CO2 remains the highest hurdle

Malcolm Latarche
Malcolm Latarche

09 February 2018


For over two decades, engine makers have been obliged to reduce emissions to meet MARPOL and other regulations, with no new emission targets on the horizon what will drive future development?

More ships have been built over the last 20 years or so than at any time in human history and that has been fortunate for engine designers and builders. The boom in shipbuilding created by burgeoning world trade and demand for specialist vessel types such as offshore and cruise ships has coincided with the introduction and imposition of increasingly stringent regulations on ship emissions.

It is easy to forget that until Tier I of the NOx Code applied in 1999, there had been no international regulation applying to ships exhaust at all and very little local regulation either. Since then there has been a gradual tightening up on both NOx and SOx emissions.

Tier III of the NOx rules apply to ships with a keel laying after January 2016 when operating in ECAs. Because of the time taken for building, that would have meant that the demand for Tier III compliant engines has only recently kicked in. Meeting the Tier I and II levels for NOx was relatively easy for engine makers but Tier III has been more difficult and the in-engine possibilities do need to be complemented by an exhaust treatment such as selective catalytic reduction on many ships. When it comes to the final deadline for SOx reduction, engine makers are off the hook because there is no in-engine means of reducing SOX so long as the fuel being used has any sulphur content at all.

That leaves only two other exhaust components to be considered; CO2 and particulate matter (PM). Both can be reduced by more effective combustion and PM can be further cut using exhaust gas treatment. Treatment need not be primarily for PM as SOx scrubbers and EGR systems will also reduce PM content.

CO2 reduction can come from making engines more efficient, but this is not the easiest thing to do. All of the low hanging fruit in regard to efficiency improvements for marine diesels were plucked long ago leaving only small incremental improvements still possible. Turbocharging developments are likely to be the most effective in the near future but beyond that engine makers will be hoping that R&D can provide now possibilities.

For engine makers, the volume of engines being sold in the boom years together with funding under research programmes such as HERCULES has so far allowed more research than may otherwise have been the case. However, future R&D budgets may be more restricted because of a fall in new orders for ships and because of budgetary restraints on governments and supra-national bodies.

Environmental lobby organisations and not a few influential organisations and individuals from within the industry itself are nevertheless pressing for more efficiency gains and switching to alternative fuels to reduce CO2 emissions. It is the latter that has the potential to produce quick results and engine makers have risen well to the challenge.

Dual-fuel competition

The number of dual-fuel engines and engines running on niche fuels such as methanol and ethane have risen at their fastest rate ever in 2017. While the number of owners that have been fully convinced of the merits of LNG is still quite small, several have taken a step towards and have ordered ships with dual-fuel engines but taken delivery of them with no LNG fuel storage system installed. Such ships will be able to meet any CO2 limitations imposed in future and will also be in a position to meet the 2020 SOx changes without adding a scrubber if the fuel mix available after 2020 is limited.

Aside from cruise ships and LNG carriers, most large vessels are powered by a single two-stroke engine built to MAN or WinGD designs. Both of these have dual-fuel versions of their main offerings available and each can claim a number of recent new orders.
MAN was first on the scene with dual-fuel two-strokes when it retrofitted the Nakilat LNG carrier Rasheeda in June 2015 but the real breakthrough came later that year when TOTE’s boxship Isla Bella became the first cargo vessel other than an LNG carrier to have a two-stroke dual-fuel engine.

Prior to that, all of the 200 or so gas-fuelled ships in operation had four-stroke engines. WinGD was not far behind when the chemical tanker Ternsund was handed over in June 2016. The contract for the engine was made by Wärtsilä prior to the transfer of business to the successor company but was a milestone regardless.

Since those deliveries, sales of dual-fuel two-strokes have grown and so has the range of ship types. LNG carriers may make up the bulk by type but there are car carriers, LPG carriers, crude tankers and container ships in service or on order. In December last year, MAN Diesel was able to boast that its in service engines had reached a cumulative total of 100,000 operating hours and also that the reference list for it ME-GI range had grown to encompass more than 200 engines.

That is more than double the 83 that WinGD has so far contracted for but arguably it was WinGD that ended 2017 with the most prestigious order. In Mid-November it was revealed that French liner operator CMA CGM had selected the 12X92DF engine as the prime mover for the nine-ship order of 22,000teu box ships.

The engines will be noteworthy as the largest dual-fuel two-strokes yet built, which is fitting since the ships will be the largest box ships ever built although it is questionable if that will remain the case. The ships which will be classed by BV will have the capability to complete a round trip from China to Europe on a single bunkering of LNG setting a new record for range for a gas-fuelled vessel other than an LNG carrier.

The rivalry between the two companies will doubtless continue in coming years as both emphasise the pros and cons of the two different technologies used. MAN’s engines run on the Diesel principle whereas WinGD’s are Otto cycle engines. In the long run, the choice will come down to personal preference of the shipowner.

The Diesel cycle requires higher compression and has a more complex and expensive fuel gas management system compared to the Otto engines, but on the plus side there is a slightly lower fuel consumption and no methane slip. MAN’s ME-GI engines also require a secondary system such as SCR or EGR to meet the Tier III NOx requirements.

MAN was not completely overshadowed in the news stakes in 2017 because it has continued to notch up sales of its ME-GI engines and In May 2017, an ME-GIE variant passed operational tests running on ethane, while an ME-LGI counterpart to the ME-GI that runs on LPG, methanol and other liquid gasses has also successfully been introduced to the market. At the end of 2017, MAN announced that its low-speed ME-GI and ME-LGI dual-fuel engines have registered a cumulative total of 100,000 operating hours.

HFO still the preferred option

Even if dual-fuel engines provide the easiest means of cutting CO2, they are not the preferred choice of all owners. HFO has been the fuel of choice for most ships for decades and although the 2020 sulphur cap is a factor in the search for alternative fuels, it is likely that most owners will either switch to distillates (MDO and MGO) or continue with HFO and a scrubber.

Neither of these choices will do much to reduce CO2. In fact, because of the slightly higher carbon content of distillate fuels compared to HFO, a switch to distillates will reduce SOx but increase CO2 output by a small percentage. Part of that increase will be offset by the 2020 EEDI Phase 2 which will require most ships to meet an emission target 20% below the 2013 reference line.
That is a further 10% efficiency improvement over that required in for ships ordered after 2015 and it is very doubtful if the whole improvement can be met by increased engine efficiency.