Methane slip and particulate matter emissions require solutions before anticipated regulations emerge, writes Gavin Lipsith
Last week I wrote about my expectations from CIMAC World Congress. Digesting the full output from the conference is the work of weeks rather than days and I will explore the biggest theme from the conference – decarbonisation – in my comment next week. But while the greenhouse gas issue dominated, there were also plenty of lessons to learn on shipping’s other emission challenges.
In the absence of fuel suppliers (with a few exceptions), it was left to lubricant and additive suppliers to ease the concerns of shipowners around the compatibility, stability and combustion of very low sulphur fuel oils. But the main engine designers remain divided on the impact low sulphur will have on cylinder corrosion. MAN is advising cermet piston rings to prevent bore polishing, while Winterthur Gas & Diesel advises that its current tribological concept will suffice.
Another current challenge is reaching Tier III NOx emissions, for vessels built from 2016 entering emission control areas in North America (and, from 2021, the Baltic and North Sea). Direct water injection and water-in-fuel (or emulsions) have long been marginal solutions to this issue. They appear to be making ground in technologies proposed by (among others) Wärtsilä, which suggested an in-cylinder exhaust gas recirculation technique, and MAN Energy Solutions, which proposed emulsifying methanol fuel to meet Tier III NOx limits.
Looking beyond 2020, the regulation of particulate matter is a question of when, not if. European Inland Waterway Stage V requirements from next year will make diesel particulate filters mandatory for inland vessels. IMO will also act, but ports are likely to act first. Coastal and port vessels will be the first to require filters, but some deepsea vessels – for example Jan de Nul’s latest jack-up vessel - are already installing them. But filters will require careful integration into existing aftertreatment systems if they are to be effective.
One of the biggest concerns on the regulatory horizon is methane slip. This will challenge gas-burning four-stroke engines that deploy lean-burn (or low-pressure injection, or Otto-cycle) technology – that is, most of the dual-fuel, four-stroke engine market. There is therefore a potential opportunity for high-pressure four-stroke engines, which are currently less popular but do not suffer from methane slip. Some key component suppliers are already preparing high-pressure technologies for this eventuality.
For two-stroke engines, the picture is different. Again, high-pressure injection eliminates methane slip almost entirely. And even for low-pressure engines methane is less of a challenge, for reasons that were expertly explained by Winterthur Gas & Diesel’s German Weisser, who took CIMAC’s prize for the best paper at the conference. That paper will be the subject of a forthcoming article.
Technologies to treat methane slip are still at the experimental stage and require fast development to be ready in time for anticipated regulations. Catalytic oxidation is a challenge at the low exhaust temperatures of lean-burn gas engines, and proposed solutions at a dedicated session focused on boosting the energy in the catalytic process by electrical fields or plasma reactors.
The use of plasma reactors and electrical fields sounds futuristic but merely highlights the forward thinking that will be required to overcome ever tightening emissions legislation. The big leap will come when shipping starts to deploy fuels that do not produce these emissions. Until then, innovative abatement technologies remain urgently needed.