Use of Small Internal Combustion Engines for LNG Boil-Off Gas Conversion: An Experimental and Numerical Analysis

Abstract

LNG technologies have long been used but only recently found widespread employment on medium and small scales compared to the traditional cycle of liquefaction, transport by ship, regasification and injection into the gas network. This has increased the direct use of LNG with the problem of limiting greenhouse gas emissions, linked to gas released principally in the event of prolonged absence of fuel drawing from the cryogenic tank. This study analyzes the energetic exploitation of BOG in small internal combustion engines. The effect on CO2 equivalent emissions was evaluated, making a comparison with the BOG emission into the atmosphere directly or after burning. A 1 kW gasoline engine was selected for a 500-litre LNG tank and converted to gas fueling. The measured consumption and emissions resulted in compliance with a lower environmental impact compared to direct BOG release into the atmosphere despite simplified technical solutions, such a cheap and light 2-stroke engine. In contrast, only a 4-stroke engine has performance such as achieving a reduction in GHG emissions, up to zero, even compared to the case of BOG combustion before releasing it into the atmosphere.