New Small-Bore Methanol Genset

While LNG dual-fuel marine gensets of the L28/32DF and L23/30DF types have been on the market since 2014, the new methanol-ingesting option offers shipowners and designers more choice at the smallest-bore end of the medium-speed range.

Full scale trials with methanol fuel on a L21/31 test engine have been conducted at MAN Energy Solutions’ Frederikshavn premises in northern Denmark, where different combustion cycles were evaluated, and the company is aiming to introduce the L21/31DF-M to its engine programme within the coming weeks.

The current L21/31 heavy fuel oil (HFO) genset, now in its Mark 2 iteration, has accumulated more than 55m operating hours, with thousands of engines in service. The L21/31DF-M design utilises the same, well proven basic technology, with the extra provisions necessary to ensure safe and stable running on methanol for genset profiles. According to MAN, the incorporation of the port fuel injection (PFI) concept “provides simplicity and an attractive capital outlay and is based on proven components”.

The L21/31DF-M power range spans the 1,000-1,980kW mechanical power band, rendering suitability to most merchant vessels. Output is on a par with that of the present L21/31 Mk2 genset, available in 50Hz/1,000rpm and 60Hz/900rpm variants, in configurations from five to nine cylinders.

While its calorific value is about half that of marine distillates, the energy density of methanol is still comparable to other alternative fuels, and its liquid state facilitates storage and bunkering at ambient temperatures. As well as virtually eliminating SOx and particulate matter(PM) emissions, the combustion of methanol yields significantly reduced NOx, obviating the need for exhaust aftertreatment.

Moreover, the possibility to operate gensets on ‘green’ methanol as a drop-in fuel increases the fuel flexibility of the new engine and the potential of methanol as an option for genset power generation in large commercial ships.

The fuel gas supply arrangements for the L21/31DF-M compare well with that in other dual-fuel applications, as a cost-optimised, low-pressure system.