Why do we need Pilot Burner and Main Burner in Gas Turbine(SGT700)?

I wish to understand why does the gas turbine need pilot burner as well as the main burner. I am working with SGT700, the burner fuel supply is split into Main gas and Pilot gas.

The main gas get mixed with the compressed air and burns inside the burner. The pilot gas is supplied at the tip and burns there. Both the pilot and the main gas valves are open during operation.

I wonder if the burners had only the main fuel supply and one of them had a pilot burner with igniter assembly, for the fire to start, how would it affect. The point I wish to discuss upon is why do we even need a pilot burner can the main burner not achieve the same goal, making them perhaps a bit bigger?

Having worked for some time in the world of LNG [liguified natural gas], for large burners, the answer I guess is probably the same.

For burners of around 0.5Mw and upwards, the simple answer is if you try to light main burner from a pilot, it will blow out !
The way round is it to light an intermediate burner.

Edit: There are at least 2 good reasons why you would never increase the pilot size - can you identify ?
Firstly. Thank you again for the reply.

moving on with the thread at hand...
1. "if you try to light main burner from a pilot, it will blow out "
For SGT's this is not the case, at the start the gas is fed to pilot burners first and then to the main burners. No intermediate burner is required.

2. Why you would never increase the pilot size?
I can think of the following reasons:
a. Inefficient burning: pilot fuel is not premixed with the air(CO emission will increase)
b. Turbine Inlet Temperature will shoot up, blades of the turbine can withstand only a certain value.

3. What about having a big Main burner instead of the split between pilot and main?
It has two flame detectors positioned diametrically opposite burners.

The flame scanner system is based on the UV-VIS spectral procedure and on the IR flame radiation analysis.
Both spectral ranges are detected separately by a dual wavelength detector and evaluated selective by means of an automatic pre-amplifier circuit and integrated frequency control.
That was the answer I was looking for.

If you don't have a pilot, the amount of unburnt gas in the chamber before ignition / before it's detected as burning, could cause an internal explosion. As you appreciate any internal explosion however small would damage turbine blades.

Old domestic gas boilers used to have a pilot light for the same reasoning as above.
But modern gas boilers don't. That is because speed of ignition / detection failure is much faster.

There are maybe not so obvious practical limits between the 2 scenarios above.
But that might some way explain why most GT's (gas turbines) have a:
- lifetime number of starts meter as well as an
- lifetime number of hours meter
Thank you!

...It would be violating the forum ethic that we started the thread on a certain note and we end up going onto another topic.

But curiosity gets the better of me:
I thought those counters were to give an idea about the usage and wear of the turbine internals.
if the machine trips too often then they look for the EOC (estimated operation cycles) to determine the wear and if the machine runs for long periods uninterrupted then EOH ( equivalent operating hours) are used to determine the wear.

is there anything more to these counters?
Not really a change of topic.
For a few years I was with Siemens in North East England where they service the smaller SGT's - down to little 3Mw.
Interesting to see a 20-25year SGT stripped and rebuilt; and generally mated up with an up to date control system.
But as far as I know they [timer and counter] were as you say, to give an idea about the usage and wear of the turbine internals.