Multifuel Engine Question
 

How exactly do multifuel engines work? I always thought that some parts changes were required to run off a different fuel type for a multifuel engine -- but right now I am working on the Ukrainian T-72AG upgrade, and on the global Security.org web site, I found the following:

"The engines in question are two-stroke multi-fuel liquid-cooled diesels with straight-flow scavenging, with horizontally-placed cylinders and opposed pistons. Both the 6TD-2 and 6TD-1 will run on various fuels including diesel fuel, petrol, kerosene, jet engine fuel (or their mixture in any proportion)." (Italics are mine.)

So apparently, you don't need to change any parts, at least in the 6TD-1 and 6TD-2 engines. Is this peculiar to the 6TD-1 and 6TD-2? Is it the result of new technology? Or is this actually the way multifuel engines have always worked?

IIRC in the original V2 rules any engine which listed all fuel types as usable could burn any fuel without any modification. Also, again IIRC, in Team Yankee there is a part of the book where the company of M1's gets refuelled with JP8 jet fuel and mention is made of improved performance, but no mention is made of whether any maintenance was required to use it. How this compares to real life though, I'm not sure.

Please indulge me if I seem to be teaching people how to suck eggs, a little bit of theory behind internal combustion engines is needed here. Please forgive me if I get it a bit wrong, I'm trying to remember this from lessons I was taught many years ago with a few quick peeks at some books to try and refresh my memory

Petrol/Gasoline engines use a highly volatile fuel, they work by pumping air into the chamber and the fuel is dragged along with it creating a fuel-air mixture which is then ignited by the electrical spark causing it to basically explode for want of a better term. The resultant combustion causes pressure that forces the piston to move. The proper mix of air to fuel is important to prevent unburnt fuel from being dumped via the exhaust system or too much fuel flooding the chamber. Later engines use fuel injection, forcing an aerosol of fuel into the airstream.

Diesel engines work by compressing the air in the chamber to superheating (typically 550 degrees C or more) then injecting the fuel in very fine droplets. The heat of the air causes the fuel to vapourise. The vapour then burns and thus builds up the pressure and forces the piston to move.
Because of this, any mix of fuel can be dumped into the same fueltank and the way the engine works will ensure the fuel burns. Unfortunately if the two fuels don't mix well, a slight delay can occur in the cyclinder when changing over to the other fuel type (typically the lighter fuel gets used last as the heavier will be the first to enter the fuel line due to gravity)

Multi-fuel diesels don't use any new technology, they revert back to the original technology which was crude enough that it didn't need any changes to be made to the timing cycle to allow it to burn any suitable fuel.
Early diesels used a glowplug to start the initial combustion cycle now they tend to use electronic ignition.
From what I understand of it, the more sophisticated diesels (e.g. electronically controlled injection and electronic ignition types) are more sensitive to fuel differences and require timing changes to ensure correct piston height/compression to control air temperature and so on when the fuel is introduced.

Then there is the third common type of modern engine - the turbine engine such as in the Abrams.

IIRC from 30 years ago, the multifuel duces and five tonners had a switch on the dash to change from diesel to mogas, but I could be very wrong.. I was a leg and only rode in them, never drove or maintained one. I do know there was never modifications necessary to change from fuel to fuel, other than perhaps the foresaid switch. I wonder if that was to turn off the electrical for non diesel operations?

I DO know that it is detrimental to put gas in a regular diesel engine, as it WILL run away... had a neighbor whose hired man filled the diesel with gas (had two tractors of the same make/model except on was gas, one diesel.. hired man usually ran the gas one, but that day was running the diesel.. latem tired, and not thinking caused him to fill the near empty tank with gas) the thing started right up and then kept increasing in engine speed until a rod came thought the side of the block... it took almost NO time for it to do so either. That was back in the early 60's.

I don't know the answer to that one either; despite many attempts by many people over the years, no one has ever successfully managed to teach me to drive a manual transmission. That includes one sergeant in Korea who made me walk the five miles back to Camp Casey when he got so irritated at me for grinding gears...

Still has the same result on most diesel engine. It's better, however, if you put diesel in a gas engine (I'm sure, I did in a Range Rover). Your vehicle will run as long as there is enough gas in the tank. I drove 100 miles after filling a gas tank with diesel. Then, your engine simply dies on you, slowly loosing power. The good news is that it doesn't break down. You'll simply have to take the engine out and clean it the best you can. Then, do the same with the tank. Only about 24 hours work. As a result you do that once only:D

No need to precise that everyone around me made fun of me. At least until my step father made the same mistake: filling a BMW M5 tank with diesel. He has been the only guy I know with a diesel sports car.:p A few years later, it was my mother's turn to do the same. Never laugh at other's mistakes.:)

That must be the best way to slow down the US Army. Make road blocks with manual transmission vehicles and they'll take hours to free the way.:rolleyes: I don't know if its true but a sergeant told me years ago (about the mid-1980's) that most russian soldiers were unable to drive properly an western truck (too complcated). Then, he told me that some were planning on slowing down the red army by making road blocks with our most modern trucks.

Although I'm licenced to, I've never driven an automatic transmission in my life; wonder if I could :D I have driven Saracens and Saladins though; they use a pre-selector gearbox. It wasn't always reliable though; finding yourself in a false-neutral with an 11 ton vehicle going backwards down a hill was pretty scary!

I'm afraid I know nothing about how multi-fuel engines work, although I'd like to. About the only thing I know is that the Chieftain's multi-fuel L60 engine was so unreliable that questions were asked in parliament about it.

You're not alone and I think that is but one, if not the primary, reason the military went to automatic transmissions in their vehicles. Do they even have a standard transmission anymore.. humm today the standard IS automatic.. perhaps I should have said mechanical gearbox.

"Multifuel Engine The multifuel engine (fig. 1-11) is basically a four-stroke cycle diesel engine with the capability of operating on a wide variety of fuel oils without adjustment or modification. The fuel injection system is equipped with a device called a fuel density compensator that varies the amount of fuel to keep the power output constant regardless of the type fuel being used. The multifuel engine uses a spherical combustion chamber (fig. 1-12) that aids in thorough fuel and air mixing, complete combustion, and minimizes knocks."

http://www.tpub.com/content/engine/1...s/14081_20.htm