The development of long haul heavy duty vehicles powered by liquefied natural gas (LNG) is technically very sophisticated. One major challenge remains in the storage of the LNG in the vehicle. For the liquefaction of natural gas it has to be cooled down to a temperature range of approximately -110°C to -162°C at pressures between 1 bar and 10 bar. The storage system within the vehicle must therefore be able to withstand cryogenic fluids and to make sure that the temperature and pressure level within the vessel increases as less as possible. Therefore the LNG tanks consist of double-walled vacuum isolated stainless steel for the purpose of minimizing the heat input into the tank. Furthermore the refueling process needs to be standardized with the aim to develop components and processes, which ensure a safe refueling and make a misuse impossible.
Requirements to the “System Layout”
For the HDGas-project two different tank systems will be developed. On the one hand a low pressure system and on the other hand a high pressure system contingent on different engine concepts required gas supply pressure. Both systems have different characteristics and therefore exhibit different components and a different dimensioning in some parts. The table gives an overview of needed components based on the usage of different tank systems.
Table: Overview about the systems used by the OEMs
The main task of the “System layout” is to define on the one hand all relevant system boundaries of the LNG tank system, like for example the determination of the interfaces between the tank and the vehicle as well as the positioning and dimensioning of components and sensors. On the other hand the specification of technical and environmental requirements, which have a direct influence on the functionality and the lifetime of the LNG tank, has a priority.
Main outcome of first studies
Results regarding the packaging of a LNG powered heavy duty long haul truck are illustrated in below figure.
The analysis of the system layout showed that the most sophisticated component of the tank system is the LNG pump. Furthermore this pump is responsible for the biggest difference between the low pressure and the high pressure LNG tank system. The pressurization of the LNG is very important in order to provide the optimal fuel supply pressure for the combustion engine. The necessary pressure for the low pressure system amounts according the agreement with the HDGas-internal OEMs to approximately 12 bar (a), whereas the optimal pressure of the high pressure system is in between 500-550 bar. This points out, that especially for the high pressure pump the technical requirements regarding the seals and the pressure built up are so high, that this component is most challenging while the development phase. According the current status the concept phase of the high pressure pump is just before the completion. Nevertheless this component carries a risk so that further attention will be directed to this pump.
Figure: Exemplary depiction of the packaging of a long haul heavy duty truck
View the report: System layout of LNG tank system by Daimler (Public summary)