"Bruce in Bangkok" wrote in message
...
On Sat, 12 Apr 2008 10:23:05 -0400, "Ed Huntress"
wrote:


"DanG" wrote in message
...
Ed. as always, I appreciate your response. I used to run a bit of
diesel
in old gasoline engines before computers and what not. I'm sure it was
as
ignorant as adding gasoline to diesel fuel.

I was believing your frank, honest style, but the technical article just
made it dance. Thanks. I wish more people would limit their comments
to
facts, not hyperbola.

Thanks for your kind comments, Dan.

Regarding that article, I thought it was very good but I think I spotted
one
error. He says that gasoline burns hotter than diesel. He apparently wrote
that article sometime in the mid- or late-'90s, and he may not have had
easy
access to the nifty engineering Java appletts available to us today. I
just
scrounged one up --

http://www.engr.colostate.edu/~allan...Flamemain.html

-- and checked the flame temperatures of diesel and gasoline at one
atmosphere (101 kPa) and ten atmospheres of pressure. The program
indicates
that diesel burns around 130 deg. C hotter in both cases.

The article had a number of misconceptions in it. As mentioned above
diesel fuel has a higher burning temperature.

True. It's not a great deal higher, but 130 deg. C (around 230 deg. F)
should make a difference. That's around 7% or so of their respective
combustion temperatures, on the Kelvin scale.

The guy says that
compounds of carbon and hydrogen are called paraffine while actually
in the trade they are called hydro-carbons.

I hesitate to get into chemistry, but what he said is technically correct.
Chains of C and H are known generically in the field as paraffins, or
alkanes.

He seemed to say that
because gasoline had a high octane number it wouldn't ignite in a
compression ignition engine. I can tell you that for sure it will, In
fact it will ignite so fiercely it will even break piston rings (ask
me how I discovered this).

I don't think he said that. He said that gasoline will resist igniting and
burning under compression. I know this goes against our experience with
high-compression SI engines, but consider this: Cetane is the basis for
rating a fuel's speed of burning from the heat of compression. Gasoline has
a cetane rating on the order of 25. Diesel ranges from a low of 37 or so to
a high of 55. Diesel will burn faster, and it will ignite easier, under
compression. Unless you go to the SME or MIT research sources, it seems
unlikely to me that we'll find much factual info about the combustion
process of gasoline in a diesel, which has timed cylinder injection as well
as compression.

As for what happened to your piston rings, we can at least confirm that
gasoline burns slowly and unreliably in a diesel, and I suspect (but can't
confirm; the facts may be available from the academic sources) that enough
remains to be burned as the cylinder reaches peak pressure that it may
detonate, like it does in a SI engine with too much advance or too much
compression. When the engine is burning diesel fuel, combustion is much
faster and the fuel probably never has a chance to reach the corners of the
combustion chamber (that's where detonation occurs in a SI engine) before
being consumed. So the diesel fuel burns faster, but also much more
smoothly.


Bruce-in-Bangkok
(correct email address for reply)

--
Ed Huntress