Smokey said, “If you ain’t...
Smokey said, “If you ain’t thinking, you probably ain’t winnin’. Photo by Trish Yunick
In an attempt to set the stage for upcoming in-cylinder combustion analysis for the CT G.R.E.E.N. engine project, there's a good chance we inadvertently broached the second subject before what should have been the first. Aside from an apology for that, we decided to put things back in order this month. What brought this particularly into focus was the Advanced Engineering Technology Conference presentation made by Dr. Andy Randolph (Engine Technical Director for Earnhardt Childress Racing) at the recent PRI Show in Orlando.
Actually, we were exposed to the wit and technical prowess of Dr. Randolph some years ago, also at an AETC, when he discussed the intricacies of in-cylinder combustion analysis. There are teachers and there are teachers. Unless you've had an opportunity to observe his delivery, it's difficult to describe its effectiveness. You would marvel. Having had experience performing test procedures of the type he discusses, I'll underscore the value and benefits they can produce.
That said, this month we'll discuss what is widely believed to be the real focal point of making engine power; the combustion space. In fact, you may want to concentrate on how a variety of conditions and causes outside this space will help toward understanding "what affects what" in determining combustion efficiency.
Briefly stated, we urge you to focus on the combustion space while changes outside this window are made, be they changes to valve or ignition spark timing, intake/exhaust system configurations, port flow quantity/quality, combustion space modifications (heads and piston crowns), method of fuel delivery and type, and related factors that can materially impact how fuel is converted into heat (power).
The intent here is also to link what we previously discussed concerning the in-cylinder tests soon to be conducted at Michigan Technological University with the following bits of information. Hopefully, in combination with the prior discussion, you'll have a reasonably solid basis for following and understanding why the MTU data stream was gathered and the potential impact on how you optimize power in your own engine projects.
For purposes of discussion, we'll assume the subject engine has the ability to evaluate and control basic functions on an individual cylinder basis, such as the current CT Project G.R.E.E.N. version we hope you have been following the past year or so. We'll let your creative imagination figure out how the same results can be obtained from engines that don't incorporate such contemporary technology. Surely you've heard about variable HEI distributor reluctors (for individual cylinder spark timing) and mechanical fixes (fuel dams, slots, and runner entry modifications) for non-EFI intake manifolds. No? Well, it might be worthwhile.
OK, to the business at hand, square one involves the assumption that a multi-cylinder engine can be viewed as a collection of individual engines. That is to say, each cylinder can and should be optimized for its own combustion efficiency.
Since typical induction systems allow inlet excursion pulses to be "felt" or shared among all cylinders (based on port design, valve timing, backpressure influence, reversion pressure, spark timing, combustion contamination, engine speed, and fuel enrichment), there can be variations among cylinders in the potential for how power can be gained through optimization of one cylinder at a time.
However, the first part of this step involves determining what overall spark ignition timing produces the best power; e.g., conventional total ignition spark mapping. Then it becomes a matter of finding out optimal spark settings for individual cylinders. In the course of the MTU testing project, this step will be
Engine testing has always...
Engine testing has always been critical. Trish Yunick
Once individual cylinder timing is optimized, it's then a matter of examining air/fuel charge optimization on an individual cylinder basis. A frequent procedure for performing such evaluations involves O2 sensors placed in proximity of the cylinder heads (as you might locate for traditional exhaust gas temperature sensors). By the use of these type sensors, depending upon the method of fuel delivery (carburetion as opposed to individual fuel injectors), the specifics for providing optimal air/fuel charges on an individual cylinder basis will vary.
For example, as compared to the time-honored EGT method, O2 sensors look more at the combustion process itself than the temperature-based results of the burn. Generally, especially if the engine uses a multi-point EFI system, this particular step is made much easier than when either making internal modifications to a carburetor intake manifold, utilizing "mechanical" fixes in the manifold.
Of course, you can also explore multiple valve timing variations through camshaft lobe design and positioning, but here's an area previously discussed in this column that probably doesn't need repeating.
But let's step more into the combustion efficiency evaluation techniques we'll be using at MTU. In this instance, we have the best of several worlds. By collecting virtually real-time cylinder pressure as a function of incremental crankshaft angles, on an individual cylinder basis, we'll have a precise look at how cylinders are pressure-balanced, along with determining the cylinder of highest pressure which, in turn, sets the pressure bar for the level we'd like the remaining cylinders to achieve. Plus, since we'll have control over individual cylinder spark timing (optimization) and fuel delivery, following the so-called "2-3 horsepower gains at a time" approach, the chances for overall power optimization are further improved.
And don't forget, we'll be doing this while comparing conventional racing gasoline to our chosen E85 fuel. Since the project has already demonstrated that E85 (coupled with EFI) is superior, on-track, to the carburetor/gasoline combination, our focus will now be more toward optimizing the package for E85.
Lofty expectations, you think? Actually, while this presumably "academic" approach to optimizing the G.R.E.E.N. engine's combustion efficiency may seem like a reach, it's intended to push the thinking of CT's readers. From the beginning, this project was designed and intended to provoke new thoughts.
Racing has never been a stagnant landscape, at least for racers who are successful. The time is pretty much gone when "chunks" of horsepower could be carved out with relatively simple and obvious modifications. Obviously, there are those who would argue that it's the skill and chassis setup and driver skill that produces a competitive edge. And, even as a died-in-the-wool mechanical engineer who believes such an approach produces winners, it's never a disadvantage to have power in reserve when you're exiting a turn or passing the flag stand.
Properly matched power and chassis combinations work, and if you fail to recognize that adapting to changing technologies and the opportunities to be gained from them, you could become a victim to a quote I again attribute to Smokey; "If you ain't thinking, you probably ain't winnin'. Copying hardly ever works."