Modeling of a vehicular LNG tank with regard to real time implementation

Abstract: The usage of natural gas (NG) as an alternative vehicle fuel is becoming more and more common, due to a factor of approximately 600 between the liquid and vapour phase density, the storage of liquefied natural gas (LNG) in cryogenic containers is desirable to enable for NG propelled long haulage vehicles. Due to the novelty of the LNG vehicular market, little research in the field “modeling of LNG vehicular tanks” exists. It is the aim of this Master thesis to add to this research, by developing a model of a vehicular LNG tank, with a new modeling strategy, using the saturation properties of methane. The model developed in the thesis is intended to be used in an embedded system, in one example for vehicular diagnosis related to LNG. Therefore consideration to implementation has been taken during the model development and the modelcan be realized in an embedded system with low usage of resources. Furthermore the usage of an Extended Kalman Filter (EKF) as an LNG tank model observer is evaluated in the thesis and concluded to be applicable. The model has been validated in dynamic operation against measurement data obtained from measurements in a heavy vehicle with a LNG tank system. In operating conditions expected from vehicles with LNG as propulsion fuel. For stationary operation the model has been validated against data from the tank manufacturer. The thesis result shows that the model states can be estimated with satisfactory accuracy, with a relative simple model. Furthermore the result shows the models' low sensitivity to parameter estimation in dynamic operation and proportional sensitivity to the estimation of the LNG tanks isolation ability, in stationary operation.