Why is high air fuel ratio used in gas turbines?

The remaining air (tertiary air) continue to the mixing chamber (6) to be mixed with the gases from the flame tube and cool the final combustion products. Because of the high air-fuel ratio, combustor produce very little carbon monoxide and unburnt hydrocarbons.

What happens when there is more air than fuel?

A lean mixture occurs when there’s a higher concentration of air to fuel than there should be. When this occurs, your engine will likely still run but will result in jerking motions within the mechanics of the combustion engine which in turn leads to damage to the engine, such as burned valves.

What is the air fuel ratio of gas turbine?

Heat is added by combustion in the Gas turbines. In this process, energy is put into the system by burning fuel in flowing gas. The combustion is maintained in a stream of air moving with a high velocity in the region of 30-60 m/s. The air-fuel ratio vary from 60 : 1 to 120 : 1.

What is inter cooling in gas turbine powerplant?

What is intercooling in gas turbine power plant? Explanation: Intercooling means removal of heat from compressed air between low pressure and high pressure compressor. Cooling the low pressure compressed air reduces the air volume and improves the thermal efficiency, air rate and work ratio.

How does air fuel ratio affect emissions?

The CO emissions drop sharply when air/fuel mixture changed from rich to lean operation. For example at full load, the CO emitted decreases by about 4 times when λ changed from 0.85 to 1.1, and it keeps decreasing to only about one-tenth at λ = 1.2.

What affects air/fuel ratio?

Air–fuel ratio is affected by the engine air flow rate at a given engine speed and load mode, and the air flow rate is determined by the intake manifold boost pressure and engine volumetric efficiency.

What is a good air/fuel ratio?

The ideal air-fuel ratio that burns all fuel without excess air is 14.7:1. This is referred to as the “stoichiometric” mixture. In this case you have 14.7 parts of air for every 1 part of fuel.

Why reheater is used in gas turbine?

Effect of reheating: This increases the work output of the turbine by keeping the compressor work constant. The mean temperature of heat rejection is also increased, resulting in a decrease in the thermal efficiency of the plant. For a given power output, the fuel consumption rate decreases.

What is perfect reheating of gas turbine?

The reheat cycle increases the turbine work and consequently the net work of the cycle. This is accomplished not by changing the compressor work or the turbine inlet temperature but instead by dividing the turbine expansion into two or more parts with constant pressure heating before each expansion.

What is best air fuel ratio for emissions?

14.7:1 ratio
The 14.7:1 ratio is perfect for idling and light throttle cruising conditions as it’s the most efficient mixture possible, meaning the best fuel economy and lowest emissions.

What does a high air fuel ratio mean?

When an air/fuel mixture has too much fuel, it is rich. When there is not enough fuel, it is lean. An AFR higher than stoich = lean. An AFR lower than stoich = rich. A lambda value higher than 1 = lean.

What is a bad air fuel ratio?

If the ratio is too rich or too lean, the engine will not burn optimally burn the air-fuel mixture which can cause performance issues or use up too much fuel. The ideal air-fuel ratio that burns all fuel without excess air is 14.7:1.

Why is the air fuel ratio in a gas turbine engine what it is?

Hi Michael— The air-fuel ratio in a gas turbine engine is what it is for the following reasons (s)— The equilibrium temperature of the combustion products is an unambiguous function of the air-fuel ratio. As the air-fuel ratio decreases, the combustion gas temperature increases.

Why is the temperature of a gas turbine engine high?

In addition, the place ‘on the curve’ of air-fuel ratio that gas turbines operate is such that temperature responds pretty strongly to air-fuel ratio. Normally, the combustion gas temperature in a gas turbine engine cycle is set as high as it can be, based on durability of various of the engine hardware— usually the nozzl

What are the limitations of a gas turbine?

The limit on the gas turbines is the temperature capability of the turbine inlet section (front turbine rows). The reason why GT have such high lambda values (stoichiometric air to fuel ratio) is mainly not the combustion stability or the emissions. It’s limited by the material temperature limits, which limits the efficiency.

What is the efficiency of a simple cycle gas turbine?

The best heavy-duty gas turbines in simple cycle have an efficiency of 42\% (aeroderivatives better then combined cycle designed GT). The limit on the gas turbines is the temperature capability of the turbine inlet section (front turbine rows).