What does draft refer to in combustion systems?

Draft in combustion systems specifically refers to the pressure difference that is created by the movement of combustion byproducts as they are exhausted from the system. This pressure difference is crucial because it impacts the efficiency and effectiveness of the combustion process. A proper draft ensures that gases produced during combustion are effectively vented outside, while also allowing fresh air to enter the combustion chamber to sustain the burning process. If the draft is insufficient, it can lead to poor combustion, increased emissions, and the potential for hazardous conditions such as backdraft or flue gas spillage into living spaces.

The other options address different aspects of combustion systems. The amount of fuel consumed is related to efficiency and operational costs, while the temperature of exhaust gases concerns heat management and emissions control. Lastly, the measurement of air density is important for understanding how air intake might vary with environmental conditions, but it does not define the term "draft."