sharing our knowledge.
Photographic gallery.  Thousands of particles under the microscope.

Cenospheres from Diesel Engine Exhaust

There are three cenospheres at the center of the image. The oblique top light shows their Reflectivity. The black, tapered cylinder is a tire wear particle. Road dust minerals complete the assemblage.

Transmitted Off Crossed Polarized light and Oblique Top Light Illumination


Cenospheres are created by the incomplete combustion of a liquid fuel. In the process of combustion hydrogen is oxidized preferentially, followed by the carbon. If insufficient oxygen is available then residual carbon is left behind. The form taken by the carbon is dependent upon the form of the fuel, its residence time in the combustion zone, how soon the oxygen was depleted in the combustion process. The result is a carbon shell with holes where the vapors created by the heat continue to escape. With fuels of low viscosity the cenospheres take on a spherical shape. When the fuel is very viscose the cenospheres can take very irregular shapes. The burning of Bunker C fuel or the burning of tar or asphalt often create very unusual shaped cenospheres. The introduction of liquid droplets of fuel into the combustion zone occurs routinely in diesel engines, jet engines, oil furnaces, and oil-fired boilers. It also occurs in the bubbling of viscose melts, such as tar, asphalt, and themoplastics during uncontrolled fires. The liquid fuel may be a liquid at room temperature; such as kerosene, diesel fuel, or oil; or it may be from the melt; such as is the case in the combustion of any thermoplastic or wax.

Significance in the Environment:

Cenospheres always indicate a liquid droplet fuel. Diesel engines burn droplets of fuel sprayed into the combustion chamber. These droplets tend to be small and so most of the cenospheres from diesel truck engines are small. Large liquid fueled boilers, such as power plants, ship boilers, etc. introduce much larger droplets into the combustion chamber and produce larger cenospheres. Fuels, like Bunker C, are very viscose and produce irregular shaped droplets as they are sprayed into the combustion zone of a boiler and irregular shaped large cenospheres are the result. These are most commonly seen in the air around large harbors. Thermoplastics melt at the high temperatures of uncontrolled fires and begin to bubble as gases produced by pyrolysis vent from the plastic. When the bubbles burst they create droplets of airborne fuel that forms cenospheres. Cenospheres from uncontrolled fires often carry a large "tarry" component of partially pyrolized fuel. Wood, coke, coal, thermoset resins, etc. will not produce cenospheres directly.

Characteristic Features:

A porous surface is a characteristic of most cenospheres and that helps distinguish them from magnetite spheres that are also black but are smooth and lack the pores. Magnetite spheres also rotate the polarization of the transmitted beam of light and so are bright at the edge when viewed with transmitted cross polarized light. Cenospheres do not have bright edges when viewed with transmitted cross polarized light.

Associated Particles:


1. (see Fuel or Oil Cenospheres heading)