Which of the following is not a component directly associated with a fuel system?

The choice highlighting the heat exchanger as not being a component directly associated with a fuel system is accurate. A heat exchanger primarily functions to transfer heat between two or more fluids without them mixing and is often associated with heating or cooling processes, which may indirectly involve fuel but doesn't constitute part of the direct fuel handling or delivery system itself.

In contrast, fuel supply piping is essential for transporting fuel from its source to the combustion area, while fuel filters are critical for removing impurities from the fuel before it reaches combustion equipment. Chimneys and vents are integral to a fuel system as they facilitate the safe expulsion of exhaust gases resulting from the combustion of fuel. Each of these options plays a direct role in the management and utilization of fuel in mechanical systems, differentiating them from the function of a heat exchanger.