Which factor most directly affects the atomization quality of fuel in a marine diesel engine?

• A. Fuel water content
• B. Fuel octane rating
• C. Fuel viscosity
• D. Fuel color

Answer: (C)

The most direct driver of how finely fuel breaks up into droplets when it’s injected is its viscosity. During high-pressure injection, the liquid must be sheared apart by the nozzle and internal flow stresses. Lower viscosity lets the fuel be sheared into much smaller droplets, producing a finer spray that mixes more uniformly with air for efficient combustion. If the fuel is more viscous, the spray remains coarser with larger droplets, leading to poorer mixing, incomplete combustion, and higher emissions.

Water content in the fuel isn’t the primary factor controlling atomization; it can affect combustion stability and injector wear, but it doesn’t govern the spray breakup itself. Octane rating relates to gasoline’s tendency to ignite under compression, not to diesel spray behavior. Fuel color has no bearing on atomization.