The latest turbocharger designs are achieving increased air flow volumes while maintaining the same standards of maintenance and reliability
Turbochargers significantly affect engine performance and help in meeting stricter greenhouse gas (GHG) and CO2 emissions.
MET turbochargers from Mitsubishi Heavy Industries Marine Machinery & Equipment Co (MHI-MME) are the exhaust gas turbine type, which is one of the global standards for turbochargers intended for marine diesel engines. Axial turbocharger models are mainly used with large two-stroke engines and radial turbocharger models are used with four-stroke engines.
MHI-MME has developed the MET-MBII series of axial turbochargers and the MET-ER series of radial turbochargers, notable for their environmental performance and compact size.
In March, MHI-MME secured its first order for its MET33MBII turbochargers for 12PC2.6B JFE SEMT-Pielstick medium-speed diesel engines manufactured by JFE Engineering Corporation.
The turbochargers will be part of the propulsion package for two newbuild roll-on roll-off passenger (ropax) vessels for Miyazaki Car Ferry Co, being built by Japanese shipbuilder Naikai Zosen Corporation. The ferries are also scheduled to be equipped with MHI-MME fin stabilisers.
MHI said the first ropax vessel will be delivered in October 2020, followed by the second in February 2021.
The company’s MET-MBII series is a new type of axial turbocharger for achieving an increase in air flow volume while maintaining the same standard of maintenance and reliability as MHI’s MET-MB turbocharger. A new compressor wheel with the optimum number of blades and blade angle distribution was developed for the MET-MBII series, aiming to increase capacity while maintaining high performance. The turbine blade throat distribution was also optimised to develop a new turbine with higher exhaust gas pressure recovery performance in the gas outlet casing.
Meanwhile, the casing, a component excluding the silencer, is the same as that used in the conventional MET-MB series. MHI said the MET-MBII turbocharger provides 16% larger air flow volume compared to the older series.
In 2018, MHI-MME began developing new models of small, lightweight and high-efficiency turbochargers with the aim of completing the first such turbocharger in 2020.
Until the end of 2019, Mitsubishi Hitachi Power Systems manufactured the turbochargers on MHI-MME’s behalf at the Saiwaimachi Factory. Opened in 1943, MHI’s Saiwaimachi Factory became a dedicated manufacturing facility for MET Turbochargers in 2003. A total of 35,378 turbochargers were manufactured at the Saiwaimachi Factory from 1965 to 2019.
In January 2020, MHI-MME took over production of MET turbochargers, relocating manufacturing from Saiwaimachi to Akunouramachi – both in Nagasaki, Japan.
Combining with largest X-DF engines
MHI’s turbochargers have been chosen for the world’s largest two-stroke, Otto-cycle dual-fuel engine model, 12X92DF, from Winterthur Gas & Diesel Ltd (WinGD).
Constructed at Chinese state-owned CSSC-MES Diesel Co, Ltd (CMD) in Lingang, Shanghai, each 12X92DF engine takes 25,000 manhours to build, weighs more than 2,100 tonnes and contains parts from more than 15 countries. The 12X92DF is rated at 63,840 kW at 80 rpm.
Each of the nine engines will be mounted into nine 23,000-teu, LNG-fuelled container vessels for France’s CMA CGM under construction at a China State Shipbuilding Corporation (CSSC) shipyard. CMA CGM Jacques Saade underwent sea trials in March.
The key driver for development of the 12X92DF was the use of a cleaner fuel – in this case LNG – combined with a so-called lean-burning combustion cycle, allowing for better control of emissions such as NOx, SOx and particulate matter.
The engine’s development formed the focus of a paper presented at the 2019 CIMAC Congress, held in Vancouver in June. The paper, presented by WinGD’s vice president of R&D Dominik Shneiter, outlined how experience in the mid bore-range was upscaled and adapted in development of the X92DF, enumerating each of the challenges and the solutions in its development.
Among those challenges was the size of the engine, making prototyping and the conversion of existing field engines not feasible. WinGD took a conservative approach to scaling up its components and simulation modelling. Several new features, such as a new bearing girder, a new gas pressure regulating unit (iGPR) and improved pilot pre-chamber, were introduced.
Development of a new control system was undertaken concurrently with the 12X92DF project, enabling better control of engine loads and conditions based on idealised combustion models running in parallel directly on the control models. This enabled better optimisation of subsystem integration for any electrical load or producer, the paper says.
Based on the experience with the smaller bore X-DF engines, a new turbocharger matching strategy for pre-mixed lean burning engines was established together with the major turbocharger manufacturers. The target was to reach the highest possible turbocharger overall efficiency at high loads. This is a departure from the characteristics of turbochargers previously applied on two-stroke slow-speed engines.
“Combining the turbocharger with the engine achieves a uniform, lean mix of gas and air for combustion”
For typical diesel engines, an accurate adjustment of the scavenge pressure by an accurate turbocharger matching with an evaluated pressure curve at part load is normal, while with X-DF engines, a larger variation of scavenge pressure is tolerated, but high efficiency at highest engine loads is desired. The scavenge pressure on an X-DF engine is fine-tuned by an exhaust waste gate that by-passes exhaust gas around the turbine as part of the performance control concept. With this system, lambda of the combustion can precisely be adjusted according to current operation and ambient conditions.
This is not the first time MET turbochargers have been mounted on WinGD’s X-DF engines. Combining the turbocharger with the engine achieves a uniform, lean mix of gas and air for combustion, and the system’s capability to utilise exhaust gas allows for cleaner emissions and greater efficiency.
The system helps vessels to comply with IMO’s NOx and SOx emissions regulations while also reducing CO2 emissions, as compared with diesel fuel, with a dual-fuel setup.
NOx Tier III standards, which require an 80% reduction in NOx emissions from Tier I standards, have been in effect since 2016 and are enforceable in emission control areas (ECAs). In the near future, the areas covered under these standards are set to expand.
MHI-MME says that combining MET turbochargers with X-DF engines will help shipowners meet the new standards that came into force under the IMO 0.50% sulphur cap as of 1 January 2020.
Besides pushing the development of its turbochargers to meet today’s stricter environmental emissions standards, MHI-MME is also implementing new augmented reality technology in support of training turbocharger repair and maintenance personnel. MHI-MME has begun using the HoloLens 2, a mixed reality device from Microsoft, in maintenance training for the MET turbocharger. The HoloLens 2 smartglassesʼs wide field of vision and high-resolution graphics allow 3D objects to be manipulated and enable a near-real maintenance work experience.