D-4S Thread
 

I was talking to a friend today that I haven't heard from in a long time. He eventually got a job with Lexus and has worked on a regular basis the 2GR/4GR-FSE and we got to talking about the subaru engine with Yamaha heads and D-4S. Actually he was not to keen on the idea of working on it or being one of very few people who have experience with tuning DI, he doesn't want to help people out of their failures.

He did though taught me some stuff about D-4S that was really interesting.

Gasoline used in a conventional fuel injected engine has a desired burn rate of stoich 14.7:1, but Gasoline used in a direct injected engine has a burn rate of stoich 40:1. So when adjusting fuel pressure on the common rail we are looking at 4x times the pressure seen in a fuel rail. This also changes AFR outputs and tail pipe emissions characteristics and tuning using conventional methods without applying new theory will damage the engine.

During Intake Charge on a conventional engine we see AFR mixtures similar to tailpipe AFRs. On Direct injection engines, we actually desire 15:1-20:1 Lean AFRs during intake stroke. Unlike conventional engines which will damage at those ratios. And turbo applications we don't want to reach lower than 13AFRs as its actually too rich and is wasting optimal power.

For the D-4S, direct injection is not used during idle, and low load. Port injection is the primary fuel system. At mid load and cruise port injection and direct injection are used in tandem. At High load and WOT port injection is not used and direct injection controls primary function.

“The D-4 incorporates a highly optimized combustion chamber: The piston crowns are fitted with a lipped, cup-like formation that focuses the injected air/fuel mixture tightly around the spark plug for maximum burn.

Intake air is drawn through helical ports that create a high degree of horizontal swirl, which Toyota says combines with the lipped combustion chamber to not only maintain highly stable combustion -- a quintessential problem for lean-burners -- but also to stratify the air/fuel mixture.

Additional swirl is promoted with special swirl-inducing high-pressure injectors. The end result is a fuel-rich mixture in the direct vicinity of the spark plug, with extremely lean air/fuel ratios near the cylinder walls.”

When looking at tuning options, we come across the problem of the different environment we see in the tailpipe. With Ultra-Lean conditions, higher NoX levels, and a higher overall exhaust temperature. A number of Wideband Oxygen Sensors (WBO2) are seeing more errors and inaccurate AFR readings. So a Wide Range Oxygen Sensor (WR02) was developed but is still not widely available.

Showed me these images too, seems pretty cool.

What do you mean by 40:1? Is that for stratified charge?
Also the 15:1 to 20:1 you mentioned, you said that was "during intake stroke". But I'm fairly sure they need to hit stoichiometric for emissions, so you mean that they supplement that in the compression stroke right?

I remember someone posted a link to an article about the D4S system on the GR engines, and I remember it mentioned they do not use stratified charge because the NOx levels were too high. That article mentioned that the principal advantage to D4S was that they were able to create nearly homogeneous mixtures, while port injection and direct injection alone are not able to. They had some charts showing how there was more fuel in certain areas of the cylinder with only one injector operating, but with both they were able to get it pretty close to homogeneous.

I still am not too sure why that Lexus article says the direct injector fires only during intake stroke for everything but cold start, I'd think that during the compression stroke it would be better since you can then cram more air in, and also use the cooling effect to directly reduce the energy requirement for charge compression.

EDIT: I also wanted to add, if D4-S works as well as they say it does, then it could be applied to late intake valve closure systems to improve combustion efficiency without the need for low valve lift and the associated throttling loss. In the other thread I mentioned helical cam lobes, and 3d cam lobes, which can be used to control output via late intake valve closure. If a 3d cam lobe or Valvematic type system uses early intake valve closure instead, then it is possible to introduce a bit of restriction at the valve to increase the velocity of the air, but if a 3d cam lobe uses late intake valve closure instead, we can use D4-S to compensate for the lower intake velocity...I am assuming this is going to be how the FR-S engine is going to be able to make the promised 200hp with just one cam profile, if it doesn't have variable lift.

Your second paragraph is a little confusing. 40:1 is the ideal burn rate but that doesn't mean the exhaust Lambda reading is going to be different?

Ultra lean would fail US emissions due to NOx. So he is either talking about the overseas versions or "stratified charge" like cerealkiller mentioned :iono:.

Piston dome isn't new. Honda is doing that with it's high compression engines for a more efficient burn. It is better than dish from what I've read so that's good to know.

Some of it seems logical but not all of it concurs with what I know about DI as a whole...

Did he mention anything related to reliability of the system? shoud be pretty mature by now, but you never know. It´ll be a bitch to tune for bigger cams that´s for sure!

He says that direct injection engines by themselves produce dangerously high levels of NoX because by nature they operate at ultra-lean conditions. But in conjunction with port injection, a specifically designed EGR, and a specifically designed lean Catalyc converter, the NoX levels are tamed for emissions.

He says that the system seems reliable as the next, his biggest concerns are for tuners.

Do not delete the EGR, and do not go straight pipe. He has seen pretty bad engine failure for those D-4S equipped engines when people start treating them like normal fuel injected engines during modding, and he sees really bad deposits of carbon and crud with cars that that run on the track almost exclusively because they run at high load/WOT which is DI only.


Im learning as a I along, and read and do research and talk with him and some other people. I have some experience with DI, but nothing crazy.

Iv been reading up on some Mazdaspeed3 guys with DI, and they are having bad engine failure at their target AFRs when tuning and finding the right rich setting for a modded engine is tricky.

I dunno it just seems so weird to me, none of the applied technology is complicated, and the theory seems straight forward there is nothing thats particularly new. But the conditions and environment in the combustion chamber with GDI and D-4S are worlds apart from what Im familiar with.

on a interesting note someone was also talking about adding Direct Injection hydrogen to a gasoline engine, which brings the AFR to like 180 or some shit and internal compression to 30:1. Im like :mad0259:

No kidding, what little I do know about Port injection is going to be next to worthless. :cry:

Don't remove the EGR? Does the EGR help reduce Carbon buildup? I figured Carbon buildup was mostly a DI only issue and Port injection is supposed to fix that by putting detergents back onto the intake side. I have heard that EGR can make Carbon buildup worse on a Port injection system.

Hydrogen is a bomb :bellyroll:. I've heard positive results from injecting it into the intake, which is similar to water/methanol injection. It's not for power though. Guys do it for the MPGs, and it only makes a small difference <10% max. You've probably heard of the Hydrogen electrolyser scams by now :bellyroll:. It does work but the scam is they are selling $50 in DIY parts for $800 and advertise ridiculous results. Just like the ecu chip scammers :mad0260:.

I would rather be injecting alcohol via DI :iono:. Much better results. :thumbsup:

He hasn't really explained to me why do not remove the EGR. My guess is that the EGR actually protects the engine from that carbon and soot. And if it fouls up replace it....vs....having no EGR and destroying the engine. And i can see this probably happening especially when port injection goes away and DI takes over the bulk of the fuel during mid-high loads.

I second meth injection over hydrogen. And that Dual Fuel shit Ford is testing that i linked you to sounds awesome. Hydrogen sounds like its the future..but honestly there is no technology out right now mainstream that makes me feel safe about using hydrogen as a fuel source for daily transportation. I'm honestly just too scared of the stuff to play around with it.

I'm having trouble imagining this car being "tuner friendly" as they advertise. How would boost complicate things? Perhaps the D-4S is the exact reason they designed the car with engine swaps in mind.

I think by "tuner friendly" they were referring to body kits, wheels, dampeners, and chassis bracing.

I'd hope for a TRD reflahed ECU...

Although I thought the way around tuning DI was to get a bigger fuel pump -- is that not panning out?

Ah... The joys of new technology. The race begins when it hits the market to be the first one to effectively tune it without blowing it up or frying something important.

Sounds complicated . . . in a way that makes me nervous.

Tell me again: How long has D-4S technology been around and on how many cars (how many units, not how many models)?

:happy0180:

AFAIK the IS350 guys still dont have ecu tuning so...

^ But IIRC that's because Toyota's ECU's are some ofthe hardest to crack ;)