Engine re-tuning requirements for biodiesel 1

[davster01]

Hi,

So far, all the studies looking at the emissions improvements of biodiesel over petrodiesel seem to be skewed in that they do not consider the potential need to re-tune engine timing to account for different cetane number of these respective fuels.

Have the members of this Community ever heard of a study that would compare performance of re-tuned engine burning biodiesel (B5,B10,B20 and beyond) vs. the same un-tuned engine?

The reason I ask this is the following: In the likelihood of biodiesel supply regional disparities, a ship travelling great distances (i.e the Artic) might start his voyage burning biodiesel while reverting back to petrodiesel.

I would like to be able to obtain an understanding of marginal gains associated with fuel-specific tuning of engines.

I am specifically looking at engines in the 0.5 MW-2MW range, slow and medium marine diesel engines. But considering there is not much information at the moment, anything would be appreciated.

Thank you
davster01

 

[JSteve2]

The emissions gains from bio-diesel are largely because these fuels have essentially zero sulfur or other trace pollutants that will be found in any petroleum based product. Further, as a slighly oxygenated fuel with a uniform or near-uniform molecular size distribution, there will be some decrease in particulates and carbon monoxide (which CO is not really an issue in diesels anyway). These emissions gains are real.

Bio-diesels necessarily have lower energy density, and from the perspective of the engine, there is a higher specific CO2 output per horsepower-hour. Of course, bio-diesel is a renewable fuel, so that CO2 is part of a cycle rather than pure release like a petroleum product. However, energy goes into the growing and making of the bio-diesel, so the final outcome of the CO2 cycle is somewhat uncertain.

There will be some, but very little, tuning that can be done based on the percentage of fuel that is bio-diesel. However, since the engine can run at similar boost levels and thus run a similar thermal cycle, I would expect final thermal efficiency to be a wash. I.e., other than the inherent lower energy density, the efficiency of the regular to bio-diesel engine is probably similar and therefore has a similar emissions profile subject to the above notes. You will probably have a lower maximum torque and horsepower running on a high percentage of bio-diesel, but that shouldn't really affect work-specific emissions.

 

[catserveng]

I have experience with CAT engines, specifically 3500 and 3600 series and Mak engines in EPG and Marine applications using B20 fuel and one Mak using B100. All of the data is from memeory and some personal notes as I no longer have access to the files.

The 3500 series engines, in EPG applications, had a 30-35%reduction in DPM and a 25% reduction in CO as compared to ULSD, Nox increased by 9%. Fuel comsumption increased by 2.5%, and was expected due to comparing fuel analysis. Two marine engines were run on B20, but due to size of vessel no actual particulate testing could be performed, however the Nox and CO changes were similar to the EPG units when using a Testo portable analyzer. Because the engines being tested were electronically controlled and CARB certified, no "tuning" could be performed. No power derate was noted and after 8,000 hours no mechanical problems were noted.

Two 3612 EPG engines were also tested with B20 fuel, again in EPG application, reduction of DPM was 45-55%, CO reduction 25-30%, Nox increase about 8%. Fuel consumption increase only 1.5%. A single engine tug with a 3608 was selected for testing, but fuel storage and handling problems caused the end user to back out of the program.
Some fuel injection timing changes were tried in 1 degree increments with no real benefit found on these particular engines.

I worked with some performance engineers and a dealer service engineer in Europe who did some similar testing on four Mak engines configured for distillate fuel at a small power plant, their results on the Mak engines were similar to the CAT 3600's on B20 fuel. One of the engines ran about 6 months on B100 fuel. From the B20 numbers a small reduction in DPM and CO were noted, but the NOx went up about 4% more, fuel consumption change was near 7% and a 3% power derate was applied. Some attempt was made to try some different cam and fuel injection timing settings, but as I remember they factory settings ended up being used for the bulk of the testing.

I also had direct experience with two marine engines, CAT C32's running on B20 in southern california. The engines ran well, and performed within tolerence. Emissions data was taken on dyno on both ULSD and B20 before installation under steady state conditions. These were also electronically controlled and CARB certified engines, so no adjustment changes. Emissions and fuel data similar to the 3500 series data above. Vessel experienced several problems with primary fuel filters plugging and fuel supply system leaks. Vessel was about 10 years old at time of testing and had run DFM for several years before switching to ULSD, then to B20. If we could keep fuel to it engines ran well, in hindsight we should replaced fuel tanks and fuel plumbing.

Hope that helps.

 

[dicer]

Catserveng, did you do any tests that involved engine tear downs and parts inspection? It's been awhile, do all the 3600's have the special liquid cooled exhaust seats, the same as the heavy fuel 3600's do?

 

[catserveng]

The 3600 testing went thru a top end period, in the same power house was an engine still running on distillate fuel only.

The engines on the B20 fuel appeared to have less top ring land and upper liner carbon deposits, exhaust valve and seat wear rates about the same, inlet valve and seat wear appeared to be less. Distillate engines do not have valve seat cooling like the HFO engines do.

As I understand it the power house still uses biofuel based on availablity, it is an approximate B20 blend, and they interchange it with their normal fuel stocks, only I have heard they try to use it more quickly to prevent issues with storage degradation and biological growth.