Landmark achievements for turbocharger

12 Apr 2011
ABB Turbocharging’s A190-L turbocharger for 2-stroke low speed engines

ABB Turbocharging’s A190-L turbocharger for two-stroke low speed engines

ABB Turbocharging has reported two milestones with its A100 turbocharger family, concerning the high pressure ratio efficiency and the ability to operate at dual ratings without modification.

The company reports that in final testing of the A190-L turbocharger for low speed two-stroke diesels, technicians measured its peak efficiency at 75.8%. “The 75.8% figure is all the more impressive because it was measured on a turbocharger featuring a higher pressure ratio than the model that achieved the previous record figure,” says Urs Gribi, vice president of engineering.  

Secondly, ABB Turbocharging’s application engineers have devised a new A100-L turbocharger configuration for low speed engines which facilitates rapid conversion from a higher power output matched to a ship’s normal cruising speed to a lower rating matched to a slower fuel saving speed – i.e. ‘slow steaming’. The concept is devised to meet the ‘dual rating’ engine specifications of a series of 10 container ship newbuildings contracted by major Singapore-based container ship operator NOL. It takes advantage of the very wide compressor maps of the A100-turbocharger to achieve this aim by varying the number of turbochargers in the engines’ exhaust gas stream rather than by fitting new turbochargers, modifying the internal components of existing turbochargers or varying the turbine geometry to alter turbocharger air delivery characteristics.

In detail, the ABB system adopted for the new container ships is designed to allow the 12-cylinder 98 cm bore engine to achieve ratings of  just over 72 MW at 104 rpm or just over 54 MW x 97 rpm. The solution comprises four A190-L turbochargers, one of which can be cut-off from the exhaust gas stream. This is achieved either via a motorised valve or a simple blanking plate. In spite of the reduced level of energy in the engine exhaust gases due to the lower engine power rating, the A190-L’s compressor maps are said to be sufficiently wide to allow the three turbochargers still in the exhaust gas flow to efficiently produce charge air at the pressures and volumes needed for the lower engine slow steaming rating.

“Substantially modifying the compressor map of a turbocharger can involve the exchange of many of its internal components,” notes ABB’s head of global turbocharger sales for the low speed engine segment, Arie Smits. “In the extreme case this can mean the turbine and compressor wheels as well as the nozzle ring and diffusers. In any event, the turbocharger has to be opened, dismantled and reassembled. But with the A100-L’s excellent compressor maps it was possible to achieve dual ratings with optimized fuel consumption by, essentially, only reducing the number of the turbochargers providing combustion air to the engines.”

According to ABB, In the early days of the recent economic downturn ships reduced speeds to save fuel by simply readjusting engine settings. This did, indeed, reduce consumption but the engines’ systems, including their air management, were no longer optimised to the new output levels. There was thus the potential to save even more fuel by, among other measures, closely adapting the turbocharging system to the engine’s new operating profile. Demand has hence grown for ‘dual rated’ engines, having systems which can be optimised to give a higher power rating for standard cruising speeds and a reduced output for slow steaming in a minimum of time and at minimum expense.  

The company explains compressor mapping as an important measure of turbocharger performance, which, together with efficiency and pressure ratio, incorporates the aforementioned values to, essentially, reflect how effectively and flexibly energy in the engine exhaust gases driving the turbine can be converted into compressed air on the compressor side.

The A100 turbochargers are claimed to combine very wide compressor maps while offering high pressure ratios of 4.7 and above in the A100-L versions for low speed two stroke engines and 5.8 in the A100-M and A100-H versions for medium and high speed engines.

Since its market launch, several hundred A100 turbochargers have been sold and, according to ABB, have proved successful in minimising fuel consumption on diesel engines designed to comply with IMO Tier II limits on NOx emissions. This second stage of marine emissions legislation has been in effect since January 2011 and specifies a 20% reduction in NOx emissions from marine engines vis-à-vis IMO Tier I.

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