German specialist rolls-out new generation of turbochargers

David Tinsley writes: Through a further development programme, it is also addressing the challenge of meeting future demands for charging systems on engines that will have to comply with IMO Type III emissions criteria.

KBB’s ST range of turbochargers reach pressure ratios up to 5.5, with high efficiency factors of 63%-70% for the various models. The ST generation is based on the company’s preceding HPR series, and is suited to diesel, heavy fuel oil and gas engines. The new ST27 family will offer two more sizes than the 2001-launched HPR type, and will cater to the output spectrum from 300 to 4,800kW. By comparison, the HPR models cover an output range from 500 to 3,000kW, with a maximum pressure ratio of 5.0, and overall efficiencies of 63-68%

KBB began serial production in 2010 of four of the ST27 frame sizes, the ST3, ST4, ST5, and ST6 models, suited to engine outputs in the 500-3,400kW range. The outline dimensions correspond to those of the respective HPR3000, HPR4000, HPR5000 and HPR6000 types, but with higher pressures and ratings. The nascent ST2 is intended for smaller volume flow rates and engines of 300-750kW, while the ST7, which has been readied for engine tests, offers higher air flow rates and applicability to an engine output band from 2,500kW up to 4,800kW.

The ST design series has been the subject of extensive qualification and field tests, including the use of an innovative CAE (computer-aided engineering) simulation concept in combination with hardware tests to demonstrate containment safety. Endurance trials entailed a 500-hour continuous test rig operation with an ST4 turbocharger on a Wärtsilä 6L20 laboratory engine of 1,200kW, and a field test using an ST5 unit on an 8L20 engine of 1,400kW aboard a Viking Line ro-ro ferry, spanning 4,400 running hours.

Several hundred of the ST3, ST4, ST5 and ST6 systems have already been delivered to customers. The ST7 model underwent its first function and performance trials during 2011 on the newly-built test rig for large turbochargers at the company’s test centre in Bannewitz.

Key aspects of the ST27 series are the improved compressor design and turbine performance. The higher pressure ratio connected with increased load prompted particular attention to bearing design and containment safety.

Essential features of the development include the following:

• Unchanged outline dimensions of the ST3-ST6 models in relation to the preceding HPR series;
• Compressor incorporating recirculation for map width enhancement;
• Cooling of highly-stressed compressor wheels;
• Boreless compressor impeller;
• Long service-life bearing;
• Non-cooled housing(with the option of water-cooled bearing housing for gas engines);
• Jet-assist option on the compressor side.

KBB is also addressing the next big developmental challenge for turbocharger makers, namely the provision of turbocharging technology for IMO III-compliant diesel engines and gas engines with overall pressure ratios of 6 to 10. Attainment of such levels will only be feasible with two-stage turbocharging. KBB has accordingly initiated the development of a low-pressure and a high-pressure turbocharger series. Prototypes of the two series are scheduled to be available in 2012 for evaluation on burner test rigs as well on engine test stands.

Another field of investigations is high-pressure exhaust gas recirculation, which requires special turbochargers for exhaust gas compression. Increasing importance is attached to simulation techniques so as to achieve optimum adaptation of very complex, future turbocharging systems to the engines.

KBB turbochargers are principally used in marine, stationary power and locomotive applications. Since 1999, KBB has been a member of the Luxembourg-based Ogepar Group, whose various interests also include the medium-speed engine manufacturer Anglo Belgian Corporation (ABC). In addition to ABC, clients include Wartsila, MaK (Caterpillar), Hyundai Heavy Industries’ Engine & Machinery Division, GE, Cummins and Yanmar.