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Delphi Develops World’s First Ammonia Sensor for SCR

Delphi’s ammonia sensor.

Delphi has developed the world’s first automotive ammonia sensor. The new technology will allow direct closed-loop control of the SCR (Selective Catalytic Reduction) systems used by an increasing number of diesel vehicles to reduce NOx.

By directly measuring tailpipe ammonia, the sensor allows the injection of urea (an ammonia-rich compound required by the SCR system) to be optimized and ammonia emissions reduced.

Control of urea injection is expected to become a rapidly increasing priority as SCR levels increase to meet new emissions regulations in both light and heavy duty diesel markets.

A vehicle’s SCR system injects urea into the exhaust stream ahead of the NOx reduction catalyst. The ammonia in the solution reacts with the exhaust gas, with conversion into nitrogen and water. Unreacted ammonia is expelled with the exhaust gasses—“ammonia slip”.

Atmospheric ammonia reacts with airborne compounds such as nitric acid to create dust-sized airborne particles, which can create a smog-like haze. Ammonia emissions from vehicles are currently only a very small proportion of total ammonia emissions, which mainly originate from livestock and factories.

In addition to its use in heavy-duty applications, a number of automakers have indicated they will use urea SCR to meet current Tier 2 Bin 5 requirements in the US and expected Euro 6 requirements from 2014. (Others, such as Honda, are endeavoring to not have to use a urea-based SCR system. Earlier post.)

Today’s SCR systems are open loop, so the urea dose is estimated by the engine control unit using predictive algorithms. To accurately control the dose, systems will need to become closed loop, which will require a post-catalyst sensor.

This can be either a NOx sensor or an ammonia sensor. Several vehicle manufacturers have chosen the NOx option, but the sensor technology is cross-sensitive to NOx and ammonia, so can confuse one with the other. The result can be inappropriate dosing decisions that while providing a dramatic improvement on open loop systems do not deliver the benefit achievable by measuring the ammonia slip directly.

—Ivan Samalot, chief engineer for exhaust sensors, Delphi Technical Center

Delphi combined expertise in oxygen sensors with its materials expertise to develop a new type of ammonia sensor for automotive applications. A new ammonia sensitive material, developed at the Delphi Research Laboratories in Troy, Mich., is deposited onto a thick film ceramic substrate similar to the one proven in Delphi’s oxygen sensors. The sensor is then mounted in a compact, highly durable stainless steel package also based on Delphi’s proven oxygen sensor technology.

The new sensor detects excess ammonia in the exhaust gas within a range of zero to 100ppm, allowing the urea dose to be continuously optimized. It also allows vehicle manufacturers to eliminate an expensive post-oxidation catalyst that would otherwise be needed to remove excess ammonia from the exhaust and allows the size of the SCR converter to be optimized for the application.

As well as taking cost out of the aftertreatment system, this feature allows substantially improved packaging. This will be important for the anticipated growth in light-duty vehicle applications and also prevents an increase in back-pressure, which could harm fuel consumption if further aftertreatment systems are added.

Vehicle manufacturers in Asia, North America and Europe are working with Delphi on development programs incorporating the new ammonia sensor, which is expected to reach production during 2010.



Now only if they can get the particulates down. My poor Prius was engulfed in a Jeep CRD black cloud this week!


To the best of my knowledge, all model year 2007 diesel vehicles sold in the U.S. are equipped with DPFs (particulate filters). DPFs have actually been show to reduce PM to levels below that of gasoline vehicles.


Sounds like someone was running rich...

Stan Peterson

This is a big technology advance.

It wasn't until the oxygen sensor became available (and cheap) that catalytic converters and engine operation could be controlled by negative feedback.

Emission levels dropped dramatically. Government standards could be and were stiffened.

So will this technology lead to great control of NOx for diesels. Even with the SCR Bluetec technologies the clean diesels barely meet standards. This will insure that NOx can be controlled reliably making T2B5 standards reliably and consistently met.

Rafael Seidl

Stan -

with open loop control, SCR is about 85% efficient. With closed loop control, that could go to 92, maybe 95%. So yes, it will become a lot easier to meet T2B5 with closed loop control, especially after 150,000 miles.

However, the main advantage is that you can eliminate the expensive second oxidation catalyst whose only job is making sure no NH3 escapes into the atmosphere. Such catalysts require a lot of precious metals. It also helps that you can adjust the ammonia dosage more precisely.

Sid Hoffman

As for the Jeep, they stopped selling diesel versions in the 2007 model year because they don't yet have a version that meets all the latest emissions requirements.


Close control of liquid injection is very tricky business. It is subject to temperature (and hence volume and viscosity) of liquid, ambient atmospheric pressure, contamination of injector, acoustic resonance of pump/pipe/injector system, and so on and on. Closed loop control is indeed revolutionary advance for urea SCR technology. Especially because slipped urea smells, well, urea.


"Now only if they can get the particulates down. My poor Prius was engulfed in a Jeep CRD black cloud this week!"

I call BS on this one.

And just for the record, last week I was behind a Prius that was giving off white smoke and an evil smell.

Deal with it, anti-diesel troll, diesel tech is superior in every way to your way-less-efficient-than-they-want-you-to-believe clown car.

Rafael Seidl

Andrey -

if anything slips through the SCR cat, it'll be NH3 not urea. And that's actually worse. The issues you raise wrt closed loop control are actually much more serious for the current open loop logic, because it cannot compensate at all.

Anon -

no need to verbally assault donee. The engine in the Jeep CRD is an Italian-made unit that does not meet T2B5. I'm not sure if it even has a DPF already. The point is, diesel emissions are improving by leaps and bounds with each generation, so pretty much none of the engines in use in Europe today will be considered acceptable as-is by 2009 (Euro 5, focus on PM reduction) never mind 2014 (Euro 6, expected focus on NOx reduction). And even Euro 6 won't be as strict as T2B5.

Americans have very strict emissions standards, and diesels there need to meet them before US consumers can benefit. Once they can, I expect many people in the market for a large sedan, SUV or pick-up truck will pick the diesel option iff the premium isn't too steep.


Carl said:

DPFs have actually been show to reduce PM to levels below that of gasoline vehicles.

Lower, even, than ambient aerosol levels, in all size fractions.

Stan Peterson


You really never control a process until you can measure and effect the result, as you and I both know. The T2B5 standards were promulgated by earnest "do-gooders" that had very little input on what the technology of the time could really do.

As a result diesel are just not a large part of the American scene,not because consumers wouldn't purchase them but by fiat of the regulators. The improvements of lower CO2 emissions were sacrificed by the "true believers" for over fifteen years as standards were tightened by arbitrary "if the Feds want 10% improvements, we California CARBites demand 15% and the would-be clowns in Mass, NY, or Maryland say we'll trump that by setting our limits at not 10, not 15, but 20 or 25. Absolute nonsense.

I really would like the feds/courts to step in, and set federal standards that no state can ignore. As the great US market is fragmenting into lots of little markets with separate rules.

We are throwing the baby out with the bathwater; one of our secrets to American industrial advance, was offering companies a large consistent market for their products.

Much like the "improved" Gasoline has led to "boutique fuel" requirements and scattered scarcity as well as needless expense for both the suppliers and consumers. It provided little real benefit other than to provide a few jobs and empires for local bureaucrats. Some of the "do-gooder" politicians noted that in the gasoline price run up, promised rationalization help, but soon forgot about it, as bureaucrats defended their rules, empires and justified their jobs.

CARB may have had a "raison d' etre" to accelerate standards due to the unique air flow in the Los Angeles basin, but that time is now gone.

I think it time to phase out CARB and all the other budding regulation empires.

What are your thoughts?


The sensor also removes the Legislator's concern that people will simply let their additive tanks run dry: The sensor can simply be linked to an OBDII style diagnostic that lights the CEL when no ammonia is detected when it should be.

Hence no excuses from the Legislators about accepting additive based reduction systems.

Rafael Seidl

Stan -

CARB exists because California decided to regulate emissions before the Feds did. CA has never agreed to cede jurisdiction to the Feds because SoCal's combination of sunshine, topography and car culture supposedly merit stricter standards than elsewhere in the US.

NY, MA, VT and ME all decided to track CARB's standards rather than EPA's. You can argue about the merits of those decisions, but these states are not in fact setting their own limits for toxic emissions nor for the enforcement procedures (e.g. OBD).

More recently, California decided to try and add CO2 to the compounds whose fleet average emissions per mile are to be limited. In the absence of concrete federal action to curb global warming, a number of states (a dozen at last count) have since decided to latch on to this effort, again tracking California rather than defining a value of their own. Together, these states comprise well over 1/3 of the US LDV market.

Of course, CO2 emissions correlate directly with fuel consumption, the auto industry immediately sued. At present, CAFE and the gas guzzler tax are set by Congress and enforced by the DOT and the IRS, respectively. The industry has spent many millions in campaign contributions to make sure fuel economy rules were both lenient and consistent across the entire US.

Legally, the issue of who has jurisdiction over fuel economy/CO2 emissions will be decided by the Supreme Court in a landmark case pitting states' rights against federal prerogatives. Sticking with a single regulator would indeed avoid balkanizing the US market wrt fuel economy. However, those 12 states are in effect arguing that the federal authorities are simply not doing enough to curb global warming. California and the other 11 states might withdraw their legislation if CAFE and the gas guzzler tax were significantly tightened. As so often, both sides are using the legal system as a crowbar to pursue what are essentially political agendas.

As you rightly point out, the average fuel economy of the US LDV fleet would be quite a bit higher if modern turbodiesels enjoyed greater market share there. This has been hampered by relatively light taxes on fuel as well as diverging priorities for the two regulators: CARB is focussed more on PM, EPA more on NOx emissions. It is very hard/expensive to reduce both of these at the same time.

However, the NOx aftertreatment systems developed for diesel engines (store cat, SCR) can also be used for gasoline engines with stratified direct injection. This is expensive, the more so because the precise arrangement of injector and spark plug is crucial to avoiding PM formation. So far, only MB & BMW have dared to revisit stratified GDI. For now, their competitors are sticking with the less efficient but much cheaper homogenous GDI based on first-gen concepts or else old-fashioned PFI.


In Europe, there is currently no equivalent to CAFE nor the gas guzzler tax. Instead, individual nations impose varying tax rates on initial vehicle registration (over 100% in Denmark) plus high taxes on fuel. The auto industry tried to head off binding legislation via a voluntary commitment to cut CO2 emissions by 25% between MY1995 and MY2008 but German manufacturers in particular are perceived as failing to meet their targets.

That is why, after months of acrimonious haggling, the EU Commission recently decided it will propose a new directive formally limiting fleet average emissions by LDVs to 130gCO2/km starting in MY2012, with an additional 10gCO2/km due to come from biofuels, tire pressure monitors etc. It is not yet clear how the average will be computed (by brand, by manufacturer, by country, across all sales in the EU ???) nor which test procedures will be applied (NEDC, CADC, with or without A/C ???), so the devil is still very much in the details. The proposal is not expected before the middle of 2008 and needs to be approved by both the EU parliament and the Council of Ministers (i.e. the national governments) before it can become EU law.


Very interesting project created a civil association "snowbird" from the Czech Republic at


Give the world to know what is reality and the truth about CO2 emissions, and diesel is certainly not the future of motoring.

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