What is true about combustion above the upper flammable limit?

Combustion above the upper flammable limit occurs under conditions where there is too much fuel present for the available amount of oxygen. In this scenario, there is an excess of fuel that cannot be completely consumed during the combustion process because there isn't enough oxygen to support the reaction fully. Therefore, the combustion cannot take place effectively, which aligns with the idea that it "can't occur due to an excess of fuel."

When discussing the other options, combustion typically requires a balanced ratio of fuel and oxygen; beyond the upper flammable limit, there's insufficient oxygen relative to the fuel available. This leads to incomplete combustion rather than efficient consumption of fuel or combustion taking place with less energy. Thus, options indicating that combustion occurs efficiently or at reduced energy levels do not reflect the reality of chemical behavior in these conditions.