Dual-fuel MaK engine hosts advance in control technology
David Tinsley looks at the MaK dual fuel engine range, the first of which has now been shipped by the Caterpillar corporation for installation in a newbuild cruise vessel.
The recent shipment of the first production example of Caterpillar’s MaK M46DF design underscored the comparatively short timeframe within which the development of the powerful new medium-speed, dual-fuel engine has been accomplished. The 12-cylinder vee-form model for AIDA Cruises’ initial newbuild at Mitsubishi’s Nagasaki yard signalled the start of deliveries to customers from Caterpillar Motoren’s Rostock factory, where an in-line six-cylinder M46DF test engine has provided a working platform for the technicians.
The 460mm-bore type offers a power rating of 900kW per cylinder at a brake mean effective pressure (BMEP) of 21.3 bar in either diesel or gas mode. So as to reach the high efficiency targets while maintaining sufficient safety margins for varying gas qualities, it was decided to equip the engine with pressure sensors in every cylinder and to integrate the data into the engine control strategy.
At this year’s CIMAC Congress in Shanghai, a presentation, entitled Caterpillar M46DF engine with new cylinder pressure based control strategies by Caterpillar Motoren’s Bert Ritscher and AVAT Automation’s Martin Greve provided insights into the advanced control arrangements. “While other known cylinder pressure based control strategies focus on Pmax (maximum combustion pressure) only, the new M46DF engine uses further characteristics like start, centre and duration of combustion for monitoring, balancing and NOx control,” they explained.
Because time to market was regarded from the outset as critical to the success of the project, Caterpillar decided to build a partnership with an experienced supplier in the field of cylinder pressure sensing and processing technology. German specialist AVAT Automation, with which Caterpillar has an established business link through the GCM34 and other engines, was selected to design and develop the Caterpillar in-cylinder pressure module (ICPM).
While striving for maximum control performance, the overarching objective has been to achieve the highest engine availability. In addition, and notwithstanding the sophistication of the technology, the designers have sought to reduce system complexity. Sensor power supply, sensor signal processing and monitoring, as well as on-line calculation of combustion characteristics and knock levels are encapsulated within the ICPM, whereas mixture control, knock control interaction and balancing are realised entirely in the electronic control module (ECM).
“Having this on-line cylinder pressure data available in a new control system, it is obvious that one developmental objective was to improve cylinder equalisation in gas operation mode,” reported Caterpillar Motoren and AVAT. “In any reciprocating combustion engine, the individual cylinders vary with respect to tolerances, wear levels, boost pressures, gas rail pressures or other parameters. Consequently, the cylinders show differences in combustion, efficiency and knock margin.”
Lending itself to future upgrades, the cylinder pressure based control system is said to offer many functionalities and customer benefits, including condition-based maintenance capabilities. Trend analysis drawn from cylinder pressure data will provide indications as to cylinder head and combustion chamber condition and wear.
The control system is to be replicated on other engine platforms, including a further new Caterpillar dual-fuel design, the nascent MaK M34DF.
In gas mode, the M46DF will meet future IMO Tier III limits on NOx emissions, as well as future US EPA Tier 4 regulations. Designed for both electric drive propulsion systems and mechanical drive systems, the M46DF will share the same footprint and the same system interfaces as the present MaK M43C medium-speed diesel engine, a feature that will facilitate retrofitting of current M43C engine installations. The debut delivery will be one of four MaK medium-speed engines powering the first of AIDA’s two 124,000gt cruiseship newbuilds in Japan. The vessel’s three other main engines will be 12M43C diesels.
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