[Gasification] Prime Mover Knock

[Kevin Chisholm]

Dear Max

My understanding is that the Diesel Cycle is a Constant Pressure Cycle 
because it draws in a constant volume of air, giving a constant pressure 
from air compression, and power is varied by varying the amount of fuel 
added to the air.

The Otto Cycle has a constant fuel/air mixture ratio, and it varies power by 
varying the amount of fuel/air mixture charged. Thus at low power throttle 
settings, the engine may take in only 50% of the cylinder swept volume, 
giving only 50% of the pressure rise that would be attained if the engine 
throttle was fully open. The Otto Cycle is thus a "Variable Pressure Cycle".

For maximum efficiency, the fuel (Otto or Diesel) should be completely 
burned at TDC, so that it has maximum opportunity for maximum expansion, and 
recovery of the pressure energy. However, this results in a lower Mean 
Effective Pressure, and that gives lower HP output. Allowing fuel to burn 
after TDC results in greater HP output, but less efficiency.

In reality, some extra fuel can be burned after TDC, to increase power AND 
efficiency, because the heat losses per stroke are basically constant, and 
the extra fuel in effect gets a free ride.

Best wishes,

Kevin


----- Original Message ----- 
From: "gasman" <gasman at welho.com>
To: <GASIFICATION at LISTSERV.REPP.ORG>
Sent: Tuesday, May 16, 2006 8:11 PM
Subject: Re: [Gasification] Prime Mover Knock





Studying Hugo Güldner's "Verbrennungskraftmaschinen",

(Julius Springer, Berlin 1911, 1913)

will give some more light:

Rudolf Diesel's intent was to achieve a CONSTANT pressure

working cycle; meaning that the top compression pressure

was to be maintained as long as the injection was going on.

It meant, that the pressure kept almost constant for the time

the injection continued. (a bit past the TDC)

This choise was dictated by the materials and methods at

disposal at that time, not a lack of theoretical insight of the

ideal cycle!


Max



----- Original Message ----- 
From: "Arnt Karlsen" <arnt at c2i.net>
To: <gasification at listserv.repp.org>
Sent: Tuesday, May 16, 2006 10:16 PM
Subject: Re: [Gasification] Prime Mover Knock


> On Tue, 16 May 2006 13:38:52 +0100, AJH wrote in message
> <5qhj621rvmkr0ievcunt7oq2eim8nkn9q8 at 4ax.com>:
>
>> On Tue, 16 May 2006 01:37:45 -0400, Jeff Davis wrote:
>>
>> >Early diesels used fuel injection by high pressure air. This
>> >atomized
>> >spray,  into the cylinder, made a soft combustion hense slower
>> >rate
>> >of pressure rise  after injection started. No diesel knock was
>> >heard.
>>
>> Jeff, this was about the biggest mistake Rudolph Diesel made, it
>> was
>> not rectified until a brit introduced fuel injection. I have seen
>> one
>> of his early Sulzer's running at "internal fire museum" in Wales.
>>
>> If you think about it using a compresses air blast is about the
>> worst
>> think to do, in effect you are expanding an ambient temperature gas
>
> ..if you cool it far enough down, yup.  Is why you'll need some
> start up
> system for the cold engine.
>
>> into the hot post compression gas in the cylinder, this expanding
>> blast robs heat from the combustion chamber and slows combustion.
>> This
>> produced the soft effect you describe but a high efficiency cost.
>>
>> Also consider that there was a big power cost in adiabatic
>> compressing
>> gas for the reservoir and then cooling it to maintain capacity, all
>> this power was just converted back to heat which was lost.
>>
>> Similarly the indirect ignition diesels sacrificed efficiency for
>> smoothness in passenger vehicles but big engines always seem to
>> have
>> favoured direct injection.
>>
>> It's the move to common rail and high pressure injection systems
>> with
>> electronic control that has enabled direct injection diesels to
>> become
>> refined without sacrificing efficiency.
>
> ..aye, but can these handle wood powder as neatly as Jan Åbom's air
> blast wood powder diesel?
>
> -- 
> ..med vennlig hilsen = with Kind Regards from Arnt... ;o)
> ...with a number of polar bear hunters in his ancestry...
>  Scenarios always come in sets of three:
>  best case, worst case, and just in case.
>
>
> _______________________________________________
> Gasification mailing list
> Gasification at listserv.repp.org
> http://listserv.repp.org/mailman/listinfo/gasification
> http://www.repp.org/discussiongroups/resources/gasification


-- 
----------------------------------------
Jag använder gratisversionen av SPAMfighter
770 spam har blivit blockerade hittills.
Betalande användare har inte detta meddelande i sin e-post.
Hämta gratis på www.spamfighter.com/pro idag!


_______________________________________________
Gasification mailing list
Gasification at listserv.repp.org
http://listserv.repp.org/mailman/listinfo/gasification
http://www.repp.org/discussiongroups/resources/gasification