So, in theory, I could put her in neutral, log the motor at various RPM's constant for a few minutes each, and use the fuel numbers, etc, to calculate the amount of energy INPUT to the system to maintain RPM?

Wouldn't give us peak output, but at least give us minimum required input?

 

thanks

I can see why you would theorize this. I can only add some fuel to the fire, lets use an example:
A stock engine is dyno'd, and then a camshaft swap is done to move the powerband north. We should all be familiar with this by now, if not I have a great picture. Lets say the camshaft went from 205*@.050 to 224*@.050 for the sake of example.

Now, you are observing the power falling and create your theory about parasitic losses. Couldn't you then test your theory by simply performing another camshaft swap, to 236*@.050 ? You would then be shifting the torque curve even farther to the right. If your theory was correct, then the engine would not gain any torque, and power would continue to fall after a similar RPM. If you are wrong about the parasitic loss scenario, then torque would improve as engine VE picks back up due to the camshaft swap. In otehr words, you would never be able to make any more power if parasitic loss was the real reason (you cant eliminate parasitic loss with a camshaft swap; it would be a constant).

I tend to feel like we can keep shifting the power to the right, and that parasitic loss is negligible in this example.




This is interesting because we all know two basic principles that seem to conflict:
1. temperature increase is energy in the system, and more temp conservation (Wraps/coatings/shields/turbines) is generally considered a "good" thing, trapping it in gives us better fuel economy and efficiency.

2. Temperature increase has a direct influence on whether or not your XX octane fuel is going to explode your engine apart or burn nice and gradual like we want it to, and temp increases also reduce air density (potentially robbing power from volume-flow rate devices like turbochargers and engines). From this perspective (water injection, methanol, ethanol, race gas, intercooling) High temp is an ENEMY and a "bad" thing we combat.

So we have an oxymoron where we want to create and trap a maximum amount of heat, while at the same time eliminate it as much as possible. Which is it? where is the borderline?

I will say this. The obvious answer that springs to mind is:
for cruise situations, trapping heat is the answer, as it improves economy. Temperature increases due to wrap/coatings/etc is minimal at a cruise situation (You are unlikely to melt or warp your Al head cruising at 15:1 with all the wrap/coatings installed)

For wide open throttle, suddenly the reverse is applied. I inject water and additional fuel to bring temperature DOWN. I reduce power output to make the engine run SAFER and provide a cushion (headroom) for whatever fuel I am using. You are likely to melt your Al head at WOT using 15:1 air fuel ratios regardless of N/A or Forced induction applications.

I feel like this example has some answers for us, related to BSFC, power/work, efficiency.

 

Yes, exactly.

That will then lead you, through your calculations of needed energy input to rotate the engine, to a given BSFC to do just that.

 

Heres something to chew on. Revving an engine at low load creates a vastly different environment in the manifolds/chamber and unpredictable changes to VE, especially when the intake valve is holding open longer (camshaft upgrades). For example on my engine with a large camshaft, I get an almost untolerable/undrivable engine lope until I apply at least a 20-30% load to the engine, where it finally evens out and becomes smooth. So revving such an engine to neutral will give you data; but that data will NOT corelate to the same engine, at the same rpm, at a different load (it does not linearly coincide) and furthermore, especially where overlap and big camshaft profiles are concerned, we still have no idea how much fuel and air is simply leaving to the exhaust without doing any work, and this number will change at higher load values (compared to neutral).

To put this another way, the same engine with two different camshaft profiles will give you completely different data; even though the actual real-world energy requirement may be identical.

 

Part in bold is incorrect under the proper conditions. 15:1 is a starting point under such conditions, not an end point by any means.

 

Wait a minute. You are telling me you personally know of an engine that runs a 15:1 air/fuel ratio at wide open throttle?

I'd love to know of such an animal. The heat evolved should exceed the melting point of aluminum, whether it were a 2L or 6L engine.

And besides that, I used a very careful wording. It does say "you are likely". And yes, you are very likely, I think most will agree, that attempting a 15:1 gasoline air fuel at wide open throttle is not going to give a good result on any typical engine. Dare you to try it though. Let us know how it works

 

Yes & no.

What you are talking about is multi-fold. Load is a factor but it is simply something for the motor to work against. The engine running puts it under a given load. The load is the pumping losses at that operating range. Response to load through throttle opening changes dynamic compression.

The cam determines the valve curtain & energy balancing. You need so much residual heat energy to continue the process. It is cyclical in nature. One can with one valve curtain is perfect for one established set of parameters. Change the parameters & the valve curtain requirements will change.

 

Adding load should add air to the cylinder, (but not always!) which may improve it's flow characteristic (velocity/inertia) which helps it stay in the cylinder. My engine lopes and spits air back out of the cylinder at low load situations; once I apply load, all of that "pump losses" and "working against" aside, it tends to stay there as the engine will smooth out; it has to do with the way air moves into and out of the cylinder. Just slightly higher load values on my engine for example will produce much fuller cylinders when the valve closes, due to the camshaft profile, and has nothing to do with the nature of the load itself.

As an interesting side fact, my measured air mass ( mass air sensor recordings ) actually decrease when I retard my intake camshaft 20* btdc, and my fuel economy gets better, and the lope completely dissapears. This is the complete opposite of what I would have expected; and it goes to show you that not all theorys have applications in the real world. Only on some engines.

 

Not only that there are engines running way more as a calculated dynamic compression. What do you think a supercharger does?

But as far as static compression, yes. I know of engines in the 17:1 range capable of running stoics AFR's at WOT on ~91RON. Richening them up costs HP.

There is even LS motors in the world doing it. This is actually one of my projects I have been working on & I am looking into adapting the tech to a manner of beast I want to try. This requires special chamber shapes, from head & piston, as well as proper fuel delivery & ignition system.

 

You just told me there is a gasoline engine with 17:1 compression ratio, using 91 or 93 octane pump gas? with a 14.7:1 air fuel ratio at Wide open throttle?

Where do you live? I want one.

 

If load increases without an increase in dynamic chammer pressure the engine will lose RPM. That is what makes the idle test a good base point. Understand there is a point where idle & WOT under load actually intersect. See my note on the 21,000RPM engine.

What you are speaking of about air spitting back is called reversion.

 

There are situations where increasing load takes the engine to a spot on the timing map where a much lower timing number is located, then you will have a decrease in dynamic chamber pressure coupled to an increase in airflow that still gains RPM because your brake mean effective pressure still goes up. I think you meant to use BMEP above in fact, not "dynamic chamber pressure" as that term is loosely translated to an "increase to pressure peak" which as I have just shown, is not always true.

Pressure in a coordinate system is measured over time, the peak has certain attributes and is applicable to our discussion, but it is NOT the whole picture. I am not saying this for your benefit, more for our readers.

 

I do to. They exist in Australia at the moment.

I have discussed LS engines with him many years ago & he began working on them. I got out of the gig for a while now to work on other things but am now going to get back into it. He used a certain head company to do the changes need to the chamber & I was informed that I could get that reshape do head when I was ready.

I am getting close to being ready. My plan was to start around 15.5:1 & go from there.

 

A few years ago I had the opportunity to run an engine at 15:1 air fuel ratio. It happened by accident at first but then became an experiment. The engine suffered a power loss (compared to running at 12:1) at these excessive lean mixture ratios, it made 40-50 additional RWHP at 12:1 than at 15:1 (we are using 93 octane fuel, engine static compression was 9:1, 122cid, 22psi boost, 7500rpm).
The EGT climbed to the point where the piston rings lost tension and the engine acquired a bit of blow-by on our final run.

I rebuild the engine, changed the rings, and observed NO damage, NO detonation, no scoring of any kind or visible problems. We made several 400~rwhp dynojet passes (about 8 runs) at 15:1 before the rings gave out, with EGT over 2100*F at the turbine. I attribute the lack of detonation to combustion chamber design and reduced timing numbers, however nothing could stop the EGT from skyrocketing and ruining the piston rings.

 

BMEP is a function of dynamic compression & chamber pressure.

There is always a definative moment of inertia & calculable. Ignition timing is a requisite of load & air/fuel mass at a given RPM, yes.

Ignition advance simply changes the spot a certain change in pressure occurs.

 

Ahhh, the flattest power in the operating range. Then one must match the gearing so when the shift is made the engine goes from the bottom of the "range" to the top of the range.

 

Apples & oranges.

Let me ask you: If energy is converted in the chamber to torque, what happens to residual heat energy?

 

Shift recovery is always desired to be at the peak torque value. What is nice is when that peak torque value is spread across the entire operating range.

 

You mean "If fuel and air is reacted in a calorie meter where it is converted to temperature and pressure, what happens to residual temperature?"

These devices are traditionally used for such experiments, and your question is vague. If we start at 30*C and the end temp is 80*C, then I know my difference in temp was 50*C, and if I do the same for pressure I now know what volume it would have occupied if the chamber could expand (as in a piston example). For the sake of such an experiment we might consider it a closed system; so your theoretic answer depends on whether or not the system is exchanging temperature with it's surroundings or not. That said, in real world situations, engines do deliver temperature to their surroundings, and from them, whether running or not.

Also you cannot keep using "heat" to integerchange with "temperature increase" they are not the same thing. I am careful with my wording to say "temp increase" and not "heat" for this reason. If we are having a real tech discussion I think we should find terminology definitions for each term so there is no confusion; that said, we are discussion temp increases, not heat of the system, which is a whole different "apple".

Furthermore, I do not see how your V8 pump gas engine is much different than my 4-cylinder pump gas engine example. Both use pistons, both have chambers, both have pump gas. Both use temp and pressure the same way. Its more like green and red apples.

When it comes to asking questions, I try to make them learning questions, where people will learn something by working out the possibilities in their minds. I also provide solutions when I am aware of them. Your question is more of an "I am right and you are wrong, I have the solution and you do not" approach, which is a negative impact on discussion.

 

Residual heat energy is very real & is a quantifiable entity. You measure it in EGT's

You said you EGT's went up as it leaned out. You also lost power so there was an increase jn residual spent exhaust gas energy. The same is true in over rich conditions as well.

What I am asking is what happens when the thermal energy present in the chamber is converted, even as in the case you experienced from a proper, for your engines tuning, meaning an overall operation stasis, from one that was improper?