When using compressed natural gas as a fuel in the automobile engines, there is a potential danger of this gas pressuire increase up to the specified working pressure in the pre-filled cylinders. This pressure increase is caused by an increase in the ambient temperature compared to the temperature of the compressed natural gas corresponding to the completion of the filling process. If after cylinder filling before methane consumption there will be rather long pause, during which the ambient temperature rises, the pressure in the cylinder may exceed the permissible operating value, cause the reduction of the residual life and eventually lead to the destruction of the cylinder with the subsequent ignition of compressed natural gas.

To obtain quantitative estimates of possible pressure increase of the compressed natural gas in the automobile cylinder caused by ambient temperature increase, it is required to use up-to-date methods of mathematical simulation. Reliability of such estimates characterizing the permissible temperature regimes of operation of the filled automobile cylinders with compressed natural gas is determined by the adequacy of the mathematical model describing the thermal processes in the typical cylinders with compressed natural gas during their filling and subsequent storage. One of the main elements of such a model is the dependence, which is in a good agreement with the experimental data, between the main parameters describing the compressed natural gas state in the cylinder. As such parameters for any gas its pressure, temperature and density are normally used, which are specified in the equation of the given gas state.

When building the mathematical model the option of the equation related to the methane state is utilized, which is the main part of the compressed natural gas commonly used in the motor transport. This option establishes the dependence between the pressure, temperature and methane density confirmed experimentally within the accuracy of a tenth of one percent. Used at quantitative analysis models related to dependence of heating capacity, viscosity, thermal conductivity and volumetric expansion of the methane on its temperature and density are also in a good agreement with the experimental data.

**S.Yu. Belousova, Lead Engineer
Ya. G. Osadchiy, Dr. Sci. (Eng.), General Director
ZAO NPP Mashtest, Moscow, Russia
V.S. Zarubin, Dr. Sci. (Eng.), Prof., zarubin@bmstu.ru
MGTU in the Name of N.E. Bauman, Moscow, Russia
V.M. Frum, General Director
OOO NPF Real-Shtorm, Izhevsk, Russia**

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