FAA Powerplant Written Practice Test

What causes turbine engine emissions?

1. Excessive fuel consumption

2. Mechanical wear and tear

3. High combustion temperatures

4. Low lubrication quality

The correct answer is: High combustion temperatures

Turbine engine emissions are primarily caused by high combustion temperatures. When fuel burns at high temperatures within the combustion chamber, it leads to the formation of nitrogen oxides (NOx), which are a significant component of engine emissions. The combustion process in turbine engines typically involves extremely high pressures and temperatures to achieve efficient fuel combustion, resulting in the production of various exhaust gases that contribute to emissions. The correlation between high temperatures and emissions is crucial because it not only influences the type of emissions generated but also their quantity. For example, higher combustion temperatures can enhance fuel efficiency, but they also increase the formation of NOx due to the reaction of nitrogen in the air with oxygen at elevated temperatures. Excessive fuel consumption can lead to higher emissions as well since burning more fuel typically produces more exhaust gases. However, the underlying mechanism driving emissions—specifically the formation of NOx—is fundamentally linked to these high combustion temperatures. In contrast, mechanical wear and tear and low lubrication quality may impact the overall performance or efficiency of an engine but do not directly cause emissions in the same way combustion temperatures do. They might contribute to increases in unburned hydrocarbons or particulate matter, but they are not the principal factor in the production of emissions associated with turbine engines.