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Converting the multi-fuel to pure diesel...

Heath_h49008

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Sound silly? Sort of. But follow this cold Sunday musing...

These engines are multi-fuel hypercycles. The fuel is injected as a liquid onto the wall/cup of the piston VERY early in the cycle and is on fire the whole time,

"Diesel" engines inject fuel as a mist at the point of ignition and it is lit by the heat of the compressed air in the cylinder.

Compression ratios in the multifuel engine are comparable to diesel engines, as are peak cylinder pressures. However, diesel "Tricks" such as propane and methanol injection do not work in the multifuel, due to premature ignition of these fuels.

Insane... do not do this at home.. it makes almost no sense.

If you were to reconfigure the injector nozzles of the multifuel to spray a misting pattern, and re-timed the injection to normal Diesel BTDC, the multi-fuel capability would be eliminated, as would the ignition source in the cylinder that precludes the use of such power adders as Propane/methanol injection.

Efficiency would have to be tested. The power generated could actually be reduced due to the shorter combustion duration, or increased with the benefit of better fuel-air mixing.

Consider it food for thought...
 

Keith_J

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You would have to drop the compression ratio too. The higher than normal compression ratio is to assure ignition of gasoline as it has a higher auto-ignition temperature than diesel. It isn't needed for diesel.

Also, swirl induction would have to be rotated 90 degrees and a toroidal bowl cut into the pistons. Major work on the head, if possible and piston machining.

Not impossible. Propane WILL work without these modifications as long as you keep the dose well below the lower flammability limit. Naturally, it would have to be tied to the accelerator pedal and governor. Maximum fuel rate must take into account air mass flow rate to satisfy the less than flammable limit maximum.

Yes, always less than lower flammable limit! The little diesel injected acts as pilot ignition. Still, such systems are best with natural gas and constant RPM, like a generator.
 

Keith_J

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Now IF you are looking for less expensive running, compressed natural gas is the winner. With natural gas Henry Hub pricing at $3.66 , it is 1/8th the present cost of diesel!

Propane is barely cheaper than diesel on cost per BTU. All conversions cost money. Gasoline plus 10% waste motor oil is still the best bet. Adjust the mix to make it 6.8-7 pounds per gallon and even bypassed FDCs will be happy.
 

Heath_h49008

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This is more of a question than an answer.

If people want the efficiency and power output of a modern diesel, and already have a functional multifuel, why not simply swap injectors and re-time the engine to do so?

Swapping entire engines and support systems seems a bit extreme in many cases. But, as I said, this is just food for thought about what is possible.

Personally, I bought mine BECAUSE of the multi-fuel capability. I have little to no interest in changing that. However, there are so many threads about modding these engines, I was surprised nobody had just made it into a diesel so their injection tricks would work... at least until they blew it up.

I'm just a crazy engineering student. I look at everything in terms of "This is similar to that... why is it different?" What can be done is interesting to me.
 

Keith_J

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Modern diesels get their power from electronic controlled injection. Old school centrifugal governed diesels linearly decrease fuel as the redline approaches, reducing torque. Unless you convert to a modern high pressure common rail system with full electronic control, you won't get the power you want by removal of multifuel capacity. Then there is the age of the rest of the design...see the gory pictures of rods punching blocks if you need any clarifications.

Drop a different engine in if you want more power. Preferably one with a suitable transmission attached.
 

Heath_h49008

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You would have to drop the compression ratio too. The higher than normal compression ratio is to assure ignition of gasoline as it has a higher auto-ignition temperature than diesel. It isn't needed for diesel.

Also, swirl induction would have to be rotated 90 degrees and a toroidal bowl cut into the pistons. Major work on the head, if possible and piston machining.

Not impossible. Propane WILL work without these modifications as long as you keep the dose well below the lower flammability limit. Naturally, it would have to be tied to the accelerator pedal and governor. Maximum fuel rate must take into account air mass flow rate to satisfy the less than flammable limit maximum.

Yes, always less than lower flammable limit! The little diesel injected acts as pilot ignition. Still, such systems are best with natural gas and constant RPM, like a generator.
The reason Meth/propane doesn't work is the presence of flame in the cylinder at such an early stage of the cycle. It would seem that ANY combustibles in the air charge would be subject to ignition/PRE-ignition. From what I have learned, unlike a normal diesel, hypercycle engines are considered to have a flame in the cylinder at all times in the cycle. The actual "Ignition" is just the quench action when the air is forced into the cup and swirls/mixes the fuel with the air charge and complete buring of what was a puddle on the cup wall is possible. I could be mistaken, but that was the jist of what I read on the subject.

The 22-1 compression ratio is a on the high side, but still normal for diesel engines. I don't see the need to lower it.

Swirl is a good point! I had not considered the issue of swirl given the misting of the fuel. Greater turbulence very well may be required for complete combustion. Swirl mixing is done by the small "ramp" in the piston now... it may still be adequate, but I'm not sure.
 

Heath_h49008

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Modern diesels get their power from electronic controlled injection. Old school centrifugal governed diesels linearly decrease fuel as the redline approaches, reducing torque. Unless you convert to a modern high pressure common rail system with full electronic control, you won't get the power you want by removal of multifuel capacity. Then there is the age of the rest of the design...see the gory pictures of rods punching blocks if you need any clarifications.

Drop a different engine in if you want more power. Preferably one with a suitable transmission attached.

I'm not advising ANYONE do this. It's just a logic problem of what is possible, and a fleshing out of what the differences are between a hypercycle and a diesel.

Just nerd fun.
 

dmetalmiki

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Oops!



Can Diesel engines be converted to run on LPG?

There are currently two ways of using LPG as a fuel for a Diesel engine;

[SIZE=+1]1. To truly convert the engine by reducing its compression ratio and provide it with spark ignition.


Lack of Spark Ignition
Diesel engines do not have this.
Spark ignition can be provided in several ways but they all amount to the same thing.
The most effective is to remove the cylinder head and machine spark plug holes into the places where the Diesel injectors were sited. This is only possible if there is enough 'meat' in that position. If not, the spark plug holes may have to be placed elsewhere in the combustion chamber. The existing holes for the original Diesel injectors may either be plugged or perhaps be used for direct LPG injection. Leaving the Diesel injectors in place would bring no benefit when the next factor is taken into account......
Reduction of Compression Ratio
This must be done before the engine could be run properly on LPG or Petrol for that matter. Diesels often run at a compression ratio of roughly 16-1 (one of the reasons they are more economical) whereas Petrol and LPG engines need a ratio of around 10-1. One way of reducing the compression ratio is to fit some form of spacer inbetween the cylinder head and cylinder block mating surfaces in order to reduce the compression ratio of the engine. This may present problems of gasket sealing because two head gaskets would have to be used. Another solution is to replace the original pistons for redesigned ones with different (deeper) crown depressions, addressing the compression ratio problem but now the costs are beginning to escalate, and it must be remembered that when both of these changes (provision for spark ignition and reduction of compression ratio) have been made, the engine isn't a Diesel any longer.

Design Limits, Stresses and RPM
Although the Diesel engine is relatively slow-revving and produces its maximum torque at lower RPM than a similar Petrol version, this is not the case when it is converted to run on LPG. The revised engine has to'rev' more when running on LPG because its maximum torque has been pushed higher up the rev. band. This can bring new problems of reliability and longevity. Even if the 'top end' of a Diesel has been fully reworked, the crankshaft, bearings and connecting rods (to mention but a few components) will suffer higher stresses at increased RPM necessary when running on LPG. Mechanical breakdown may result in far less time, whilst increased wear and reduced component life are certain. FinaIly, note that in all of the above cases the converted engine will cannot be a true Diesel or even a dual fuel engine as it will have lost its higher compression ratio and the means to inject Diesel.
Conclusion
The above factors combine (along with many others not discussed here) to make actual conversion of most Diesel engines uneconomic. It would be simpler and quicker to fit a Petrol engine.

[SIZE=+1]2. To mix LPG with the existing Diesel fuel before induction (Fumigation, not Conversion)[/SIZE]

Various attempts have been made to achieve this with varying amounts of success. Go LPG! have examined many systems and installations and after much consideration have come to this conclusion;
Overall, the Savings are Not Huge...
None of the LPG / Diesel mix systems examined have resulted in Diesel consumption being reduced by more than 25%. Those savings made must also have LPG costs (for the LPG that replaces some of the Diesel fuel consumed) subtracted from that 25% saving. This results in final savings of only the low teens of %, or thereabouts.
There are other problems to consider as well - The unmodified Diesel engine was relatively slow-revving, producing its maximum torque at lower RPM than a similar Petrol version. This is not the case when it is converted to run on Diesel and LPG mix. The revised engine has to'rev' more when running on Diesel / LPG mix because its maximum torque will have been moved higher up the rev. band. This can bring new problems of reliability and longevity. The crankshaft, bearings and connecting rods (to mention but a few components) were all designed to rev. at a lower rate. These components will suffer much higher stresses (stress increases at the square of RPM) at the increased RPM necessary to get sufficient torque when running on LPG. Mechanical breakdown may result in far less time, whilst increased wear and reduced component life are certain. Given the low overall savings achieved (to date) and the cost of the adaption ( often equal to that of an injected Petrol engine conversion) many miles would have to be covered before any real savings are realised whilst reliability has been reduced. This does not seem to be an economically viable alternative.*
* Summer 2008 - We keep an open mind.
As world Diesel prices continue to rise sharply, there may be more economic benefit in mixing LPG with Diesel. We are still waiting to see a system that works well and comes with audited figures for reliability and the cost savings achieved. If such a system comes along, with UK LPG accreditation, we'll do some long-term evaluation before a decision is made to offer it to our customers.



Benefit becomes Burden
There are some other benefits apart from saving fuel cost.
The Diesel engine becomes quieter and more responsive when using the LPG / Diesel mix. The classic Diesel 'Knock' can be greatly reduced. The main reason for increased smoothness and reduced noise (vibration) is that the LPG element begins its combustion before the Diesel fuel does, a result of 'detonation' due to the compression ratio being so high. The engine may also get up to its optimium temperature more quickly, whilst harmful emissions like Particulates and Carbon Monoxide can be reduced. These all appear to be benefits.
Sadly, a new set of problems arise when the Driver begins to use the increased performance of an engine that wasn't designed to rev to the new, higher levels. As a result of this apparent improvement in performance, one of the best attributes of the Diesel engine (relative longevity and reliability) is dramatically reduced by the Diesel / LPG adaption.
Conclusion
On a purely fuel cost-reducing basis this adaption or fumigation system does not appear to be an attractive or useful alternative for the average Diesel motorist. That doesn't mean that the people working on these projects should stop, we hope they succeed. Perhaps their research will continue and go on to give us all a better solution.
Overall Conclusion
Above it has been shown that niether true conversion of a Diesel engine nor the mixing (Dual fuelling, Fumigation) of LPG with Diesel give economic benefits large enough to make either choice worthwhile for the average motorist. With current LPG and Diesel technology as it stands, it would be more economical to simply remove the Diesel engine and fit a Petrol equivalent, which answers our original question -

'Can Diesel engines be converted to run on LPG?'
[SIZE=+1]The answer, to date, is a qualified 'No'.[/SIZE]
[/SIZE]
 

patracy

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You can convert a multifuel to pure diesel by installing tractor pistons, heads, injectors, and IP. But why spend all the money to loose functionality? There's no gains to be had. The tractor engines actually were rated with less power and less RPMs.
 

Heath_h49008

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That's right... White used a variation of these engines as diesels, didn't they?

I'm seriously just shooting the breeze about combustion theory inside these engines, I'm not making plans or anything of the sort.

As for Pure propane etc... the engine won't do it. There is no ignition without diesel fuel to light it. No ignition. It also won't run on pure alcohol for the same reason.

But then again, these are NOT diesel engines. It has many similarities, but the combustion process is fundamentally different. But that's why it's fun to play with on a theoretical level.

Just for fun here.
 

JasonS

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But then again, these are NOT diesel engines. It has many similarities, but the combustion process is fundamentally different. But that's why it's fun to play with on a theoretical level.

Just for fun here.
Broadly speaking internal combustion engines are either spark or compression ignition (diesel). Lacking spark plugs, it would appear that the "multifuel" is a compression ignition engine :wink:.

The efficiency of the "multifuel" would be increased with the lower compression ratio but it wouldn't likely be worth the effort. I did read about one person who redesigned the piston bowl for tractor pulling but, this too, is too much work for little gains. We are not tied to this engine like the tractor pullers.
 

deuceaid

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My friend ( was in army- and not a member here yet ) got his deuce from the mill , and it was all ready diesel only,,, so why would they do this? ( it has warning labels and all about using diesel only)
 

patracy

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My friend ( was in army- and not a member here yet ) got his deuce from the mill , and it was all ready diesel only,,, so why would they do this? ( it has warning labels and all about using diesel only)
They bypassed the FDC. The engine can still run on a range of fuels, as the internals remain the same. But it will not automatically adjust for various fuel densities. It was done due to the FDCs having the tendency to leak into the engine, diluting the oil with fuel.
 

deuceaid

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Patracy, maybe I will call you Neo now ( I thought You were just a computer geek ( not a derogatory word in my book ) but You have some MV knowledge Too! )

I was only looking for the first half of the clip, but couldnt pass up the whole thing :p

[media]http://www.youtube.com/watch?v=2HgwHWH49bw&feature=related[/media]
 

Goose2448

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The mulitfuel was designed for a purpose, which it serves very well. If you want to run straight diesel, just put it in the tank, no need for all this engine work. I hear they like diesel the best anyway. If you want more power, find a different engine, I6 is the best for this application IMHO. If you add more power, up grand the trans, breaks, and tires. And always Take Pictures.

If it aint broke, dont fix it
 

plym49

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Sound silly? Sort of. But follow this cold Sunday musing...

These engines are multi-fuel hypercycles. The fuel is injected as a liquid onto the wall/cup of the piston VERY early in the cycle and is on fire the whole time,

"Diesel" engines inject fuel as a mist at the point of ignition and it is lit by the heat of the compressed air in the cylinder.

Compression ratios in the multifuel engine are comparable to diesel engines, as are peak cylinder pressures. However, diesel "Tricks" such as propane and methanol injection do not work in the multifuel, due to premature ignition of these fuels.

Insane... do not do this at home.. it makes almost no sense.

If you were to reconfigure the injector nozzles of the multifuel to spray a misting pattern, and re-timed the injection to normal Diesel BTDC, the multi-fuel capability would be eliminated, as would the ignition source in the cylinder that precludes the use of such power adders as Propane/methanol injection.

Efficiency would have to be tested. The power generated could actually be reduced due to the shorter combustion duration, or increased with the benefit of better fuel-air mixing.

Consider it food for thought...
I get it, running a multifuel on diesel is not the same as a diesel running on diesel. I am also in favor of thought experiments; it's a great learning tool and also fun.

Please help me out with the highlighted quote above. How is it that the fuel is burning the whole time? I mean, at the bottom of the stroke compression is just beginning. At whatever degrees before TDC, there is enough heat to autoignite a 'conventional' spray in a regular diesel. I take it from your quote that in the multifuel a self-igniting (self-burning?) conditionis achieved way before TDC. How is it that this happens - maybe what I am really asking is how many degrees before TDC does it get hot enough for the fuel to burn? And then what happens as you get near TDC?

I would really like to understand exactly what is happening in the multifuel combustion chamber.
 
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