Absolutely

 

Well, we agree/disagree at the same time... while I understand it, I also understand that my ability to convey that into words doesn't always work right. And I was trying to keep it simple. HG popping is a cause/effect thing. Absolutely it is too much cyl pressure that causes this. But then you you have to examine how this happened. There is more than one way to do this for sure. And it is my firm belief that boost/DP ratio can contribute to this. Why can some (stock headbolts and HG) engines survive multiple passes at 55-60 psi boost and the HG is fine while others pop at 45 psi?

I did oversimplify the use of the term MAP... but I am sure you understand this is why II offers the same turbo with three different turbines for example.

Anyway, I'll respectfully hold my position on this one even if I didn't state it correctly...

 

Unless you actually understand how it works.

 

Well, we agree/disagree at the same time... while I understand it, I also understand that my ability to convey that into words doesn't always work right. And I was trying to keep it simple for the simple question of the OP that didn't need an encyclopaedic response . HG popping is a cause/effect thing. Absolutely it is too much cyl pressure that causes this. But then you you have to examine how this happened. There is more than one way to do this for sure. And it is my firm belief that boost/DP ratio can contribute to this. Why can some (stock headbolts and HG) engines survive multiple passes at 55-60 psi boost and the HG is fine while others pop easily at 45 psi? And these numbers can vary greatly dependent on mods... for instance, with my first hx35/40 over 3b set up I could hit 60 psi boost with about 75 psi DP. That setup is only flowing about high 80's in lbs/min of air. My next setup was flowing 113 lbs/min from the primary at as high as 85psi boost with DP a little over 100psi (studs and stock HG) this would support your position except there are those that have had HG failure at a lot lower boost and DP levels. Now with a cam and porting, my primary flows in the low/mid 130's in lbs/min, my HP is up but I only see 60psi boost and 60psi DP... The point of that is.. a lot more air + a lot more fuel = a lot more power which typically is from more force on the pistons from more cylinder pressure. I have to say I have seen more HG failure from folks trying to get 45-50 psi from their stock turbo than I have from folks seeing 55 psi from a silver bullet. So you have to ask why?

I did oversimplify the use of the term MAP for the purpose of the OP... but I am sure you understand this is why II offers the same turbo with three different turbines for example. On the compressor side it doesn't change, but a turbine (and EH) changes the way the exhaust (well the amount anyway) flows and for the purposes of the user, how that turbo responds.

Anyway, I'll respectfully hold my position on this one even if I didn't state it correctly... I always reserve the right to be wrong... heck, Nathan Wright's always having to run around and clean up (correct) behind me. It wouldn't be the first time here either.

 

Correct, if the light stayed static but that heat will light it sooner and increase expansion time raising pressure.




I believe this.

 

As far as MAP goes...I know when I am out of the MAP of my turbo...at 45-48psi I see a 1:1 ratio...but at 50psi I see a 1.3:1 ratio. The MAP for the Super B Special is around 45-47psi, I can see it plain as day when I exceed that with boost, my DP starts to rise dramatically.

So I agree with soulezoo...ratio of DP/Boost is determined on the MAP of the turbo.

 

Ah, now I see where your going. Down the wrong road but the direction is clear.

Not gonna happen, mixing combusted exhaust with the incoming charge is a design to reduce cylinder pressures not increase them. Less oxygen in the charge results in less burn, less pressure, and less exhaust flow that lowers DP.

Again, excessive drive pressure CANNOT and WILL NOT increase cylinder pressures. It also CANNOT increase timing. If anything it has the opposite effect.

This scenario cannot happen in a DIRECT INJECTED fuel system. Until you have fuel you have no combustion. Combustion happens when the injection happens. It cannot happen any sooner so there is no ttiming advance by raising charge temps.

Diesel combustion is purely stoichiometric, you only get as much burn as you have oxygen. Once the oxidizer is gone combustuion temps cool and peak pressures drop. The more combusted charge you mix the less the temps and pressures and the less power you get, DP included.

Literally, the more drive pressure you have the LESS likely you are to pop an HG due to the lessed oxygen content in the air charge.

Again, at this point EGT's are much more of an issue the DP ever will be.

 

As I pointed out previously, once you are out of the compressor map the boost to drive pressure will diverge. Doesn't mean the map defines the DP it just means the turbine size and design at its limits there.

Did you mean boost at 1 and DP at 1.3 or opposite? If boost is exceeding DP then you are not neccessarily out of the turbo's compressore map.

 

I was just yanking your chain a bit. I knew where you were going but the original post just did not read right without further explanation.

I don't disagree with your explanantion and questions except on one small point, excessive drive pressure is a sympton not a cause.

Your statement about why some pop at 45 psi and other will hold 50 psi is dead on. I would hazard a guess if circumstances were examined closely fueling and reultant EGT's would be the largest contribution to failures. As to why do stock chargers see more failures is telling also, quality of the air supplied by a single cannot compete with even a small set of twins at the same boost. Less oxygen is gonna drive cylinder temps higher and probbaly reduce pressures but heat has its own dangers also.

The fact that one can stress a HG on VE engine at a lot less psi and drive pressure than a CR tells me there are other factors here that will contribute. Notably cylinder pressures and cylinder temps.

 

Been down the wrong road before....that's how I find new places LOL

Are you than saying the ignition doesn't take place at the injector tip and it still does it in the bowl of the piston in an super heated cyl?

 

For sure, the road not taken can lead to some interesting places.


If it did, how long do you think the injector tips would last?

What do you define as a super heated cylinder?


To understand the questions a little better let me throw some numbers and ideas out there for consideration.

1. Cylinder temps pre-combustion can easily reach 1200-1500 degrees BEFORE injection depending on load and fueling.

2. Max cylinder temps in the center of a combustion event can easily exceed 5000 degrees depending on fuel and air available.

3. What we are reading on EGT gauges is only 1/4 to 1/3 of actual cylinder temps.

4. Combustion events must occur in air without the fuel stream hitting any part of the engine and far enough away from the engine components to not super heat them.

The last one is extremely important to the question about where combustion starts. I guarantee if you put 3000 degrees to a tip it will disintergrate. Having combustion start that close to a tip is gonna cause a big BOOM! I think everyone has seen pictures of torched heads and pistons when spray patterns are not optimal and routed onto engine surfaces.

It doesn't happen that way for a couple of reasons. Diesel fuel needs to mix with ait to combust efficiently. Diesel will combust at the same rate irregardless of the charge temp as that is its nature. Given the fuel is leaving the nozzle at 23k psi and it has to spread a bit to mix with oxygen molecules combustion will be fairly far away from the tip irregardless of charge temp. We have all seen what happens when a cumbustible gas is shot form an orfice under pressure. Combustion does not start at the orfice but rather farther along the stream when enough oxygen has mixed to support ignition. Gas well fires are a good example.

How much preheating will you really get by mixing combusted gases with a cooler denser charge? This is a normal route to reduce cylinder temps and pressures in emissions engines so its really nothing new to an engine designed to run that way.

Since the exhaust gases are oxygen depleted and mixed with the fresh charge isn't more realistic that will retard combustion and limit the burn length rather than the other way around?

 

No 6 oh no - Agree with everything but stoichiometric combustion of diesel results in a little bit lower peak temp of 4100 degree F (2550 Kelvin).

Good overall comments on the subject though.

 

Yep, it will. That plus multiple events and in-cylinder EGR are the solution Cummins uses to control high cylinder temps and pressures for emissions purposes.

However, its pretty clear that pushing into higher drive pressure areas it is gonna be a fuel rich environment not stoichiometric. Hence my comment temps could run to 5000 degrees depending.

 

The air is already in the cyl so I dont understand the point?
Nothing can combust until heated to a gaseous state there for higher temps will result in sooner combustion. Agreed?
We are not mixing the fuel with the air as much as heating it to a gas with-in a controlled temperature for its ignition. Agreed?
The O2 in a cyl transfers the heat to the fuel there for higher temps will transfer the required heat faster. Agreed
Did I loose you or are still following where I'm going LOL
I may have oversimplified my statement that the TIP will in itself blow a HG.
I believe it is a huge factor in how much heat is left in the cyl.
My personal experiences are limited to just 5 of my own HG failures between the three trucks (P-pump , VP and CR) but there has always been the same common denominator, excessive DP and EGTs. I have never had high EGTs without high DP but I have yet to have a DP gauge hooked up to my CR so....
I have seen a CR go many pulls over 650hp with its DP and EGTs with-in check without spitting a HG yet watched countless stock turbo 12vs chunk a HG at less than 350hp but screaming DP and EGTS

 

The air is present but the fuel is in a solid stream on injection. Fuel cannot combust unless an oxidizer is present. If the fuel molecules are too close together there are not enough oxygen molecules to support combustion. There is a time lag as the fuel spray disburses and mixes with oxygen molecules to support continued combustion.

It really doesn't matter how hot the charge is. If there is insufficient oxygen to support combustion it doesn't happen. Diesel fuel does not vaporize like gasoline so you really don't convert it to gas for combustion but force the state change of the fuel and oxygen into something else. Combustion actually starts on the edges and proceeds thru the denser center as a flame front with the center having the highest temps.

Not disagreeing with any of this. Just saying DP is more a symptom of other problems, chiefly EGT's, than a direct cause for he HG going. Cylinder pressures and temps are the direct cause, high DP is the result of too small turbine design and quite likely a lot of fuel being exhausted still expanding in the exhaust track.