Visualizing Rotary Injection Timing

[hugemikeyd]

my engine is an S4 6port NA engine which has the same specs for the exhaust port as an FD, so I should be good

[hugemikeyd]

I took the time to collect all of the port timings for the FC S4, FC S5 and FD and put them into 1 chart:

 

Interesting to note, either the intake port timing completely changed for the FD or Mazda decided to use a different TDC in prior years...

[Copyninja]

That is great and what would be even better is the reflective soi timings for stock, streetport, bridgeport that correspond to the links btdc timings. 

[Adamw]

On 5/8/2024 at 3:15 AM, hugemikeyd said:

I was trying to take the Haltech chart and convert it to Link, which I tried taking each number and dividing it by 3 assuming that Haltech was using e-shaft degrees,

Why do you keep dividing by 3?  I've said several times the injection angle is using E-shaft degrees in all ecus.  

The haltech table you show is different because it is using end of injection, you would need to know the injector duty cycle at each RPM to translate that into start of injection, but in very rough terms that would probably give you a start of injection of around 90deg BTDC.  This is why I say it makes more sense to use start of injection with a basic side port engine when the exhaust port closing is the biggest influencing factor, with start of injection you dont need to factor in duty cycle, just a single value will work for all RPM's/loads. 

With an NA P Port or similar the intake reversion may become a bigger influence than the exhaust port influence so in some cases the end of injection may become the more appropriate reference, but for most I would say SOI.  

 

On 5/7/2024 at 10:12 PM, Copyninja said:

However, the 130deg btdc is noted at 70% dc, but what if the duty cycle is 90% or higher?

You typically dont want to run a rotary with duty cycle any higher than about 70% which is why I chose that value for the drawing. You can see on the drawing even at 70% the end of the injection event is getting close to the point where the intake port closes on one rotor face and opens to the next.  If you inject past this point then some of your fuel ends up going into the wrong combustion chamber, so you potentially have one rotor face leaner than it should be and the next rich. 

[Copyninja]

12 hours ago, Adamw said:

You typically dont want to run a rotary with duty cycle any higher than about 70% which is why I chose that value for the drawing. You can see on the drawing even at 70% the end of the injection event is getting close to the point where the intake port closes on one rotor face and opens to the next.  If you inject past this point then some of your fuel ends up going into the wrong combustion chamber, so you potentially have one rotor face leaner than it should be and the next rich. 

I see that is very interesting. I am above 70% dc at a lowly 1bar of boost using 2x 850cc and 2x 1500cc injectors. 

Currently running over 90% DC at 23-24psi boost. is there anything that can be done to optimize injection angle? maybe start injecting earlier like 140ish deg?

Are you able to explain how injector pw and dc correlate to injection angle?

[Copyninja]

while on this topic - if the SOI is 130btdc does the link G4x know the rear rotor fires 180* after the first one?

[Adamw]

Just like ignition timing, "BTDC" is referencing TDC of the cylinder/rotor that the event is occurring in.  So yes, rotor 2 injectors are 180deg out of phase with rotor 1. 

[Copyninja]

Thanks Adam 

[Copyninja]

How many degrees of injection timing is available on the stock 130btdc to inject fuel for each chamber?

https://drive.google.com/file/d/1EpbTluaBj990w9jp86KCay_VpUo0qnX3/view?usp=drive_link

Am i wrong to think a large street port, bridgeport and semi pp will have a smaller injection window than a stock port? 

Adam - whats the SOI max duty cycle you would recommend for the large street port, bridgeport and semi pp, if the stock port is 70%? 

[Adamw]

18 hours ago, Copyninja said:

How many degrees of injection timing is available on the stock 130btdc to inject fuel for each chamber?

Roughly 270deg or 75% duty.  

 

18 hours ago, Copyninja said:

Am i wrong to think a large street port, bridgeport and semi pp will have a smaller injection window than a stock port?

Typically the idea with porting a wankel is similar to fitting a performance camshaft in a piston engine, you open the ports earlier and close them later to give it more "duration" - the ports are open for longer.  Some of this extra duration adds more overlap so the SOI needs to be moved later to avoid this, however the intake port will also close later so your available injection window will usually work out roughly the same (very roughly).  

[Copyninja]

Thanks Adam