Investigation of cryogenic seal durability for LNG piston pumps

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Westport Power Inc., headquartered in Vancouver, BC is a global provider of essential technologies and proprietary solutions that allow engines to operate on economically and environmentally sustainable fuels such as natural gas, propane and hydrogen. Natural gas engines offer advantages of lower emissions of greenhouse gases, nitric oxides, and particulate matter than gasoline or diesel based engines and thus, can play an important role in the shift toward a lower carbon transportation system. Development and optimization of the engines and LNG tank systems are an important part of facilitating the broader implementation of natural gas engines. An important component of such systems is the reciprocating LNG pumps used to transfer the liquid natural gas from the LNG storage tanks. The reciprocating piston pumps draw liquid natural gas from the tank into the cylinder through a check valve during the intake stroke of the piston. It is then compressed and pressurized from the 20 to 230 psi typical of the storage tank pressure up to 4500 psi, before being exhausted through a second check valve during the compression stroke of the piston. The piston in the reciprocating pumps includes a set of ring seals around the piston to impede flow between the piston and cylinder. These ring seals play a key role in determining the efficiency and durability of the pumps. There is leakage flow through the ring seals during the high pressure return stroke process, and also friction between the seals and cylinder that depends on the contact pressure of each seal and the piston speed. The performance of the seals is degraded by wear that depends on the contact pressure, friction and sliding velocity between the ring seal and cylinder. Thus, it is important to understand the flow through the seals in order to optimize the performance and durability of the seals and in turn the reciprocating piston pump. The overall objective of this project is to model and compute the flow through the seals in order to assess the contact pressure and friction, and determine the leakage flow through the seal sets for different operating conditions and seal set designs. The results will be used to identify factors that have the largest influence on seal performance and optimize the seal design.