|The different elements of systems optimization. The blue shaded elements are assigned to fuel injection equipment providers such as Siemens VDO. Click to enlarge. Source: Siemens VDO|
At the 28th International Vienna Motor Symposium this week, Siemens VDO discussed its work in developing a system-based approach to combustion optimization and exhaust-gas aftertreatment.
This approach will enable diesel engines in all vehicle classes to meet the more stringent Euro 6 standards, which will go into effect in 2014, without sacrificing their fuel economy advantages over gasoline engines and without high cost overruns, according to the company.
Meeting the tougher Euro-6 emissions requirements, especially the proposed NOx limit of 0.08 g/km, will require a coordinated “engine-emission management” concept in which different modules are interchangeable. Interlinked control of injection rail pressure, boost pressure and EGR control with temperature management, as well as De-NOx control will be mandatory, Siemens notes.
The Euro 6 emissions standards will an 80% reduction in PM emissions and a 70% reduction in NOx emissions from the current Euro-4 levels. (The resulting NOx limit is still higher than that permitted by the current US Tier 2 Bin 5 limits). Combined with the emissions restrictions is the need to meet European CO2 limits, targeted to come into effect shortly before Euro 6.
It will not be possible to achieve the ACEA-CO2 targets without a high share of Diesels in the passenger car fleet. These targets require for the EU6 introduction a reduction of the CO2 output of roughly 35% with reference to the year 2005. The average level 2006 in Europe was approximately 170 g/km. This challenge can only be solved by a combined optimisation of combustion process, air supply, fuel injection system and exhaust gas after-treatment.
|Click to enlarge.|
One key approach for reducing engine-out emissions of both PM and NOx is development of advanced combustion regimes that require a more uniform distribution of fuel and air in the combustion chamber, and with the combustion temperature controlled to avoid the characteristic areas of NOx and soot formation. (Chart at right.)
Siemens wants to optimize the combustion without falling into the range of HCCI combustion, which at present, “will be suitable only for the lower and intermediate load range. Therefore, [these alternative combustion processes] have to be combined with conventional processes, which compel compromises in drivability during the transition.”
Siemens VDO instead is shooting for optimization of the classic combustion process, with increased EGR rates, better injections management and higher degrees of charging in the emissions relevant areas of engine operation.
Siemens VDO developed an experimental program with the aim of lowering the engine-out emissions as far as possible, in order to minimize the use of expensive measures of exhaust gas aftertreatment.
|Siemens VDO Experimental Configuration|
|Engine||2.0-liter-4V-EU4-engine, combustion chamber shallower and wider, swirl app. 75% of an EU4 application, compression ratio 16:1|
|Injection system||PCR2, multiple injection, 8-hole nozzle with a cd of 78% and hydraulic flow reduced by 13% with reference to the EU4 application, adjusted rail pressure|
|Air and EGR||Improved EGR cooler, optimised EGR valve, smaller turbo charger|
Results were first measured on a stationary test bed and then in emissions test on a concept vehicle.
|Potential of engine-out NOx reduction. Click to enlarge.|
Siemens VDO found that for a 1,590 kg class vehicle, it was just about possible to reach the Euro-6 NOx limit without aftertreatment. The optimized combustion process and adjusted multiple injection contributed 38% to the NOx reduction. Improved charging contributed another 14% reduction, and increased cooling of the EGR gas contributed another 7% in the study.
A heavier vehicle of 1,800kg mass exceeded the limit by 15%. Even higher weight vehicles will require NOx aftertreatment.
A company-internal cost estimate showed, that the optimisation of the engine periphery alone (TC, EGR components, exhaust gas after-treatment and injection system) can lead to a cost increase of more than the double compared with the EU4 injection system.
Siemens VDO is working on an electronic engine management system that is flexible and open enough to manage all the conceivable combinations of these individual modules—including additional aftertreatment systems—either within a single construction series or on one platform.
With an eye to future generations of engines with increasingly homogeneous combustion, Siemens VDO is also working on more sensitive sensors, with which combustion within the respective cycle can be analyzed, enabling more precise actuators to be immediately influenced.
“Diesel Engine for Passenger Car and EU 6: Entire System Approach for Development of Fuel Injection System, Air/EGR Path and Emission Aftertreatment”; S.Bauer, Dr.rer.nat.H.Zhang, Dr.-Ing.A.Pfeifer, Dr.-Ing.K.Wenzlawski, Siemens AG/Siemens VDO Automotive, Regensburg