Completely Random

[idM1028]

I've been trying to wrap my head around this for a while and I just know the deuce-and-a-half guys are going to pop in here and make me feel like an total idiot.
How is it the multi-fuel M35's can run on just about anything? To me the engines sound like a diesel (can't find a whole bunch of specs, but if I recall correctly CR is around 21:1), but they can run on say, gasoline. But if you try to run on gasoline that pretty much ACTS like diesel (i.e. doesn't like to combust readily, say 120 octane or so AV-gas) they don't seem to like it that much. But d*** it, you can run them on pretty much anything else! Either way, I just like knowing how things work and this sounds like the ultimate internal combustion engine for the zombie apocalypse.

 

[panshark]

if you have a busted up old car that hasn't seen a tune-up since the day it was new, you might notice that it doesn't quite shut off when you turn off the key. Ca-clunk, ca-clunk....shudder, ca-clunk. That's because it's dieseling. It's still burning fuel without an electric ignition source. It's able to do this based on heat and pressure, using gasoline as a fuel.

A major component of the Multi-fuel is the Fuel Density Compensator, which allows the truck to allow for thicker and thinner fuels.

A higher octane fuel is dangerous because it has a lower requirement than a LOW octane fuel to ignite under diesel conditions.

That's the best I can do at 1:30 in the morning. Hope this helps.

 

[dozer1]

As you read through these alternative fuel threads you begin to pick up on this lil tidbit (at least I seemed too) Sure the multi will combust (pop, diesel, burn, guzzle) just about any fuel. Its optimumized for diesel tho, so a good trick is to try and make your other fuels as close to diesel as you can. Like WMO for instance. Many like to thin it with gas to make it flow better and pop a little easier and hotter. What is a good ratio you ask? Well that is covered in this forum many times I would bet. Now take gasoline. Thicken it with some oil to make it more like diesel. ect ect ect. They did a good job of designing that engine a long time ago with that fuel density compensator (FDC) to be able to do this. Great engineering for a combat situation or ofcourse the Zombie apocalypse which is looming right around the corner.

 

[Barrman]

Piston shape and injector placement is what makes it able to burn just about anything. Design of the ip and other parts are what allows them to live on the drier fuels. The FDC just makes it so power "feels" the same on different fuels.

 

[pmramsey]

The one forbidden fuel is aviation gasoline. Aircraft engines are low compression and they also require a "slow" burning fuel. Years ago, I had an employee that was topping up his car tank several times a week from our av-gas pumps. I caught him and said nothing. Within a month or so his engine died. Av-gas is still burning when it leaves the cylinders and everything down stream becomes toast over time. It is one of those moments that I will always fondly recall watching this kid chew the skit out of his nice 454 motor.

 

[dozer1]

The one forbidden fuel is aviation gasoline. Aircraft engines are low compression and they also require a "slow" burning fuel. Years ago, I had an employee that was topping up his car tank several times a week from our av-gas pumps. I caught him and said nothing. Within a month or so his engine died. Av-gas is still burning when it leaves the cylinders and everything down stream becomes toast over time. It is one of those moments that I will always fondly recall watching this kid chew the skit out of his nice 454 motor.

I respectfully disagree with this. AVgas is a high octane gas for high compression gasoline engines. It resists "dieseling" or pre-ingiting under compression, so the spark can light it in a controlled manner. The resistance to dieseling is the problem in a muli-fuel.

 

[pmramsey]

I respectfully disagree with this. AVgas is a high octane gas for high compression gasoline engines. It resists "dieseling" or pre-ingiting under compression, so the spark can light it in a controlled manner. The resistance to dieseling is the problem in a muli-fuel.

Av-gas aircraft engines are low compression. Most are in the 8.5 to 1 range. Av-gas has a very low ignition point. Most gasoline engines in use today were originally designed for 80 octane. When 100 LL became the only av-gas available, aircraft owners and manufacturers had to modify their engines. Running av-gas in a high compression engine is asking for trouble plus it provides zip cylinder lubrication.

 

[wreckerman893]

While the data plate says not to use aviation grade gas it it like any other "dry" fuel......if you cut it with enough diesel or WMO it will knock down (no pun intended) the octane rating and the deuce will burn it without damaging the engine. I have done this before in an emergency situation and no damage to the engine was detected.

You are basically extending what fuel you have by adding gasoline to the mix......the trick is to add the"emergency fuel" to your tank before it is bone dry.

Technically any fuel except diesel is an "emergency fuel".

The idea was that if the supply lines got interrupted the deuces (which were then the backbone of the logistics chain) could run on scavanged fuel that could be obtained locally.

One of the reasons I would not touch an A3 deuce is the loss of the multi-fuel capability.

There may come a day in the not too distant future when deuces are one of the few vehicles still operating on a day to day basis except for official vehicles.

 

[dozer1]

Av-gas aircraft engines are low compression. Most are in the 8.5 to 1 range. Av-gas has a very low ignition point. Most gasoline engines in use today were originally designed for 80 octane. When 100 LL became the only av-gas available, aircraft owners and manufacturers had to modify their engines. Running av-gas in a high compression engine is asking for trouble plus it provides zip cylinder lubrication.

Running avgas in a high compression GASOLINE engine is fine and often done by motor sport enthusiests . Once lit with the spark plug, that low flashpoint burns it thoroughly and quickly. Very controllable and predictable.

The deuce has no spark plug to light it. The high octane rating would resist detonation in what is basically a diesel engine. I guess I always assumed that is why it is not recommended in a mutli-fuel deuce. This is a wrong assumption? If so I will happily stand corrected.

 

[pmramsey]

As late as the early 1990s, leaded 110 octane was available at a few Union 76 stations and this proved to be solution for the high output racing engines we built.

The photo to your left is a 1956 Grumman S2F. The last of these were retired from the fleet in 1983. They have a pair of P&W R-1830 engines that develop 1525 hp each when usng 145 octane leaded fuel. The color is green. This is what is called high-octane AVgas. 100 LL is is highest octane readily available today. It is hardly high-octane despite what Wikipedia says. (Who writes that stuff anyway.) In the 1950s-60s-70s, automotive racing engines once ran extremely well on the 145 leaded stuff. The so called high octane sold today will not push my S2F faster than 200 mph and it is designed to do 285 mph flat out. However, the fuel flow remains at 4800 lbs an hour on take off. Pull the power back to an "indicated" 65-70 percent and lean to peak T.I.T and I am lucky to do 160-170. Many Cessnas walk away from me most days.

 

[nk14zp]

Avgas - Wikipedia, the free encyclopedia

 

[Darwin T]

I respectfully disagree with this. AVgas is a high octane gas for high compression gasoline engines. It resists "dieseling" or pre-ingiting under compression, so the spark can light it in a controlled manner. The resistance to dieseling is the problem in a muli-fuel.

well the dash plate says NO avgas so i think i will avoid it. when we were making it here at the refinery i work at it was 110 oct leaded gasoline (looked like blue coolaid).

 

[pmramsey]

If you can get your hands on some Jet A at your local airport, this works fine in the duce. Being super-super clean, it will clean up your fuel system like nothing else. I snag some of the such on occasion as I am the slum landlord at the local airport and frequently in warmer weather an GA turbin cannot take off due to weigh on a hot day. Fuel is off loaded and the FAA says it canot be reloaded into another aircraft. It instantly becomes hazardous material that someone must pay to haul away.

I amended an earlier posting in this thread to give you a photo of what a REAL high-octane fuel burner looks like.

Be aware that it TOO should be blended. It does not have starting additives for cold weather, it likes to grow bugs, and it washes down the cylinder walls to be used consistly without added lubrication blended.

 

[idM1028]

Ok thanks everybody. Didn't want this to become an argument about AV-gas! Thanks for the link to the AV-gas article. This should be required reading before posting on this article. My understanding was most AV-gas was fairly high-octane. I can recall hearing stories from my dad about his days as an A&P mechanic for Great Lakes Airlines. Apparently they had an aircraft tug they ran on AV-gas (which was readily available at the airport) The only problem was the AV-gas they had was fairly high octane (resists combustion) If they shut it down for longer than 5 minutes in the winter time the only way to get it started back up was to put it inside until it warmed up (sound like diesel to anybody?) But there is wreckman’s AV-gas incident which, if I recall correctly, occurred when he was much younger and stationed in Germany. Well, that and the infamous paint-thinner incident. I find my self with fuel prices where they're at (about $3.85 for a gallon of diesel where I buy it, which is the cheapest in town) longing to run something other than diesel in my CUCV. The prices for fuel seem to be $3.20 a gallon for off-highway diesel and the possibility of at least $1,000 fine or free on post with the fuel key, some looking over of shoulders and the possibility of a court-martial.

 

[41cl8m5]

All this talk about octane is scratching my head. I went to Colorado Areo Tech back in the 90's and the instructors said octane is the resentance to pinging/dieseling (preignition). The higher the number the higher the resistance. The number could only go to 100. Numbers over 100 is the "performace rating" of gas mostly used in aviation. Can't remember off hand the explaination as to the number increasing what it did or was for.

 

[dozer1]

Here ya go for the octane def. Octane rating - Wikipedia, the free encyclopedia Info jives well with my training in Motorcycle Mechanics Institute back in the late 80's. It has been a long time, that was a good memory refresher

 

[budman67]

I have been reading and rereading the threads in this section for a
few weeks now,in regards to the OP,I read in the TM9-2320-209-10-1
section III table 2-6 the allowable fuel for these multi fuel trucks.
I hope this helps,as I am still learning myself.

 

[chupa]

What he said...

 

[budman67]

I was looking carefully,but saw no mention of WVO or WMO.
This list I am assuming is for ready to use fuels,it does list
octane ratings for gas,85 or less CONUS pump.

 

[jesusgatos]

Here's a link to another thread on this topic, with some more links...