What is a key indicator of incomplete combustion?

Incomplete combustion occurs when there is an insufficient amount of oxygen available to completely convert the fuel into carbon dioxide and water. One of the most visible indicators of this process is the presence of smoke. Smoke is composed of unburned fuel particles and various byproducts that result from the incomplete burning of hydrocarbons. When combustion is efficient, the process produces a clear gaseous byproduct, such as carbon dioxide. In contrast, smoke reveals that not all of the fuel is being burned properly, indicating inefficiency in the combustion process.

Other signs of incomplete combustion may also be present, such as particulates and ash, but smoke is the most readily observable and serves as a clear reminder of insufficient air supply or malfunctioning combustion systems.