You might remember a while back, when we brought you Smarter Every Day’s video showing you the inner workings of a see-through carburetor, captured in super-slow-motion. Well, Destin is jumping back into the fuel-delivery arena. This time, he’s looking at a mechanical fuel injector (specifically from vintage tractors) at 28,000 frames per second. For comparison, a standard cinematic video is shot at 24 frames per second, and his standard video is uploaded in 60 frames per second, meaning he can show us what’s happening 466 times slower than normal speed. 10 seconds of the high-speed video will yield 77 minutes of footage at 60 fps, or 3 hours and 12 minutes at 24 fps. All from 10 seconds of footage.

Similar to an electronic fuel injector, the mechanical injector uses an internal valve to meter fuel from the nozzle. Unlike an EFI injector, the valve in the mechanical injectors being tested is controlled by a spring and ball as opposed to solenoids. When the fuel pressure reaches the desired level, the check valve opens up and the injector sprays.

Here, you can see the difference between a good and bad spray pattern from a nozzle. The top one has lots of liquid streams, which are dense concentrations of fuel, without much air. The bottom spray is far more atomized, which allows enough air to be mixed in with the fuel for much more complete combustion.

That makes an injector tester a much more manual affair than a modern EFI injector flow bench. As Jacob from Cross Creek Tractor explains, “It works a lot like a floor jack. You shut off the valve, and pump the unit to build the pressure needed to overcome the spring in the injector. Then you can check the pressure the injector pops off at and the spray pattern of the fuel.”

Much like an EFI injector, when testing a mechanical injector’s spray pattern, you’re looking for an even flow from all of the holes as well as an overall even pattern coming out of the nozzle. Makes sense that those design features would remain the same, regardless of the method of actuation. Beyond the utility of a testing apparatus, anyone who has ever seen a fuel injector being tested has had some intrusive thoughts.

Well, today, Destin’s intrusive thoughts won, and he decided to do what we all have thought about… turning a fuel injector tester into a flame thrower. Time for some honesty here – I didn’t think I could possibly be any more of a fan of Destin and his channel. Then he strapped a propane torch to the end of a mechanical fuel injector tester, and, well… I guess it was possible to become more of a fan.

When the reserved rocket scientist lets out his inner pyromaniac… All in the name of science, of course.

So, while I could pretend to try and talk about the scientific value of playing with high-pressure fuel and various forms of high-incendiary torches, let’s be real. It’s just freakin’ cool. Besides appealing to all of our inner pyromaniacs, the actual flame imagery captured by high-speed videography is amazing to watch. Plus, there are definitely some learning opportunities happening, if you can look away from the fire long enough to listen.

Jokes aside, there really is a lesson to be learned here regarding stoichiometry and combustion, and it’s presented quite well. After all, the name of the channel is Smarter Every Day. You’d better believe you’re going to walk away having learned something (other than “fire is pretty,” of course).

Ok, some real science here. As the fuel stream exits the nozzle, it atomizes. Right when it exits the port on the nozzle, the AFR is 0, since it is entirely fuel. As it moves outward, air is mixed in as it atomizes, raising the AFR number, until eventually the ratio of air to fuel is sufficient to allow combustion. In this photo, you can see precisely where that occurs in the stream.