If Smokey Yunick was still with us today, I suspect he'd be smack in this middle of this issue. He once told me that carburetors are little more than "controlled leak" devices and that electronic fuel injection in everyday circle track engines was an inevitable option that should be explored and developed at a practical level. Before we dig into the subject, let's take a moment to review some combustion properties that play into the benefits of EFI, as compared to carburetors. While we won't address related topics such as system economics and complexity, both of those elements appear becoming of less user concern than in the past.
On multiple occasions in the pages of this magazine, we have attempted to describe the complicated process of converting liquid fuel to heat (power) by combustion. It is the method by which fuel is atomized and the point of introduction into an inlet airstream (or combustion space) that become problematic to an efficient burn. In addition, while the net effect is mixture passage into the combustion space, flow in an induction system or path is elastic, interrupted and loaded with a variety of pres-sure excursions that tend to "un-mix" air/fuel charges. And the farther upstream in an induction system fuel is introduced, the more influential the problem causers become.
In particular, we know that to initiate and sustain a uniform combustion flame rate, it's helpful to have created air/fuel charges consisting of the smallest possible fuel droplet size. And the mix should be as uniform and homogeneous as possible, throughout the combustion space. Simply stated, carburetors have a difficult time favorably contributing to this objective, if for no other reason than they function well upstream of combustion spaces. In a recent conversation with CT Senior Technical Editor, Bob Bolles, it became apparent that maybe some further discussion on the subject might be helpful to CT's readership.
Here's a perspective to consider. At the risk of oversimplification, imagine that large fuel droplets require more time to be consumed in the combustion process. And, conversely, smaller droplets take less time. In a combustion space of poorly mixed air/fuel charges (especially if there's a range of droplet sizes), there will effectively be an accompanying range of air/fuel ratios in this space. Accordingly, when the burn begins, flame rate will not be uniform and, very possibly, an inefficient net burn occurs.
In the early 1970s, I received a call from a man named Jack Priegel. He was the president of Autotronic Controls Corporation in El Paso, Texas. His company was developing a fuel atomizing device using what amounted to an ultrasonic device through which liquid fuel was being broken into droplets reported to be in the sub-20 micron size. Atomized fuel looked like "smoke" once it passed through the device. But he had what he thought was an intake manifold problem because the device was located where a carburetor would have normally been placed. Despite this handicap and the fact fuel was being taken out of suspension by pulsating airflow, his system demonstrated the potential benefits from a dramatic reduction in fuel droplet size. Jack was funding the project by the sales of a product his company devised just to keep his induction system efforts alive. Actually, that product was a multi-spark ignition system. The induction system was discontinued when sales of the product went through the roof and we all know the impact MSD ignitions have had on motorsports. But that's another story.