I suscribe to diy turbo and they sometinmes have good discusions adn i just wanted the share the knoledge.


second, there is some cool combustion chamber stuff that is showing that you really don't want a heterogeneous mixture in the combustion chamber for maximum power and efficiency, that you really want to generate a chamber filled with the richest mixture around the plug and getting progressively leaner as you move away from it toward the pistons.To do this you COMPLETELY AVOID TUBMBLE and concentrate on generating a
swirl using the chamber shape. Some engine tests have shown that you can get incredible detonation resistance this way and run very lean overall mixtures (averaging about 18:1). The idea here is to create a condition where you can ignite the charge very quickly (rich mixture around the plug), but the lean areas will not ignite till the pressure in the cylinder drops some from the piston moving down the cylinder, the end result being that the combustion event supplies a larger impulse over a longer portion of the power stroke. Ultimatly resulting in more power,broader power band and better mileage.
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This is what is referred to as 'stratified charge', right? I've heard
that diesels approach this scenario more than any N/A engine. Isn't the injector event timed such that it sprays into hot, compressed air, where it ignites as it is sprayed?

In a diesel it is. And I've heard of it being called that and a number
of other things in 2 strokes. I'm not sure about a 4 stroke gas engine.
Some of the lean burn engines worked on a similar principal with a
stratified, lean charge in the main combustion chamber and a small
prechamber that has a much more easily ignitable mixture that is used to
light off the charge in the combustion chamber.

I believe that this is the way that they're going with some of the
direct injection gas engines.

 

I had a lecture on this once. They were experimenting with combustion chamber fuel injection to eliminate the throttle, and increase efficiency. I think the major problem was that with the really lean mixtures you cannot run a normal catalytic converter.

 

no throttle? intresting. How would you slow the engine down with no throtle? The only was i can think of is cut of the fuel how does it work, is it faster or slower decelerating than with the throtle? why cant they use a normal cat? does it not work or it screws with the engine?

 

Yea slows the engine by decreasing the amount of fuel, just like a diesel. Not sure which one would slow down faster, I would imagine a throttled engine.
From what I heard normal cats can't run in an extremely lean situation, for example there are no cats on diesels. I'm not sure why they don't work, I would guess that with very little fuel burning in the cat that it wouldn't stay hot enough too burn off any HCs, COs or NOs. That is just a guess though.

 

But i believe that the leaner you run the hotter the combustion is exmple, you burn a hole in your piston from running lean. So it may be that its too hot (doubt because they would just locate the cat further back). Anyone know anything about not running a normal cat with no throttle??

 

The effects of running lean are mitigated by the rest of the conditions in the combustion chamber. If you have a very readily available O2 source then the combustion process will be looking for more fuel (metals will burn… if you want to see a hot flame, mix some magnesium, aluminum and iron oxide filings (the finer the better) and light it… but don’t do it someplace important or a lot of it, you will not be able to put it out till it’s done on it’s own).

If you can control the conditions, and most importantly control detonation you can use a lean mixture to slow combustion and increase the length of time that the combustion process exerts significant force on the piston, ASSUMING that you can still ignite the mixture. It works similarly to richening the mixture (which is why max HP and Torque are made at richer then stoichometric), but it much harder to control and the consequences when you mess up are worse (rich… you use more fuel then you have to, lean… you use things that you really want to keep in side the engine as fuel, like piston tops and the edges of valves, more likely you just get detonation and blow holes in things).

If you lean it enough that the mixture misfires you pretty much do not produce power on that cylinder’s power stroke which will slow the engine. Most manufacturer’s use it for their rev limiters, but this is not what I would call a graceful way of slowing an engine down