The short answer is; with heat. That is why 100% of the smoke machines approved and mandated by OEMs use a heat source.
‘Cold fog’ machines have been used in theatrical stage antics for many years. They have been desirable on stage because cold fog is heavy and settles low on the stage. Any machine that does not use a heating element is considered a cold fog machine. A cold fog machine simply atomizes a liquid solution. (Just about any solution can be atomized, even water). What you get is a very wet fog that can be very unfriendly in today’s sophisticated automobiles – most especially in a vehicle’s fuel vapor recovery (EVAP) system.
EVAP systems are equipped with an activated charcoal that must maintain its integrity; otherwise you’ve just made matters worse. In other words, the wet fog can saturate the activated charcoal, rendering the EVAP system ineffective which could affect the system’s performance and vehicle warranty. Another disadvantage is that the wet fog has a tendency of quickly condensing inside the system being tested, lacking that buoyant “hang time” required to properly travel through an entire test system.