Yes, gallery cooling to keep the heat off the crown better. In addition, the valve seats and valves were also changed to handle the heat better.

The overall massive spike in temp was eliminated by using multiple events but the fuel still has to be burned and create xxx BTU's to make the power. Massive temp and pressure spikes were reduced in favor of an overall longer burn of more even heat. Therein lies the catch.

A massive spike then tailing off like a jerk pump imparts less heat to the piston than a longer even burn. The rate of heat transfer is fixed therefore the longer the piston is exposed to the heat the more is transferred. The CR timing is late but it also extends well beyond what a jerk pump does to create the in-cylinder EGR effect. A long even burn transfers mor eheta to the piston, makes the same power plus lower emissions than throwing the same amount of fuel into the cylinder earlier.

At a certain temperature and volume the fuel will take the same time to burn, no matter WHEN the burn is started. Starting the burn later the pressures drop as the piston moves down so 1 piece of NOX formation is removed, cylinder pressure.

Yep, the coolant temp shows just how much more is imparted in the cylinder and used for power. The EGT's show where it went. But, in the emissions scheme it has risen beyond what was acceptable.

Cooler\hotter combustion is a function of how much fuel can burn given the available oxygen, not neccessarily leaner\richer. It depends on where the mixture is to start with. If you are already fuel lean then more air will cool the combustion temps. However, if it is fuel rich more air will cause it to burn hotter faster.

Every piece of documentation and engineering theory indicates that modern diesel are built to run fuel rich because it is easier to remove the soot than the NOX. This also limits the amount of pressure and heat generated because the combustion never gets to stoich. Add air and bring the event to stoich, it will be hotter from the complete combustion of all the fuel.

Try to measure and appply this to what the gauges read will absolutely drive a person nuts. The dynamic load nature and the ability to go from 30:1 to 10:1 in hundreths of a second and then back agian depending on load and throttle position is simply not measureable. All we have is the math to prove it.

 

Ok I think I stand corrected and what has been said makes sense. Then how do we stop melting pistions on the CR trucks if they are supposed to run cooler or is it due the emission stuff when we start messing with the fueling parameter is were the problem is? So are reground cams and EFI live going to be solution to customer tune them?

 

With the piston design on the 04.5-07 you need more airflow, they just aren't as durable a design as 03-04 and 07.5+.

 

Good discussion! Thanks for the question.boB

 

So, add more air, increase the air:fuel ratio, and the temps will go up?

This is exactly what happens in a gas engine. Lean mixtures (>15'ish) turn the headers cherry red, and increase cylinder temps. If the engine is running hot, the computer adds a little fuel to bring the ratio and the temps down.

Listening to what you say, the EGT gauge will not exactly match the mixture. What about ball park? If the temp is generally high, then the mixture is generally lean? If you're trying to save fuel, that is a good thing? To a point, of course. Wouldn't want to burn a piston because of a lean mixture. OTOH, why waste fuel keeping the EGT low? 1100* would be better than 900* for economy?

This is exactly the opposite of a gas engine. Some race teams are experimenting with a pyrometer in every header tube, and changing the individual injecter pulse based on individual EGT's. I read about that a couple of years ago, and I'm not sure where that experiment went.

And, I seem to recall that turbo's are generally more efficient when they're hot. I know in the morning if I start the engine and drive away, there's lots of black smoke and a lot of turbo lag. But if I let it warm up just a few minutes, that doesn't happen.

In a previous experiment, I found my truck gets better gas mileage when everything is allowed to warm up well. Keeping the front cover on and fully closed certainly improved mileage by a measurable amount. That lead me to believe that heat was good for a diesel. If it runs "hot", that was a good thing. Previous discussions here indicated that a coolant temp of 210-220* was better than 195-200*.

The secret to getting the most out of any piece of equipment, is to learn how it works, and why it works. That's why I ask these silly questions. Thanks for helping me to understand.

 

Not quite. If you don't have unburned fuel, adding air will cool the EGT. If you have enough fuel that isn't burned based on a lack of available air, adding air will cause this fuel to burn, which will raise the EGT. Grossly simplified explanation: If you've got a lot of black smoke, you've got unburned fuel and adding air will allow this fuel to burn, raising temps. If you don't have a lot of black smoke, adding air will reduce EGT.

If the temp is generally high, you're simply burning a lot of fuel. Diesels get better overall mileage because they can operate on a very, very lean mixture without parts failure, whereas a lean mix in a gas engine is very hot. Gas engines control airflow as well as fuel to modify the air:fuel ratio, thus altering cylinder temp. In a diesel there's nothing regulating airflow, and all temps are related to the volume of fuel injected; if you're already burning that fuel efficiently then adding air will cool temps.

Not even close to a silly question. This thread has been awesome for general knowledge of diesel engine operation!

 

This is exactly the opposite of a gas engine. Some race teams are experimenting with a pyrometer in every header tube, and changing the individual injecter pulse based on individual EGT's. I read about that a couple of years ago, and I'm not sure where that experiment went.


This has been done in recip piston airplanes for years. A digital "trending" gauge was exciting to see some 15-20 years back (an overall, rolling average of temps, not just individual temps).

 

Lots of good info here. Takes time to digest it. I'm pretty good with gas engines - not so good with diesel yet.

For many of us- apparently - the goal is not maximum power, but maximum efficiency. I keep my Smarty Jr. set to economy all the time, even while towing a light load. In my daily commute, I get 18-19mpg.

A diesel can run fairly lean mixtures safely, to maintain light cruise and light load economy. I would expect that it needs a little more fuel to tow a load, though.

It does not appear that the 5.9 engine uses an O2 sensor - I can't see one on my truck, and I can't find a replacement part number. So the truck runs in open loop all the time. Not as efficient as it could be. My race/street car runs in closed loop on the street, and it's very efficient. On the track I used leaded fuel, so I have to remove the senser.

I don't see that anyone has installed a real gauge to check the mixture. It's not a difficult job, and the parts are readily available. I'm thinking that a good wide band sensor and a way to adjust mixture across a very narrow range would be a good idea. Preferably something automatically done. Use something like an aftermarket tuner with an O2 sensor? A Smarty wouldn't work, as it's noty connected all the time. Maybe a Bully Dog or Edge product.

 

Becuae a diesel doesn't have to opertate at a specific air:fuel ratio a gauge wouldn't tell you much. Idle is over 100:1 and stoich is 14.5:1, HUGE range. Gassers run in a specific range because they have to.

There is really no open/closed loop for diesel either based on the ratio of air:fuel. Air is not metered on diesel, they use as much air as they can get. So also no real way to adjust the ratio as it varies so much.