|The Nissan SULEV diesel features MK combustion and a new HC-NOx trap.|
Nissan Motor is developing an advanced diesel powertrain that includes a new HC-NOx trap for emissions control that may be able to meet California’s standard for super-ultra-low emission vehicles (SULEVs). Nissan plans to do further research and development of the clean diesel technology for commercial application in its future products.
To meet the SULEV standards, hydrocarbons (NMOG) in vehicle emissions must be exhaust reduced by about 90% and NOx levels must be reduced by 70% versus US Tier2 Bin5 and California LEV standards.
|Emissions Standards, 120,000 miles/11 years|
|US Tier 2 Bin 5||0.090||4.2||0.07||0.01||0.018|
Nissan has already announced plans to introduce a 50-state, Tier 2 Bin 5 diesel engine in the United States for use in the Nissan Maxima in 2010. The passenger car will be powered by an all-new Alliance engine co-developed with its partner Renault. (Earlier post.)
The SULEV diesel uses three main components to achieve its emissions status: a modulated-kinetic (MK) combustion regime to reduce engine-out NOx and PM, high-performance catalysts in the new trap technology, and advanced engine control systems to deliver more precise control of oxygen in the exhaust for better fuel efficiency and lower emissions.
MK combustion, developed by Nissan, is one of several new low-temperature, non-sooting combustion regimes being explored to reduce emissions from diesel engines while maintaining their high efficiency.
An analysis of MK combustion by Lawrence Livermore National Laboratory notes that:
MK is achieved by increasing EGR to a relatively high value (~30%) while at the same time delaying fuel injection (from ~7° BTDC for regular diesel combustion to ~3° ATDC for MK) and increasing the swirl ratio (from ~3 to ~5). These operating conditions increase the ignition delay, allowing the injection process to be concluded before ignition occurs. At these conditions, significant air-fuel mixing occurs before combustion, resulting in nearly homogeneous combustion that produces low soot and low NOx. As in the case of SRDC [Smokeless Rich Diesel Combustion, developed by Toyota], MK is limited to low power conditions due to the need for a short injection process that can be concluded before ignition occurs.
Nissan’s Hydrocarbon-Oxides of Nitrogen (HC-NOx) trap catalyst technology incorporates a HC-trap layer in the NOx-trap catalyst. The HC-trap layer traps the HC which is oxidized to generate hydrogen (H2) and carbon monoxide (CO), which in turn react with the NOx gases trapped by the NOx-trap layer to produce nitrogen (N2) and carbon dioxide (CO2) gases, in addition to water vapor (H2O) as end products. The chemical reactions effectively reduce HC and NOx resulting in cleaner tail-pipe emissions.
|Structure of the HC-NOx-trap catalyst and emission control system. Click to enlarge.|
With this new HC-NOx trap catalyst technology, Nissan believes it will be able to achieve cleaner diesel emissions in future vehicles that will meet the stringent SULEV-standards set by the state of California.
Under the Nissan Green Program 2010, Nissan has announced plans to expand clean diesels to surpass current emission standards.
Nissan also announced that it will launch a new clean diesel engine for use in the X-TRAIL sport-utility-vehicle in Japan in the fall of 2008.