Cetane and Power 1

[TugboatEng]

Let's say I have a compression ignition engine and I double the cetane of the fuel it normally runs on. Is it possible that the shorter ignition delay of high cetane fuels may reduce power at lower engine speeds with a fixed injection quantity and timing?

 

[Lou Scannon]

I guess anything is possible depending on the details. In a modern common rail engine with multiple shots and/or rate shaping, I doubt cetane in excess of the minimum required would produce any noticeable effect.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

 

[enginesrus]

Depends on the compression ratio.

 

[TugboatEng]

14:1.

Lou, the engine was tested on diesel #2 but is being operated on HVO. I am trying to account for the loss of performance.

 

[gruntguru]

How much power loss?
HVO tpically has a lower calorific value (~4%) and with identical injection rate you will lose power accordingly on that account alone.

je suis charlie

 

[Lou Scannon]

Are you able to read/datalog control parameters?

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

 

[TugboatEng]

Our problem is that it seems there is more than 4% loss at lower speeds. I'm trying to hit this problem from all angles.

 

[gruntguru]

The lower calorific value would have more effect at lower LOADS (4% loss in IMEP => >4% loss in BMEP).
If it is definitely a low speed effect, is it easy to retard timing and re-check?

je suis charlie

 

[TugboatEng]

It's a federally certified engine running on state mandated fuel. The manufacturer of the engine did testing of the new fuel on a generator set but as far as I can tell there has been no testing done on variable speed engines.

 

[catserveng]

Tug,

Ran into to this issue several years ago in SoCal, some crew and supply boats servicing rigs in off Ventura complained of power and fuel consumption issues on both varying degrees of bio-diesel and HVO fuels after a change in fuel was mandated by the local air board.

We did a program with CAT, Cummins and Southwest Research/UC Riverside to study the actual effects. There was a paper written and submitted to CARB and the EPA, but I can't find my copy of it and a web search didn't find it.

What we found was that Biodiesel, depending on blend caused a notable increase in fuel consumption, with B-5 increasing 1-3% and B-100 5-8%. Versions of the HVO fuel available at the time of our testing had 7-9% lower heating value than #2 diesel. Engines with mechanical fuel systems and NOT EPA certified could have fuel rack adjustments made to help maintain power output, but there were still issues noted with power and acceleration performance. We did find on some older mechanical fuel controlled engines we could adjust injection timing and compensate for some of the performance issues. Please note I dug up some of this info from some old emails and files, but the bulk of my info from the time was submitted to SwRI and when I retired I didn't keep a lot of the old paperwork.

Electronic engines with fuel rates controlled by the ECM could not be field adjusted to compensate for the fuel density and combustion characteristics of the Bio derived fuels. We did some test cell work at CAT and found we could improve fuel consumption and performance on some models of the engines being tested, but the engineering team found that at that time the certification process costs would be excessive, and both CARB and EPA were resistant to allowing modifications to type certified engines already approved. I understand Cummins did a similar path with same results. A local EMD dealer was able to get near #2 diesel power/performance on biofuels, but fuel consumption went way up, at least based on conversations with some of their techs. Our baseline diesel fuel was #2 Red Dye Diesel with an API gravity of 38, since most to the engines we were testing had defined performance data using fuel with an API gravity between 31 and 35, fuel consumption was already higher in most cases using the low sulphur diesel fuel.

I'll reach out to an old SwRI contact to see if he can get me a copy of the paper, and I did ask around to some older CAT contacts, seems there has been some work on newer biofuel blends, but not really much progress since the emissions certification process is pretty intensive these days.

From my own field work over the years I can tell you performance testing of higher performance CI engines has indicated many times that variable speed engine applications varied significantly different than constant speed applications, especially with emissions certified engines.

Hope that helps, MikeL

 

[Lou Scannon]

With different fuel formulations (e.g. E85 vs gasoline, or biodiesel vs diesel from petroleum, when the calorific heating values differ, it would be fair to make comparisons based on thermal efficiency, but not necessarily fair to make comparisons based on mass or volumetric fuel efficiency.

both CARB and EPA were resistant to allowing modifications to type certified engines already approved

That seems like hiding their heads in the sand. If a fuel they approve or mandate can change the performance noticeably, why would they expect emissions to be remain compliant, without testing and recalibration of engine-fuel combination in question?

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

 

[TugboatEng]

Thanks for the insight. I have suspicions about constant speed vs variable speed testing.

It sounds as if our dealer has factory permission to adjust the smoke limits on the engine. I want to work with the factory to develop a better smoke control protocol. I think this can be done with acceleration rate limits instead of rack limits. By utilizing acceleration limits the engine will have torque available in the event or emergencies.

Lou, the CARB is totally out of control. They're forcing us to replace 5 year old engines with new ones that require extensive modification to the vessel. Our engines only operate at 15% lifetime load so there is very little emissions reduction available. Hopefully the Chevron ruling pulls the reins in on these organizations.

 

[mfgenggear]

Tug did the manufactures have any suggestions.
I am not a diesel mechanic.
How ever it seems the correct timing control and jetting may be required. What is the timing set for these engines , eg retarded, or advance
Any time the governments get involved it turns engines in to dogs

 

[TugboatEng]

All of that information is trade secret, the manufacturers are very tight with it.

 

[mfgenggear]

Tug
Can you hire a service tech from the manufacturer. To adjust settings.
How us the chief mechanic know how to correct problems. Good grief

 

[TugboatEng]

The settings are not only locked but not visible. Changing any mapping will require a new program be written for the engine by the factory and then flashed onto the ECM with a time sensitive factory password. Writing a new program may require recertification. This is an emissions certified engine and part of receiving certification is locking everybody out of the ECM.

I am between a rock and a hard place which is why I'm coming at this problem from every angle.

 

[mfgenggear]

These kind of laws is why the tuna fleet left san diego years ago.

 

[Lou Scannon]

Is there a process whereby you can open an issue with the manufacturer or dealer? Sounds like you're working that angle already... Probably your best bet. Good luck

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

 

[XR250]

I know my tractor had noticeably less power when running Bio-diesel. Between that and gelling in the winter, I switched back to the Dino version.

 

[enginesrus]

With higher cetane the desire to ignite faster, would be similar to advancing the spark in an SI gasoline engine, the early ignition would start applying excessive combustion pressure as the piston approaches TDC,
that always causes a power loss.
Could try something similar to this.

https://www.tfxengine.com/