Cummins AdBlue dual-dosing system now on offer to OEMs

By Categories: NewsPublished On: Thursday 25 March 2021

Engine and exhaust aftertreatment manufacturer Cummins is to offer its innovative urea dual-dosing system to other OEMs after initial success in the latest iteration of the Scania V8 engine (pictured).

Matt Henry, technical lead at Cummins Emission Solutions, explains that the system features a single pump feeding AdBlue to two separate nozzles, which can be placed at different locations in the vehicle’s exhaust system. This allows engine designers to address issues of poor AdBlue to ammonia conversion rates at lower exhaust temperatures, and reduce NOx outputs and AdBlue crystallisation at low engine loads and ambient temperatures.

“On the Scania, we used the first nozzle to dose the exhaust upstream of the particulate filter,” he recounts.

“It’s neither necessary nor desirable to remove all the NOx from the exhaust at this stage because a NOx-rich gas mix helps to clean the PM filter. The first nozzle’s location, just downstream of the turbocharger and exhaust throttle, is a high-temperature, high-vibration environment so it does present certain challenges, but the advantages in emissions control more than balance the effort that were made to overcome them.

“The second dosing unit is in a conventional position on the exhaust aftertreatment box itself.”

Scania was able to use the improved aftertreatment to delete the exhaust gas recirculation system previously fitted to its top power model, contributing to a weight saving of 70 kg and increasing its output from 730 to 770 hp while making fuel savings of two per cent.

“With a conventional layout, the SCR cat can struggle to get hot enough to remove sufficient NOx: it’s too far away from the engine,” Mr Henry points out.

“The traditional solution is ‘thermal management’, which actually involves burning fuel for no purpose other than to heat the exhaust up.”

Operators of some vehicles will sometimes encounter issues with urea crystals forming and blocking the system. This is particularly prevalent in engines operating in low-load and high-idling situations when ambient temperatures fall, although Mr Henry maintains that the very fine droplet size produced by Cummins dosing units means they are less prone to this problem.

Nonetheless, crystallisation can occur in some engine exhausts if surface temperatures fall below 200°C, and maximum NOx conversion rates are only achieved at temperatures above about 250°C.

Some engines have an additional diesel injector in the exhaust manifold to maintain temperatures, while others use an additional injection event in the combustion chamber, which takes place after the exhaust valve opens. Volvo uses a novel system by which uncooled exhaust gas is recirculated back into the combustion chamber to speed warm-up.

The Cummins system allows an additional SCR catalyst to be added upstream of the PM filter where temperatures get hotter quicker as a fuel-saving alternative.

“A second, conventionally-sited, catalyst completes the removal of the NOx,” Mr Henry confirms.

Cummins sees the system coming into its own with the arrival of Euro VII emissions limits for heavy-duty diesel. Mr Henry says that while both the date and the limits are still being negotiated between the vehicle manufacturer’s representative body ACEA and the EU member states, it is understood that the final regulation will further curtail already low NOx limits while, for the first time, measuring CO2 outputs. Measurement cycles will move closer to ‘real world’ conditions.

The Cummins dual-dose system addresses both these challenges simultaneously by improving NOx conversion at otherwise problematic low temperatures, and reducing or removing the wasteful combustion of fuel and consequent emissions for the purpose of maintaining exhaust temperature.

It will also come increasingly into play as engine manufacturers seek to reduce the energy wasted as heat ejected through the exhaust.

Understandably tight-lipped on specifics, Cummins confirms that it is now working with a number of other OEMs on the introduction of new exhaust technologies, although it has yet to specify the units on its own engines.