Intercooled 300DT Pictures - Page 5 - PeachParts Mercedes-Benz Forum

leathermang · #61 10-19-2002, 11:12 AM

OK, Larry, since we have both said we don't understand the "why".... would you mind if I asked how you came to" know they happen" ?

What is "excessive waste energy" ? Where is it formed and where/how would it be measured? This sounds like another way(if you leave out the "heat" statement) to say that fuel is being sent out the exhaust pipe.... but if it has not ignited due to lack of oxygen I would like to know how it is causing heat....

BlueBabyBenz · #62 10-19-2002, 02:40 PM

Pardon the Interruption..(Apologies to Tony Kornheiser and Michael Wilbon)...

At the risk of sounding stupid, it sounds to me like Larry is saying that when the mixture is too rich, the combustion has a tendency to produce heat rather than force. I did not glean from his take, that the fuel was necessarily unburnt.

I think I remember reading somewhere that diesel engines convert a higher percentage of the stored energy in diesel fuel, than gasoline. Something like...

Diesel 37% force (motive power), 63% wasted (I'm assuming largely heat)

Gasoline 25% motive power, 75% wasted.

So, if I put these two together, it sounds like Larry is saying that when the mixture is too rich, the ratio of motive power to wasted energy starts to drop down from 37%.

Or did I dream all this last night?

leathermang · #63 10-19-2002, 04:42 PM

What I am asking is how it could produce heat without oxygen. By excess fuel we are talking about past the point where the fuel/oxygen ration allows burning... how can the excess fuel make heat without oxygen to allow it to burn ?

BlueBabyBenz · #64 10-19-2002, 04:55 PM

Well, I'm thinking, and it is strictly a guess, that before the point where the fuel mixture is so rich that no more fuel can be burned, there is a point where the nature of the combustion becomes less efficient. I'm defining less efficient to mean a reduction in the ratio of motive/heat energy.

If you were to pinpoint the exact fuel/oxygen ratio where efficiency is optimized, then began increasing fuel, there would be a degradation of efficiency. It is within that range that heat energy would rise faster than motive energy.

I agree that once you reached the point where absolutely every additional fuel contribution went unburned that neither heat nor motive power would result. Then the unburned fuel would essentially dissipate out the exhaust and in to the atmosphere.

Grdenko · #65 10-19-2002, 08:19 PM

ridge, you mention that a side effect of the intercooler is lower combustion temperatures, but dont diesels need high temperatures for best performance?

mplafleur · #66 10-20-2002, 10:38 AM

There is a lot of things happening during combustion. For instance I know in a gas engine that leaning the fuel mixture will produce higher exhaust temperatures. This is not because because the combustion is hotter (it isn't), but because the leaner mixture causes the timing of the explosion to change. In fact, it as the mixture gets leaner, it will move closer to when the exhaust valves are open, that is why the exhaust is hotter.

I can't speak for diesel combustion. In a gasser, you have a spark to start the process. In a diesel, it's the flashpoint for temperature as a pressure increase causes the temperature to rise.

Question: Does the mixture change the temperature of the flashpoint?

Changing the temperature where you start cerainly would effect the timing of combustion since you won't have to compress as much to get to the flashpoint.

Is this right, or am I complicating things?

#67 10-20-2002, 11:51 AM

Another element to the waste energy/usable energy division is "flame propogation." In combustion within firearm chambers there are pressure curves. Different gunpowders cause different pressure curves. Some powders cause very fast rising pressure, while others are more slow burning, causing slower rising pressure that rises at the correct rate to continue building pressure as the bullet moves down the barrel requiring more combustion to maintain pressure as this volume increases.

This flame propogation or flame speed is probably the element that we are not considering here.

I apologize for the limit to my knowledge and experience, particularly regarding the "why" and "how" questions.

There is a point at which most people stop questioning a fact after they have seen adequate evidence that it is fact.

I have seen several diesel truck engines that had been "turned up." These engines had orifices in the return lines changed to smaller ones to increase fuel flow at the injectors to make more power. This unauthorized modification was always commissioned by a driver that did NOT own the truck. The result was MORE POWER at the expense of DRASTICALLY SHORTENED ENGINE LIFE.

This shortened engine life was due to excessive combustion chamber heat, and in some cases excessive soot in an engine that was not getting frequent oil changes.

After you see the results enough times, you don't question the theory of "why" or "how" it happens, you just know that it happens.

I remember when I was a child I was completely fascinated about the fact that television signals came through the air and put a picture on the TV set. I did not understand at all how this worked. But I could see the result on the TV set. This was adequate evidence for me that it did, indeed work.

Later in life, as I studied electronics I learned how this worked. Although I did not go into communications electronics, I understand the basic principles. This principle could also be taken to a level of physics that I would not understand. There is a limit to how deep I can make the explanation, but I still know the basics and I know that it is indeed fact.

Bottom line is; if you put more air into a diesel engine via intercooling, turbocharging, increasing displacement or whatever, it will make NO additional power without providing more fuel. Also if you put TOO MUCH fuel into a diesel engine without adequate airflow, you will create more power at the expense of decreased engine life. These are facts in my mind.

I cannot answer all the "why" and "how" questions. I know that this is fact and I'm as willing to accept this as fact as I am willing to accept that the sun rises in the East and sets in the West.

If you want to ponder this further, you must take into account the pressure vs. time curve. If the pressure rises very quickly and the combustion process does not continue, there will be one effect on the engine. If the combustion continues as the piston descends in the cylinder, then the pressure will remain somewhat constant and continue to drive the piston down without that excessive pressure peak at the beginning, there will be a different effect on the engine.

I will leave it to everyone else to determine what makes the grass and leaves green. I will simply accept the fact that they are indeed green.

Have a great day,

Ridge · #68 10-20-2002, 01:30 PM

Gosh, all I asked was would anybody be interested in a CD with plans for the intercooler conversion.

Now my two cents. I'm a pilot of prop driven small planes and from experience, I know that if I land at Flagstaff, Arizona which is at 7000 foot altitude on a hot day with a load of people and bagage and then try to take off at full throttle under those conditions the following will happen: I and the other people will die at the far end of the runway in a flaming high speed taxi.

On the other hand if I pay attention to 'density altitude' and volumeric effiency, and I wait until the early hours of the next morning when the air temperature is 30 degrees cooler, I will soar with the eagles.

After reading through all the "Analysis" on this thread, I called one of my former collegues who spent his life teaching diesel mechanics and in the course of that instruction won 15 national diesel competitions.

I used my fly or don't fly story on him and he verified that I was exactly right. Colder air has a denser concentration of oxygen molecules for a given volume than the same volume of hot air. Therefore, the existing fuel charge burns slightly more completely, resulting in more power!!!!!!! No additional fuel is necessary as it was already there but just not being burnt as efficently.

My expert further added (along with other posts here), that when the manufacturers of large diesel trucks started intercooling their trucks the resultant drop in the cooling loads was such that they were able to substantially reduce the radiator sizes on the trucks which allowed them to stramline the cab bodies. The expert states that without intercooling this streamlining would never have been possible.

The large trucks produced more power, got better mileage and as a consequence of much better cooling were more durable.

Now does anyone think these large corproations were going the intercooler route for any reason other than better efficiency? I think not.

I'm still going to wait until there's cooler air before I take off. That is unless my airplane is turbocharged 300D and intercooled!

Ben

leathermang · #69 10-20-2002, 02:20 PM

As a Huey slick pilot in Viet Nam all of 1969 I was often in situations where I was in marginal control of the number of persons getting into my aircraft and certainly did not have the option of waiting for a better density altitude to time my takeoffs...No one has a more visceral appreciation of Density Altitude than I ....

That cold air is more dense than hot was never the question.

"Therefore, the existing fuel charge burns
slightly more completely, resulting in more power!!!!!!! No additional fuel is
necessary as it was already there but just not being burnt as efficently." --Ridge

I find this a very interesting statement and assumption.... if it is true for some specific engine with which you are dealing I suggest it means that the sensors feeding the fuel injection circuit are not set at proper settings...

It would suggest that not enough oxygen is in that particular cylinder compared to the amount of fuel being injected...

I certainly agree that the word 'slightly' is appropriate in that case and is the reason I asked if anyone had done the math on these circumstances.....

If you put substantially more air into the chamber (as with the 18% lower figure mentioned earlier) I do not think it would be a measureable increase in power without the addition of fuel to keep the fuel/air ratio at near proper relationships...

If we go with the example of the air getting hotter due to the compression of the turbo fan... and needing cooling in order to place more air into the cylinder... then placing more air into the cylinder and heating it BY compressing it... brings to question how the temps inside the combustion chamber wind up being cooler rather than hotter... The working temps of the turbo diesel necessitated the addition of the oil squirters for the bottom of the pistons when that increase in air volume happened....why would additional air at the start of the compression stroke due to cooling of the air not produce the same effect... higher combustion chamber working temps ?

I just thought that after the performance figures were mentioned ( not that you claimed them for your unit or car ),, that an examination of the physics would be in order for all interested in Diesel engines...

Your construction implementation was truly beautiful... and is in NO way reduced by a review of the physics of the situation with regard to potential performance gains..... Greg

#70 10-20-2002, 02:30 PM

So....... Does the diesel expert say that the gains realized from turbocharging and intercooling were achieved with ONLY those modifications? Does he say that there were ABSOLUTELY NO changes in the fuel delivery?

If that is his contention, I find it quite strange that in the very same seventies era Cummins engines with turbo chargers and in some cases intercoolers, there were different injectors and orifices installed.

BTW, does that airplane have a diesel engine? If it does it will be the first I ever saw.

Another puzzle that arises in my mind. If the engineers in Stuttgart, who I don't consider dumkopfen, could increase fuel efficiency and power by only adding something as simple as a heat exchanger with no other changes, and seeing no compromise such as long term durability, why would they not do that?

You could make the similar argument about something like camshafts, intake manifolds and exhaust systems on the American high performance V8's of the sixties. You could say that with these changes, we picked up horsepower, and you would be correct. But if you said these changes were all that were made you would be wrong, the carburetors, ignition curves, etc. were also changed to allow such results.

In case you didn't pick up on it, I'm in favor of your intercooler, and quite impressed by your work. I'm trying to help you understand that there is more that can be done to make this modification even more powerful and fuel efficient, but I guess this is just more proof of the old saying that; "you can lead a horse to water but you can't make him drink."

Have a great day,

#71 10-20-2002, 02:40 PM

I wrote the preceeding post without seeing leathermang's post first, we basically wrote them simultaneously. I saw the post immediately after submitting mine.

Although he was coming from a totally different angle than myself, and very obviously more articulate, I thought it interesting that we were both supporting much the same view.

BTW, I am a low time, pilot myself, although I am not current, and also understand denisty altitude. I also understand that there are power AND aerodynamic effects of same. There also is control of the mixture in some airplanes to partially compensate.

Have a great day,

mplafleur · #72 10-20-2002, 04:01 PM

Well, the plane am am going to build WILL have a diesel engine in it, a two stroke in fact. But that is for another day...

I too, a low time, non-current pilot do not contest the fact that air charge density effects the effieciency of the engine. As I also am in the business of delivering powertrain control modules, I might draw upon my experience and say that I would like to sample the air charge temperature and density and use that data to adjust fuel mixture and timing.

#73 10-20-2002, 04:30 PM

Michael,

Yes, that will be the great day, when in a diesel, the air flow and density is measured and the fuel flow adjusted in real time as it is done in most all modern gasoline car engines.

In fact, that is what allows ANY flow improvement in a modern gas engine to result in more power, because the system, when operating in closed loop mode, automatically adjusts for more air flow.

I think the fact that many have learned that on a gas engine, increasing air flow results in more power, they get the idea that this will happen on ANY engine. Diesels are just a much different breed.

I have not read any about the newer generation diesels such as the CDI, it could be that they do have the ability to run in closed loop mode.

Have a great day,

leathermang · #74 10-20-2002, 05:04 PM

I too wrote my last post without seeing Larry's... so there was some repetition in mine...
I am glad you stated the part about "no added fuel,no added power" .... we are saying the majority of things in agreement...
I hope that Ben finds a way to measure the temp before and after his intercooler does its thing and that we figure out what the math is to approximate the amount of power which may (if the sensors are responding correctly) be being produced...
There were an awful lot of variables included in all the anecdotal examples given ....

Ridge · #75 10-20-2002, 11:19 PM

Gentlemen,

The reason that I called the diesel expert was that I hoped that he'd be on the net and could come to this site so we all could quiz him but alas, he doesn't even have a computer.

Wish mplafleur was out this way so we could instrument the car and really see exactly what's happening. I can tell you that if you pull over immediately after a freeway run, pop the hood and feel both the inlet and outlet of the intercooler, you can't leave your hand on the inlet side while the outlet is ambient temp.

As a point of info, the Germans had a four diesel engine floatplane that they used for the TransAtlantic mail run before the Second WW.

A German company, Zoche builds a five cylinder, diesel radial aircraft engine and the French firm Socata builds a flat opposed six that is diesel. They believe that it will be the aircraft engine of the future as it's almost as light as the gas engines but you can find diesel fuel in any third world country. In the U.S. many airports don't stock Avgas any more, so the French plane would fuel up with jet fuel. Also, diesel is much cheaper than avgas and the diesel engine is more fuel efficient.

I'm off to see the diesel expert Tuesday to show him the "Super Diesel" and will ask him some of the questions debated here.
Maybe later I could get him over to the house and on line one weekend, to answer all comers.

Time to relax, been painting all day.

Ben
www.reproduce100s.com