Engine Tuning - In Cylinder Pressure - Supercharged Engine

[nitro2]

Thanks for taking the time to explain!

Do you have any experience with using small tubing to connect sensor when it was not possible to put it where you wanted?

The idea that someone posted recently about some kind of system that connects one sensor to a switch/valve to a series of tubes connected along the duct is interesting to me. I understand that the diameter/volume of the ducts would impact the results so I want to choose the optimum tubing. I am thinking something steel brake line tubing or copper tubing with collet type fittings.

A long small ID tube is great for measuring average pressure at a point, but if you are wanting to measure fluctuating pressure the tube idea won't work, the sensor needs to be as close as possible to what it is measuring in that case.

[nitro2]

Clint,
Thanks for posting the pressure graph. There is a wealth of information contained therein.

In your experience, which pressure curve would a very good engine simulation program present as
being typical for that engine?

Also, would not an engine with a 40% combustion pressure variation run very rough and exhibit
noticeable vibration?

2000 HP blown V8s always run rough lol, no matter how good the combustion is.

That being said it is important to remember that the screenshot showing the pressure trace for the 4 cylinders was how the pressures looked for just that one cycle, the next cycle is different, the following cycle is different again and so on and so on. There is both cylinder to cylinder variation and cycle to cycle variation going on at the same time. If a person just looked at cycle after cycle for 4 cylinders for 1000 cycles and tried to make heads or tails out of it, it would be extremely difficult, that's why looking at pressures on a scope has minimal benefit. The TFX software does the heavy lifting and summarizes what really matters so one's brain doesn't get bogged down looking at 1000 individual cycles x 4 traces lol. I'll show that too in a bit.

Next I will post what the traces look like cycle to cycle for 1 of the cylinders then discuss the cycle to cycle variation.

[David Redszus]

Thanks for taking the time to explain!

Do you have any experience with using small tubing to connect sensor when it was not possible to put it where you wanted?

The idea that someone posted recently about some kind of system that connects one sensor to a switch/valve to a series of tubes connected along the duct is interesting to me. I understand that the diameter/volume of the ducts would impact the results so I want to choose the optimum tubing. I am thinking something steel brake line tubing or copper tubing with collet type fittings.

Jon
If the aspect ratio of the tubing is known, along with the pulse rate, it should be possible to calculate
the natural frequency in the tube and forcing frequency, to determine harmonic amplification of the pressure.
I mean a correction factor equation could be developed.

[SchmidtMotorWorks]

Thanks for taking the time to explain!

Do you have any experience with using small tubing to connect sensor when it was not possible to put it where you wanted?

The idea that someone posted recently about some kind of system that connects one sensor to a switch/valve to a series of tubes connected along the duct is interesting to me. I understand that the diameter/volume of the ducts would impact the results so I want to choose the optimum tubing. I am thinking something steel brake line tubing or copper tubing with collet type fittings.

A long small ID tube is great for measuring average pressure at a point, but if you are wanting to measure fluctuating pressure the tube idea won't work, the sensor needs to be as close as possible to what it is measuring in that case.

That makes sense, do you know of any good strategy to relocate the sensor 20 times?
Probably just 20 bungs and 19 plugs.

[nitro2]

Thanks for taking the time to explain!

Do you have any experience with using small tubing to connect sensor when it was not possible to put it where you wanted?

The idea that someone posted recently about some kind of system that connects one sensor to a switch/valve to a series of tubes connected along the duct is interesting to me. I understand that the diameter/volume of the ducts would impact the results so I want to choose the optimum tubing. I am thinking something steel brake line tubing or copper tubing with collet type fittings.

A long small ID tube is great for measuring average pressure at a point, but if you are wanting to measure fluctuating pressure the tube idea won't work, the sensor needs to be as close as possible to what it is measuring in that case.

That makes sense, do you know of any good strategy to relocate the sensor 20 times?
Probably just 20 bungs and 19 plugs.

Yes or 2 sensors relocated 10 times for such a bench test.

[nitro2]

nitro2, that pressure graph is awesome. That kind of information graphed out is displaying the essence of what is happening inside the cylinder! Much appreciated.
Any temperature numbers that correlate with the pressure graph?
Very interesting information. Well done.

The software calculates temperatures, there is no way to actually measure temperatures per degree, except with out of reach (cost wise) technology, and also with a semi affordable technology that consumes the temperature sensor. Either way costly to measure.

[nitro2]

Pressure phenomena. Basically depends on how the charge goes off, whether it rings the chamber and the location of the sensor. On some engines it happens on every cycle, on others it happens sporadically, on some it doesn't happen at all.

Nitro, What does an FFT analysis show of the ringing, typically does it scale with bore or instantaneous volume of something else?

Generally the ringing frequency is bore related. The cause of the ringing is not 100% clear, it is definitely related to the initial burn rate to some degree but is not wholly related. There is a randomness and unpredictability to the ringing (occurs on some cycles but not others and some engines but not others even for the same basic pressure trace magnitude, bore, and rpm) so there is more than meets the eye.

[nitro2]

I am also wondering if a direct injection spark ingnition engine would have much more consistent combustion cycling?

Generally speaking, yes.

Anything that makes any aspect of the cylinder filling, fuellng, mixing, swirling, squishing, tumbling, sparking, exhausting processes etc. more repeatable from cycle to cycle will decrease the cycle to cycle variability.

Reducing cycle to cycle variability will increase torque/power so long as the thing decreasing the variability is also the right thing to be doing. You want the engine to be doing something consistently right, not consistently wrong, if it is doing something consistent cycle to cycle but it is the wrong thing, then you might as well just go back to having more variability.

[nitro2]

Any data on what happens to the intake pressure wave and reflection under boost in the intake manifold?

shawn

Yes, for sure. It's coming after awhile of combustion discussion.

[CMIdiesel47448]

Any data TFX receives from customers is automatically regarded as confidential, so I am limited to what I can post, basically limited to data from deceased customers and/or engines that are now changed a LOT from the way they were when we received data.

Unless otherwise indicated, posted data is for the engine as tuned via conventional tuning methods, BEFORE ANY cylinder pressure tuning was undertaken. The idea is to look at the various things that are going on in the engine that are not right, which is what anyone sees when they first have cylinder pressure data, they see everything that is not right.

Lets start off with just one trace so everyone understands what they are looking at before moving on.

Below is cylinder pressure data from a 600+ ci supercharged engine. Only one combustion cycle is plotted for this particular screenshot.

4 of the 8 cylinders (cylinders 1,3,5,7) are plotted. Each cylinder trace is color coded to the cylinder buttons i.e. Cyl 1 button is blue and the trace is blue, Cyl 3 button is purple and the trace is purple, Cyl 5 button is yellow and the trace is yellow, Cyl 7 button is red and the trace is red.

The x-axis is crank angle, read left to right, -60 is 60 BTDC, 0 is TDC, the EVO vertical line is at exhaust valve opening, 110 is 110 ATDC. The y-axis is pressure in psi.

The numerical values on the right hand side cover various things, such as RPM, IHP (per cylinder and for the whole engine), peak pressure, peak pressure location, energy release, etc. In this particular trace the numerical values on the right hand side are for Cyl 5.

Obviously there is quite a difference in pressures for cylinders 1,3,5,7 for this combustion cycle. There's a lot more to see than just that, but I'll leave it there for now, as there are probably questions related to this screenshot that should be answered first.

Combustion Cycle 316.jpg

What is your crank angle sampling resolution? Are you using a shaft encoder? If yes, what make/model? If no, then what? Assume from some subsequent posts you are using a flush mount transducer, but I’m curious how you’ve done it. Please elaborate.

Thanks, Damon

[CMIdiesel47448]

I am also wondering if a direct injection spark ingnition engine would have much more consistent combustion cycling?

Generally speaking, yes.

Anything that makes any aspect of the cylinder filling, fuellng, mixing, swirling, squishing, tumbling, sparking, exhausting processes etc. more repeatable from cycle to cycle will decrease the cycle to cycle variability.

Reducing cycle to cycle variability will increase torque/power so long as the thing decreasing the variability is also the right thing to be doing. You want the engine to be doing something consistently right, not consistently wrong, if it is doing something consistent cycle to cycle but it is the wrong thing, then you might as well just go back to having more variability.

Eagerly awaiting a discussion on IMEP variation before/after combustion optimization...

Thanks, Damon

[hoffman900]

It's been on Youtube for almost 8 years now, but I still keep coming back to Dr. Andy Randolph's video on the NASCAR engine.

He shares plots of burn durations for a given cylinder and briefly gets into their variability.

Another good one is the developed of the Ford RY45 circle track engine. They found via pressure sensors that one cylinder was above their target cylinder pressure, in relation to rotating components and their cycle life. I believe they lowered it via ignition system advance changes. That's a good example of "detuning" a cylinder in order to protect the entire package. A drag race engine may not be as sensitive, but a offshore powerboat / road race / circle track / Bonneville combination would.

[David Redszus]

If anyone is interested, I can email copies of Andy Randolph's SAE paper(s) regarding combustion variation.
Send me your email address.

[Roundybout]

I’m also curious about how much variation there needs to be in order to feel it in the butt dyno. Is there an average variation that’s considered good? On the best producing cycles, are those the cycle/combustion events that are the goal and anything lower an an issue that needs to be addressed? Or are the best because they’re on the verge of detonation and the average is the goal and spikes up and down are anomalies we’ve yet to figure out how to fix. Is it even possible to have a single never mind multi-cylinder engine produce the same combustion events repeatedly. Under different loads, throttle positions, temps, on and on.

Thanks for sharing this info. Fascinating topic.

[hoffman900]

Screen shot from Dr. Randolph. You need to watch as he goes over what is happening here.

640A9F30-1E31-4E46-A534-6DCC171D1C42.png

* note: that loss is for a single cylinder. It adds up fast. This also measured on an application that is very highly developed alread.