Various fuels used by gas turbine power plants are liquid fuels and gaseous fuels such as natural gas, blast furnace gas, producer gas coal gas and solid fuels such as pulverized coal. Care should be taken that the oil fuel should not contain moisture and suspended impurities.
The different types of oils used may distillated oils and residual oils. The various paraffins used in gas turbine are methane, ethane, propane, octane (gasoline) and dodecane (kerosene oil). Out of these gasoline and kerosene or blend of the two are commonly used.
Qualities of Fuel
Some of the important properties to be considered while selecting the fuel for gas turbine are as follows:
1. Volatility
This property has a major effect on starting and combustion efficiency of the engine particularly at low temperature and other adverse conditions. The volatility of the fuel should be such that it is conducive to a quick and successful restart blowout of flame. Highly volatile fuels are also not desirable as they have the following disadvantages:
i) They are more susceptible to fire (although they have less tendency to explode).
ii) They are conducive to vapour lock to excessive loss of fuel during flight because of evaporation of certain lighter hydrocarbons. Therefore, in case of aircraft gas turbines in which the quantity of fuel used is sufficiently high, the fuel wastage will also be more if the fuel is highly volatile.
2.Combustion products
The products of combustion should not be in the form of solids because they tend to deposit on the combustion chambers, turbine blades and vanes and cause a loss in efficiency.
3. Energy contents
Fuel should have greater heating value so that fuel consumption may be less.
4. Lubricating properties
The fuel should provide a certain amount of lubrication of friction surfaces of fuel pumps.
5. Availability
The fuel selected should be available in large quantities so that it is cheaper.
Comparison of kerosene oil and gasoline
Kerosene is quite commonly by used in aircraft gas turbines. It is not as volatile as gasoline and, therefore, there is less possibility of vapour lock and fuel loss. But its combustion efficiency is low compared to gasoline. The lubrication properties of gasoline are poorer. About 5 to 20% of a barrel of crude may be refined kerosene whereas 40 to 50% of a barrel of crude oil may be refined into gasoline which shows that gasoline can be available in large quantities.
