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Old 03-06-2010, 06:07 PM   #6 (permalink)
mechman600
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All true. Very true.

Here's the deal. I have a LOT of experience with diesels, and I understand them fully. I am a commercial truck mechanic on a dealership level (Peterbilt) who spends 99% of my time at work diagnosing/repairing engines, and these engines are basically giant versions of car diesels. Truck engines got into 100% computer management back in the early 90's, long before automobile diesels did. They have EGR, diesel oxidation catalysts, diesel particulate filters, variable valve timing, common rain injection, and now selective catalytic reduction as well. And all of these have been a "joy" during their various teething problems in the last number of years (read: nightmare).

There are my credentials, if needed.
Now to my preliminatry testing.

If you pour some diesel fuel on a table and try to light in on fire, it simply will not. Nothing will happen. Weird, but true. This is why diesel fuel is a much safer fuel. However, if you spray it as a mist, it will burn like crazy. Last night I loaded my spray bottle with diesel fuel, pumped 'er up, and sprayed a mist (not even that fine of a mist) through a flame, and voila, a massive fireball with very little smoke. And keep in mind the temp of our shop last night (I'm on evening shift this week) was only about 10C/50F, so pretty cold. So, misted diesel burns very well at pretty much any temperature. It doesn't require hot compressed air to burn; it only does to autoignite. And that's [maybe] what the spark plug will do.

Post 2007 Cummins engines have an injector on the outlet of the turbocharger, aptly named the "hydrocarbon doser," to provide raw HC for the catalyst for DPF regeneration. This doser works on pressures of only 200-300 PSI. I often do flow tests on these injectors by removing it, hooking up an extension supply line and harness, and enabling a test with the diagnostic software while the engine is idling so I can measure flow in a certain period of time. What I'm getting at is that this mist is a VERY fine mist of diesel fuel that lingers in the air for five minutes or more. So if done properly, I really don't think there will be an issue with atomization and making a combustable mixture in the cylinder. I just wonder if a single spark plug will be sufficient to light the whole thing on fire.

The mist from my spray bottle will not work for testing on my motorcycle. Too much fuel comes out. I'm thinking of turning a ball point pen into an injector. Hmmmmm.....

Last edited by mechman600; 03-06-2010 at 06:20 PM..
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