Continental showcases “Super Clean Electrified” connected, optimized 48V mild hybrid diesel; post-Eu6d
At the 38th International Vienna Motor Symposium this week, Continental is showcasing a 48-volt hybrid diesel vehicle which meets very stringent RDE (real driving emissions) limits on CO2 and NOx. The Continental Super-Clean Electrified Diesel combines electrification-based engine optimization and an electrically heated catalyst integrated in the exhaust aftertreatment system to achieve a 60% reduction in real-world NONOxx emissions and a simultaneous 2% reduction in CO2 emissions measured against the baseline Euro 6b vehicle.
The first 48-volt diesel hybrid has already gone into production in Europe, and a second production launch is already in the pipeline for 2017.
The Continental engineers implemented the clean diesel in several stages. They began by replacing the standard injection system with Continental’s PCRs5 piezo common rail injection system. This operates with maximum injection pressures of 2,500 bar. With the help of highly dynamic valve timing it is possible to perform multiple, very closely spaced and very precisely metered injections per cycle.
In this way a minute amount of fuel can be injected into the cylinder after the combustion event. This fuel is ignited only when it reaches the catalyst, thereby accelerating catalyst warm-up. This has important implications because the SCR catalyst has to reach a certain minimum operating temperature before it can begin converting nitrogen oxide emissions.
Tests show that this single measure—post-injection—can cut the SCR catalyst light-off time by around eight minutes, resulting in a reduction in cumulative nitrogen oxide emissions under the future WLTP (Worldwide harmonized Light-duty Test Procedure) driving cycle of 37%.
However, using only post-injection would increase fuel consumption by around 4%. Enter the 48-volt hybrid system based on a belt-driven starter-alternator. The electric motor, with a rated output of around 15 kW, not only allows braking energy to be recuperated and stored as electricity in a small lithium-ion battery but can also assist the internal combustion engine during short, sharp bursts of acceleration.
|48 volt electric machine with integrated inverter. Click to enlarge.|
This reduces the peaks in nitrogen oxide emissions under very sudden, heavy throttle application. By cutting the relative proportion of accelerating power that has to be supplied by the combustion engine—“phlegmatization”—the 48-volt system can reduce NOx by a further 3% over and above the reduction achieved by post-injection. At the same time CO2 emissions are cut back by an additional 3% approximately.
A further reduction in emissions is achieved by the use of a close-coupled electrically heated catalyst (EMICAT). Irrespective of the engine operating strategy,the heated catalyst, with a transient power rating of 3 kW, quickly brings the downstream-mounted SCR catalyst up to operating temperature, allowing it to start converting nitrogen oxides.
|A fuel saving electric heatable catalytic converter on 48V basis. Click to enlarge.|
The aqueous urea solution (AdBlue) used for SCR catalysis is injected into the exhaust stream immediately downstream of the heated catalyst. This arrangement guarantees good mixing of the exhaust gas and the urea, so that it is not necessary to fit a separate mixer. The heated catalyst reduces nitrogen oxide emissions by a further 14%. Fuel consumption is unaffected, since the electrical energy used for heating purposes is supplied entirely from braking energy recuperated by the 48-volt system.
An additional significant reduction in emissions is achieved with the help of connected Energy Management (cEM). The Super Clean Electrified Diesel presented in Vienna uses a cEM Traffic Light Assist (TLA) function to achieve a further reduction of nitrogen oxide emissions as well as a reduction in fuel consumption. The TLA predicts when the next traffic light—which may not yet actually be visible to the driver—will be on red and can then use this additional information to improve coasting, recuperation and braking management.
The beauty of ‘connected Energy Management’ is that we can implement a more energy-efficient driving strategy simply by using an improved database. When the cEM control unit is aware of the upcoming route (thanks to the navigation system or learning algorithms), it can decide in advance when the vehicle should coast and when it is best for it to recuperate braking energy, thereby saving fuel and emissions.—Dr. Oliver Maiwald, Head of Technology & Innovation with Continental’s Powertrain Division
In total, the measures featured on the test vehicle presented in the lecture in Vienna deliver a very significant 60% reduction in NOx, while at the same time achieving slight 2% drop in fuel consumption compared to a Euro 6 Diesel standard car.
In other words we have resolved a classic conflict of objectives in diesel engine development, showing that a clean diesel engine with emissions well within the legal limits doesn’t have to consume more fuel.—José Avila, President of the Powertrain Division and Member of the Executive Board of Continental
Auerbach, M., Ruf, M., Bargende, M., Reuss, H. et al. (2011) “Potentials of Phlegmatization in Diesel Hybrid Electric Vehicles,” SAE Technical Paper 2011-37-0018 doi: 10.4271/2011-37-0018