The key to cleaning up diesel nitrogen oxide emissions on modern engines is the addition of ammonia to the exhaust stream. The most common way of doing that right is the injection of a urea solution into the exhaust as used in the Mercedes-Benz developed BlueTec system. The only problem with that is that the urea supply must be replenished periodically, typically at about 15,000 mile intervals.
In order to help car-makers optimize the use of the urea to maximize service intervals and minimize emissions, Delphi has developed an exhaust ammonia sensor. The sensor will sit in the exhaust stream much like an oxygen sensor to directly measure the ammonia content. This signal can then be used by the power-train control to more precisely meter the injection rate. The Delphi press release is after the jump.
Delphi Launches World's First Ammonia Sensor
New technology allows closed loop control of SCR systems, reducing pollution and helping diesel operators save money
The world's first automotive ammonia sensor has been developed by Delphi Corporation (PINKSHEETS: DPHIQ).
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 optimised 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.
"Vehicle exhausts are now many times cleaner than even just a handful of years ago, but that is no reason for not striving for further gains," said Guy Hachey, president of Delphi Powertrain. "With the growth of diesel vehicles using intensive SCR, ammonia emissions are a potential problem that we want to help our customers address before it becomes an environmental issue."
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.
A vehicle's SCR system injects ammonia, in the form of liquid urea, into the exhaust stream ahead of the NOx reduction catalyst. The ammonia reacts with the gas, converting it into nitrogen and water. Unreacted ammonia, known as 'slip', is expelled with the exhaust gasses.
The use of SCR is expected to increase dramatically both in light-duty and heavy-duty applications. The technology is already well established in the European heavy duty truck market and will become increasingly important in the U.S. market to deliver compliance with new heavy-duty regulations to be mandated from 2010. SCR will also be used on passenger cars in the United States to help deliver compliance with Tier II Bin 5 regulations for light-duty vehicles and is expected to increase in popularity in Europe to help meet Euro VI regulations to be mandated from 2014.
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," said Ivan Samalot, chief engineer for exhaust sensors at Delphi's technical center in Brighton, Mich. (USA). "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."
Delphi's solution is to combine expertise in oxygen sensors with its materials expertise to develop a new type of ammonia sensor that is ideal 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 popular 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. As well as significantly reducing ammonia slip, this can create financial savings for high-mileage operators who will use significantly less urea. It also allows vehicle manufacturers to eliminate an expensive postoxidation 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.
The Ammonia Sensor is one of Delphi's many innovative engine management, fuel injection, valve control and aftertreatment solutions. Covering diesel, gasoline and biofuels, Delphi's technologies provide simple, reliable solutions to complex challenges, helping its customers develop vehicles that offer outstanding performance, refinement and emissions at an affordable price. 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.