The prices of fuels constantly change around the world. Their height depends on many factors, like government excise tax, prices on global markets and many more. Long-time gas users in Poland and some other countries of temperate climate can see a certain pattern when it comes to the prices of LPG. They might notice that the prices increase a little every winter. Where does this pattern come from? The reason is simple, it is caused by seasonal change in the gas composition.

The product sold under the trade name “LPG” is the mixture of propane and butane. These substances highly differ from each other in their physical and chemical properties. Modifying their proportion you can be sure that gas installation will work correctly in current atmospheric conditions. In Poland the regulations about this matter are the part of the PN-EN 589 norm.

This organic gas is commonly used as lighter fuel and the component of the LPG. Its evaporation stops at -0,5 Celsius degrees, so it is non-flammable during frosts. For this reason, it is necessary to limit its amount in the mixture in the winter season.  

This odorless, colorless substance with a density greater than air is a component of crude oil obtained in the distillation process. In combination with butane, it is used in the production of LPG and is a more expensive component of the mixture. It evaporates at temperatures up to -43 degrees C, which is why it plays a key role in the mixture sold in the winter season.

Mixture characteristics

The key part is the proportion of propane and butane mixture. In Poland these gases are mixed together in a ratio of 40:60. But the proportion is reversed, depending on the time of the year. While a higher concentration of propane allows you to use the installation in frosty weather, the advantage of butane allows you to reduce fuel prices in the summer and adjust the mixture pressure to higher temperatures.

The pressure – what is it and how does it affect the operation of the gas installation?

It is nothing else than the molecular interactions of a substance. We know from school’s physics lessons that the pressure is the result of the collision of particles of a substance with the environment. The more of them  are in a given space, the greater is the pressure. The pressure is also influenced by the mobility of molecules, which changes, for example, under the influence of temperature. Another variable are the properties of specific substances.

LPG, dominated by propane, makes the mixture ideal during frosts. However, in summer it would increase the pressure in the installation, which could negatively affect the engine’s operation. In the case of a mixture consisting mostly of butane, we have exactly the opposite situation. LPG with a predominance of butane will be perfect for the warmer part of the year, but unfortunately in winter it will cause ignition problems.

For the proper functioning of the gas installation, switching to the winter fuel plays a key role – if the gas station missed this moment, it could cause a lot of trouble for customers. In order to protect drivers from ignition problems, the Polish government imposed an obligation on gas stations to replace the mixture periodically. Polish law indicates that on December 1st a mixture containing 60% propane must be available at all stations.

Changing to the summer version is not such a critical issue – it can be said that its biggest advantage is the lower price. An installation filled with the winter version of the fuel will operate at temperatures above zero, and by the time the real heat comes and the temperature will be able to increase the pressure in the installation, the gas will certainly be used up. In Poland the summer version is available on stations from April 1st.

What about other countries? It depends. The proportion of propane and butane and time of its change is adapted to the prevailing climate. In warmer countries, the change in mixture proportions may not occur at all – in such a case, gas containing more butane is sold all year round.

The increase of the LPG price  in the winter is not the result of annual fluctuations in the fuel markets or conspiracy of gas station owners. This is influenced by seasonal changes in the composition of LPG. It is caused by the properties of the two main components of LPG – propane and butane. While butane is great for hot weather, it can cause ignition problems in winter. Much more expensive propane is great during frosts, but it may lead to an increase in pressure inside the installation during summer heat. For this reason, the proportion of the mixture referred to in trade as LPG gas is changed twice a year. In Poland the winter mixture is available from December 1 to March 31, the summer mixture throughout the rest of the year. Refuelling stations in our country usually approach these issues conscientiously, so drivers can safely fuel up LPG and not worry about the operation of the gas installation in their vehicle.

Graphic sources: Vectorportal.com,  CC BY; Needpix; FreeSVG; Wikimedia