Ski-doo fuel injection animation. Looks to be quite a simple system.
http://www.ski-doo.com/technologies/...gies/2-strokes
I like the voice coil style injector, and it looks like there is no air injected with the fuel and the fuel itself is delivered to the fuel injector body at quite low pressure. The injection pressure is developed by a plunger piston driven by the voice coil and as we all know from speakers the movement of a voice coil can be very accurately controlled.
Orbitals air assisted fuel injection system.
With these clean technologies and the inherent power and simplicity of a two stroke its hard to imagine that strokers won't make a serious comeback sometime.
But I am not sure if trying to adapt 4T EFI car technology to a high revving 2T like I am trying to do is going to work.
Car technology EFI seems to work ok on a big single that tops out at 8 - 9K rpm and I can pretty easily get my engine to rev to 8 or 9K rpm OK too but much past that and the fuel injection time exceeds the transfer port window open time.
When the injection time exceeds the transfer port open time a portion of the fuel required is left floating in the transfer duct and I think the problem with that is that on the next cycle this slug of fuel is blown right around the scavenge loop and out the exhaust port leaving the trapped mixture that follows behind it on the lean side.
And no matter how much more fuel (longer) you try to inject into the transfers the trapped mixture in the cylinder is still lean. This could easily explain why I keep getting deto at high rpm no matter how much I increase the fuel injection map numbers.
So with my transfer duct injection setup. Calling for more fuel is self defeating and I think the answer (if there is one) is in fast opening injectors, the balance between injector sizing and in timing the end point with width of the injection squirt so as to coincide as much as possible with the airflow in the transfer duct that is finally trapped in the cylinder and not the first slug of purging air that loops out the exhaust port and is lost, not much point in having that wasted air super fuel rich and the following trapped charge lean.
For my bike, at 12k ish the delivery ratio is about 120% of the cylinder volume and the amount of air (charging ratio) in the cylinder at BDC is only about 80% of the delivered air and less than that actually gets trapped (trapping efficiency) at exhaust port closing, so you can see that a fair swag of air is lost out the exhaust port.
And my guess is that the bulk of the air that is lost is the first air entering the cylinder as the transfers start to open and if there was extra fuel already in the transfers that would be lost with it.
So unlike a 4T where you can get a head start by storing fuel behind the inlet valve ready for it to open you cant do the equivalent thing with a 2T's transfer port window without loosing it down the exhaust pipe.
It is looking like the moral of the story is to keep the transfer port injection time shorter than the real time that the transfer ports are open and at 12.5k that is about 1.5ms.
Transfer port injection has the potential to clean up the 2T's emissions as the first lot of purging air can be sent through with little fuel in it but if I can't get it to work on my bike above 8-9k rpm I will have to go to inlet injection and aim to get a more homogeneous fuel mixture in the crankcase just like a carburetor does.
Bookmarks