Fuel Oil Characteristics

In this section we will discuss some important characteristics of fuel oils:

A. Viscosity

This property is a measure of fluid’s resistance to flow. Heavier fuel oils are very resistant to free flow at the room temperature. Such oils are heated to reduce their viscosity before they can be safely burned in a boiler.

Saybolt Universal Seconds (SUS or SSU) criteria is used to measure viscosity. This number is determined by testing a sample to find out how many seconds a given amount takes to flow through an orifice. For example for water the SSU number is 31.

Viscosity of various oils is:

No. 1 Oil: 31 SSU (100 deg F)

No.2 Oil: 35 (100 deg F)

No. 4 Oil: 77(100 deg F)

No. 5 Oil: 232 (100 deg F)

No. 6 Oil: 170 (122 deg F)

B. Flash Point

This is the lowest temperature at which an oil will flash (combust), when in contact with an ignition source. Lighter oils have a low flash point, while heavier oils have a higher flash point. The flash point is determined by heating a sample to find the temperature at which enough vapor is generated to cause combustion.