Generators, aviation fuel to diesel 4

[preacherman]

Hi All

I am in need of some assistance as i have been asked a curly question by my son and need help to answer it. Please forgive the ignorance in the question he asks

We've got some generators only small ones) that are currently running on jet aviation fuel (kerosene). We want the generators to run on deisel instead. Is this possible. Are diesel engines similar to kerosene engines?

1.Can the engines be converted to diesel??
2. How much work/rework is involved

Thanks

Lindon

 

[thruthefence]

Are these generators reciprocating or gas turbine.I think kerosene has some waxy components that may affect the operation of turbines.

 

[MiketheEngineer]

Call the mfg??

 

[nreid]

I'm actually the son that asked the original question, so I'll provide some more information.

We are doing a study for a very remote site where there is very little doumentation available. We have a site visit booked but at the moment, all I have to go on are some photographs and a P&ID.

The generator sets are only about 50kVA so reciprocating engine. They are currently running on AVTUR-FSII. I don't have information on the manufacturer.

I have little knowledge of diesel engines but I suspect that these are actually normal diesel engine generator sets running on AVTUR.

Do my suspicions sound feasible? Can a reciprocating diesel engine run on AVTUR without major modifications? Can these generator sets run on diesel after running on AVTUR?

Any assistance will be appreciated.

 

[catserveng]

You are likely correct in assuming it is a diesel or compression ignition engine running on the aviation fuel. The US military does it all the time.

The two most common issues faced, at least in my experience,

1. The aviation fuel has a lower BTU per gallon/liter than "standard" diesel. Some manufacturers allow the change in fuel stop setings to allow a higher fuel rate if light fuels were used. If it was running on light fuels and now you want to change, you need to assure the fuel settings don't allow for too much fuel or you may overload the engine.

2. The aviation fuels had lower lubricity and some steps may have been taken to either provide extra cooling or something else to help prevent fuel system problems. If you're doing a site visit take a careful look at the existing fuel supply system and make sure it meets the engine manufacturers guidelines.

In some rare cases I have run across engines that have had minor fuel injection timing changes, so when you do change the fuel type, assure the engine does not smoke excessively , or have any other operational issues.

If you can find details on the model of the engine and it's power rating, the manufacturer can provide you a fuel specification on the preferred and allowed fuels the engine can operate on.

Hope that helps,

Mike L.

 

[nreid]

Thanks Mike,

Great response. Exactly what I needed to know.

 

[rmw]

Father and son, huh? I don't think I've seen that combination on the fora before.

Good luck on the investigation. Remember too, that automotive diesel has changed a lot too since these engines were put in and set up (assuming they aren't very new.)

The de-sulphurized diesel of today (if that is what you are in to) also has lower lubricity than the old stuff.

rmw

 

[TheBlacksmith]

I oversaw this "conversion" on a fleet on Navy Boats using 71 series GM diesels years ago. The diesel fuel (DFM, Nato symbol F-76) was cheaper than the aviation fuel (JP-5, Nato symbol F-44). We just starting filling up with the diesel fuel and kept an eye on the filters; no problems noted. We did get a little smoking, which we solved by going to a one size smaller, higher popping pressure GM injector.

 

[dicer]

CI or diesel engines are easily converted to run on multiple fuel types. Like the mention above of the military doing it all the time. And yes even gasoline.
As a note small engines have been converted to run on kerosene using SI. But the low octane of kerosene requires a compression ratio reduction.

 

[preacherman]

Great replies guys. Thanks for taking the time. I have a question re using a diesel motor with alternate fuel and motors that have been used to run on fuels other than diesel.

With a petrol engine the compression ratio's range generally from 8 - 12. Diesel's work on compression ratio's from 14 - 25. What compression ratio can a kerosene injected motor operate safely and economically. Will the generators/ motors need to have their CR upped? Will there be detonation/efficiency issues?

 

[patprimmer]

Diesels are not really about CR and octane as you actually deliberately use detonation as the ignition system and timing comes from injector timing. ie the fuel can't ignite until after it is injected into a cylinder and the conditions are over the auto ignition point for the fuel.

The problems with alternate fuels are more related to viscosity, impurities, and lack of lubricity. Oh and also maybe required a:f for maximum power and tendency to leave undesirable deposits behind.

Regards
Pat
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[dicer]

What diesels are concerned about is cetane, and that is an inverse of octane. A low cetane fuel like gasoline needs a very high compression ratio to work properly. If memory serves Kerosene is pretty close to diesel in cetane area, well just smell the on road diesel nowadays, it smells very close to kerosene, and kerosene has been known as diesel number 1 and normal diesel is number 2, just a bit lower heat value with kerosene than diesel, so the power output will be reduced. The nice thing about kerosene is it doesn't gum or grow bacteria like diesel does, and stays fluid in colder climates that diesel will gel in.

 

[catserveng]

I think Pat has it pretty right. In my experience older engines with simple lower pressure fuel injection systems have a huge fuel tolerence, while newer engines designed to meet strict emissions standards have limited tolerence to fuel changes.

I used to work quite a bit with smaller power plants in the Pacific, some in the Carribean, and in Central and South America, all mainly CAT powered plants, but many mixed power stations as well.

I was amazed by some of the things I saw used for fuel. On one island they had 12,000 gallons of old gasoline, 20,000 gallons of contaminated jet fuel and a basement full of used lube oil with some hydraulic oil mixed in. The plant operator mixed this stuff with #2 diesel fuel every day and topped off the day tank for two CAT D399 engines, they smoked, they hammered but they ran and used up the junk I'm not sure how else they would have gotten rid of. One of the other engines on site was a 567 series EMD, it was mistakenly fed this witches brew one day, ran about an hour and stuck several injectors. Now that old EMD was a tough engine, there are many competative products I came to admire over the years, but it's fuel system could not tolerate the change in lubricity and the engine smoked terribly before it stopped, likely due to the much lower cetane rating of the mix.

Another site mixed rancid palm oil with diesel and jet fuel (also contaminated) and ran it in two older engines, one CAT and one Blackstone until it was all used up, they killed a newer CAT 3412 with the fuel, again a fuel system failure that resulted in a burned piston.

In general I've found lower BMEP engines with pintle (single hole)fuel nozzels and precombustion chamber fuel systems very tolerant to fuel quality changes. Direct injection engines with higher BMEP and fuel injections pressures become much less tolerant. Lighter fuels tend to burn more completely and have less cylinder deposit issues, but can cause more fuel system component failures. Heavier fuels usualy need more air to burn completely and tend to form more cylinder deposits, but their fuel system component life, if the fuel was properly filtered, was about the same as using #2 diesel.

Before I left the CAT dealer I worked for we did a turn key plant for the Pacific that included one used PC type engine rated smaller than the new units, but mainly provided to burn diluted waste lube oil to dispose of it, the engine only runs about 2000 hrs/year but keeps using up the waste oil.

Mike L.

 

[rmw]

A low cetane fuel like gasoline needs a very high compression ratio to work properly.

HUH????

Kerosene is often mixed with diesel in colder climates in the northern USA to produce what he refers to as #1 Diesel when true #1 diesel isn't available. The resulting lower pour point prevents fuel system jelling at the lower temps. But that blended #1 diesel of the automotive (trucking) world is still a certain proportion #2 diesel usually at least 50%.

Pure #1 diesel can be produced at the refinery and is made by setting the beginning and end points of the distillation process at the appropriate temperatures, but it requires a change to the process so you better be ready to make a lot of it at once. For smaller quantities it is easier just to blend some kerosene to obtain the desired pour point during the coldest months or during surprise cold snaps.

And yes, as an unscientific observation, the truck drivers I employed back in the day bitched because the #1 didn't produce as much power as straight #2 diesel. They loved their horses.

I once lived near a terminal on a products pipeline in the deep south, and from time to time during the summer if you didn't pay attention to where you fueled, you would be buying fuel pulled from the pipeline that was the winter diesel on its way north (during the summer) for next winter's use. That was in the days before coloring was forbidden and you could always tell when you had gotten winter diesel because it was nice and red. It ran like crap too.

It was the opposite in the winter. You could get a load of (the north's) next summer's straight #2 fuel being shipped during our winter. I generally tried to fuel from stations I knew obtained their diesel from local refineries since they were blending more for the local climate. My day job at the time took me into local refineries as well as the pipeline terminal so I knew which tanker fleets loaded where.

Kerosene is more akin to jet fuel grades, and those obviously can't be allowed to gel at the temps found at 30K feet altitude. Ironcially, on my day job I work with industrial jet engine turbines designed to run on #2 if they have a liquid fuel option and they won't run on jet fuel grades - different burners than their aircraft engine cousins.

And, to Mike L's point, I have personally mixed gasoline with lubricating oil in a Ford 7.3 IDI engine on more than a couple of occasions in order to be able to make it just a few more miles to a diesel fueling station without any noticable or lingering problems. Really get some stange looks from 'stop-n-rob' clerks when you buy a couple of gallons of gasoline and 4-6-8 quarts of oil and that was the total sale.

I regularly mixed ATF with diesel as a water absorbent and did that in Cummins, Ford and Detroit Diesels that I have owned. (Sorry Mike, I never owned a Cat.) Seems the dispersants in ATF are excellent in emulsifying water in diesel, better in some cases than the commercial products as observed by some unscientific testing I did in my garage.

The first truck driver that turned in a receipt for several quarts of ATF that he told me he put in the tank to get rid of water took me by total surprise. I was quite the skeptic until I ran the aforementioned test.

Back when I drove diesel vehicles (sold my last one 5 years ago) I rarely changed a fuel filter that I didn't fill it with ATF rather than diesel. Hated that stench of #2 on my hands.

rmw

 

[dicer]

I agree Catserveng, divided combustion chambers are very forgiving of fuel types. I like those old D353, D342, D399 etc. engines some of the best and most durable engines ever. They had a few problem areas but still good engines.

rmw why the hum? Its a true statement. We are talking the CI world not SI.

 

[rmw]

I guess I never saw gasoline as a fuel in a DI engine (of a type being discussed here, of course), but I'm a learner here.

rmw

 

[catserveng]

The beauty of a forum like this one is the large diversity in experience. Generally you wouldn't consider gasoline as a fuel for a CI engine, but is some cases the ability to dispose of marginally usable waste products, like 25 year old gasoline or jet fuel contaminated with water and rust, makes a pretty good compromise if the engine will handle it. I've seen these type engines run on stuff the original designers never dreamed of, hopefully a designer would find it gratifying that his design was more robust and tolerent than intended.

For all the years I worked at a CAT dealer, on-road diesel, mostly #2 was the preferred fuel. My first experience with an engines owner not wanting to use diesel fuel came from a site that was a remote military base with the primary fuel stock on the island being jet fuel for helicoptors. They burned more gallons per hour than they would have with diesel, but didn't have the concerns of accidentally mixing fuel and causing other potential problems for the aircraft.

From some old operating literature, fuel used to account for 75% of the 10 year life cycle cost of a typical high speed diesel engine. With shortages, desire to use waste streams, reduce logistical concerns and complexity, or just to save a buck or two I'd expect that people will find a broader range of stuff to feed their engines with, at least till the air board folks get wind of it.

Mike L.