LPG has been used as fuel in the car industry for many years and now, with Exmar and Statoil’s orders for ocean-going ships fitted with the dual fuel ME-LGIP engine, LPG will be used on marine engines as well. The new engine series is currently being developed to match all types of bigger merchant ships. This order was made in consequence of the new 2020 0.5% sulphur fuel cap, but this step forward has not stopped the discussion and interest in lowering CO2, NOx, SOx and particulate emissions even further. On the contrary, it has actually been further fuelled by the latest IMO meeting targeting a 50%-cut in greenhouse gas emissions from ocean-going shipping by 2050 compared with 2008.
Because the world fleet has increased since 2008, and thus CO2 emissions as well, it has been realised that this goal cannot be met without the use of carbon-free fuels. In shipping, 30 years corresponds to the lifetime of a ship, and owners will therefore soon need to consider this when they select the propulsion solution for their next ship. And as marine engine maker, MAN Diesel & Turbo needs to be fully prepared.
Using LPG as fuel on the two-stroke ME-LGIP engine offers similar emission benefits as with LNG, which reduces emissions significantly compared with MDO. Therefore, there are very good environmental reasons for using this fuel in coastal areas, on inland waterways and on deep sea. The LGIP engine solution system can also be applied on engine sizes from 5 to 85 MW, which are suitable for tankers, bulk carriers, container vessels, etc.
It is expected that the need to reduce CO2 emissions will fuel a continued growth in shipping. And because sea transportation has proven to be less CO2 polluting than both trucks and trains using fossil fuels this trend is expected to continue. Furthermore, the world population is increasing as well, and this is expected to increase the shipping fleet. So significant CO2 reduction is mandatory in shipping, and this can be improved by using carbon-free fuels such as bio-LPG/LNG, and the so-called “electric fuels”, etc. There are also plans to remove CO2 from methane to produce carbon-free ammonia, but in order to be fully carbon free, the CO2 should be removed by, for example, injecting it into the seabed. MAN Diesel & Turbo already have dual fuel engines in our engine programme that can operate on LNG and methanol, but ammonia as a fuel has not yet been investigated for use on two-stroke engines.
This paper describes the technology behind the ME-LGIP dual fuel MAN B&W two-stroke engines, using LPG as fuel, and its associated LPG tank and fuel supply systems. The engine requires a gas supply pressure of 50-bar and controlled to a temperature of 45°C. At this temperature and pressure, the LPG is liquid, and different fuel supply solutions are available for generating this pressure for the liquid. Hence, the ME-LGIP for LPG will use liquid gas for injection, contrary to the ME-GI for LNG, where the methane is injected in gaseous form. All the way from tank to engine, the LPG remain in liquid phase, and conventional pumps can be used to generate the pressure. Furthermore, we have lately found that this engine technology, with minor modification, can also be used to burn ammonia, so the paper will also describe the modification needed in order to build an engine that is able to burn LPG as well as ammonia.
Safety is a concern when both LPG and ammonia is used as fuel on an engine located in an engine room. This is because LPG in gaseous form, contrary to methane, is heavier than air and will drop in case of leakage, and because ammonia in a gaseous form is toxic. This safety has been analysed, and our safety considerations and precautions will be described in details.