^^^im just takin a wild guess but mabe its the other way around but really i dont know and all it was is a hypothesis(educated guess)....but im open to being proved wrong and getting it right for future refrences..

 

I wasnt trying to prove you wrong I just dont want anyone to get a direct injection car and run it at boost in the mid 13 afr's

 

Well, in theory it could make it more resistant to knock because there is no fuel to detonate until you inject it much like a diesel. That is really the only reason you might be able to run a bit leaner than port injection.

 

It can run leaner because of the way the fuel swirls around the chamber. It has a rich enough mixture to burn right at the spark plug, but it's super lean everywhere else.

The nature of DI also allows a higher compression ratio as compared to regular fuel injection. All the turbo DI cars coming out have CRs above 10 I think. Spraying the gas directly into the chamber and having it vaporize cools down the charge in the cylinder reducing the chance for detonation.

Well, that's off the top of my head, but I think it's pretty accurate. Here's some info on DI from Audi:

http://www.audiworld.com/news/01/iaa/fsi/content.shtml

 

It would seem to my simple brain that DI would be very easy to control knock...don't inject until you want it to burn. Seems to if you want to get fancy, you could squirt a little fule and ignite to produce the flame front and then inject the remainder, similar to a diesel...that should produce a very clean burn and a long burn if you wanted.

Of course I'm certainly no automotive engineer.

 

Hey Shiv, you said you got the xede to work on the 335? That is great !! Is it the Evo specific xede?

 

Unfortunately, the mitsu XEDE is different from all the other XEDEs due to its frequency-based MAF sensor. The BMW xede is the same unit we use in Honda, Lotus and Miata applications. You *could* use the Mitusbishi unit and use one of the extra analog in/out pairs for MAF but you'd be short a pair when it comes to controlling the widebands. Its still too early to tell if all the ins/outs in the XEDE will be used. If not, the Evo unit will work in the Bimmer just fine. We'll know soon enuff

Shiv

 

Ah, german engineering..... Just wait until you try to push it a little more... you will have to deal with high auxilary fuel pump that pressurizes the line around 1400 PSI to be able to inject fuel directly into the cylinder... This will stop this bimmer from making lots of WHP!!!!!

It's probably using ME9.1 BOSCH ECU (Torque based systems) as well...
This was the reason why I dropped AUDI A4 2.0T and switched over to EVO IX MR....

 

I dunno im just having a hard time understanding how they calculate the atomization, diesels use glow plugs so that analogy isnt correct,Theres several reasons why Diesels use glow plugs but heres the main one. because diesel fuel is such low octane. the glow plug heats up the highly compressed air to ignite the fuel charge. but i still cant figure out why a DI engine can run leaner mixtures.
Unless they completly changed physics while I was in the restroom it just doesnt make sense. and il try to explain why trying to keep it simple and as short as possible. ***** Begining of ramble if you dont like technical info or just dont care skip this next part******

As far as knock is concerned is that the fuel does not burn anywhere near instantaneously at TDC (top dead center)It takes about 0.5 ms (around 7.5 degrees of crank angle at 2500 RPM) after the spark occurs for the fuel to start burning beyond a small ball around the spark plug. This region of burning then spreads throughout the cylinder, and the burning is mostly complete somewhere around 30 to 50 degrees of crank angle after the spark. Now, clearly, if we ignite the fuel mixture directly at top dead center, the piston will have travelled down quite a distance before a considerable part of the fuel burns. This fuel, then, is unable to help push the piston down as much, and thus the engine is less powerful. Because of this, the spark is set to occur before the piston hits TDC.
So in order for this theory of a DI engine being able to run leaner the fuel pressure would have to be so extremly high that the fuel and the air can atomize at such speed at 75% of the way up on the compression stroke, but the problem with this is that there simply isnt enough time for the spark and explosion to make any meaningful pressure inside of the cylinder.

The only thing I can think of that will make this theory partially true is that the DI engine is just burning a cleaner mixture, Not engine is not actually running any more lean its just the sensor located in the exhaust is seing less fuel because of the more complete burn. creating the illusion of a leaner mixture. But still i cannot see that there is that much more fuel lost in a conventional engine to make this theory work. if at all its a very negligable difference in exhaust stream measured fuel.

Additionally (as if this post wasnt long enough already) The problem I see with tuning direct injection to much higher power levels is that when you need bigger injectors bigger injectors just simply will not and cannot be as precise as a smaller injector. and these engines seem to rely hugely on precision again im sorry for long post

 

Now I got it.

 

Glow plugs are just to preheat the COLD air in the cylinders on a COLD start. They in no way, on any diesel I've worked on in the last twelve years, act as a "spark plug". The heat for combustion in a diesel comes from the tremendous compression in the cylinder. When a gas is compressed it heats up...compress it enough and the temperature rises enough to ignite the fuel.

 

ur right. Well even comparing a diesel to a petrol engine isnt fair because all of our explosions happen in the combustion chamber.

 

I’ll try to explain DI the best I can and this is all from memory from a seminar I attended like 7 years ago, so I may be wrong on some of it. Friend of mine was actually doing research on a Mitsu DI engine…. Anyways, DI uses very high fuel pressure, in the couple thousand psi range. If you look at the pistons of a DI engine, they have what looks like a ski ramp on the top. As the fuel is squirted into the combustion chamber, it hits the top of the piston and the ‘ski ramp’ directs the fuel up towards the spark plug.

Fuel only ignites in a certain range of A/F; either too rich or too lean, it won’t catch with a spark. So basically, with the way the fuel is squirted in and directed to the spark plug (by bouncing off the top of the piston), that fuel is of the correct A/F to burn when the spark goes off. The rest of the cylinder has very lean A/F in it; once the ‘good’ stuff starts to burn though, it’ll burn the rest or something. So, you end up with an overall lean A/F. This of course leads to lots of NOx, which is why DI engines haven’t been used here until now. Now they have these new NOx control systems (info on the Audi website somewhere).

The new technology that’s being developed is Homogeneous Charge Compression Ignition (HCCI), which is basically like a diesel cycle but using unleaded gas. Suppose to be 5-10+ years away though depending on who you talk to.

A bit off topic, but your gas water heaters are always mounted a couple feet off the ground. This is because if there is a gas leak, it’ll settle down by the floor below the water heater. If the water heater were on the ground, a spark from the electronics could cause the gas to ignite. That’s related to the whole A/F ratio spark range thing I mentioned… learned that in class and thought it was pretty interesting.

 

This is fairly accurate, but very simplified. Also, it is actuallly running leaner. That is exactly what the O2 sensor reads and that is what is occuring. Look at it this way, with the same amount of fuel injected, a DI engine will run leaner because of more efficient combustion and create more power, assuming all other things equal.

 

But with the same amount of fuel injected the engine itself isnt running more lean just less gas escapes thru the exhaust stroke and gets measured by the sensor,