What grade of fuel oil may be ignited by an electric spark from electrodes powered by an ignition transformer?

The correct answer is Grade #2 fuel oil. This type of fuel oil is light enough to be ignited by an electric spark produced by electrodes connected to an ignition transformer. Grade #2 fuel oil has a lower viscosity and is more volatile compared to the heavier grades, which allows it to vaporize and ignite more easily in the presence of an electrical ignition source.

Understanding the characteristics of different grades of fuel oil is critical in boiler operations. Grade #1, for example, is even lighter and more refined than Grade #2, which might also allow for easier ignition; however, Grade #1 is not typically the standard used in industrial applications where igniters and transformers are involved. Grades #3 and #4 are heavier and more viscous fuels, which require different ignition methods, often involving preheating or other means to ensure complete combustion due to their higher flashpoints and lower volatility. Therefore, Grade #2's properties make it suitable for ignition via an electric spark as commonly used in industrial boiler applications.