Unveiled at a major event at MAN Diesel & Turbo’s Copenhagen Diesel Research Centre in May 2011, the ME-GI engine allows the use of either oil or gas fuel while working in the highly efficient Diesel cycle. With an order book that continues to be filled up, on this page, René Sejer Laursen, from MAN Diesel & Turbo in Copenhagen, answers questions on the culmination of many years’ work. On the right, we hear from Teekay, the customer.
Now that there are orders for vessels with the ME-GI engine, what makes you so confident that you have the experience for such a gas-injected model?
The ME-GI is a diesel engine, and we have been designing diesel engines for more than 100 years. The ME-GI’s electronic hardware and most of the software is based on our ME type electronics that have been in successful service for over a decade. We first installed a 40 MW stationary 12K80MC-GI in Japan in 1994. This, along with extensive testing on our in-house research engine, as well as demonstrations in front of customers at our licensees in Japan and Korea, has provided convincing evidence that we have perfected the gas components and supporting systems.
What is pilot oil and what is it needed for?
The pilot oil starts the combustion process, as the ignition of methane is slow. In a high-pressure ME-GI DF engine, gas is injected only after the combustion air is compressed, after which it is ignited by the pilot oil injection. The gas burns immediately after injection, causing a total and complete burning. Hence there is no need for derating to avoid knocking, and the large methane slip as is normal with the Otto cycle is virtually non-existent. In a low-pressure DF engine, gas and air are mixed before compression in the cylinder. Unintended ignition can take place (knocking), which is one of the primary reasons these engines are significantly derated in power.
What is the amount of the pilot oil?
We guarantee a maximum pilot fuel of 3%.
Otto-cycle engines require high quality gas – What about the ME-GI?
If we look at the quality of natural gas worldwide, less than half has a methane number higher than 80. In an Otto-cycle, low-pressure engine, power will be reduced quickly with a lower methane number. By working in the Diesel cycle, where knocking is not an issue, high gas quality is not required.
How much methane slip will there be on an ME-GI engine, and what’s the effect?
The methane slip on the ME-GI is virtually undetectable due to its operation in the Diesel cycle. When measurable, it is some 0.2 g gas per kWh. The methane slip from an Otto-cycle engine during routine operation can be up to 5% of the gas and, during manoeuvring, can be 10%. This represents a direct efficiency loss since methane is, in fact, the fuel and this is an unburned or wasted portion that needs to be added to the gas consumption number. Note that methane is over 36 times worse than CO2 as a greenhouse gas. Additionally, since it reflects unburned gas that performed no useful purpose in the engine, it is an important factor in the specific gas consumption.
Is the high-pressure system safe? What safety systems are on the engine that will detect gas leakage?
The system is extremely safe, and has multiple interlocks to ensure safe operation. The gas is in the inner pipe of the double-walled piping, and the external pipe is ventilated a minimum of 30 times per hour. The inner pipe is tested to 1.5 times the operation pressure of 300 bar, and the thickness of the outer pipe is sized to take 1.5 times max. rupture pressure coming from the inner pipe. In the event of leakage, hydrocarbon detectors will change the engine over to fuel operation while purging the system of gas. Such a change-over will take place without the engine stopping and is hardly noticeable. In a high-pressure system there is no need for explosive devices on the engine or bursting discs in the exhaust stack as would be required in a low-pressure system.
At what loads is the ME-GI capable of operating on gas?
At 10% load, the engine will switch from gas burning to purely fuel oil operation. It will then switch back to gas operation automatically when the load goes above 10%. The process is completely transparent and the operator does not have to do anything, as it is all controlled by the ME-GI control system. Can the ME-GI burn ONLY fuel or gas, or…? The ME-GI can burn whatever portion of gas or fuel desired, subject to the 10% low-load switchover to gas.
Regarding emissions, it has been indicated that the MAN B&W two stroke ME-GI engine will require an EGR or SCR when Tier III emissions rules come into effect in 2016. Is that the case?
When Tier III comes into effect, the ME-GI will utilise either EGR or SCR to achieve appropriate NOX levels. This is a consequence of the high efficiency of the Diesel cycle because NOX is formed when burning gas at high temperatures With a lower combustion temperature, less NOX is formed. However, that also means a much lower efficiency. Otto-cycle engines that run only on gas will not require EGR or SCR due to the lower temperature/efficiency but, if they are to run on fuel oil, will require SCR. In effect, they would not be dual-fuel engines, they would be gas engines as they cannot burn fuel without after-treatment. Note that there is no need for scrubbers with an ME-GI system.
What power ratings are the ME-GI engines available in?
The entire MAN B&W product line of two stroke engines from the 5-cylinder S30 at 3,200 kW, to the 14-cylinder K98 at 87,220 kW are available as ME-GI. In addition, all stroke lengths (L, S and G) are available as ME-GI. Because the necessary hardware changes from ME to ME-GI are not major, it is not a significant issue to make as a gas-injected engine. Lead time is essentially the same as for a standard ME engine, which can vary from yard to yard and depends on the current order backlog.
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Source: MAN Marine Engines & Systems
