D-4S Thread

[NESW20]

what about EGR flow? or will that be accomplished with valve timing and overlap and such?

[markitect]

I stumbled across this article from when Lexus first started using D4-S, it's a good concise explanation.

http://www.autos.ca/auto-tech/automo...fuel-injection

[Marrk]

^^ Thanks, mark'.

Where exactly are the direct injectors placed?

[markitect]

Typically they are placed in the head right at the edge of the cylinder, angled to spray at or just below the spark plug, and to intersect with the incoming air.

This lets the fuel get picked up by the incoming air, and gives the swirl effect while injecting during the intake stroke; and it allows the fuel to be directed to the spark plug for the burst right before ignition.

[Marrk]

mark', the reason I asked was that I couldn't image placing an injector in the combustion chamber . . . but I guess it's possible.

[Aurex]

Originally Posted by Marrk

mark', the reason I asked was that I couldn't image placing an injector in the combustion chamber . . . but I guess it's possible.

The direct injection technology has been used for a few years now on snowmobiles and a select few outboard two stroke boat motors. Its actually quite slick.

Kind of off topic.......but Mazdas 16x wankel rotary (to me) is more like a two stroke motor than a fourstroke in the sense that it uses ports instead of valves. The efficiency increase seen on that motor if it ever gets released in a vehicle will have vast improvements over the current renesis rotary.

Another good example is BRP's two stroke snowmobiles. They can get up to 26+ mpg (pretty impressive) on the trail and the tuning potential is greatly increased when compared to carbs or efi. It also allows them to run a really lean oil mixture since no oil is injected into the combustion chamber, it is injected into the crankcase.

Just some food for thought.

[Dimman]

Aurex: In racing it is considered such. They use 2X a rotary's displacement when figuring out equivalency as they get 2X as many power strokes than a piston engine. Or something... Stupid triangle motors...

[Aurex]

Interesting to know.

back on topic though.....

What I want to see is what kind of fuel efficiency the direct injection will bring to the ft86/brz and its new motor. My STi is a PIG on fuel. I CAN get decent fuel economy out of it, short shift, stay a little under the speed limit on the highway etc.

But I would think that this thing should be in around the high 20's on the highway if not breaking into the low 30's with the direct injection. Is that too unrealistic to expect?

[serialk11r]

Direct injection doesn't provide as large of an efficiency increase the way Toyota is using it with non-stratified charge. I think that article isn't exactly correct, a paper that someone linked explaining D4-S in detail explained the purpose of having both port and direct is to get a more homogeneous mix in the cylinder. D4-S does NOT use stratified charge.

With VW style stratified charge it's theoretically possible to increase part load efficiency a bit since they remove the throttle, but this creates a lot of NOx emissions and efficiency still drops at part load since at very high AFR the pressure ratio is crap.

The direct contribution of direct injection would be increased compression ratio/better spark timing, and in the case of D4-S, better combustion efficiency since the fuel is more evenly distributed. Not to say this is a small improvement, but it's not very big either, as increasing compression ratio a huge amount like from 10:1 (typical cars running on 87, with port injection) to 15:1 brings less than 10% theoretical improvement in efficiency. As far as combustion efficiency goes, I don't know how much improvement they can get over run of the mill port injected engines...

As for the rotary being like a 2 stroke, this is not a good analogy because a rotary is like 3 4 stroke engines sharing one set of ports. There is no overlap between intake and exhaust stroke, and there are 4 distinct strokes. Direct injection on a rotary wouldn't bring much improvement because the main issue with the rotary is that the combustion chamber shape is very VERY bad, and a slightly smaller but still annoying problem is that compression ratio can't be very high since the shape of the engine won't permit it. In all other ways, the rotary is actually better for efficiency. Lower friction, less losses to vibration, no losses at the valves.


I'll just remind everyone again, the KEY step to improving fuel efficiency, particularly for turbocharged motors, is variable intake duration. At idle, using late intake valve closure instead of a throttle on some motorbike engine (with the "Williams Helical Camshaft") reduced fuel consumption by 80%. Toyota, BMW, and Nissan claim over 10% overall efficiency improvement with Valvematic, Valvetronic, and VVEL. When you consider that just adding (in Toyota's case at least) an adjustable rocker to the head improves efficiency on an already pretty efficient Toyota ZR motor by more than 10%, while Subaru completely reworked their thirsty EJ motor, reducing friction by a massive 28% and reworking the combustion chamber for 10%, you see why pumping loss through the throttle is the biggest problem for efficiency (aside from gearing, which can completely kill fuel efficiency when it's retardedly short). In the case of your STi, you have very short gears, a thirsty engine in the first place, and a pretty big turbo sapping extra power at part load by creating backpressure, so it's no surprise it's not fuel efficient. Direct injection can only slightly remedy the problem.

This car can probably get into the 30s for mpgs since it's coming out in 2012, so they'll be careful not to kill the fuel economy by not having a tall cruising gear, and it's a high compression ratio N/A engine. If the Civic Si can do over 30 on the highway with its short gearing and relatively primitive engine tech, this should be able to do at least as well.

[itsbrokeagain]

Originally Posted by serialk11r

Direct injection doesn't provide as large of an efficiency increase the way Toyota is using it with non-stratified charge. I think that article isn't exactly correct, a paper that someone linked explaining D4-S in detail explained the purpose of having both port and direct is to get a more homogeneous mix in the cylinder. D4-S does NOT use stratified charge.

With VW style stratified charge it's theoretically possible to increase part load efficiency a bit since they remove the throttle, but this creates a lot of NOx emissions and efficiency still drops at part load since at very high AFR the pressure ratio is crap.

The direct contribution of direct injection would be increased compression ratio/better spark timing, and in the case of D4-S, better combustion efficiency since the fuel is more evenly distributed. Not to say this is a small improvement, but it's not very big either, as increasing compression ratio a huge amount like from 10:1 (typical cars running on 87, with port injection) to 15:1 brings less than 10% theoretical improvement in efficiency. As far as combustion efficiency goes, I don't know how much improvement they can get over run of the mill port injected engines...

As for the rotary being like a 2 stroke, this is not a good analogy because a rotary is like 3 4 stroke engines sharing one set of ports. There is no overlap between intake and exhaust stroke, and there are 4 distinct strokes. Direct injection on a rotary wouldn't bring much improvement because the main issue with the rotary is that the combustion chamber shape is very VERY bad, and a slightly smaller but still annoying problem is that compression ratio can't be very high since the shape of the engine won't permit it. In all other ways, the rotary is actually better for efficiency. Lower friction, less losses to vibration, no losses at the valves.


I'll just remind everyone again, the KEY step to improving fuel efficiency, particularly for turbocharged motors, is variable intake duration. At idle, using late intake valve closure instead of a throttle on some motorbike engine (with the "Williams Helical Camshaft") reduced fuel consumption by 80%. Toyota, BMW, and Nissan claim over 10% overall efficiency improvement with Valvematic, Valvetronic, and VVEL. When you consider that just adding (in Toyota's case at least) an adjustable rocker to the head improves efficiency on an already pretty efficient Toyota ZR motor by more than 10%, while Subaru completely reworked their thirsty EJ motor, reducing friction by a massive 28% and reworking the combustion chamber for 10%, you see why pumping loss through the throttle is the biggest problem for efficiency (aside from gearing, which can completely kill fuel efficiency when it's retardedly short). In the case of your STi, you have very short gears, a thirsty engine in the first place, and a pretty big turbo sapping extra power at part load by creating backpressure, so it's no surprise it's not fuel efficient. Direct injection can only slightly remedy the problem.

This car can probably get into the 30s for mpgs since it's coming out in 2012, so they'll be careful not to kill the fuel economy by not having a tall cruising gear, and it's a high compression ratio N/A engine. If the Civic Si can do over 30 on the highway with its short gearing and relatively primitive engine tech, this should be able to do at least as well.

BMW has changed over to a valvetronic setup on their new single turbo 6 cylinders in the 3 series, which has made it such a pain to tweak...the throttle blade has little if any business in the engine, most of the work is done by the valvetronic altering the lift of the intake valves, and the throttle being merely used to prevent boost overshoots and some heavy throttle angle. Throttle response is crap compared to the previous engine which used the throttle in the normal fashion. Hopefully Toyota hasnt shyed away in the same direction.

[serialk11r]

The throttle isn't used at all actually, it's only used if the valvetronic system fails. It's a fail safe to prevent the engine from going out of control.

In theory, throttle response should be better, because there's no volume between the throttle and cylinders. But I suspect they programmed the ECU to ignore quick throttle inputs so people don't crash themselves or something.

[ryridesmotox]

Originally Posted by Marrk

mark', the reason I asked was that I couldn't image placing an injector in the combustion chamber . . . but I guess it's possible.

Diesels do it... The new common rail diesels inject fuel into the combustion chamber at full compression under loads of up to 50,000 psi. Gasoline engines do it at less than 3,000 psi because Gasoline motors don't use the introduction of fuel to initiate combustion like a diesel does. We still use spark plugs. That is because diesel is a more stable fuel...

Now as far as tuning goes I would like to add another topic for discussion... I'll start with my "hypothesis" as it were... the D-4S system is going to be epic for Ethanol and forced induction here is why...

In my engine, direct injection only, it is very difficult to control fuel delivery under boost at WOT through the mid range. Take a look at the attachments I have include, they deal with Ethanol fueling. Due to ethanol's properties it is difficult for the HPFP of my motor to keep up. The D-S4 engine should be able to take care of any fuel issues because it has secondary port injectors. If the ECU can be unlocked, and a turbo added... the possibilities are quite extraordinary.

On the log pick titled e85logpic2 you see the desired fuel pressure vs. actual in the second row of figures blue (FP Des psi)and orange (FP Rail psi) graph lines. Notice the RPM, 4400, just after at initial tip in on a 3rd gear pull 60-100mph. With the port injection You could run alot more fuel and use Ethanol more effectively. Oh by the way due to the efficiency of airflow, I have to mix my E85 with 91 octane at a ratio of 50/50. I would not be able to feed the motor with even close to enough fuel with straight E85. That is the downfall of direct injection, bigger injectors are big bux and hard to come by. With the port system on here, the extra fuel will just get thrown in, no problem.

On e85logpic1 you can see how, on the same pull, the fuel easily catches up in the upper ranges. This is due in large part to the cam driven HPFP that is used in my car. Other DI systems may or may not run into this problem, just something to think about I guess.

[quik1987]

Originally Posted by PAImportTuner

Everyone on here would agree that an air/oil seperator would fix this issue on port and direct injected cars. Just connect it into the pcv system. The Norrismotorsports is the cheapest system I've found short of using a $20 Lowes tractor air/oil separator that you have to empty out weekly versus the $110 one you can empty between oil changes because it holds more content.

Husky brand @ Lowes




http://www.mikenorrismotorsports.com...atch_Cans.html

just want to bring this back to light as we know more about the engine and cars are being delivered soon.

[Marrk]

Originally Posted by quik1987

just want to bring this back to light as we know more about the engine and cars are being delivered soon.

Sorry if I missed something. Could you explain this? What more do we know?

Many thanks.