LDS VS LDT and the real differences

[doghead]

this is a 465c.i.

wrong.

 

[Flyingvan911]

Maybe a modest improvement in durability or horsepower is a more reasonable goal. Any part that is stronger would be a big benefit. Fewer holes in crankcases.

 

[JasonS]

but in stock cast form the block its self is not going to take it.

You are exactly right. Number six breaks loose. I have read about one person who tractor pulls with a 478 billet block because he broke so many stock ones.

It may be "bulletproof" at designed levels but it will never be a 5.9 cummins. My suggestion is to forget about re-inventing the wheel, appreciate it for what it is, and don't try to make it what it is not.

 

[wanderingwillys]

An internal - combustion engine is nothing more that a large air pump (compressor) to move more air you must increase intake air by turbo / blower or cam timing . Could the cam timing gears be diferent from one to another. The LDS could have advanced cam timing over the LDT.

We have a winner - the reason for the added power of the LDS comes from two things: Increased air flow / pressure and the advancement of the COD point (commencement of delivery)

When you guys are debating this engine you have to remember one thing - IT IS NOT A DIESEL.

The MAN design which they ironically called the M-System or Whisper engine - it is a hypercycle engine; the combustion chamber in the top of the piston is designed to do one thing - create turbulence.

This piston style creates what is called squish - the majority of the piston top is flat (very unlike any other large diesel which now uses ORCA type piston crowns) the M-system uses almost 80% of the piston top for squish - as the piston approaches TDC the air velocities in the chamber can reach nearly 400ft/sec as the air is inverted and forced into the chamber. This combined with the inlet port design creates very high swirl rates allowing fuel to be poorly atomized and even deposited onto the floor and walls of the piston crown chamber.

Because of the poor atomization the fuel takes longer to evaporate and become entrained in the air charge - this slower flame front creates the characteristic lack of diesel knock in these engines (hence the whisper namesake) - to combat this the swirl and squish rates are driven very high, this creates very high velocity air flow which improves the uptake of the fuel.

This also allows for the burning of multiple fuel types in a compression ignited engine - if you were to try and modify a typical diesel to burn any range of fuels that the hypercycle engine can feed on you will blow the head off and likely brake the crank - a standard compression ignited arrangement will never allow you to run gasoline at 22:1 compression ratio if it is fully atomized - the charge will detonate long before the piston passes TDC.

To gain high turning efficency you need to apply the peak firing gas pressure some 3 to 7 degrees after TDC to maximize the tangential turning effort and minimize the load on the main bearings.

Any type of engine using diesel fuels needs to have an excess of air - in large machines it is close to 2.5:1 between the supplied and required air for combustion - now think what else this air does: provides cooling

The reason you have high EGT is the deficit in air - when you turn up the pump you begin to drive the engine into creating more power - the exhaust gas comes out with high velocity and volume - this drives the turbine and thus the compressor wheel of the turbocharger harder and faster as they are linked by the rigid drive shaft.

The problem arises when you ask the compressor wheel to pump more air - the turbocharger is designed around a specific air amount - go to either side of this plot and the output falls off - if you are really good you can overload the compressor so severly that you get component stall (or barking) this is instability in the compressor where it is reaching the point at which the compressor cannot overcome the booster pressure already in the engine manifold and it is easier for the wheel to in effect cavitate than it is to pump more air - this is a transient state as the barking is the noise created by the system resetting itself.

It is very violent and hard on the compressor; if done enough times the compressor blades will experiance a fatigue failure and you will destroy the turbocharger.

The gist of this novel is this - to get more power you need more fuel - to burn more fuel and not thermally overload the engine you need more air...

Advancing the timing raises the firing pressure, adding fuel raises the EGT - adding excess air cools it down - advance and additional fuel makes power - larger turbocharger (or a charge air cooler) keeps it alive.

HTH

Matt

See it even happens to the big boys - engine overloaded by placing larger propellers on a tug - surged for 8 hours then exploded - EGT was through the roof...

The last pic is a 320mm piston with a traditional top - a swell in the middle with a trough all around the avoid the spray of the injection nozzle...

 

[jesusgatos]

What's with all the attitude guys? This isn't the kind of thing I'm used to seeing around here. I don't think this guy ha posted anything that warrants the kind of response he's received. The kind of threads pop up occasionally, and worse (zombie/apocalypse-proof air filtration?), and you know what - I almost always read something interesting (that air filtration thread is a good example).

I have read about one person who tractor pulls with a 478 billet block because he broke so many stock ones.

See, now I think THAT is interesting. Know anything more about these billet blocks?

We have a winner - the reason for the added power of the LDS comes from two things: Increased air flow / pressure and the advancement of the COD point (commencement of delivery)

When you guys are debating this engine you have to remember one thing - IT IS NOT A DIESEL.

The MAN design which they ironically called the M-System or Whisper engine - it is a hypercycle engine; the combustion chamber in the top of the piston is designed to do one thing - create turbulence.

This piston style creates what is called squish - the majority of the piston top is flat (very unlike any other large diesel which now uses ORCA type piston crowns) the M-system uses almost 80% of the piston top for squish - as the piston approaches TDC the air velocities in the chamber can reach nearly 400ft/sec as the air is inverted and forced into the chamber. This combined with the inlet port design creates very high swirl rates allowing fuel to be poorly atomized and even deposited onto the floor and walls of the piston crown chamber.

Because of the poor atomization the fuel takes longer to evaporate and become entrained in the air charge - this slower flame front creates the characteristic lack of diesel knock in these engines (hence the whisper namesake) - to combat this the swirl and squish rates are driven very high, this creates very high velocity air flow which improves the uptake of the fuel.

This also allows for the burning of multiple fuel types in a compression ignited engine - if you were to try and modify a typical diesel to burn any range of fuels that the hypercycle engine can feed on you will blow the head off and likely brake the crank - a standard compression ignited arrangement will never allow you to run gasoline at 22:1 compression ratio if it is fully atomized - the charge will detonate long before the piston passes TDC.

To gain high turning efficency you need to apply the peak firing gas pressure some 3 to 7 degrees after TDC to maximize the tangential turning effort and minimize the load on the main bearings.

Any type of engine using diesel fuels needs to have an excess of air - in large machines it is close to 2.5:1 between the supplied and required air for combustion - now think what else this air does: provides cooling

The reason you have high EGT is the deficit in air - when you turn up the pump you begin to drive the engine into creating more power - the exhaust gas comes out with high velocity and volume - this drives the turbine and thus the compressor wheel of the turbocharger harder and faster as they are linked by the rigid drive shaft.

The problem arises when you ask the compressor wheel to pump more air - the turbocharger is designed around a specific air amount - go to either side of this plot and the output falls off - if you are really good you can overload the compressor so severly that you get component stall (or barking) this is instability in the compressor where it is reaching the point at which the compressor cannot overcome the booster pressure already in the engine manifold and it is easier for the wheel to in effect cavitate than it is to pump more air - this is a transient state as the barking is the noise created by the system resetting itself.

It is very violent and hard on the compressor; if done enough times the compressor blades will experiance a fatigue failure and you will destroy the turbocharger.

The gist of this novel is this - to get more power you need more fuel - to burn more fuel and not thermally overload the engine you need more air...

Advancing the timing raises the firing pressure, adding fuel raises the EGT - adding excess air cools it down - advance and additional fuel makes power - larger turbocharger (or a charge air cooler) keeps it alive.

HTH

Matt

See it even happens to the big boys - engine overloaded by placing larger propellers on a tug - surged for 8 hours then exploded - EGT was through the roof...

The last pic is a 320mm piston with a traditional top - a swell in the middle with a trough all around the avoid the spray of the injection nozzle...

This too! Thanks for posting.

 

[mudguppy]

What's with all the attitude guys? This isn't the kind of thing I'm used to seeing around here. I don't think this guy ha posted anything that warrants the kind of response he's received. ...

the un-welcome-ness and intolerence of 'in-step perception' is getting much worse around here. accelerating, actually.



i still don't understand the differences in piston design between the MF and (for example) small Cummins.

 

[doghead]

Well, in this case/thread, perhaps the fact the the OP(relative newb) starts a thread, states he is gonna get to the bottom of this issue, then proceeds to post "facts" that are not correct or relevant. Then drops off and never comes back to follow up.

And then in this thread, another newb comes along, makes incredible statements (without stating details such as reason why, end goal, budget....).

This pattern continues time and time again. Eventually the long term forum members see this and grow tired of it. The comments are not made to "crush" their dreams, we're just a bit more down to earth. ie. what the heck you gonna do with a 3000 rpm 300hp engine in an M35a2? Let's talk about brake, trans, t-case, tire mods, needed to go along with this plan.

I would follow and only ask reasonable questions and watch in awe, a thread like this making such incredible statement(goals), if it were from a long term MV owner, and he had unlimited resouces and didn't state that it is simple or easy,"so watch me do it to prove you wrong"

Quite simply, if you never owned a muli-fuel engine, you just don't have any experiance or understanding of what your dealing with.

 

[mudguppy]

... i still don't understand the differences in piston design between the MF and (for example) small Cummins.

examples:

pic 1 - photo of my 5.9 before rebuild
pic 2 - 6bt piston
pic 3 - 24v ISB piston
pic 4 - 6CT piston
pic 5 - Cummins family; 6CT: back row, far right, 6BT: front row far left, 6BT marine: front row far right


what do the MF pistons look like?

 

[mikew]

Here's the MF pistons.

They are flat topped, with a round "hole" in the center and a "ramp" that swirls into the hole. The arrow points to the ramp.

 

[gringeltaube]

............................
what do the MF pistons look like?

http://www.steelsoldiers.com/showthread.php?43459-ldt-465-1c-vs-lds-465-multifuels-3.html#post484694


G.

 

[mudguppy]

... They are flat topped, with a round "hole" in the center and a "ramp" that swirls into the hole. ...

awesome, thanks.

so, besides the 'ramp' that induces swirl in the bowl, they don't look any different than the 'BT or 'CT Cummins pistons. obviously the Cummins have a cone or rise in the middle of the bowl - i theorize this is there to force the in-rushing air/fuel into the sides of the bowl. this sounds like the function of the 'ramp' to create the swirl.

to me, mechanically the combustion chambers (piston bowls) do not appear to be significanly different. they seem to exhibit the same 'squish' area/ratio.... and isn't this the same terminology 'quench area'? my understanding of 'quench area' is a mechanical method of focusing the air/fuel mixture into the combustion area for a more complete ingnition and burn.

so why is the MF not a diesel, again? i mean, afterall, diesel engines are not truly 'diesel engines'; they are 'compression ingnition engines.' so why is a MF not a 'compression ignition engine'?

and how does this help explain the differences in power between the LDT and LDS engines?

 

[mudguppy]

...to me, mechanically the combustion chambers (piston bowls) do not appear to be significanly different. ...

ok, read the 'Principles of Operation' as described in TM-9-2815-204-35. that helps explain the combustion process and what the swirl is supposed to be doing.

but back to the main thread topic.... ?

 

[JasonS]

My comments in red:

When you guys are debating this engine you have to remember one thing - IT IS NOT A DIESEL.

It is by Continental's definition a compression ignition engine; how is that not a diesel?

The MAN design which they ironically called the M-System or Whisper engine - it is a hypercycle engine; the combustion chamber in the top of the piston is designed to do one thing - create turbulence.

This piston style creates what is called squish - the majority of the piston top is flat (very unlike any other large diesel which now uses ORCA type piston crowns) the M-system uses almost 80% of the piston top for squish - as the piston approaches TDC the air velocities in the chamber can reach nearly 400ft/sec as the air is inverted and forced into the chamber. This combined with the inlet port design creates very high swirl rates allowing fuel to be poorly atomized and even deposited onto the floor and walls of the piston crown chamber.

Because of the poor atomization the fuel takes longer to evaporate and become entrained in the air charge - this slower flame front creates the characteristic lack of diesel knock in these engines (hence the whisper namesake) - to combat this the swirl and squish rates are driven very high, this creates very high velocity air flow which improves the uptake of the fuel.

This also allows for the burning of multiple fuel types in a compression ignited engine - if you were to try and modify a typical diesel to burn any range of fuels that the hypercycle engine can feed on you will blow the head off and likely brake the crank - a standard compression ignited arrangement will never allow you to run gasoline at 22:1 compression ratio if it is fully atomized - the charge will detonate long before the piston passes TDC.

There have been a number of non M-chamber multifuel engines over the years; multifuel operation does not appear to require anything beyond high compression ratio (according to the Taylor bible etc).

To gain high turning efficency you need to apply the peak firing gas pressure some 3 to 7 degrees after TDC to maximize the tangential turning effort and minimize the load on the main bearings.

Any type of engine using diesel fuels needs to have an excess of air - in large machines it is close to 2.5:1 between the supplied and required air for combustion - now think what else this air does: provides cooling

The reason you have high EGT is the deficit in air - when you turn up the pump you begin to drive the engine into creating more power - the exhaust gas comes out with high velocity and volume - this drives the turbine and thus the compressor wheel of the turbocharger harder and faster as they are linked by the rigid drive shaft.

The problem arises when you ask the compressor wheel to pump more air - the turbocharger is designed around a specific air amount - go to either side of this plot and the output falls off - if you are really good you can overload the compressor so severly that you get component stall (or barking) this is instability in the compressor where it is reaching the point at which the compressor cannot overcome the booster pressure already in the engine manifold and it is easier for the wheel to in effect cavitate than it is to pump more air - this is a transient state as the barking is the noise created by the system resetting itself.

It is very violent and hard on the compressor; if done enough times the compressor blades will experiance a fatigue failure and you will destroy the turbocharger.

The gist of this novel is this - to get more power you need more fuel - to burn more fuel and not thermally overload the engine you need more air...

Advancing the timing raises the firing pressure, adding fuel raises the EGT - adding excess air cools it down - advance and additional fuel makes power - larger turbocharger (or a charge air cooler) keeps it alive.

HTH

Matt

See it even happens to the big boys - engine overloaded by placing larger propellers on a tug - surged for 8 hours then exploded - EGT was through the roof...

The last pic is a 320mm piston with a traditional top - a swell in the middle with a trough all around the avoid the spray of the injection nozzle...

 

[JasonS]

See, now I think THAT is interesting. Know anything more about these billet blocks?

Based on what I have read, the multifuel block is weak and the number six tends to break loose. There are a few threads on the tractor pulling sites which talk about. IIRC, the tractor puller was breaking ~5 blocks per season and went to a billet block.

I have also read about someone who ditched the obsolete m-combustion chamber and went with something newer. IIRC, they welded up the pocket.

This is all fine and good IF you can't run something stronger and more efficient (ie. cummins). Hard to justify otherwise.


I get tired of all the cheerleaders claiming that the multifuel is somehow a wonderful piece of engineering; it is not. This is not to say that the multifuel is a POS; lots of early diesel engines had flaws (yes, cummins too!). However, there is no reason why we can't call it what it is.

 

[JasonS]

Comments in red:

Well, in this case/thread, perhaps the fact the the OP(relative newb) starts a thread, states he is gonna get to the bottom of this issue, then proceeds to post "facts" that are not correct or relevant. Then drops off and never comes back to follow up.

And then in this thread, another newb comes along, makes incredible statements (without stating details such as reason why, end goal, budget....).

This pattern continues time and time again. Eventually the long term forum members see this and grow tired of it. The comments are not made to "crush" their dreams, we're just a bit more down to earth. ie. what the heck you gonna do with a 3000 rpm 300hp engine in an M35a2? Let's talk about brake, trans, t-case, tire mods, needed to go along with this plan.

Understood, however you can be a little more civil. There have been numerous talks about brakes, trans, t-case, etc. There is not reason to exclude engine discussion.

Quite simply, if you never owned a muli-fuel engine, you just don't have any experiance or understanding of what your dealing with.

I hope that you don't really beleive this. I am sure that major diesel engine designers who have never "owned" a multifuel know about the M-combustion chamber and multifuel design. Owning does not make you an expert. There have been "new" developments in understanding that challenged (and corrected) long standing "experts."

 

[wanderingwillys]

My comments in red:

I would grudgingly admit that it is a very very close relative to what we normally call a Diesel - but just as a 2 stroke marine engine does not use the Diesel Cycle (it uses an Otto Cycle) although most people call them diesels - the hypercycle is different mainly because of the high compression ratio - 16 or 17:1 is common on most diesels and we have 22:1 here

Also the way in which the fuel is atomized makes a large difference in the dynamics of the air and fuel interaction inside the combustion chamber, the multifuel uses a fairly basic injector which does not make a particularly fine mist or atomized spray because it does not have to... the turbulence in the chamber makes up for this fact - the long delay in ignition and the slow rise in peak pressure also make these engines different - close cousins for sure but different.

As for the other styles of multifuel engines there are many ways to skin a cat - some use a precombustion chamber which acts like a little rocket nozzle as the fuel in the prechamber burns, some use shrouded valves, or specialized inlet ports, and some just use a different style of piston...

I think the thing that sets these engine apart is the injection style and turbulence generating features engineered into the combustion chamber...

It comes down to nomenclature in the end - when I think of lower case "diesel" I lump all compression ignition engines together - where as when I think of upper case "Diesel" as in Rudolf's engine I narrow the scope...

Riddle me this - what would you call an EMD 645 engine - it has exhaust valves and liner intake ports but is a trunk style engine...

 

[wanderingwillys]

You guys are hung up on the piston cooling... there is one reason: air

You add more fuel via the larger injection pump and increase the timing advance; making said fuel burn closer to TDC - this makes the power go up - also makes the heat go up...

To combat the heat you add more air so the mixture burns completely - you can fake the extra fuel with the LDT pump but the turbocharge cannot keep up so you go into thermal overload.

 

[mudguppy]

i'm just questioning where the air is coming from. i know that diesels (and this MF does operate off of the diesel principle) make power by increasing fuel and stay alive by increasing air.

but the turbos have already been stated to be found interchangable from the LDT to LDS - and not that they are swappable, but are suitable substitutes. is this not correct?

anyway, so if the turbos are not producing larger amounts of air to manage the increase in fuel (LDT vs LDS, that is), then where is the increase coming from?

the only other difference stated that would relate to this is the intake rocker arm ratio. so the intake rocker arms and injection pump (with respective injectors) are really the only differences with regard to power increase?

 

[mudguppy]

to the administrators:

since this post is being moderated, it was suggested that i send complaints about a moderator upward.

so how can i do that when the moderator i would like to make a complaint about has lowered my PM box count to the point that i cannot send PMs?

 

[Squirt-Truck]

Soooooo, what have we determined is the differences in and LDT and an LDS?
According to our combustion/engine guy, the difference in compression ignition "diesel" and M.A.N. "Hypercycle is that the diesel ignites atomized fuel and the hypercycle ignites vaporized fuel which minimizes the pressure spike (knock).

FWIW attached is an LDS piston picture, the "notch" is where the injector tip fits and the "single hole" nozzle delivers the stream of fuel.