dual injection is just a long overdue solution to carbon build up?
 

I've been checking some topics in this forum and saw that there are quite some people here with alot of knowledge about engines.

now i've got a theory but no knowledge to really back it up.

I'll try to explain.

What i found out it is that direct injection causes alot of NOX build up.. hence the 2 metal cats in the exhaust manifold before the normal cat. Because of emission regulation car companies are trying everything to reduce these emissions and have invented the EGR valve to re-use exhaust fumes.

These exhaust fumes carry alot of carbon wich eventually attaches itself on the valves wich eventually causes bad closing and compression drops.

High quality fuel has additives that can clean this..but when you only got direct injection, the fuel never gets on top of the valves.

So here is my theory: Dual injection is just a way to clean your valves when the engine is in partial throttle and isnt a revolutionary technique to make powerfull yet economical engines.

Now that i think of it.. would disabling the EGR (im assuming the engine has one as every modern engine has one) and force direct injection all the time increase tuning potential?

discuss!

NOx levels rise as AFR goes lean, it's not related to the style of fuel injection.
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The carbon deposition problem on GDI engines is due to EGR and/or PCV routing "dirty" air through the intake and the gasoline not being injected far enough upstream to perform its wonderful solvency and wash away the deposits. Gasoline is a fantastic solvent; it doesn't need over-marketed "additives" to significantly improve is ability to clean.

The best solution for GDI engines is to not have either PCV or EGR; then the only source for "dirty" air is whatever gets through the air filter.

So yes, Toyota's D4-S is just a band-aid for being legally stuck having to keep PCV on the car from the factory. Damn red tape.

but without EGR and PCV ( never heard of it ) the manufacturers wouldn't be able to meet the required emissions.

I have a old 2003 2.0 fsi engine and they've replaced pretty much everything to make it run reasonable. only after a custom remap it ran like it should and it only does it on 98..on 95 it idles like crap.

I hope the FT86 will rune fine on just normal 95 petrol as 98 is becomming more rare at the fuel stations in holland.

we have a thread about this already

you should revive it so a bunch of stuff that has already been said/debated doesnt repeat

In my experience, which may or may not apply here, DI is good at low engine speeds and high engine speeds. When you hit the highest airflow efficiency of the motor, the torque range, most gasoline direct injection systems have problems keeping up with fuel demand on more aggressive tunes and with forced induction. Sure, the solvency of gasoline helps keep the valves clean when using a egr.

As RyePhile stated, leaner running engines cause more NOX buildup. Generally DI motors like to run leaner than port injection. And the carbon buildup is just a byproduct due to the increased NOX levels and added exhaust gasses being routed to the intake. Most engines are tuned rich from the factory due to catalyst(s) needing to generate heat to be efficient.

PCV = Postive Crankcase Ventilation. At least in the USA the car isn't allowed to vent any emissions apart from the tailpipe. As such, the oil vapor from the crankcase is recirculated through the intake tract and ends up getting burnt onto the backside of the vales. This is a particular problem on the VW FSI; something VW rectified by implementing a complicated two-stage "catch can" system within the valve cover on the new 2.0 TSI engine...though it's not perfect.

The D4-S system should band-aid that problem in terms of washing the valve backsides with the port injectors. The best solution is a VTA catch can, however that's not legal for OEM's to equip. Aftermarket to the rescue.


-->ryridesmotox: Catalytic converters need to be ran essentially at Stoich to be most effective. However, most OEM tunes run rich at WOT to chemically cool the pistons/cylinder to survive their longevity tests. This isn't good for the Cat, but the engine longevity is more important than the Cat at WOT. DI setups don't need to run as rich [as in they can come closer to targeting peak torque at WOT] because the DI quenches knock so effectively, there's no need to run rich to cool the combustion to prevent knock. It's not that DI systems "like" to run leaner, it's than they can run leaner at WOT. Again, the carbon buildup on the backsides of the valves is due to the lack of port injectors not being there to use gasoline to wash away the deposits from the EGT and/or PCV.

thanks ryephile! this explains alot! and MR Jay I found the thread regarding the d-4s engine thx!

I've had so many troubles with my FSI engine that i've sworn never to buy a car with a direct injected engine again.

but i've recently discovered the ft86 and i've fallen in love with it! i just hope they've got it right with the duel injection.

Only thing I find strange about the engine is not the amount of torque but at what rpm it is released (6600 rpm if im not mistaken) this seems a bit late? my fsi does 200nm at 3500rpm.

Some articles on the net speak of 4000 rpm wich seems more realistic to me.

It creates peak torque later because it is more usable when pushing the car when racing, think about it, when your racing a car that redlines at 7500, when are you ever below 4900? Would you rather have the max torque at 6600(considering after each shift in a high revving engine lands arond 5900). 7400 - 5900 = 1500 / 2 = 750. 5900 + 750 = 6650 you will have at least 95% of your max torque while shifting gears.
Or would you rather have max torque at 3000 RPMs so by the time you get to your rev range when your racing(5900 -7400RPMs) you only have 80%- 60% of max torque.....
You decide....

I highly doubt direct injectors not supplying sufficient fuel is a problem typically. It's only a problem if you are running a ton of boost and need a lot more fuel. VW TSFI engines are turbo, direct injected, and make a ton of torque. This isn't a problem for the vast majority of people, as most people do not do these mods. If you do a mod that is that serious, you'd better be prepared to face these challenges.

You have a fair point there. I do hope they're able to release 70 to 80 % of that torque at lower rpms to enable relaxed driving. I drove a clio 197 once and it was useless below the 5,5k rpm mark.

I think we'll just have to wait for real power/torque figures @ different RPM.

the k20 in the civics also have a 86X86 bore stroke and make pretty flat torque curves after 3500 rpms and peak at 6300 and doesnt really drop until past redline... if this engine breathes better than the k20 + direct injection we should see good torque numbers across the entire range

Like I said in my post... on more aggressively tuned motors. I was hoping that maybe Toyota was thinking about the future tuning of the engine and helping us out with fueling by installing the Port Injection System.

I'm not doubting your knowledge a bit, but I have one question. Every time I have seen an engine run richer, it always leads to more heat in the exhaust on a pyrometer, which would lead me to believe that cylinder temps are higher. Not sure why its like that.

I'm sorry, in my last post I mistyped and wrote EGT instead of EGR. EGR [exhaust gas recirculation] is what I meant to say.

EGT is not a terribly relevant measurement for gasoline/spark ignition engines. Both AFR and timing affect EGT, and viewing solely the EGT doesn't tell you anything useful other than the exhaust temps are indeed higher, which isn't what's going on in the cylinder. Peak EGT is usually at Stoichiometric, and retarding the ignition causes EGT's to rise.

My advice would be to throw away the EGT gauge and get a good set of datalogging for RPM, Ignition, IAT, MAF/MAP, WBO2, fuel rail pressure, injector duration, throttle angle, and cam phasing.

That's not an inherent issue with direct injection, it's just that in that case the engine is modified and you are pushing components harder than they were being run off the showroom floor.

This is true only if by "leaner" you mean that the engine-out AFR is leaner than lambda=1, meaning leaner than 14.7:1 on pure gasoline. Here is a chart showing the general trend for engine-out emissions:

http://www.ft86club.com/forums/attac...1&d=1320785068
That is from a Toyota technician training manual on emissions.

They can be run leaner than port injection under full load because the high pressure fuel injected directly into the combustion chamber absorbs more heat. Then there is also the matter of lean mixture formation under part load, either homogenous lean or stratified lean. Neither of those strategies are used during normal running of current production engines.

The NOx levels on these new engines are lower than older port fuel injection engines that many of us are used to. This is because these engines must meet Euro 5 and other such strict emissions standards. The composition of the deposits depends on how much oxygen is present in the area where they are forming.

It depends what you mean by "tuned rich." Under WOT operation a richer mixture is used to reduce exhaust temperatures so that the converter does not suffer accelerated wear due to heat. Under cold start the key is mixture formation. On a standard port fuel injection engine you have atomization problems as the fuel is sprayed on to the back of the valve. On a direct injection engine the key is mixture formation.

The Toyota D-4S system, like most other production systems today, uses stratified charge under cold start and only cold start. The D-4S system uses a shallow piston bowl to create a "weak stratified" mixture. A deeper piston bowl would cause stronger stratification but also leads to more fuel sticking to the piston.

It's relevant for the life of all components connected to the exhaust system. In aftermarket performance tuning you're not so concerned about catalytic converter life or cat lightoff though.