Open Source EFI

Overview 

This aspect of my upgrade has taken quite a while, it's a huge deal.  I've pulled together all my researching and here it goes...

I started this aspect of my upgrade thinking I would use one of two existing EFI systems proven for the Lycoming 4-cylinder.  For various reasons like complexity/education/design/cost.  I changed my mind and decided to build my own from open source.

I did a _TON_ of research... Let's start at the beginning.

Baseline Requirements

The system must be...

1. Safe... 100% electro-mechanically redundant
2. Simple
3. Efficient
4. Independent injection tuning
5. Compatible with my existing mechanical fuel system
6. Practical (not a science project, set-it/forget-it)

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Sub Systems

An EFI system consists of the following sub-systems;

EMU

The Core processor that takes in all the sensor information and triggers the ignition to fire and the injectors to pulse.  I'll discuss why below, but for this project, I selected Speeduino.

Sensor

• Throttle Position
• Crank position
• Inlet Temp
• Manifold Pressure
• CHT

Ignition

• Coil
• Wire / Boots
• Plug adapters
• Spark plugs

Fuel

• Injector
• Injector Boss (holders)
• Throttle Body
• Lines
• Fuel splitter
• Standby valve

When, not if...

backups better be proven and simple... and they are; 

• Ignition - There's still one Slick Mag
• Fuel - There's still a mechanical fuel pump and a pilot actuated T-valve that turns off the fuel to the EFI and directly dumps fuel into the slider throttle body.

It is critical that total electrical failure means the engine will keep running, just like every reliable engines has done for over a century.

Why?

Speeduino?

There are many open, semi-open and proprietary EMU solutions out there.  This is the first and maybe the largest decision of the project.  I specifically wanted an active and well supported 100% open source EMU solution.  Many EMUs don't support four independently tuned injectors.  Some very expensive variants of the Megasquirt can support it.  But it's vague.  Ultimately I found speeduino had good independent tuning and fit the bill nicely with a very neat and understandable tuning profile.  I also went with an upgraded SPEEDUINO TEENSY 3.5 8X8 which uses a powerful Teensy 3.5 MCU which increases sensor fidelity and gives ample processor head-room for performance and more accurate timing.  It also natively supports independently tuning all four injectors.

Magneto-crank sensor?

An EMU needs the crank sensor input to set timing.  There are many solutions and I could have gone cheaper and just installed a few fly-wheel-magnets and a HAL sensor on the nose of the engine block, I really wanted a solid bolt-on solution.  I went with the ElectroAir EA-001 ignition timing kit.

Slider Throttle Body?

The purpose of the throttle body is to control the engine by lowering manifold for anything less than full RPM power.  Otherwise, it has no reason for being on the engine.  The simplest possible restriction you can put on an engine is a slide valve.  This is very similar to the "Aerovee Injector" but it doesn't have a throat, it is just the slider sitting between the filter air box and the oil-sump-intake.  Unregulated injectors like these have many annoying side-effects like "drippy carbs" and difficult to precisely tune.  Nominal fuel delivery mode is very precise electronically controlled injectors.  The TBI aspect of this system are utilized for redundant in-flight fuel delivery backup, those il-side-effects of the TBI are either non-existent or unimportant... Just keep it turning!

• Throttle Position - A linear rheostat is designed into the slider
• Fuel Spray-Bar - A stainless tube sprays backup fuel when the EMU fails

Injectors

The injectors themselves are Harley Davidson EFI injectors.  They have similar profiles and no spray pattern.  On paper, they flow enough fuel for this application.  We'll see when it is assembled.

There are two choices in how to secure the injectors to the intake.  You could either weld them to the side of the intake tube or bolt them to the injector ports on classic mechanical "IO" cylinders.  My engine was already setup for mechanical fuel injection.  I wanted a screw-on replacement for the "dumb injectors".  So I asked around on facebook and to my shock, a local pilot and amateur CNC machinist stepped up to the challenge and did one truelly amazing job!  It's hard to tell this is built by a hobbiest, they are VERY VERY high quality.  The base is made from stainless to resist vibrations / stress cracking, the tops are aluminum for weight and machining simplicity.

The real benefit of this system is that the cap screws direclty into my existing mechanical fuel injection system, which is really quite good quality already.

The Plan...

I will tackle this in three phases...

1. Ignition system 
2. TBI
3. EFI

Install the EMU and all sensors and setup for electronic ignition.  Setup the TBI backup fuel injection, ground-test only.  Only then will the EFI be added.  Finally, everything will be thoroughly ground tested and if it all checks out in normal and backup-mode... flight.