Cetane Rating of Fuel--IDI Diesel Starting

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moose60
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Cetane Rating of Fuel--IDI Diesel Starting

#1

Post by moose60 » 13 years ago

My understanding of Cetane is that it's a rating of how easily a fuel ignites.
Low Cetane fuels can contribute to ignition knock, and possibly harder cold starts. But, of course there seems to be a point of diminishing returns somewhere around C 55 or 60 where we will see no benefit.

Our US diesel seems to have C 40-47, with 40 being the lowest allowed for ASTM D2. Most European nations seem to sell fuel with significantly higher Cetane (total hearsay on my part).

My real question concerns biodiesel vs. diesel in a cold start application. Biodiesel that meets ASTM will have Cetane of AT LEAST 47. Most (depending on oil type) will be above this (some even into the 60+ range).
BUT biodiesel has a significantly higher flashpoint than D2(try throwing a lit match into a small container of each, also ASTM specifies a high flashpoint.)

With the same C rating, I think that Biodiesel (assuming it's not gelled) will be a little harder to start a vehicle on. I wonder though, if in practice the higher Cetane will make the fuels function almost the same?


When I fuel my truck with D2 the combustion clatter is really noisy (almost alarming with the window down) on a 35-40* morning until the engine is close to operating temp. Using biodiesel, the truck is much quieter in all conditions.
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philip
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Re: Cetane Rating of Fuel--IDI Diesel Starting

#2

Post by philip » 13 years ago

moose60 wrote:When I fuel my truck with D2 the combustion clatter is really noisy (almost alarming with the window down) on a 35-40* morning until the engine is close to operating temp. Using biodiesel, the truck is much quieter in all conditions.
ASTM vs Homebrews

Noisy combustion while warming
-Philip
Passed 08May2008
My friend, you are missed . . .

1982 Datsun 720KC SD-22

"Im slow and I'm ahead of you"

moose60
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#3

Post by moose60 » 13 years ago

Philip-
We seem to have had differing experiences with BD and cold engine clatter. The difference is quite noticeable in mine, quieter under all conditions on BD (but especially when cold). I had already read the topics in the links provided, but disagree with some of the conclusions.


I'm happy with the truck (but I think I will need to have some front end work done soonish). It get 35+ MPG pretty much all the time. Closer to 35 around town on BD, and 30-40 on D2 and highway use. I lose 2-3.5 MPG when running on BD.

I don't have enough experience with fuels of (known) differing Cetane to make a blanket proclamation, but I think that a fuel with a higher Cetane would result in less cold clatter (combustion lag). A higher Cetane only seems to indicate the ease at which a fuel ignites, not the rate at which a fuel burns.

If a slow to ignite fuel is being injected into a cold combustion chamber, there will be some (very small) delay in the initial ignition of this fuel. The result is that ignition will occur later (retarded) and there will be a greater quantity of fuel present to burn. This greater quantity of fuel than normal igniting causes the knock. A higher cetane fuel will have a shorter ignition lag, and therefore less knock due to less excess fuel being present at the point of ignition.

In summation: Without changes in injection timing, I have experienced less combustion cackle using higher Cetane fuel.
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#4

Post by philip » 13 years ago

Based on the bulk of your last post, where are we at at odds? When you mention BD reducing cold combustion knock, what is the concentration? 100% BD or some ratio like 80% BD with 20% D2?

I have searched for a research engine graph depicting ignition lag time in degrees of crankshaft rotation at some fixed RPM from cold to operating temperature ... have yet to find.

Considering the amount of injection timing retard I have found to pretty much squelch cold combustion knock, the effect of cold combustion chamber surfaces has much more than a "very small" effect on ignition lag.

What do you make of this ... from one of the well known BD outfits?

BD IP timing suggestion
"Timing
Optional: Retard the injection timing by 2-3 degrees -- this overcomes the effect of biodiesel's higher cetane number. The engine loses a little of the extra power you get with biodiesel, but it runs quieter and the fuel burns cooler, reducing NOx emissions. (See also NOx emissions and biodiesel.)"
-Philip
Passed 08May2008
My friend, you are missed . . .

1982 Datsun 720KC SD-22

"Im slow and I'm ahead of you"

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asavage
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#5

Post by asavage » 13 years ago

Try not to quote journeytoforever . . . they have a LOT of misinformation there. They may be a good place to start, but do let your research continue elsewhere.
Regards,
Al S.

1982 Maxima diesel wagon, 2nd & 4th owner, 165k miles, rusty & burgundy/grey. Purchased 1996, SOLD 16Feb10
1983 Maxima diesel wagon, 199k miles, rusty, light yellow/light brown. SOLD 14Jul07
1981 720 SD22 (scrapped 04Sep07)
1983 Sentra CD17, 255k, bought 06Jul08, gave it away 22Jun10.

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philip
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#6

Post by philip » 13 years ago

Shhhhhhhhhhhhh!

You just wrecked some fun I was gonna have with the Moose.
-Philip
Passed 08May2008
My friend, you are missed . . .

1982 Datsun 720KC SD-22

"Im slow and I'm ahead of you"

moose60
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#7

Post by moose60 » 13 years ago

Al and Phil-


Much of the stuff on the JTF website has been debunked quite sometime ago. They have advocated for some truly ridiculous "recipes" (ie. on titration) for making BD, as well as at least one worthless final product quality test. On the subject of BD http://biodiesel.infopop.cc has more up to date info. Also on the subject of starting out http://www.biodieselcommunity.org But I'm sure that you two guys already know about most of this stuff.

Philip-
I only differ from you in that I experience BD (mostly ASTM B100, and other concentrations as locale dictates) giving less combustion noise. I attribute this partly to the higher cetane of the fuel.
Now, I'm not trying to be snotty, but please try to cite a source for your quotes. This is a common requirement for anyone who wants to follow up or check on text from a source that is not in its original context.





Even More Off Topic:
I'm a little surprised that we haven't seen much discussion on this board of the stuff that the folks at Diesel Secret are selling. Maybe folks can smell a scam? I have a Nigerian Uncle who just needs to contact someone with credit a little better than mine so that he can get an inherited fortune out of his country. This helpful American would stand to gain 114% of 17.6 Million Euros. Email me quickly so that I can put you in touch with my Uncle, and send you a FREE Diesel Secret Spam. I meant to say info packet. :roll:

Happy New Year Folks
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philip
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#8

Post by philip » 13 years ago

moose60 wrote:On the subject of BD http://biodiesel.infopop.cc has more up to date info. Also on the subject of starting out http://www.biodieselcommunity.org But I'm sure that you two guys already know about most of this stuff.
Cursory perusal ... both of these sites are what I call "BD enthusiast" sites ("zealot" is a bit strong) because they spend precious attention on engine mechanics and tuning for B100 or blends. I concern myself far more with tuning engines and engine component longevity because I decided homebrew was not for me and later on discovering buying ready-to-run ASTM B100 was just too expensive. A Los Angeles fuel stop has B20 at the pump but that's yet another story. :x
moose60 wrote:Philip-
I only differ from you in that I experience BD (mostly ASTM B100, and other concentrations as locale dictates) giving less combustion noise. I attribute this partly to the higher cetane of the fuel.

Now, I'm not trying to be snotty, but please try to cite a source for your quotes. This is a common requirement for anyone who wants to follow up or check on text from a source that is not in its original context.
When you tell of a reduction in combustion noise, you are referring to cold engine only, correct? When there is such a sharp reduction in cold diesel knocking by raising cetane, that speaks more to the low cetane number of your undilute D2 for the engine's requirements.

The other end of raising cetane for an engine at operating temperature is ... the maximum pressure in the cylinder occurs closer to TDC (optimal is in the 10-14 ATDC range) which dramatically increases loads on piston and connecting rod, will reduce power due to reduction in mechanical efficiency (piston/rod angularity with crankshaft position), and sharply increase NOx formation unless the cetane improver has less BTUs.

So ... we retard the timing enough to reestablish peak combustion pressure occuring in the 10-14 ATDC range again which also just happens to be the answer to excessive cold engine combustion knock in SD's and perhaps another reason for the small MPG loss in some cases.

Regarding my quoting, the pale blue text is a LABEL (with/without underscore) for a working clickable link. It's a trick Al showed me. :)
Last edited by philip 13 years ago, edited 2 times in total.
-Philip
Passed 08May2008
My friend, you are missed . . .

1982 Datsun 720KC SD-22

"Im slow and I'm ahead of you"

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#9

Post by asavage » 13 years ago

I used to hang out at biodieselnow.com, but have sort of stopped.

"Diesel secret" is not worthy of discussion, IMO. If someone can't be bothered to Google it, they deserve what they get.
Regards,
Al S.

1982 Maxima diesel wagon, 2nd & 4th owner, 165k miles, rusty & burgundy/grey. Purchased 1996, SOLD 16Feb10
1983 Maxima diesel wagon, 199k miles, rusty, light yellow/light brown. SOLD 14Jul07
1981 720 SD22 (scrapped 04Sep07)
1983 Sentra CD17, 255k, bought 06Jul08, gave it away 22Jun10.

moose60
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#10

Post by moose60 » 13 years ago

Philip,

I agree that the D2 I'm using is probably of rather low cetane. I'm sorry that I missed the link above your post. I guess that I didn't pursue the blue text any further because it wasn't underlined. Now I know.w
I also agree on the fan(atic) nature of some sites. Those two sites just have better info on processing and testing of final product.
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philip
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#11

Post by philip » 13 years ago

moose60 wrote:Philip, ... Those two sites just have better info on processing and testing of final product.
To you and Al: my interest in any biodiesel website is NOT the manufacture of fuel. My interest is taking a finished product and getting the engine to run well and for a comparable length of time on the stuff ... if feasible. THIS kind of information is woefully absent on the Internet compared to the how-to of making fuel.
-Philip
Passed 08May2008
My friend, you are missed . . .

1982 Datsun 720KC SD-22

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#12

Post by asavage » 13 years ago

I'm with you, Philip, and most of the "How to make Free [sic] Fuel" primers gloss over the "How to dispose of the Glycerine" part.

While I can imagine wanting to play with producing biodiesel, just managing the commercial BD we buy is hard enough ;) Fuel handling can be messy, esp. when you're trying to keep a shared dispensing area safe and clean.

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#13

Post by philip » 13 years ago

Maybe winter is over here. Last few days in the 70's and 80's, 45* overnight.

Even today ... 60* but overcast. So, my experiments with winterized fuel and heated air are on 'hold' for now. SUCHA burden. Wink
-Philip
Passed 08May2008
My friend, you are missed . . .

1982 Datsun 720KC SD-22

"Im slow and I'm ahead of you"

moose60
Posts: 168
Joined: 14 years ago
Location: Seattle WA

#14

Post by moose60 » 13 years ago

Perhaps you shipped your winter north. We are colder than normal. Overnight low around 20 deg last night, high today 29 deg. Over the next week our highest temp forecast is around 40deg, with most nights around freezing. But, it's wonderfully sunny.

Thanks Philip.


Al-
I hear ya on the issue of fuel spills and cleanliness becoming more difficult when working with groups of people.

Philip-
I also wish that there was more good info on BD and its' long term effects etc. on engines. I did run across a good paper a while ago tat studies the speed of sound in BD vs. D2, as this affects the rate at which pressure rises. This contributes to slightly earlier start of injection when using BD. That is, is you keep everything the same (inj timing etc.) the actual inj. event will happen slightly sooner. The paper also discussed viscosity issues, especially related to injection timing. If anyone is interested I will try to post a link (if I can find it again).
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#15

Post by asavage » 13 years ago

moose60 wrote:I also wish that there was more good info on BD and its' long term effects etc. on engines.
?????
Biodiesel has been in use for a long time in automotive and industrial use. I think its effects are known.

WVO/SVO has also been in use for decades -- but not in automotive or industrial. Lister engines and the like love the stuff -- but these are engines with cast iron pistons and max speeds of 650-950 RPM, that are making 20 HP from 3200cc! These are not automotive engines.
I did run across a good paper a while ago tat studies the speed of sound in BD vs. D2, as this affects the rate at which pressure rises. This contributes to slightly earlier start of injection when using BD. That is, is you keep everything the same (inj timing etc.) the actual inj. event will happen slightly sooner.
I assume you meant ignition event. With a higher cetane rating, the "ignitablity" (under compression) is better/faster than D2.
The paper also discussed viscosity issues, especially related to injection timing.
BD, at room temperature, does not have significantly different viscosity than D2 -- although WVO/SVO certainly does!
Regards,
Al S.

1982 Maxima diesel wagon, 2nd & 4th owner, 165k miles, rusty & burgundy/grey. Purchased 1996, SOLD 16Feb10
1983 Maxima diesel wagon, 199k miles, rusty, light yellow/light brown. SOLD 14Jul07
1981 720 SD22 (scrapped 04Sep07)
1983 Sentra CD17, 255k, bought 06Jul08, gave it away 22Jun10.

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