Why do commercial airplanes smell like fuel smoke before take off?
This is often a result of when the planes push back from the gate or if there is a direct tail wind on the ground. The pressurization system for aircraft uses bleed air from the compression stage of the engine. If the engines are running at push back or idling when a tail wind hits them the brief reversed airflow can cause some vaporous fuel to make its way forward in the engine and come through the air system causing the smell. This page covers it pretty well. Patrick Smith also touches upon it here.