Design and Development of LNG Fuel Tank for Vehicle Application

Abstract

LNG has emerged as a fuel for vehicle transportation because it is widely available, renewable and offers reduced green-house gas emissions. Natural gas is denser as low temperature liquid compared to compressed natural gas. Natural gas when stored as cryogenic liquid gives three times as much gas in the same space compared to compressed natural gas.

LNG is a purely methane (CH4) gas containing 98 % methane. LNG is cooled at very low temperature. It is stored as cryogenic liquid under pressure up to 1.69 MPa. The LNG fuel tank is cryogenic container which stores LNG as highly refrigerated liquid at low pressure. The tank is insulated so as to store LNG as cryogenic liquid. The system includes an inner vessel fitted inside evacuated outer vessel to provide necessary insulation. The inner vacuum space between the inner and the outer vessel consist of super-insulation of aluminum foil and fiber glass. The inner vessel is structurally supported within the outer vessel to absorb the loads applied on it during the motion and shield them from heat leakage from the environment.

The inner vessel is subjected to 1.69 MPa pressure at temperature of -162 ˚C and the outer jacket is subjected to ambient temperature and pressure conditions. It is necessary to critically design the components of the fuel tank. Various international codes are available for designing pressure vessel. The fuel pressure itself provides the necessary driving force for delivering the fuel to the engine. For this purpose the system contains fuel delivery system that includes the fuel controlling devices. The cold pressurized fuel flows out of the tank when the engine demands fuel. The system also contains heat exchanger that delivers the fuel at required warm conditions to the engine.

The project covers the mechanical design of inner and outer vessel as per ISO 21029-1:2004. Analysis of critical parts that includes the head-shell junction and the support system specifications is also carried out. It also contains the designing of helical coil and tube heat exchanger, ullage tank and the mountings which mount the tank on to the frame or chassis.