Friday, March 07, 2008

First a boring brief summary of what is bad for combustion, processes which form carbon and we can usually see black smoke:

1) lots of fuel with little air to circulate with at high temperature (1000K and more, air is not where the fuel is and vice versa)
2) fuel spending too much time in a zone with extreme temperatures without oxidiser (oxygen) or reducer (pyrolysis and carbonisation)
3) bad fuel dispersion so that fuel particles form a very rich mix with little air to burn with. (low droplet speed, large droplets, etc.)
4) ...

Now interesting summary of bad combustion forming white smoke:
1) fuel that is injected too late, has little time to ignite and combustion starts late
2) fuel that ignites too late due to its chemical properties, or much lower speed of sound of the liquid (foamed, emulsion)
3) fuel which needs high temperatures to burn properly but does not instantly give out enough heat to support that (water rich emulsion, improper chemical composition)
4) fuel which can only burn slowly so that the flame and combustion ceases prematurely due to pressure/temperature drop at expansion. (bitumen burns slowly, yet ocean ships have lots of it in fuel, 100RPM engines don't care)
5) fuel which contains inert material (metals, etc.) which form condensate during gas cooling

Pyrolysis is decomposition by heat without the presence of oxygen; forms carbon and combustile gases, gasification is decomposition of substance by heat with the presence of some oxygen, its aim is to make combustile gases only. And that is the aim of prechamber design - to convert liquid fuel into preheated, easily combustile, easily flammable combustile gases or mix with dispersed fuel droplets.

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