Natural Gas and Liquefied Gas have become two “clean” alternatives to gasoline and diesel. Francisco Sanz, expert in fuels, analyzes each of these fuels
Compressed Natural Gas (CNG) is a gaseous fuel of fossil origin not derived from petroleum. Its chemical composition is based on methane, CH4, a hydrocarbon with a high hydrogen index (H / C ratio) generating less carbon dioxide per unit of energy produced during combustion with respect to other heavier hydrocarbons.

CNG is obtained from oilfields or independent deposits and its composition and characteristics vary depending on the field from which it is extracted, but the physical and chemical properties are practically similar. It has a boiling temperature at atmospheric pressure of -161 ° C, so at room temperature it is in the gas phase. Hence, the need to store it at high pressures, usually between 200 and 250 bar for use as fuel in vehicles. The relative density of CNG is lower than that of air, in the case of leaks, its tendency is to accumulate in the high areas.

As for Liquefied Petroleum Gas (LPG), it is a fossil fuel that is usually dissolved in oil. Therefore, it is obtained during the refining of the oil and by-product in the catalytic fractional distillation units (FCC). The chemical composition of LPG consists of at least 20% propane (C3H8) and a maximum of 80% butane (C4H10) according to the specifications included in RD 61/2006 for the use of LPG in the automotive sector. The condensing temperatures of LPG are higher than that of CNG, so it is less expensive to liquefy this gas with respect to CNG.

The relative density of LPG is higher than that of air, at atmospheric pressure, so in case of leakage it will tend to be stored in the lower parts of the site. Regarding the calorific value of CNG and LPG, the CNG is about 50,200 kcal / kg while that of LPG is 46,000 kcal / kg. Therefore, lower powers are obtained with LPG with respect to CNG.

BY FRANCISCO SANZ PÉREZ – Madrid – 02/26/2018 – ABC (Translation Soft)