ukmiata

Situation: Miata with Renesis conversion, running well on an Adaptronic e1280s standalone at around 190rwhp but I like to optimise everything.

Question : What is the optimum time in the cycle to stop injecting fuel?

As far as I understand, for a piston engine the best time to stop injecting is just before the intake valve opens.

But for a rotary, what is the best time? (and does it vary with rpm and MAP)

I could set it up to stop injecting just before the rotor passes the intake port but spraying fuel onto the side of the rotor doesn't seem intuitively sensible.

Any suggestions?

ukmiata

No direct injection of course, just standard injectors in standard locations.

I have been reading up on conventional engine tuning where claims were made that getting the fuel injection to finish just before the inlet valve opened was optimum, something to do with getting the best mix of fuel/air in the cylinder.

The ECU I'm using has a table to control this so someone must have thought it was useful for conventional engines at least.

If it's just rubbish then I wont change anything.

MazdaManiac

iTrader: (3)

On most modern aftermarket engine management systems, the injection duration can be calculated backwards from the end-of-injection point.

So, yes - it does (or can) matter.

ukmiata

Thanks for the info, that is the way this particular ECU works.

So what should I set the end-of-injection angle to? (have a 3D MAP/rpm table).

Should I go for a few degrees before the primary port opens under all conditions, or go later in the cycle at higher rpms when the secondary and auxillary ports open?

ukmiata

Got some info on this from the owner of Adaptronic (Andy), he designs his own ECUs and has tuned many rotaries, including building his own miata 13b turbo conversion for racing.

The view was that :

1. Completing the injector firing just before the inlet port opens is best (factory ECU does this).
2. The effect of altering injection timing was big for a peripheral port triple rotor, affecting fuel usage and transient throttle response.
3. For standard port sizes, there won't be much difference.

So I may as well aim to match the stock ECU setting.

arghx7

for Series II engines

MazdaManiac

iTrader: (3)

^^ Very nice!

TeamRX8

iTrader: (25)

that is clearly an oversimplification and not the case as demonstrated in the factory diagram above

it varies by engine speed as it should

ukmiata

Tx for posting the pics.

So my attempt at working this out is:

Renesis timing (dont know why this table wont format the way I want)

Primary.. : 3 155 65 (ATDC open, ATDC close, ABDC close)
Secondary : 12 126 36
Auxillary : 38 170 80

From the timing diagram, "Standard Position" for injection stop is 88' BTDC (275'CA = 91.7' BTDC) so around midpoint of port opening.

Then add speed based correction.

=> At start up, advance is 180'CCA from top diagram (455'CA - 275'CA = 180'CA)
=> On other graph, at high speed, the advance looks to be about 10% of the above, say 18'CA

From the graph, estimate :

Max rpm, advance is 6' (rotor angle) => so total is 88+6 = 94' BTDC
Min rpm, advance is 60'(rotor angle) => so total is 88+60 = 148' BTDC

So at low speed ~1krpm, the fuel injection period is say 3ms (20'rotor angle)
=> 114' to 94' BTDC
=> 66' to 86' ATDC => mid way through primary port opening time (only port open at low rpm)
=> basically spraying into the combustion chamber directly.

At high speed ~9krpm, the fuel injection period is say 11ms (66' rotor angle)
=> 214' to 148' BTDC
=> -34' to 32' ATDC => around time all ports start to open


So I should configure my ECU to stop injecting at :

idle :86'ATDC
max rpm : 32'ATDC

and no need to allow for MAP in this.

arghx7

I admit I'm not 100% sure how to interpret certain parts of this. If you read carefully, in some places it says BTDC 275' CA. For the injection timing on engine start, it says the timing is fixed at BTDC 455 degrees crank angle. This makes sense because cranking fuel is batch fired (both injectors fire simultaneously) so having a fixed timing makes sense.

Let me see if I can work through this in my head--this is me trying to interpret what I read, and I'm not 100% certain about this.

-- If the engine is cranking, injectors will be fired at 455 degrees BTDC as measured at the eshaft. So it's firing way early, and the timing is fixed. This is straightforward.

-- During normal running, first the end-of-injection is calculated. It starts with 275 degrees BTDC and then it will advance the injection based on engine speed. I'm not certain on this but I'm guessing it advances the injection timing as rpm increases.

-- to determine injection start position, it takes the base 275 degrees, adds in the rpm compensation, then uses the calculated injector pulsewidth. So the more fuel that's being fired (longer pulsewidth), the earlier the injector will open.


I'm not sure how that translates into what you are ultimately trying to do for your engine.