X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Fri, 30 Dec 2005 23:14:40 -0500 Message-ID: X-Original-Return-Path: Received: from imo-d05.mx.aol.com ([205.188.157.37] verified) by logan.com (CommuniGate Pro SMTP 5.0.5) with ESMTP id 906774 for lml@lancaironline.net; Fri, 30 Dec 2005 19:15:29 -0500 Received-SPF: pass receiver=logan.com; client-ip=205.188.157.37; envelope-from=REHBINC@aol.com Received: from REHBINC@aol.com by imo-d05.mx.aol.com (mail_out_v38_r6.3.) id q.28f.33d4e9f (3924) for ; Fri, 30 Dec 2005 19:14:36 -0500 (EST) From: REHBINC@aol.com X-Original-Message-ID: <28f.33d4e9f.30e7276c@aol.com> X-Original-Date: Fri, 30 Dec 2005 19:14:36 EST Subject: Re: [LML] Re: Where has all the power gone? X-Original-To: lml@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="-----------------------------1135988076" X-Mailer: 9.0 for Windows sub 5120 X-Spam-Flag: NO -------------------------------1135988076 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Craig, Rob wrote: I think you are considering torque here rather than energy or power. You need to factor the rotation of the crank shaft into your integral. Then you will get the same result as the simple piston pressure/displacement annalysis. I wish there was a way to express tone with the written language. I'm intrigued by your thoughts...I'm not being argumentative. If there was no friction....no momentum.... and the fuel burn was instantaneous...wouldn't the engine simply stop at TDC? The force would be infinite straight down through the piston, rod and crank....?? If you want to get a head ache...contemplate moving the piston centerline to the ATDC side of the crank, thus producing a slight rod angle at TDC. Craig Berland First, I have a pretty thick skin so I don't take offense till things get pretty blatent. I also tend to assume this of others, which isn't always the case. Besides, I rather enjoy a good argument. At least until it degrades into name calling. Second, I'm not aware that I said that our theoretical Otto cycle engine had no momentum. If I did, then I was mistaken (and it wouldn't be the first time). Third, with no friction and no momentum, the most likely place to stop would be bottom dead center. The power stroke, exhaust stroke and compression pressures all work in this direction. Precisely TDC is another potential point the system could stop, but without momentum or some other force, how was the compression stroke completed? I don't see that an instantaneous fuel burn rate is important here, so long as there are no shock waves or swirl forces to cause the piston to rock and disrupt the perfectly vertical crank and rod. Of course if we attached another 5 cylinders, then the power stroke of another piston would move the crank forward anyway. Fourth, the force would not be infinite. Infinite force would require infinite pressure and that would require infinite energy... Then again, I suppose one could argue that perfect fuel would contain infinite energy, but this would make engine control somewhat difficult. Fifth, I already have a head ache so I would rather not contemplate nonaligned cylinders. While I haven't come accross such an engine, I have seen a handfull of auto designs where the wrist pin was off center in the piston. My recollection is that this was done to reduce piston wear. (slant 6 ?) I never looked into it. Finally, I was replying to George's comment about crank - rod geometry with respect to efficiency. I interpretted what he said as noting that the change in mechanical advantage as the rod and crank angles depart vertical (horizontal in a Lyconental) results in increased torque for a given pressure. (did I misread something?) This is certainly correct, however torque alone does not tell us much about either power or energy. One has to multiply the torque by the rotation or the rotational speed to compute these values. At the top and bottom of the stroke, the mechanaical advantage of the system is low, resulting in low torque values, but the angular dispalcement is high. At mid stroke just the opposite is true. When we integrate the torque x angular displacement curve of the crankshaft, we find that it yields exactly the same energy as the integral of the pressure x piston displacement curve (ignoring friction). This makes sense because in a frictionless engine all of the pressure force energy applied to the top of the piston is transfered through the rod to the crank shaft. No offense taken and none intended, Rob -------------------------------1135988076 Content-Type: text/html; charset="US-ASCII" Content-Transfer-Encoding: quoted-printable
Craig,
 
Rob wrote: I think you are considering torque here rather than energy o= r power. You need to factor the rotation of the crank shaft into your integr= al. Then you will get the same result as the simple piston pressure/displace= ment annalysis.
 
I wish there was a way to express tone with the written language. = I'm intrigued by your thoughts...I'm not being argumentative.  If ther= e was no friction....no momentum.... and the fuel burn was instantaneous...w= ouldn't the engine simply stop at TDC?  The force would be infinite str= aight down through the piston, rod and crank....??
If you want to get a head ache...contemplate moving the piston centerli= ne to the ATDC side of the crank, thus producing a slight rod angle at TDC.<= /DIV>
Craig Berland
First, I have a pretty thick skin so I don't take offense till things g= et pretty blatent. I also tend to assume this of others, which isn't always=20= the case. Besides, I rather enjoy a good argument. At least until it degrade= s into name calling.
 
Second, I'm not aware that I said that our theoretical Otto cycle engin= e had no momentum. If I did, then I was mistaken (and it wouldn't be the fir= st time).
 
Third, with no friction and no momentum, the most likely place to stop=20= would be bottom dead center. The power stroke, exhaust stroke and compressio= n pressures all work in this direction. Precisely TDC is another potent= ial point the system could stop, but without momentum or some other force, h= ow was the compression stroke completed? I don't see that an instantaneous f= uel burn rate is important here, so long as there are no shock waves or swir= l forces to cause the piston to rock and disrupt the perfectly vertical cran= k and rod. Of course if we attached another 5 cylinders, then the power stro= ke of another piston would move the crank forward anyway.
 
Fourth, the force would not be infinite. Infinite force would require i= nfinite pressure and that would require infinite energy... Then again, I sup= pose one could argue that perfect fuel would contain infinite energy, but th= is would make engine control somewhat difficult.
 
Fifth, I already have a head ache so I would rather not contemplate non= aligned cylinders. While I haven't come accross such an engine, I have seen=20= a handfull of auto designs where the wrist pin was off center in the pi= ston. My recollection is that this was done to reduce piston wear.= (slant 6 ?) I never looked into it.
 
Finally, I was replying to George's comment about crank - rod geometry=20= with respect to efficiency. I interpretted what he said as noting that the c= hange in mechanical advantage as the rod and crank angles depart vertical (h= orizontal in a Lyconental) results in increased torque for a given pressure.= (did I misread something?) This is certainly correct, however torque alone=20= does not tell us much about either power or energy. One has to multiply the=20= torque by the rotation or the rotational speed to compute these values. At t= he top and bottom of the stroke, the mechanaical advantage of the system is=20= low, resulting in low torque values, but the angular dispalcement is hi= gh. At mid stroke just the opposite is true.
 
When we integrate the torque x angular displacement curve of the cranks= haft, we find that it yields exactly the same energy as the integral of the=20= pressure x piston displacement curve (ignoring friction). This makes sense b= ecause in a frictionless engine all of the  pressure force energy appli= ed to the top of the piston is transfered through the rod to the crank shaft= .
 
No offense taken and none intended,
 
Rob
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