at work stuck!!! how does a multifuel engine work?

[paul connor]

Can any one explain or indeed send me a link. trying to explain to my work mate??? :?

[Richard Notton]

Can any one explain or indeed send me a link. trying to explain to my work mate??? :?

 

They are all diesels, well, compression ignition engines.

 

Anything combustible that can be injected, that is, atomised so each particle has a lot of air around it will work.

 

Dr. Diesel did not intend his original engines to use diesel oil as we now know it, but rather the vast amounts of unusable waste around at the time; coal dust. His problem came with bore wear owing to the ash, the coal dust works well enough.

 

Remember with a diesel there is no air-fuel ratio, a full cylinder of plain air is ingested, compressed and then fuel injected from a tiny bit at idle up to the maximum that the volume of air can combust, any more and you get black smoke which is a drop of fuel in a carbon outer shell.

 

Domestic cooking flour will work too if you can "spray" it, in fact flour mills have to have rigorous procedures as the dust if ignited will explode and raze the lot to the ground. Indeed may innoculous particulates are explosive as an air-born dust including cereal grain and nut shells.

http://www.mnhs.org/library/tips/history_topics/73washburn.html

http://www.biofuelsjournal.com/articles/Seven_Grain_Dust_Explosions_Reported_in_2003__Down_from_Eight__in_2002_____04_08_2004-22184.html

You can Google dust explosions and read the HSE documents.

 

Many diesels don't burn the fuel oil you expect, large oil tankers use the crude they carry, many other large ship engines use bunker oil which is like road tar and the RN generally uses AVTUR for everything so a single fuel supply makes logistics easier.

 

Your diesel will burn about anything, a gallon of Mazola direct from Sainsbury's will do; the problems are the fuel viscosity which the smaller system cannot handle so thicker oils often need heating, lubrication of the injection pump and particulates that choke the filters like the waste oil from the local chippie, although many do use it as-is in the summer with pre-filtering only.

 

The well known UK mil multifuels are only diesels with the capability to pump thicker viscosities and have their mechanical injection pumps engine oil lubricated rather than the commercial arrangement of fuel lubrication where diesel oil is assumed. However, when using wholly non-lubricating fuels you are required to add some engine oil at a low rate to lubricate the injector pump pistons.

 

You don't really need to compensate for specific gravity as the US multifuels attempted since with the max injection rate set for diesel oil everything else just drops the power a bit owing to a lower calorific value.

 

Surely there aren't many people running Mk.2 432's or Chieftains on costly diesel oil, all you have to do is go along to any national breakdown service with a 205L drum and they'll be happy to give away the "contaminated" diesel/petrol (or vice versa) mix rather than pay for industrial hazardous waste disposal, its all correctly tax paid too.

 

[paul connor]

ahh many thanks, so would i be right in saying waste oil would also burn? if mixed with petrol and diesel.. as well as water contamination not a real issue

[Mark]

Thats what I use Paul, as long as it is clean and always use pure diesel now and again.

[Richard Notton]

ahh many thanks, so would i be right in saying waste oil would also burn? if mixed with petrol and diesel.. as well as water contamination not a real issue

 

You do have to be a bit careful with "contaminated" fuel from the breakdown people, water will definitely not go and will collect at the bottom of the tank, so its worth decanting supplies into a non or semi-opaque container such that you can inspect it.

 

Engine oil is definitely a bit thick for many things but it will go and there is a danger for very worn diesels when a complete runaway can occur with a hot engine owing to the piston leakage when it starts to diesel on its own engine oil. Cutting the injection system with the stop system of course has no effect, you need to hope the brakes or some immoveable object is stronger than the engine and stall it.

 

I've seen this happen many years ago, quite exciting too.

 

Chieftains also had a habit of doing something similar with oil seal failure in the blower casing causing the engine to ingest engine oil at a goodly rate, sometimes a quick thinking driver could stall it and sometimes it was a bale-out before the engine exploded in self-destroying revs.

 

Allegedly, the known problem was also a good way of either ducking exercises and/or having REME replace a troublesome or weak engine; just pour a few pints of oil in the intake and report it as a seal fault. . . . . . . . . .

 

Incidentally, having mentioned the 432 RR K60 engine and the Chieftain's L60, plus the Detroit Diesel types, you have to be a bit careful with what appears to be a big supercharger of the Rootes type having interlocking rotor lobes commononly found on these two-stroke diesels (don't be fooled by the Detroit's exhaust valves, its a two-stroke); similarly with many very large marine diesels having apparently a turbo-charger. More often than not these are scavenge pumps since these types are generally two-strokes and the "blower" is used only to clear the cylinders of exhaust gas, officially the nomenclature change happens around 1psi; at the point of starting compression, up to 1psi is scavenge whilst above that it is supercharge.

 

Of course you can make really big diesels:

http://people.bath.ac.uk/ccsshb/12cyl/

 

[AlienFTM]

Chieftains also had a habit of doing something similar with oil seal failure in the blower casing causing the engine to ingest engine oil at a goodly rate, sometimes a quick thinking driver could stall it and sometimes it was a bale-out before the engine exploded in self-destroying revs.

 

This is the usual cause, then, of the legendary Chieftain runaway engine? Nice to know. I have heard of it often enough but never heard an explanation as to why.

 

There's a good first-hand description here (last but one post on the page):

 

http://www.arrse.co.uk/cpgn2/Forums/viewtopic/t=61346/postdays=0/postorder=asc/start=0.html

 

As I understand it, the Chieftain will run on petrol, but the ignition timing settings are a compromise between those for diesel and petrol, so to paraphrase Doctor Johnson*, it runs indifferently on either.

 

It did occur to me during the Tesco et al fuel fiasco a couple of months ago that Chieftain owners the world over would be flocking to wherever this duff fuel was and only charging a pittance to take it off their hands. Or would this fuel not work in a Chieftain either?

 

* Dr Johnson started work on his English Dictionary a couple of years after an ignominious action on the battlefield by 13th Light Dragoons. His definition of Dragoon, then, was something like:

 

Dragoon: a soldier who performs indifferently mounted or on foot. In those times, indifferently could mean the same as er "the same," though observers believe he was making an early and clever play on words.

[TooTallMike]

Engine oil is definitely a bit thick for many things but it will go and there is a danger for very worn diesels when a complete runaway can occur with a hot engine owing to the piston leakage when it starts to diesel on its own engine oil. Cutting the injection system with the stop system of course has no effect, you need to hope the brakes or some immoveable object is stronger than the engine and stall it.

 

I've seen this happen many years ago, quite exciting too.

 

A runaway (dieselling) engine still requires oxygen to burn the oil, so you can stop one by covering the air intake with a suitable piece of wood or metal. Rag is no good as it will be ingested by the engine and apparently the flat of a hand is definitely NOT recommended for the same reason :shake:. I have a suitable piece of ply stowed in the engine bay of my diesels. nb. covering the intake only works if there are no leaks further down the plumbing.

[Grumpy]

 

As I understand it, the Chieftain will run on petrol, but the ignition timing settings are a compromise between those for diesel and petrol, so to paraphrase Doctor Johnson*, it runs indifferently on either.

 

 

 

 

The Tatra is multifuel and will run on petrol or diesel or any combination of. To run on petrol you start on ethanol and there is an electric primary fuel pump that is switched on to elevate problems with petrol “steam” bubbles in the fuel injection system. The manual recommends a maximum of 10,000 km of petrol before you switch back to diesel.

 

Main problem is petrol burns much slower than diesel so the injection timing has to be retarded to account for the slower burn. To run on mixture of petrol / diesel, Tatra supply you with a hydrometer to measure the viscosity of the fuel,you then set the fuel injection pump timing accordingly via a little lever in the cab. The manual does recommend that if you are going to run on petrol to chuck a couple of gallon of engine oil or DERV in with each tank refill just to keep the pump lubricated.

 

[Adrian Barrell]

A runaway (dieselling) engine still requires oxygen to burn the oil, so you can stop one by covering the air intake with a suitable piece of wood or metal.

 

 

Indeed, the twin Detroits in the M4A2 Sherman and M10, which are prone to sucking oil through the blower shaft seals, have a solenoid operated flap in the blower air inlet as an emergency stop. I think the later vehicles had it deleted and certainly many engines you see now do not have it but it always seemed a good idea to me