A lesson on Cetane/Timing

[ISX]

Maybe some of you have read this page http://mopar.mopar1973man.com/cummins/general/2-cycle-oil/cetane/cetane.htm well I am going to prove it. Words don't always get the idea across and I want you all to see what happens when you vary the cetane. First off, cetane is the ignition quality of fuel and by that I mean it determines how long it takes the fuel to ignite when heated to it's autoignition point. The bigger the number, the shorter it takes to blow up. We can show this with math and crap, OR, we can show this with some extreme fuel choices. I think you all know motor oil does not ignite very well. On the other hand, power service will ignite quickly. Motor oil has a very low cetane, power service has a very high cetane. Now here is how the engine works with cetane. The piston comes up and has so much compression that it heats the air to a very high temperature, higher than the autoignition temperature of fuel (~450F). A little before top dead center, fuel is injected into the combustion chamber. This fuel absorbs the heat that is in the very hot air, and ignites. Cetane comes into play when the fuel ignites as I stated previously. So why is this so critical? Well the engine only has a limited amount of time to get the fuel to ignite. When they say the timing is 14 degrees before top dead center, they mean the fuel is injected 14 degrees crankshaft rotation before TDC. Obviously it would be a disadvantage for the fuel to ignite before TDC since it would be trying to push a piston down that is still trying to come up. RPM play a key role in this. The faster an engine is turning, the less time BTDC the engine has to get the fuel to ignite. This is why truck pullers advance their timing to degrees over 20, because they are revving so high that they need more time to get the fuel to burn, so they inject it in sooner. If your engine turns slower, say 1000RPM, your most efficient timing might be somewhere in the single digit degree range, because it has a lot of time before it gets to TDC. As the engine RPM goes up, timing needs to advance so that the engine will be injecting fuel at the perfect time, not too soon and not too late. The knocking is actually a sign that it is injecting too soon because it is igniting before TDC. When I advanced my timing, it would knock at idle, when I retarded it back to stock, it was back to being quiet. The p7100 trucks have static timing, so mine is always the same. I just showed how timing needs to change so p7100 trucks must be set for the best setting for most drivers. Retarded enough to start good, yet advanced enough to be efficient at cruising RPM. Now that you know about timing and cetane, I can explain why you see what you see in the video. My truck idles with the needle just scratching the line under 1000, on diesel fuel. So with cetane at 40 or whatever the summer fuel I get is, it ignites and provides the power for that rpm. When I changed over to the motor oil, my RPM dropped a lot. Motor oil contains the same amount of energy as diesel, if not more, so it would make sense that my rpm would go up, but that obviously doesn't happen. So what gives! Damn oil is worthless! No, the truth is that the oil has a very low cetane compared to diesel. So the delay is very long. So long that the oil ignites after the engine has reached and gone past TDC. The oil is only exploding on part of the power stroke because it took so long to ignite. In theory, if we advanced the timing a lot, we could get the RPM's back up. Now lets say you are running vegetable oil. Now your cetane is very high. It will knock more because it is igniting very soon. In this case it would be beneficial to retard timing.

http-~~-//www.youtube.com/watch?v=fAmgB2sJlPg

[AH64ID]

While I think part of the theory is correct, I don't think thats really a good comparison. There are a lot more reasons than just Cetane as to why it idled very low. The flash point of #2 is about 125*F, where oil is much higher (The oil I run is 460*F). At idle speed there just isn't much combustion temp, so the oil won't fully burn or ignite. You could add Cetane booster to it until it matched #2 and it would still run like crap at low loads and rpms. The real test will be to have several rigs run the dyno without and then with Cetane boost in the truck. On the same day as close as reasonable possible to each other. I am still doing more research on this, as I have $80 is Cetane boost in the garage... I have never seen a false claim from Amsoil, and looking at there web-site its good stuff, but Mike's chart is hard to argue. But I only run a small increase, and really probably only should in winter, if at all...

[ISX]

I was trying to make it as extreme as possible. I doubt it would have done much otherwise. It might not be the best example but it does get the point across as to what cetane and timing do. I know there are 100 other variables but I was just trying to hit the main ones. Something interesting though, 2 stroke actually raises my idle. This was when it was at 16* timing. Makes me think the 2 stroke was perfect at that timing but diesel was a little inefficient. Of course that is only at idle speed. I put my timing back to the stock 13.5* the other day so I am not sure if the motor oil would have been any better if it was at 16*.

[AH64ID]

I found this from Cummins.

? Cetane Number

? General Description – Cetane number is a measure of the starting and warm-up characteristics

of a fuel. In cold weather or in service with prolonged low loads, a higher cetane number is

desirable.

? Test Method – ASTM D613, ISO 5165

? Fuel with a cetane number greater than 55 may cause increased torque peak smoke. Reference

ASTM D613, ISO 5165.

--- Update to the previous post...

Yeah its a really hard thing to test, without being on a dyno.. Based on that info I found from Cummins I will still use Cetane boost, but in a smaller dosage and mostly when I am empty or low load in winter.

But then again I haven't noticed a bit of difference with or without it, and had too many variables since I stated using it to comment on hp, mileage, etc.

[ISX]

The only thing I see it doing is making it start better. I can get B20 here and I ran it a few times in the winter and it started a lot faster. But I also didn't get as good of mileage. Higher cetane stuff just burns up too quickly. Look at a gallon of oil and a gallon of gasoline. Light them both up and the gas burns up quick and the oil will burn for hours. I think higher cetane fuel is done burning before the engine has completed the power stroke whereas lower cetane will burn throughout the power stroke. Get too low and it won't burn up all the way, so there is a limit.

[Mopar1973Man]

Yeap I agree...

A BTU, short for British Thermal Unit, is a basic measure of thermal (heat) energy. One BTU is the amount of energy needed to heat one pound of water one degree Fahrenheit, measured at its heaviest point.

So 1 oz of oil would burner loner producing more BTU's (lower cetane) compared to 1 oz of gasoline which burns quickly producing less BTU's (high cetane) The only time I see high cetane being a real need is for racing applications where the RPM's are 4K and the piston speed is so fast that the fuel needs to burn fast enough to keep pushing at a high rev application. But for typical street use I don't see a need for above 45 Cetane.

[AH64ID]

I agree with the winter use.. My truck runs great on B20 (when it doesnt gel:banghead:), and I didn't notice much of a mileage hit when empty cruising, but it was quieter, had more fuel pressure, and smelled great!But gas doesn't have cetane, at least I can't find anything stating it does. Cetane is the fuels ability to compression ignite correct, and is only rated on diesel. Gas burns much faster than oil becuase the vapor pressure is MUCH higher. At the very low end the vapor pressure of gas is around 4.5. The vapor pressure of kerosene is .1, and motor oil will be a lot lower than that. Again, its really hard to quantify any of this data on Cetane differences, those 100 other variables are to blame, not Cetane. I know I keep finding ways to burst your bubble, but all the data needs to be considered.

[ISX]

Yeah your getting way to complex for what I am trying to show lol. I know gas and oil are different and have all the different properties. This is solely for people to get a better understanding of cetane. So although gas and oil are different, they show the principles of cetane very well (if you don't think into it too much ).

You are very right though. Gas doesn't have cetane and everything is based on something completely different. Oil also is based on things different from regular diesel. I mean it's not really meant for burning like say, 2 stroke is. The fumes from the exhaust were horrid with that motor oil in it. Smelled like gas and diesel fumes mixed together lol.

I am going to try and organize all of this and put it together in another discussion since you are getting more advanced than I wanted this thread to be lol. I do like all of your info and want to hear more, so let me get a different thread going that better emphasizes the stuff you are testing out.

[AH64ID]

But I'm really not going that complex... just stating that there are several other things that have a much larger impact on your results than Cetane.

[ISX]

Alright well I have a better idea. Tell me what I need to do in order to show how cetane works. I don't do things with text I do them with videos, things people can see. I can go on all day about stuff from sources but a lot of people don't understand it, that is why I do videos of this, so they can see what high and low cetane does. So if the way I showed it is not showing how cetane works, then what can I do to show everyone how it works. Every additive boasts raising cetane, 2 stroke oil lowers cetane, what exactly does it do! It starts better on higher cetane, yes, but after it starts, then what does cetane pertain to? I want to show it with a video not something a book says. Idling shows how efficient it is burning and the cetane number is one of the factors of efficiency. If the cetane is too high or too low, it will not be efficient. I wanted the fuel rate to be the same so what better way than idle speed. Maybe I will get some cetane booster and run a heavy dose to show what happens. Just let me know what I need to do and I will do it

[AH64ID]

From the research I have been doing its very hard to test the effects of Cetane. You would need 2 samples of the same fuel, and have one with an additive that boosts the Cetane. But I can't think of a single way to determine ignition point.

I am really not sure your going to be able to make a video showing the effects of Cetane.

Since diesel fuel is the only fluid that has a Cetane rating and there is supposed to be a minimum I don't think you will find a sample with a very low Cetane, and then a very high Cetane.

What is there that shows 2 Stroke lowers Cetane?

Unlike octane where you can go from 87 to 93 and notice a difference in ping, there just isn't anything on a diesel that shows that level of difference..

*Maybe* if you had a powerstroke and had 2 tanks, one with #2 and one with #2 and a Cetane boost and did some cold (20*) starts without use of the glow plugs you could show easier starts and less white smoke.. but white smoke isn't a common issue with Cummins, but I have seen it plenty on OBS Strokes.

But to show the differences in one property of a fuel all the other properties need to be equal, even for a simple test.

--- Update to the previous post...

From what I gather Cetane has the largest effect on cold starts. After the engine is running it should provide a smoother, and quicker ignition; however, that's really hard to quantify. The advanced timing should provide for more hp from the same amount of fuel, which should equate to better mileage (as less fuel is needed to make the required hp), but that contradicts what Mike's ATSM chart shows...

Really the best thing will be to dyno a truck, 4 runs. The first 2 with normal #2, then add cetane boost (enough for a 7 point boost) and run 2 more runs and compare the graphs. That will tell you honest effects of cetane on the engine.

--- Update to the previous post...

If it really does advance the timing it will be quantifiable.. SW1 on my Smarty Jr is good for 10/100 over stock on timing only. Timing has the biggest impact (at least on a 3rd gen) in the 1500-2400 rpm range, so I would even be happy if the Cetane boosted hp there and lost hp at the upper rpm range, say for a -20/+50 gain?

[ISX]

Alright I got some ideas. To keep everything equal I just drain some of the fuel out of my tank and use it. Show idle before and after adding cetane booster. I will also get some results on going the same route same pump same shutoff point at the same speed before and after adding cetane booster and see if I have any mileage difference.

If we can't show how it works, we can surely show the effects it has on efficiency. I think I might even just run a gallon jug so I can see how much it used instead of with some cheesy pump shutoff. Then I can have 3 gallons, one with cetane boost, one with 2 stroke, and one normal.

You think that will work? Any other ideas?

--- Update to the previous post...

Yes cetane makes it easier to start. It was night and day difference between regular and that B20 in the winter. So we can prove that much. I want to get other tests in there. I know mike has a dyno run with and without 2 stroke but he shoulda got a cetane booster run also.

[AH64ID]

Without a dyno thats the best we can probably do.

[ISX]

I should be able to get it pretty accurate. If you think about it, it kinda does the same thing as a dyno. If it takes more fuel then it is obviously producing less power and vice versa.

[AH64ID]

Yep.

[Mopar1973Man]

Now another thing that boh of you are forgetting about is the EPA requirements... Cetane and fuel specs are designed to meet EPA requirement regardless of BTU content, cetane, etc.. So if Cummins show a requirement for >45 Cetane fuel this is because its has to deal with EPA emissions. It has nothing to do with net power. So now if you could scientifically test fuels across the board and try different thing without the EPA requirements I bet you'll find a way different story to be told...

[AH64ID]

That makes sense. Min number is probably derived backwords from timing requirements for emissions.

[Mopar1973Man]

So of course if the cetane to drop too low <40 cetane the burnability of the fuel would be so poor that emmission would increase rapidily. But of course if you drive the cetane upwards to 55 then the fuel would burn up completely before the end of the power stroke. So once again there is a balance ot the cetane mystery. Here is the best way to look octane to cetane. http://forum.mopar1973man.com/attachment.php?attachmentid=1663&d=1283554927

[elshadow001]

I continually am looking for information on my truck, and trying to make it last as long as I can. I am retired with a limited income, so I do all I can to survive. I now know after finding this forum, and reading stuff on others that mostly it is all about politics and others things like clean air. Those in a position for the government don't give a dam about how long a truck lasts, and most likley would like to see them off the road. Here is a interesting link http://alternativefuels.about.com/od/thedifferenttypes/a/ulsd.htm Read between the lines. They are telling you to get rid of that old piece of crap your driving, and go in debt, and buy our new clean air machines. To many times I have seen this happen in my life, and then they just merley say oh well, we have newer better faster cleaner ones now. Pure B.S. The link basicly says lubrication lubrication that is what will save your engine. Well sorry people but I for one am going to be a ahole and put a little smog in the air more then the new clean machines. However consider that I drive around 1000 miles a year ( guessing now ) One truck left idleing over night in a truck stop will put a whole lot more in the air then what I am doing buy adding two cycle oil to my fuel in a lot of years, and no one ******* about that. End of my Rant.

[guesswho512]

One truck left idleing over night in a truck stop will put a whole lot more in the air then what I am doing buy adding two cycle oil to my fuel in a lot of years, and no one ******* about that

funny you should say that. a week or 2 after buying my truck, i went on a business trip to Taunton, MA. when i went thru NY, they had sign posted every saying if your diesel idled more than 5mins you were going to get a ticket! still to this day i have not payed as much for fuel!