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Do new GDI engines have throttle plate?

Do new GDI engines have throttle plate?

Do new GDI engines have throttle plate?

(OP)
A friend pointed out that a GDI engine could run w/o a throttle plate like a diesel and be governed by the fuel/ignition controller. This would reduce backwork and improve fuel economy except at WOT.

Is anyone doing this?
 

RE: Do new GDI engines have throttle plate?

I don't know what 'backwork' is.

Running without a throttle plate would increase pumping losses because the engine would always be running at 100pct air flow.
If it ran, it wouldn't be running an Otto cycle.   I'm not sure it would run at all with that much excess air.

If the ECU were not set up to compensate somehow (and I'm not convinced it could be), the engine would most likely IMHO detonate, overheat, and self-destruct, while running like crap.

You are welcome to try it on _your_ engine.  winky smile

 

Mike Halloran
Pembroke Pines, FL, USA

RE: Do new GDI engines have throttle plate?

I stand corrected.  It can be done, and all it takes is roughly twice the high tech stuff it takes to run an electronic Diesel, plus the extra mass for some fancy valve gear.

I'm still fuzzy on how they can get a stoich or rich mixture without throttling the intake.  ... unless they're throttling by diddling the valve timing or lift.

 

Mike Halloran
Pembroke Pines, FL, USA

RE: Do new GDI engines have throttle plate?

Stratified charge?

- Steve

RE: Do new GDI engines have throttle plate?

Very stratified charge.   

RE: Do new GDI engines have throttle plate?

Ah.  I think I understand.  Because of the high injection pressure, they can shoot in all of the fuel for a cycle within a very short time just before the spark, so the charge can be locally stoich or rich, and the remainder super-lean.

Thanks all for the education.


I think I'll wait a while to do it to my lawnmower...
 

Mike Halloran
Pembroke Pines, FL, USA

RE: Do new GDI engines have throttle plate?

BMW's HP-DI with Valvetronic does not have a conventional butterfly throttle.  Valve timing meters the amount of air that goes into the engine.  This system runs lambda 1 to be compatible with a 3-way catalyst (TWC).

VW/Audi (T-)FSI has a throttle and also runs at lambda one with a TWC.  Ditto Mercedes-Benz and GDI systems from GM, Ford, Hyundai, etc.

All the above implementations could also run in lean/stratified mode, but the ineffectiveness of a TWC (and the high tailpipe NOx that would result) in that regime and the need for a lean-NOx trap catalyst (more complex, more expensive) results that nobody is currently implementing it where Euro 5 / Tier 2 Bin 5 regs need to be met.

All the above are still considered Otto engines.

RE: Do new GDI engines have throttle plate?

(OP)
Might be an atkinson cycle if the intake valve is open long enough to backflow into the manifold on the compression stroke.

RE: Do new GDI engines have throttle plate?

There's plenty of disagreement even in engine circles regarding the distinction between the Miller and Atkinson cycles but they ultimately achieve much the same thing and some even (mistakenly) use the terms interchangeably.  The thermodynamic cycles when plotted on P-v and T-S diagrams and the true implementations of each cycle are very distinct and much more complex than simply varying valve timing in an otherwise conventional engine.

For the purposes of most discussions I use the convention that the Miller cycle refers to late intake valve closing causing some of the cylinder charge to flow back into the intake ports, while Atkinson denotes very early intake valve closing before BDC resulting in a pre-expansion before the compression stroke proper.

RE: Do new GDI engines have throttle plate?

   TDI - I am afraid I must disagree with your description of the Atkinson Cycle.  If you go back to the original idea of an Atkinson Cycle it was with a engine that had a physically longer expansion stroke than compression stroke - thus having a higher TE.
  The modern equivalent of this I would have thought would have to be the high geometrical CR/LIVC approach.

  The Miller Cycle is never as clear to me but I think to be classed as "Miller" it must involve a supercharger plus an element of Atkinson Cycle. Just why the supercharger is a better method of cylinder-filling I have never quite been able to picture.
 
 The EIVC approach I don't think has a cycle name and is much less effective than Atkinson (especially) or Miller.  
    

RE: Do new GDI engines have throttle plate?

You don't have to agree with me, you just need to read some scholarly work on the subject for yourself:

Schutting, E. et al.  Miller- and Atkinson-Cycle on a Turbocharged Diesel Engine. MTZ 06I2007 Volume 68.

RE: Do new GDI engines have throttle plate?

In the above reference, the authors use EIVC as Miller and LIVC as Atkinson.  Mazda uses the term Miller to denote LIVC with supercharging; Toyota uses Atkinson to denote LIVC in the naturally aspirated Prius engine.  You can see that there's no real agreement on the nomenclature convention.  A survey of literature shows that Miller and Atkinson can denote both EIVC and LIVC, but Miller is usually combined with some form of forced aspiration, but Atkinson is (usually) normally aspirated.

RE: Do new GDI engines have throttle plate?

(OP)
"Just why the supercharger is a better method of cylinder-filling I have never quite been able to picture."

I'd think because your exhaust energy availability is relatively lower.

RE: Do new GDI engines have throttle plate?

I never paid much attention to that concept, but I always figured that the supercharger was mainly there as a checkvalve to prevent the airflow sensor from getting an irregular signal.

 

RE: Do new GDI engines have throttle plate?

TDI - you originally wrote above: "Atkinson denotes very early intake closing before BDC resulting in a pre-expansion etc."
 I don't see how this can be construed as Atkinson by anbody's definition.  

RE: Do new GDI engines have throttle plate?

Draw a P-v diagram and you will see how expansion is longer than compression (the latter of which is to include the pre-expansion), which is the intent of the Atkinson -- and Miller -- cycle.  Better, find the MTZ article I cited; it will even illustrate the P-v diagram for you.

RE: Do new GDI engines have throttle plate?

(OP)
A thermodynamic cycle doesn't dictate the mechanism. Brayton is a turbojet, or a turbodiesel.

I can see how late or early IVC on a piston engine could give you a miller or atkinson cycle.

I found the article in german, looked for it in english, not a member of MTZ.

RE: Do new GDI engines have throttle plate?

"A thermodynamic cycle doesn't dictate the mechanism."
-Agreed.

RE: Do new GDI engines have throttle plate?

Commercial engines using Miller cycle use high pressure ratio turbocharging in order to realize the power density needed to have a cost-effective product.

RE: Do new GDI engines have throttle plate?

What commercial engines use the Miller cycle in turbocharged form?

High PR turbocharging implies a diesel application. I'm not aware of any production diesel engines that actually use the Miller cycle, although since it is only a camshaft profile change away, it's possible that it is present but not advertised as such.

RE: Do new GDI engines have throttle plate?

GE-Jenbacher stationary gas engine.  

RE: Do new GDI engines have throttle plate?

TDI - despite much searching I still have yet to find the Schutting et al paper.
  I am afraid I take a somewhat simplistic and less "scholarly" view of the Atkinson Cycle.  I regard any engine which has a high CR (too high for "normal" use) combined with any strategy to reduce the combustion chamber pressure after compression as "Atkinson".  Whether this strategy is LIVC, EIVC, automatic throttle plate control or any other method of limiting the pressure - it is still Atkinson.
 I can see why you favour EIVC as being closest to "true" Atkinson but I think it still needs the CR component to be called Atkijnson.
  Without the high CR component, LIVC and EIVC I think should be regarded as engine load control/reduced pumping loss strategies.  I have found from personal experience that LIVC is more effective than EIVC.
  The following is probably less "scholarly" than Schutting et al but I agree with their views - which I think are expressed very clearly.
http://www.mechadyne-int.com/vva-reference/
   I should point out that I have no connection with Mechadyne and I don't think that their variable valve strategies are very practical - but I like (and agree with) their explanations of the various part-load strategies.

       

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