LNG & ALTERNATIVE FUELS
ME-GA EGR PROMISES ‘30-50%’ METHANE SLIP REDUCTION MAN Energy Solutions’ unveils a new high-pressure exhaust gas recirculation (EGR) after treatment option for its ME-GA engine platform While the final headline methane emissions reduction was yet to be confirmed, it was expected to be “30 to 50 percent”, while EGR version would lower specific gas consumption by around 3 percent and lowering the specific fuel oil consumption in diesel mode by 5 percent. Importantly, the EGR version would allow the ME-GA to meet Tier III requirements in both fuel oil and gas modes without additional aftertreatment. MAN ES plans to make the EGR option available from late 2021, to the same schedule as the basic and SCR versions of the ME-GA. The technical details of the new version will be available on MAN ES’s CEAS Data platform in October, Hansen said. The ability to bring the new solution to market in such a compressed timescale partly reflected the fact that MAN ES has extensive experience with designing and delivering lowpressure and high-pressure EGR versions. “We have 33 EGR engines in operation and 211 engines on order. Our licensees are familiar with our solutions.” EGR DESIGN Unlike other two-stroke manufacturers’ Otto cycle lowspeed engine aftertreatment options, MAN has opted for a high-pressure EGR system. While the HP EGR system introduced requirements for a blower and a small associated parasitic load increase, it meant that the system could be integrated into existing engine room designs. “We can place the EGR on the engine - with the exception of the water treatment system - and the limited volumes of the solution, compared with LP EGR solutions, means it does not require any modification to existing engine room designs.” The HP EGR to be used with the ME-GA was very similar to the design of EGR systems used with ME-C engines although the material specifications would be adjusted to reflect the properties of VLSFO and LNG, rather than HSFO. This was likely to lower the price point of the ME-GA EGR version, Hansen noted. Around 30 to 50 percent of the exhaust gas from the engine is drawn into the EGR receiver, where it passes through a pre spray to lower its temperature, before passing through a cooler spray step. After passing through the EGR cooler stage, and a subsequent water mist catcher, the gas is passed through a blower to increase pressure back up to scavenging air pressure, before being fed back into the compressor and the engine. The advantages of employing an HP EGR solution also extended to the volume requirements of the system. The solution required less pipework than LP EGR solutions and had a smaller footprint, while a number of design features minimised space requirements. One such example was the application of an innovative purging concept from the ME-GI Mark II design. Rather than purging the engine by injecting nitrogen from the GVU, returning the gas via the return pipe to the GVU, we simply apply nitrogen at the engine end.
22 | OCTOBER 2020
By reversing the flow, the existing piping can carry the purged volume. This lowers the cost of piping, reduces the required components on the engine, and “ultimately we expect it to lead to higher reliability”, Hansen added.
8 A rendering of MAN ES’ new 5G70ME-GA lowpressure engine
COMBUSTION While MAN ES’ engineers were initially conducting research into Otto cycle engines, they focused on maximising the fuel efficiency of the process. “We knew that the engine would require Tier III abatement systems for fuel oil mode, and our abatement experts told us that this technology held out the potential for improvements while they were looking into different solutions.” However, we found that introducing an EGR solution improved the stability of the combustion process, Hansen added. A second phase of research into the potential of the technology was underway, examining how the circulation of larger percentages of scavenged air than typically used in
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