlet channels, the soot particles are captured in the inlet channels.

The particulate filter must be regenerated regularly so that it does not become clogged with soot particles and its function impaired. During regeneration, the soot particles collected in the particulate filter are burned off (oxidized). The Engine Control Module (ECM) has several ways to control the increase of exhaust gas temperatures during active regeneration:

  • The intake air supply is regulated;

  • The exhaust gas return is deactivated to increase the combustion temperature and the oxygen content in the combustion chamber;

  • Shortly after a delayed “late” main injection, the first post-injection is initiated to increase the combustion temperature;

  • Late after the main injection an additional post-injection is initiated. This fuel does not combust in the cylinder, but instead vaporizes in the combustion chamber;

  • The unburned hydrocarbons of this fuel vapor are oxidized in the oxidation catalyst. This ensures an increase in the exhaust gas temperature to approximately 650 °C (1202 °F) as it reaches the particulate filter;

  • The boost pressure is adjusted so that the torque during the regeneration operation does not change noticeably for the driver.

To attain the BIN5/LEV2 emission level, Volkswagen used the LNT for exhaust gas after-treatment. This NOx storage catalyst supplements the particulate filter system. In this application, Volkswagen placed the NOx storage catalytic converter away from the engine in the vehicle underbody, thereby reducing thermal aging. This also takes advantage that the CO and HC that have already been oxidized by the particulate filter, allowing an optimum NOx conversion in the NOx catalytic converter.

The exhaust system has two lambda sensors.

  • The lambda sensor upstream of the oxidation catalytic converter regulates the air-reduced operating modes for the NOx catalytic converter. It is also used for the initial value for the air model stored in the engine control unit. This air model helps determine the model-based NOx and soot emissions of the engine.

  • The second lambda sensor, which is placed downstream of the NOx catalytic converter, detects an excess of reduction medium in the regeneration phase. This is used to determine loading and the aging condition of the NOx catalytic converter.

Three temperature sensors integrated into the exhaust system enable the OBD functions for the catalytic components and are used as initial values in the regulation of the regeneration operating modes ad the exhaust temperature model.

Use of the LNT requires new regeneration modes. Unlike particulate filter regeneration, a sub-stoichiometric exhaust gas composition is necessary for the regeneration of the NOx storage catalytic converter. In sub-stoichiometric operation, the nitrogen oxides stored during the lean operation are reduced by the exhaust enriched reduction media consisting of HC, CO and H2.

A further regeneration mode is provided by the sulfur removal of the NOx storage catalytic converter (DeSOx Mode). This is necessary as the sulfur contained in the fuel causes sulfate formation which slowly deactivates the NOx storage catalytic converter. The de-sulfurization procedure was designed for a sulfur content of 15 ppm parts per million (ppm).

Due to the high thermal stability of the sulfates, significant levels of sulfur reduction are only possible at temperatures above 620 ˚C (1150 ˚F). This sub-stoichiometric mode is very demanding in terms of engine management. To be able to set air mass and exhaust gas recirculation independently on each other, two separate control circuits are used. The air mass is set using the intake manifold throttle valve. The exhaust recirculation rate is set using a model-based regulation concept.

A suitable combination of high pressure and low pressure EGR, with corresponding compression temperatures, enable stable rich operation even in the low load range with the fuel qualities that are typical for the US. In addition to this, the injection strategy for the rich mode is changed. Up to six injections are used depending on characteristic values to attain a stable and low-soot combustion. This is particularly important in the sulfur reduction process to prevent soot accumulation in the particulate filter.

To attain the necessary exhaust gas temperatures in DeSOx operation, Volkswagen used very late, non-combustion post-injection. The fuel partially reacts at the oxidation catalytic converter with the residual oxygen contained in the exhaust gas and creates residual heat for the sulfur reduction of the NOx storage catalytic converter.

DeNOx-ing. The the engine control module prioritizes the NOxregeneration mode. The software takes into account the necessary engine operation and regeneration conditions as well as the catalytic converter properties. A loading and discharging model is stored in the engine control module for DeNOx regeneration. This maps the characteristics of the DeNOx storage catalytic converter. The load condition of the catalytic converter is modeled during engine operation that is dependent on the exhaust temperature and volume velocity as well as the calculated raw NOx emissions.

If the NOx load value exceeds a threshold value which represents the optimum conversion rate for the catalytic converter, the regeneration is conducted when the operating condition of the engine permits a regeneration mode to be activated. Two criteria, which relate to the lambda signal or a NOx discharge model, are available for determining the end of regeneration.

Gen 2: SCR. In addition to making modifications to the engine, Volkswagen subsequently introduced a Selective Catalyst Reduction (SCR) system in the Passat 2.0L TDI for NOx treatment. (Earlier post.) When the exhaust gases exit the engine, they pass through the oxidation catalyst and diesel particulate filter. This component converts gases and traps the soot in the oil. The soot is burned off through regeneration cycles.

Gen2
Gen 2 emissions system. Source: Volkswagen. Click to enlarge.

After exiting the oxidation catalyst/diesel particulate filter assembly, the gases are sprayed with a reduction agent (urea) using the SCR injection valve. The gases then enter the SCR reduction catalysts. A NOx sensor downstream of the SCR reduction catalysts monitors the effectiveness of the reduction and is used to influence the amount of reduction agent used.

As with the LNT system, the parameters of all the elements that play into the aftertreatment are controlled by the ECM.

Gen 3: the EA288. In 2014, Volkswagen of America announced a major technology change. The strategically important new 2.0-liter EA288 diesel engine (earlier post) would replace the current generation 2.0L TDI, and would power the 2015 Golf, Beetle, Beetle Convertible, Passat, and Jetta. The EA288 is based on the Volkswagen MDB, its modular diesel engine toolkit (Modularen Diesel Baukasten) (earlier post).

The new EA288 engine was to replace all the 2.0-liter diesels then fitted in Audi and Volkswagen TDI Clean Diesel models. This turbocharged, common-rail, direct-injection four-cylinder engine produced 150 hp (112 kW)—an increase of 10 hp over the outgoing engine—and 236 lb-ft (320 N·m) of torque. This powerplant shares only the bore spacing with the previous diesel engine that had the same designation.

As part of this major redesign, the engine also features an entirely new exhaust aftertreatment system—a compact unit close-mounted to the engine, helping to lower heat and pressure losses. The system is modular. It can use an SCR system, or NOx storage, or oxy cat—essentially whatever the engine needs, without affecting the rest of the engine. At the time, Volkswagen said that the flexibility of the MDB would allow the engines to meet the coming EPA Tier 3, California LEV III emissions standards.

The EA288 TDI engine with the BIN 5 rating uses a low-pressure EGR system to reduce engine-out NOx emissions. The EA 288 aftertreatment system combines an oxidizing catalytic converter and a diesel particulate filter into a single module. This close arrangement allows the oxidizing catalytic converter and the diesel particulate filter to heat up quickly, and the operating temperatures of the catalytic converter can be reached faster.

In its Bin 5 design with SCR, the diesel particulate filter has an SCR coating.

Gen3
Gen3
The aftertreatment module for the EA 288. Source: Volkswagen. Click to enlarge.

In addition, the exhaust flap control unit has a throttle valve with an electric motor drive located downstream of the diesel particulate filter. The exhaust flap control unit can slow exhaust gas flow, helping to regulate EGR. The exhaust flap control unit is actuated by the ECM.

September 21, 2015 in Diesel, Emissions, Regulations | Permalink | Comments (14)

Comments

If the cheating is true, it is better for VW to admit quilt sooner than later. I feel sorry for the owners of these vehicles. They should not be required to submit to a fix that would undermine power and performance. Also, I think a reengineering solution in general is much too complex and costly. I believe VW will end up settling for a very large amount instead.

What happens to the current inventory? I believe the 2015s are equipped with SCR and UREA. Perhaps the reengineering is much more suble on the current year?

it's too bad hydrocarbons fuels were still so cheap that we are willing to burn it in 20% efficient, internal combustion engines that require exhaust emissions systems that are worth more than the basic engine.

VW would do well to scrap their diesel ideas and show how serious they are about EVs. EVs will replace the ICEVs down the line; it's just a matter of time based on how long the oil companies can delay progress and innovation.

It is a problem that VW only apology for a breach of trust between VW and its customers and the public. However, it is far more serious than a breach of trust that in a legal sense is not a crime. We know that WHO has linked air pollution to 7 million premature death per year globally. Stated differently, 12% of all people on our planet dies prematurely because of air pollution. In order for that number not to increase further it is extremely important that the legislation on air pollution limitations is respected in all industries. The auto industry is responsible for a large part of the total global air pollution and therefore also a large share of those 7 million premature death per year that can be linked to air pollution. When a car company like VW manufacture cars that cleverly can emit 10 to 40 times the legal level of air pollution while avoiding detection at normal EPA test procedures it is far more serious than a breach of trust. It is VW committing mass murder in the USA on a scale that outperforms 9/11. It is simply not enough to say we are sorry you can't trust us. VW needs to pay up in a big way that will hurt them seriously financially so that they cannot afford to commit mass murder in the USA a second time and so that other automakers also get the message that air pollution is not to be taken lightly as people's lives in massive numbers depend on those systems that limit air pollution. I sincerely hope that the legal end game of VW's defeat devise is a 18 billion USD penalty to VW so that VW and the industry start to treat this issue with the seriousness that it demands.


WHO on 7 million air pollution death.
http://www.greencarcongress.com/2014/03/20140325-who.html

Lad:

You keep repeating that diesels are 20% efficient when you have been told many times that they are over 40% efficient, which is why they are used in spite of their pollution.

Why are you wilfully repeating nonsense?

To Lad and Davemart about efficiency. The EPA indirectly provide a good instrument for roughly estimating overall vehicle efficiency. Tesla's Model S get 100 mpg gasoline equivalent and we know it as a BEV is about 80% efficient. The Prius is rated at 50 mpg so it is up to 40% efficient when compared to Model S but Model S is 2200 kg and the Prius is about 1350 kg so we need to mark down the efficiency number for the Prius. A good guess is that the Prius is about 35% efficient. Many diesel cars that weight 2200 kg only get 25 mpg on diesel that has about 13% more energy than gasoline. They can therefore at most be 20% efficient as they only get 25% of the Model S mpg rating and we need to factor in the higher energy content of diesel. There are diesel engines that do better but not much. The new VW Passat gets 35mpg combined and factor in the higher energy content of diesel it is about 30 mpg or 30% times the 80% efficiency of the Model S so about 24% total efficiency. You can drive a diesel engine at 40% efficiency at its peak but that does not represent overall vehicle efficiency in a real world situation where it nealy never is at its peak efficiency and also has losses elsewhere in the cars, such as, transmission, tyres and air-condition.

As a rule of thumb BEVs are 80% efficient, full hybrids are up to 35% efficient, new diesels are 24% efficient and fuel cells are 35% efficient but only half of that or 17% efficient if they use renewable electricity where you loose 50% for the electrolysis and the compression of the hydrogen.

Well, I hope that article makes it all a bit clearer.
It tells you how the VW diesel catalysts work.
It doesn't say what they did or did wrong.

It makes me wonder how they got into such a mess - did they just try it once to get past a single test, hoping to fix it later and then find that couldn't get out ?

How many people knew - there must have been quite a few if it was going on for 7 years.

I suppose it came about from the culture of fudging the EU NEDC tests, which is done quite openly. In that case, the testers are as guilty as the car companies, it is a bit like taking drugs in sport - if everyone is doing it, you will lose if you don't, and the testers are winking at you.

However, this is different, it is so blatant, and the real results are so far out of line wit the test - if they were 10 or 20 % over, it would be one thing, but they are 10 to 40 TIMES over, which is disgraceful.

I better stop ranting as I have work to do, but this is some story.

An anecdote. I had a 2004 Renault Espace 2.2 dCi and I could get 35.7 mpg out if it which was the rated level. Then I got a 2012 Ford Galaxy 2.0D, rated at 50 mpg, but I can't get much better than 40 mpg out of it - not much actual progress in 8 years.

Henrik:

Discounting this and that is a different subject.
How come you are not taking out for charging losses for batteries?

In any case the discussion is not about the efficiency of electric cars, but simply the efficiency of diesel ones.

'Diesel engines generally achieve greater fuel efficiency than petrol (gasoline) engines. Passenger car diesel engines have energy efficiency of up to 41% but more typically 30%, and petrol engines of up to 37.3%, but more typically 20%. That is one of the reasons why diesels have better fuel efficiency than equivalent petrol cars. A common margin is 25% more miles per gallon for an efficient turbodiesel.'

https://en.wikipedia.org/wiki/Fuel_efficiency

Toyota's have now hit a fairly staggering 40% efficiency for a petrol engine.

That is not, of course, total drive train efficiency, which is a different subject, but refers to the efficiency of burn, so Lad was clearly utterly inaccurate in his statement:

'it's too bad hydrocarbons fuels were still so cheap that we are willing to burn it in 20% efficient, internal combustion engines that require exhaust emissions systems that are worth more than the basic engine.'

That does not mean that I personally do not favour petrol over diesel, even at the cost of some efficiency, or electric over petrol, but inaccurate statements don't help.

It will be interesting to see if the new running mode will require more urea. I suspect that VWAG decreased this amount to extend the time between refills. They should be fined punitively for this!

Henrik - My 1600 kg 2001 VW Golf TDI with 1.9L engine and now ancient rotary fuel pump averaged 48 mpg on 100% biodiesel and 52 mpg on regular D2. I believe it was well over 20% efficiency. Todays 1.4-1.6L TDI engines with 2000 bar common rail fuel systems can easily top 65-70 mpg in the Golf platform. This might not be Prius efficiency here, but it's damn close.

It's too bad there isn't a Prius-'D', with, say, a 1.2L 3 cylinder diesel in it. That would probably break 90 mpg if driven mindfully.

Diesel emission systems are complex and there are several ways to meet some of the requirements. Maybe, I should be retired but I currently work 2 jobs. I am a minority owner and an engineer for a small company building some specialized agricultural machinery. We currently use a Tier 3 115 hp John Deere engine but will need to switch to a Tier 4 final engine in the not too distant future. I spent an afternoon last week talking to a John Deere rep about the different engine options and decided that it was best to go with an option that included a diesel particulate filter as it probably runs cleanest and could meet the new Euro 6 requirements. It is also more fuel efficient and uses less urea but off course it costs more upfront. Typical tradeoff. In some cases, you can get rid or the urea by running more cooled exhaust gas recirculation but then the combustion temperature goes down which brings down the NOX generation but also brings down the fuel economy.

My other job is advising the students working on the FormualSAE team (small formula type race car with about 60-80 hp) at the local university. Mostly, I advise the students on engineering design issues but I think that I will talk briefly on ethics tonight.

On a different subject, I have seen diesel efficiencies as high as 53% and the large 2-stroke ship diesels were running about 49% efficient. This is old data so these numbers are probably low.

Oh the humanity !

This isn't a case of accidentally inserting a fudge factor. It is a cynical, deliberate deception....most likely fully sanctioned by VW upper management.

Aging hippies and europhiles are stunned. A german automobile company lying? Now if it was GM, they would say, we could understand and even expect it !

Teutonic hubris strikes again !

The local paper stated that Chrysler-Fiat and GM will soon be investigated for similar fraudulent behavior.

Will they manage to cover up again!

ICEVs have been polluting the air, making us sick and killing us (at the rate of 6+ million/year) for decades and nobody has been charged yet.

The same could be said of CPPs and NGPPs.

Why not require VW to pay for infrastructure and conversion of vehicles to Dimethyl ether (DME). VW/Audi TDI Engine is an excellent engine and platform to be used with DME (dimethyl ether). DME is a clean-burning, non-toxic, potentially renewable fuel. Its high cetane value and quiet combustion, as well as its inexpensive propane-like fueling system, make it an excellent, inexpensive diesel alternative that will meet strict emissions standards.

Since this news came out the price of platinum has dropped about 8% while palladium has soared 15%, as the headlines have all been about reduced sales of diesels, hence substitution of palladium using gasoline cars for diesels. My take on this is different, and I would appreciate some expert feedback. I understand that in these light diesel engines VW used engine technology rather than particulate capture, as the primary tool. If that technology is now shown to be flawed, won't they have to use more particulate capture and burning, like larger diesel motors, which will require INCREASED platinum loadings in all their diesel cars.

And I assume market share for diesels will continue to be unaffected by consumers who prefer efficiency over other criteria, and don't like buying pre-burned gasoline (loaded with oxidized govt. mandated additives) that has significantly lower BTU's than diesel.
I drive a MB GLK250 with a biturbo diesel and I get around 40MPG in the mountains of CO. That's a 4400lb vehicle with a 3500lb tow capacity, AWD, 9" of ground clearance.

A number of years ago Artemis UK developed and demonstrated in a modern vehicle a hydraulic hybrid technology to save much fuel with any kind of combustion engine. City driving saves half the fuel compared to the operation of the same vehicle tested before conversion. Motorway driving saved only 30 percent. If you actually understood how a motor vehicle operates when you drive it you can understand the opportunities for energy and fuel savings. Hydraulic hybrids are the cheapest possible way to lower fuel consumption for internal combustion vehicles. Bosch bought the system for highway vehicles and sits on it. MHI may have bought the liscence back when it bought Artemis to joust at windmills. (Seven megawatts being tested in northern UK now)

INNAS NOAX has proposed its very clever and efficient hydraulic inventions, without their NOAX low emisstions, crankshaft free, piston engine, for a similarly efficient hybrid automobile and demonstrated them in a lift truck.

Both Bladon Jets and Capstone turbines have had their diesel or jet fuel burning units demonstrated in personal vehicles. These turbines can also burn any other liquid or gaseous fuel with slight change and still meet NOx and COx standards without change and produce particulates in lower amounts than any proposed standards without extensive treatment. ..HG..

Verify your Comment

Previewing your Comment

This is only a preview. Your comment has not yet been posted.

Working...
Your comment could not be posted. Error type:
Your comment has been posted. Post another comment

The letters and numbers you entered did not match the image. Please try again.

As a final step before posting your comment, enter the letters and numbers you see in the image below. This prevents automated programs from posting comments.

Having trouble reading this image? View an alternate.

Working...

Post a comment

Green Car Congress © 2017 BioAge Group, LLC. All Rights Reserved. | Home | BioAge Group