WOODWARD L’ORANGE Tackling the issue of methane slip There is high uncertainty which fuels will be used in the marine sector in the future. The switch from oil based fuels to gas offers a benefit in both aspects, sulphur and greenhouse gas emissions, while also being very attractive in price. Gas is almost sulphur free and the chemical structure of LNG (mostly methane, CH4) offers an inherent advantage in CO2 emissions because of the 25% lower carbon content. However, methane is one of the most important greenhouse gases with a global warming potential of GWP100 = 28 (time horizon 100 years) compared to CO2 (GWP100 = 1). Special care has to be taken to avoid methane slip in the combustion process. Typical values for methane slip are 5g/kWh for spark ignited and low pressure dual fuel engines. Gas engine concepts need to be compared not only based on CO2 but on total greenhouse gas emissions. Ignoring methane emissions would lead to a dangerously wrong choice of technology. But taking full advantage of the potential of using gas would be a huge step towards IMO 2050 targets. Most gas engines today are used for stationary power generation with mobile applications becoming more and more popular. Due to higher transient requirements, mobile applications tend to use more direct means of gas injection like multiport or direct gas injection. In on-highway applications often rich-burn (λ=1) combustion with three-way catalyst is used to reach current emission targets. Raw methane emissions, which are produced by homogeneous gas engines, are reduced by around 95%. In the marine segment, today’s gas engines use lean-burn combustion with spark or Diesel pilot ignition (low pressure dual fuel). These engines can easily comply with all of today’s emission legislation. However, lean burn engines cannot use three-way-catalysts and therefore have significant emissions of unburned methane. This originates from incomplete combustion on cold cylinder walls and combustion chamber surfaces (quenching) and from the combustion chamber crevices. Marine gas engines are often operated with dual fuel technology with injectors able to trigger precisely a small pilot injection for the gas mode, but also supplying 100% HFO in Diesel mode. Another option are GD-injectors which offer high pressure gas direct injection in combination with a Diesel pilot injection. Direct gas injection has some advantages that justify the use of the more challenging high-pressure gas technology. The gas is ignited by a self-ignited Diesel pilot and burned inhomogeneously as in typical Diesel combustion. Therefore, the gas is almost completely converted and methane slip minimized. This also eliminates knocking risk and specific cylinder powers known from today’s Diesel engines can be realized. By direct injection and without throttling, high efficiency and good transient response are achievable. Challenges for injection systems are the handling of different pressure levels on the gas side (typ. 200–500 bar) and on the liquid fuel side (typ. 600– 2.200 bar) plus the operation of the injector at different ratios between gas and liquid fuel (typ. 5–100%). One aspect is the evaluation of all sealing surfaces under different operating conditions. Another aspect is deformation of the highly complex injector geometry under operating loads. To allow the use in marine engines, Woodward L’Orange has developed a new dual fuel injector family, prepared to inject high pressure gaseous fuels as well as several low energy liquid fuels. It is designed for high speed engines and can easily be adapted to medium speed engines. Test results show that the goals concerning CH4 emissions and efficiency are reached. The methane emissions can be reduced to negligibly low values. Operating points up to mean effective pressures of 27 bar were demonstrated. Compliance with IMO III legislation (using SCR after-treatment) could be reached. This allows designing engines with power densities and dynamic performance known from today’s Diesel engines while compliance with future emission regulation, especially regarding methane slip, is achieved. The technology also seems ready to be used with other future fuels like methanol or even ammonia. n HANSA International Maritime Journal 09 | 2019 Schiffstechnik | Ship Technology Für jede Anwendung das richtige Pumpenprinzip Verdrängerpumpen von NETZSCH Für jede Anwendung gibt es ein optimales Pumpenprinzip. Deshalb bieten wir Ihnen als führender Hersteller, der drei verschiedene Pumpentechnologien anfertigt, den für Ihre individuelle Anwendung passenden Pumpentyp. NOTOS® Schraubenspindelpumpe, NEMO® Exzenterschneckenpumpe und TORNADO® T2 Drehkolbenpumpe NETZSCH Pumpen & Systeme GmbH Tel.: +49 8638 63-0 info.nps@netzsch.com www.netzsch.com 39
