Which of the following factors can affect combustion efficiency?

Combustion efficiency refers to the effectiveness with which fuel is converted into usable energy during the combustion process in heating systems. Several factors impact this efficiency, and the correct answer acknowledges that both fuel temperature and combustion air play significant roles.

Fuel temperature is critical because warmer fuel can vaporize more efficiently, allowing for better mixing with air and leading to more complete combustion. Inadequately heated fuel can lead to higher emissions and reduced efficiency due to unburnt hydrocarbons and other by-products.

Combustion air is equally important. The correct ratio of air to fuel is crucial for complete combustion. Insufficient air can result in a rich fuel mixture, leading to incomplete combustion, increased emissions, and lower efficiency. Conversely, too much air can also cool the combustion process and diminish efficiency, but the primary issue is ensuring that the right amount of air is provided.

Considering these aspects, it is clear that both fuel temperature and combustion air significantly influence combustion efficiency, making the choice that encompasses both factors the most comprehensive response.