Direct injection/port injection explained?
 

I have a pretty good idea how port and direct injections work.

What I'd like to know, or have explained so I can visualize, is just how our hybrid PI/DI works.

Does the car run solely off of DI until a certain RPM or load?

Does the car run off of PI until the DI is needed?

Does one, or the other chime in intermittently when needed?

I'm hoping someone can splain this to me so I can at least visualize how and/or when these two injection systems work together, and when one or the other works alone.

I assume the port injectors are used towards redline since it is the port injectors that are increased in size when tuning for big power and E85, but I don't know when the DI is utilized, and what exactly it is good for or better for compared to PO.

Thanks for any help.

Mike

DI/PI injection is used depending on RPM and load; the car will switch between the two and use them simultaneously and constantly change depending on the demands of the driver.

You CAN use DI exclusively if you choose to, even with FI (at lower output levels)

Only the PI injectors are changed, because the DI injectors can't really be changed (to higher flow units) at this point.

I've once seen a chart which did show at which rpm the port injection and DI injectors were used, I can't find it anymore sadly, maybe someone could find it.

EDIT - Just found the video!

[ame="http://www.youtube.com/watch?v=zc8aUxBZlsU#t=50"]2013 Scion FR-S | D-4S Technology Explained - YouTube[/ame]

Thanks, that helps.

What about something a little more in-depth? Like when does one or the other turn on, or off? When are both on?

I'm getting my car tuned in a week or 2, and was hoping I could have a better understanding of just how my tuner is going to figure out which type of FI is used and when.

For FI (I'm getting a FB kit installed) at WOT, dose the tuner run the DI at say, 90% and then just ramp the PI up as needed?

What about partial throttle? Does the ECU switch between PI and DI or use both together instantly?

Edit: Just watched that little vid and that explains things very well. Thanks very much!

You just asked enough to write a few textbooks on. If you can do that, you'd be doing it for a living :D

The time they change would depend on load and throttle demand and RPM and if the engine is cold or warmed-up. So there's no definitive answer. We aren't in the simple VTEC on/off days anymore.

Try this..

http://www.ft86club.com/forums/showthread.php?t=3172

there is a map in the ecu that controls the ratio of port to direct injection. it's completely configurable, and oddly enough the factory map uses the di heavily at higher rpm (up to the 5200rpm scale of the table), which i'd imagine to be backwards. for my turbo setup i had to increase the higher rpm range port ratio to keep up with the fuel required.

here's a pic of the stock (hot) map:

https://www.evernote.com/shard/s251/...ls-Desktop.png

in total there are three maps (cold, warm and hot) and another to control the temp thresholds at which they switch.

Nitpicking, but the cams lobes were not spinning to actuate the valves in that explanatory video.

Thanks for posting that graph.

I'm new to tuning, and can't really understand the graph, but I'll look into how to read these graphs.

It's just a 3-dimensional lookup table similar to a spreadsheet, columns and rows that together reference a value. So for a given load (column) and rpm (row) it find a value (the percentage of port injection). Values in between are interpolated.

What happens after 5200 rpm?

The detail at the end about early port injection + late-ish direct injection was really helpful for me. In engineer-speak, it seems that they're creating a stratified charge situation that is sufficiently rich to ignite in open-loop and cold conditions (even with high compression helping) and still gives you the fast warm-up benefits of a lean-burn engine. That's incredibly cool and probably the reason for the knocking we hear during fast-idle warm-up.

On a similar note, I heard about Ford and VW using the variable exhaust valve timing to do a controlled backfire to spool up the turbo. Would be interesting if our cold start strategy does this to warm up the catalyst too.

Word on the street was that many of the OEMs were using inefficient methods to speed up their catalyst light-off times, in an attempt to game the EPA emissions requirements. Invest fuel (and reliability) early so that you can get to closed-loop fueling faster than the competitors. They were also trying to "game" the oxygen sensors into getting useful data before they reach their minimum rated operating temperature.

It's all about the catalyst, baby!:party0030:

Does anyone know how the dual injection timing is controlled? I've seen the variable that controls the quantity split, but I haven't seen much on timing. I take it they are independent (not simultaneous like in the video).

It's hard to say. We're going off an advertisement. They are describing a very late port injection timing, which is normally terrible for HC emissions unless you're very careful with AVCS. And we don't know the valve timing under the conditions they are describing. They talk about a late direct injection event, but we don't know what % of the fuel is delivered there. It could be one very quick spray to affect mixture motion--it's kind of hard to have stratified combustion when a bunch of fuel was sprayed into an open intake valve.

Just an FYI, the European Audi engines that are turbo with port + DI use DI only during cold starts. They have two injections per cycle, which is basically a conventional way of doing things. And that engine meets stricter emission standards than an FT86.
I think you're just referring to scavenging during spool up by advancing the intake cam and retarding the exhaust. That's normal. STi's can do it, but they are limited because they are port injected. Audi has a different exhaust cam profile they use now during spool up.

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I don't see the cat lightoff strategy on the FA20 surviving the upcoming emission standards. There's too much HC and particulates to overcome. That's one of the reasons why Audi uses DI only.

If the cat doesn't light off in time, or the engine-out emissions are too high, the engine doesn't get certified and doesn't go to production. So I'm not sure what the original source of that claim is from.

There are a bunch of tricks in the bag. Some involve lean burn and expensive o2 sensors that light off very quickly. Some involve smog pumps (secondary air injection) or HC trap catalysts. Some involve tumble control valves, or expensive DI systems, or valve timing tricks.

http://i597.photobucket.com/albums/t...ps47d69c9b.jpg

The left map is start of injection for the DI, in decrease BTDC firing. All those values are in the intake stroke (except the oddball ones at 370 degrees).

I haven't seen the PFI injection timing maps. Sometimes there is a fixed end of injection and a varying start of injection. Sometimes the SOI is fixed and the EOI changes. Sometimes it sprays into an open valve, sometimes it doesn't.