<b>LNG Propolsion Concept</b>
LNG stands for Liquefied Natural Gas which is used as an alternative propulsion concept. In 2013, United ARAB Shipping Co. (UASC) ordered container ships (with 18,000 TEU) that are designed in such a way that they can later be converted to use LNG in a comparatively uncomplicated manner.
The new Helgoland is the first German ocean-going ship to have a dual-fuel drive, i.e. one that can be supplied with both conventional diesel fuel and liquefied natural gas (LNG) for operation to comply with the emissions regulations applicable from 2015.
Reederei AG “EMS” has also converted its ferry Ostfriesland to run on liquefied natural gas. At the beginning of 2014, the shipping company had already signed the first delivery contract in Germany for LNG as a marine fuel with Bomin Linde LNG. Since the natural gas has first to be cooled down to approx. -163 ° C (at this temperature the gas liquefies), appropriate tank systems must be provided both on the ship and on land. After the ports of Hamburg and Brunsbüttel, the ports of Bremen are also following the trend of reducing pollutant emissions in the ports through the use of LNG as an alternative fuel for merchant ships. In addition, the construction of an LNG port filling station is being pushed.
For the use of LNG, the gas engine or the dual-fuel engine come into question. This engine is constructed as a reciprocating piston engine comparable to the Otto or Diesel engine. The fuel-air mixture is ignited in units based on gasoline engines by external ignition using a spark plug, in units based on diesel engines by self-ignition with a small amount of ignition oil (diesel fuel) injected. The company Wärtsilä uses a diesel engine for high pressure gas injection, i.e. with auto-ignition of the fuel gas injected directly into the combustion chamber at high pressure. The engines working according to this process achieve the highest mean pressures of all internal combustion engines.
The MAN company developed the “PGI process”. This method works according to the same method as the pilot injection principle, but bypasses the disadvantage of the additional fuel required, since it uses the gas available as a pilot injection quantity to initiate ignition. The components are a “pilot gas high-pressure injection valve” and a starting aid (incandescent body), which are integrated in a cooled prechamber. The directly controlled injection valve injects a small amount of pilot gas into the prechamber shortly before the top dead center of the piston with a pre-pressure of 230 bar generated by a compressor. An approximately stoichiometric mixture is established there, which ignites on the hot surface of the incandescent body, which is only heated electrically during the start-up phase. With this method, the ignition point is thus controlled directly via the injection point of the pilot gas.
An external mixture formation can take place by means of gas mixing units before or after a possible turbocharger; internal mixture formation is possible through separate gas inlet valves or injection needles.
LNG Propulsion Concept
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