1) About LPG (technical properties)

Nowadays, searching for an alternative fuel that would replace diesel or gasoline seems to be a necessity in response to still growing prices of these kinds of fuel and tougher ecological restrictions. It is no doubt that these new kinds of fuel are cheaper and less harmful to the environment than the most popular gasoline. One of these kinds of fuel is LPG - Liquefied Petroleum Gas, which is a mixture of propane and butane. In its raw state, this mixture is odorless but the odorant is added. The proportion of this mixture depends on various factors (propane- has a better vaporizing capacity and will vaporize at any temperature above - 42°C). LPG is a product of crude oil downstream or directly extracted from oil or gas streams as they emerge from the ground. At a pressure about 0.83 MPa and the ambient temperature it has liquid state and its volume is smaller than in gas phase. At drop the pressure this fuel turns into gas phase so it is stored as liquid and combusted as gas. LPG in gas state is heavier than air so when mixed with air it tends to sink towards the ground (That's why parking LPG powered vehicles is forbidden in underground car parks).

Liquefied Petroleum Gas is supplied in a container under the maximum pressure, which is about 0, 6 MPa. When the exhaust valve is open, liquefied mixture of propane and butane runs through a channel to gas filter connected to an electromagnetic valve and if the valve is open, the mixture in liquid state goes to an evaporator- pressure reducer. In the reducer the mixture pressure is reduced to a value similar to atmospheric pressure and in heat exchanger, which is a part of the reducer, the mixture is evaporated and gas heated.

LPG physical properties cause that when changing from liquid state- state in which LPG is stored in LPG container, to gaseous state there appears a prominent drop in temperature - here coolness of the reducer body. The duty of the reducer/ evaporator connected to an engine cooling system is also fuel heating enabling its use. The heat given by a cars coolant system helps to prevent excessive cooling of the reducer body arising out of gas expansion. When the engine is not working, the reducer valves are closed cutting off the inflow of propane gas. When the engine is working, the reducer with the help of the control unit ECU  (propane computer) adjusts the amount of gas injections applied to the LPG mixer, depending on the rotation speed and load asserting proper complements of the mixture. Taking into account these both fundamental functions of the device that is mixture transformation from liquid to gaseous state as well as pressure regulation and the amount of gas supplied to the mixer, foreign terminology uses converter/ controller instead of a reducer. According to international regulations, gas system should be equipped with automatically working shut- off valve located between the gas tank and the mixer. It is necessary for safety while operating a vehicle running on LPG.

Propane- butane mixture unlike gasoline does not cause washing off oil from the cylinder and prevents oil thinning in oil can. Because of gas combustion there is no carbon deposit on the cylinder. Gas car tests show that there is only a mere power and engine dynamic reduce. It depends on the type of assembled gas installation. At a normal driving the difference between gasoline and propane is not noticeable, while speeding up the car behaves very well. It is due to the fact that octane rating of propane is higher than of gasoline and scores approx. 90- 95 (for regular gasoline  80-85). For Sequential Gas Injection these differences are perceptible only in laboratory tests. The other obvious advantage is economical issue - in most countries the price of LPG is half the price of gasolinel. Another important advantage is ecological issue. Engines running on LPG are much more environment friendly because their emissions do not contain sulphur, benzene, lead, and many fragrant hydrocarbons typical for unleaded gasoline. These harmful substances are not present in liquid gas. Besides, in comparison with other kinds of fuel, the exhaust fumes contain:

• 10 to 15% less carbon dioxide
  
• 20% less carbon monoxide
  
• 50-60% less hydrocarbons and nitric oxide