You seem to be missing a bit of code… and I needed to fix the formatting of what you did post… as per the directions…
Meanwhile your void loop() should only contain the basics like blynk.run() while you put your sensor functions in a timed loop using BlynkTimer.
I recommend you read through the Documentation, Help Center and try out the examples in the Sketch Builder (all these links are also at the top of this page) to get a good understanding of how programming with Blynk works…
I also recommend this link to Arduinos Reference Page… experimenting with code and searching for programming tutorials via Google will help you understand how to merge Blynk in with other Arduino code.
And finally you can try searching this forum again for keywords like MQ2 and Smoke Sensor, to see what others have done.