© Daimler Truck AG

Reli­able fans for the long term

It usually takes some time before the main­te­nance lamp flashes in the natural gas bus. But there is room for improve­ment! Another inte­grated axial compact fan from ebm-papst is helping to reduce main­te­nance costs even further.

When the Citaro NGT bus from commer­cial vehicle manu­fac­turer EvoBus GmbH passes by, drives chil­dren to school, takes parents to work, or brings grand­par­ents to the shops, it not only emits less CO₂ than a diesel bus, but also keeps costs low for trans­port compa­nies with gas-powered fleets. Its main advan­tage? Low gas consump­tion with seam­less perfor­mance.

The struc­ture on the roof is what distin­guishes it visu­ally to other buses: this is not just its most distinc­tive feature, but also contains the ingre­dient for its sustain­able mobility concept. It conceals tanks made from a stable composite mate­rial, in which the fuel required to power its petrol engine is stored: the compressed – yet still gaseous – methane, on which the bus runs to get from A to B.

From the roof to the engine bay

It goes without saying that its alter­na­tive drive also mani­fests itself in the engine bay: right at the heart of this eco-friendly bus is a petrol engine, modeled on a diesel engine. The natural gas engine burns fuel in a clean manner yet still achieves a high output. To comply with the low exhaust gas emis­sions values, two lambda probes are installed in the flow of the exhaust gas of the pre-cata­lyst.

They deter­mine the residual oxygen content in the exhaust gas, thereby providing the signal for contin­u­ously perfect control of the combus­tion air ratio for reduced pollu­tant emis­sions. However, in this func­tion in a natural gas bus, they can heat up quite consid­er­ably. This is because petrol-engine combus­tion reaches higher temper­a­tures than in a diesel engine. So ideally they need to be kept cool – for as long as possible.

For the lambda sensors of the natural gas bus, it is impor­tant to keep a cool head – and for as long as possible. An addi­tional axial fan from ebm-papst now reli­ably cools the lambda sensors so that they can continue to do their job for a long time. (Photo: Daimler Truck AG)

Next stop: auxil­iary fan

So how do you increase the longevity of these exhaust gas probes? By providing them with addi­tional cooling. What was needed was a small auxil­iary fan that cools the lambda probes locally. It was decided that the perfect device for this task was an axial compact fan from ebm-papst. The fan had to be compact, and generate a high enough air flow and speed that provided the exhaust gas sensors with suffi­cient cooling.

A sepa­rate solu­tion had to be found for the elec­trical actu­a­tion process, as the existing control unit was not ideal for this. It was a tricky task that required a careful approach with multiple devel­op­ment loops. It took just under a year of testing before all the para­me­ters were correct.

“We now have a model that enables ambient temper­a­ture-depen­dent control and thus achieves a consis­tent effect all year round – whether at 40 degrees in summer or at low temper­a­tures in winter.”

Oliver Baier, Busi­ness Devel­op­ment Manager at ebm-papst

A small device with a big impact

And they couldn’t be more correct: “Thanks to the elec­trical connec­tion, we now have a model that enables ambient temper­a­ture-depen­dent control and thus achieves a consis­tent effect all year round – whether at 40 degrees in summer or at low temper­a­tures in winter,” says Oliver Baier, Busi­ness Devel­op­ment Manager at ebm-papst. “The ambient temper­a­ture is used to deter­mine how fast the fan has to rotate so that the air flow is suffi­cient to cool the lambda probes.”

The auxil­iary fan is now installed as stan­dard on the side flap of the engine bay to the rear, where it draws in the ambient air through slits and blows it directly at the exhaust pipe on the catalytic converter. The reli­able cooling effect on the lambda probes will enables them to perform their task for a long, long time. And when it comes to noise, the fan is also bound to impress: at around 60 dB (A), it is another low-noise compo­nent of the natural gas bus. In conclu­sion, the green heart of this eco-friendly bus, with its high number of strokes and cooler temper­a­tures, will be able to beat for a good while longer and save consid­er­able costs.


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Axial compact fans

High air performance with medium pressure increase