Fuel injection??

[bob58o]

I’m still trying to figure out how the “cam” works in this carb. It seems the cam is part of the “metering chamber.” Perhaps the throttle cable opens the butterfly and when pulled far enough it pulls the needle out a bit more? Still trying to figure out what this “metering chamber” thing is.

 

[Denny]

I think it operates like a vacuum secondary carb Bob. The higher the vacuum the more it opens.

 

[65ShelbyClone]

I thought I posted this already, but apparently just drafted it.

Looking at Tillotson's explanation of operation, they carefully call it "a form of" mechanical injection, meaning they have used the term with a lot of imagination. Beyond that, the last paragraph on page 1 describes it as functioning exactly like a common three-circuit carburetor. If breaking fuel into finer particles is what provides the power and emissions improvements, fine, but it takes very high air velocity to do that which is why the carb throat is so small. The engine output charts tell the story; it becomes a restriction above 3500rpm on a 190cc mower engine. It's going to peak even lower on the rev range as displacement goes up. To be fair, it's only designed to replace stock carbs on stock, governed 160-190cc utility engines.

Thing is, you could probably still patent a carburetor design today that is no better than a carb from 70 years ago if the design and/or method of doing it is novel. Plenty of junk tech has been patented and lots of patents exist just to stifle competition or to provide patent trolls something to sue people over.

I remember when mechanical fuel injectors were called carburetors. WTH is a mechanical fuel injector that a carburetor is not. I don’t understand how it works differently from a carb. A carb basically uses air pressure right? Which is based on density, volume, and air speed. What else does the mech FI use? Is there an RPM gear or something? Instead of using the amount of air consumed at each RPM like a carb does? I guess the question is… what tells it how much fuel to inject?

Mechanical fuel injection is usually a constant-flow type and there is some sort of metering valve connected to the throttle that varies flow vs throttle input and pressure goes up with RPM, further changing the flow. Bosch K-Jetronic and Rochester Ramjet systems had a big vacuum metering device to make them more accurate in response to actual engine load.

 

[Denny]

Mechanical fuel injection is usually a constant-flow type and there is some sort of metering valve connected to the throttle that varies flow vs throttle input and pressure goes up with RPM, further changing the flow. Bosch K-Jetronic and Rochester Ramjet systems had a big vacuum metering device to make them more accurate in response to actual engine load.

That paragraph is probably the most accurate description of how the Ram-Jet system is designed to work that I have ever seen. Never studied the Bosch system, and Hilborn Is even simpler yet.

 

[65ShelbyClone]

(A form of) real fuel injection:

Arduino Mega, bare NO2C board, and a 700kPa MAP sensor.



Unfortunately the Speeduino firmware can only go up to ~500kPa due to how the MAP value is handled in code. It can be modified to work with higher values, but until I can do that, 59psi of boost will just have to do. Actually, it would be 62psi at my elevation.

 

[Master Hack]

HUH?

 

[jpndave]

He's joking. 59psi is an insane amount of boost these engines wouldn't even take without blowing apart. That's over extreme Formula 1, drag race, diesel territory, etc.

 

[65ShelbyClone]

Yeah, just kidding.

 

[Master Hack]

He's joking.

I was lost after this:

Arduino Mega, bare NO2C board, and a 700kPa MAP sensor.

 

[65ShelbyClone]

Arduino is a series of microcontroller boards and an accompanying programming environment designed for students and hobbyists. There are a wide variety of expansion boards called "shields" that a given Arduino model plugs directly into. They range from simple perf boards for prototyping your own circuits to CNC controllers for building your own 3D printer. Speeduino is effectively an Arduino EFI shield and the WTMtronics NO2C is a lower-cost variant with fewer features, although still a lot of them. They are speed-density systems and have to measure manifold pressure with a MAP sensor. The most common sensors for it are either 250kPa (21psi of boost) or 400kPa (~44psi). The MPX5700 is one option for pressures higher than that.

 

[bob58o]

Boost, like life, only begins past 60.

 

[Master Hack]

Arduino is a series of microcontroller boards and an accompanying programming environment designed for students and hobbyists. There are a wide variety of expansion boards called "shields" that a given Arduino model plugs directly into. They range from simple perf boards for prototyping your own circuits to CNC controllers for building your own 3D printer. Speeduino is effectively an Arduino EFI shield and the WTMtronics NO2C is a lower-cost variant with fewer features, although still a lot of them. They are speed-density systems and have to measure manifold pressure with a MAP sensor. The most common sensors for it are either 250kPa (21psi of boost) or 400kPa (~44psi). The MPX5700 is one option for pressures higher than that

Oh, l get it now! Why didn’t ya say that in the first place?

 

[65ShelbyClone]

I was trying to be efficient.

 

[panchothedog]

I think this thread started out about induction for a small one cylinder engine. Sure looks like a stinking carburater, a hand full of jets, and 15 to 20 minutes to dial in the right one would be a whole lot easier. KISS

 

[bob58o]

If I ever get the stoopid charger engine to work with a carb, I’d eventually like to learn Speeduino or whatever and engine management stuff. Robot Cantina did a build or two adding EFI and troubling shooting a DIY system. Really I just want to look cool on my minibike with a laptop and fuel map at red lights. I could do that with a carb and really confuse people. lol Fuel maps printed on a large folded sheet of paper.

What’s another option for small engines? Micro-Squirt / Mega-Squirt ?

 

[jpndave]

Megasquirt is too big a form factor. Microsquirt might work. I have one here from an abandoned Harley project that never got installed. If I get a minute I'll take a pic of it next to a clone block or something for reference. Throttle body with injector, fuel pump and the basic sensors would need to be added. Crank position sensor too. With that there you just as well let it fire the plug. There's a fair bit more power required so the engine would need a decent charging coil. I've thought about it more than once. When we do the v-twin versions it will get more practical. The weight penalty isn't as big a percentage of the engine either.

 

[Denny]

Bob, for a carburetor you would have to use an old manual typewriter. For a fuel map you would need one of those roll up old classroom world maps. Then you would look cool at a stoplight. Maybe be wearing a Fargo type winter hat too and black plastic rimmed glasses with medical tape in the middle.

 

[Thepartsguy]

Can the laptop be disconnected from the speeduino so it’s not required at the red light?

I am subscribed to a youtube channel who uses I think arduino to make his Christmas tree lights flash in patterns to songs. I swear he said the laptop had to stay connected to run the whole deal.

Would just be annoying carrying a laptop in a side bag to make it all work.

 

[65ShelbyClone]

Yes, it functions without a laptop. A computer is only used for tuning, datalogging, or uploading firmware. I think there are board options that have onboard SD card logging as well. I know MegaSquirt 3 does.

MicroSquirt is a likely option where space is at a premium like minibikes or motorcyles. It's based on the MegaSquirt 2 which is pretty old now (really all the MS designs are), but there's not really anything wrong with or obsolete about it. What I don't like is that it's still expensive and doesn't have an onboard MAP sensor. They instead made the end user have to use a big external one and find a place to put it and the extra wiring.

This is what they haven't been willing to find space for in three different board designs:



MegaSquirt isn't really the cheap option anymore either. Speeduino has filled that role although I'm digging through the code and even though I'm not a programmer, I'm still having an occasional WTF moment about why they did things a particular way.

 

[bob58o]

Yes, it functions without a laptop. A computer is only used for tuning, datalogging, or uploading firmware. I think there are board options that have onboard SD card logging as well. I know MegaSquirt 3 does.

MicroSquirt is a likely option where space is at a premium like minibikes or motorcyles. It's based on the MegaSquirt 2 which is pretty old now (really all the MS designs are), but there's not really anything wrong with or obsolete about it. What I don't like is that it's still expensive and doesn't have an onboard MAP sensor. They instead made the end user have to use a big external one and find a place to put it and the extra wiring.

This is what they haven't been willing to find space for in three different board designs:

View attachment 151038

MegaSquirt isn't really the cheap option anymore either. Speeduino has filled that role although I'm digging through the code and even though I'm not a programmer, I'm still having an occasional WTF moment about why they did things a particular way.

What is best method for crank position sensor with Speeduino? I know Hall Effect Sensors and Timing gears with a tooth removed are sometimes used. Is the the main way to do this on DIY small engine EFI builds?