Making diesel-electric hybrids ultra-green


With ASDS installed on a hybrid vehicle, instant NOx reduction is guaranteed when switching from electric to diesel mode. Adding ASDS to a hybrid vehicle will make for an ultra-green solution

Imagine yourself in a hybrid bus travelling on the M4 from the outskirts to central London. On the highway, the diesel engine takes care of the propulsion, but after the first red light, the battery-driven electric motor kicks in.

For the next couple of kilometers, the bus runs in electric mode with the diesel engine turned off, effectively acting as a zero-emissions vehicle. Then the electric driving comes to an end. The diesel engine is powered back on, and the battery is recharged. This cycle of switching between all-electric and diesel mode then continues all the way through central London

Read more Amminex chosen to clean London's toxic air

Hybrids are an effective solution for keeping both CO2 and NOx emissions low and make for a fast and cost-effective alternative to an all-electric powertrain, but until now the constant start/stop operation has had a drawback. Every time the diesel engine is turned on after a period of electric driving, traditional AdBlue emissions systems have a delay before becoming operational again, meaning NOx emissions will pass untreated through the exhaust for a period of time.

The independent consultancy Emissions Analytics has recently published a study confirming that cold starts affect NOx emissions from diesel engines considerably. One minute after turning the engine on, the NOx emissions were measured 32 percent higher than those of a warm engine.

“The thermal management of exhaust systems for engines where the exhaust frequently cools, such as with stop-start technology or hybridisation, is of growing importance in limiting NOx emissions,” the study concludes.

Instant-on ASDS solves the problem
The solution is called ASDS. The NOx-reducing technology from Amminex will kick in instantly when the diesel engine is turned on, delivering outstanding levels of NOx removal. Data collected from a Euro V hybrid bus in London reveals that the average NOx reduction rose from 32 to 85 percent in dense city traffic just by upgrading to ASDS. With a Euro VI catalyst, the NOx reduction will be more than 95 percent.

And according to Chief Technology Officer Tue Johannessen from Amminex, the data from the bus demonstrates a crucial point:

“During the typical eight minutes of electric driving, the temperature of the catalyst drops to 150 degrees. And it takes almost five minutes after switching the diesel engine back on, before the exhaust gas reaches the operating temperature needed by AdBlue-based solutions. ASDS, however, starts dosing ammonia to the catalyst the moment the engine is turned on,” he explains.

The immediate dosing is also proving valuable for vehicle manufacturers when developing new patterns for switching between hybrid vehicle engines.

“The instant performance of ASDS gives freedom to optimally use the hybrid powertrain without being limited by engine temperatures. This way, we can optimize CO2 and NOx reductions without sacrificing one for the other.”