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Title: Few questions about ignition Post by: masterj on March 13, 2012, 03:46:43 PM Hey folks! :) I'm trying to update logic in my me7 wizzard and need your help! :)
First of all -> What is the average turbulent spark flame speed in gasoline? I've found that it might be in range of 1.35-2.2 meters / sec. Could someone confirm it? Or even better post graph showing different speeds at different AFRs... Then another question -> What is the distance from the spark plug to the top edge of the piston top when it is TDC (1.8T engine)? If someone help me out here I might be able to produce much better ignition angle generator! Title: Re: Few questions about ignition Post by: ta79pr on March 13, 2012, 07:04:30 PM not sure if i am answering the correct question, but in Banish's book, he states that most gasoline engines have "effective flame propagation speed of 706 to 985 in/s (18 to 25 m/s). This means that a flame starting from a central spark plug in a 4.00 inch bore engine can reach the cylinder wall in about 2.5 milliseconds...." p.57-58.
Title: Re: Few questions about ignition Post by: rajivc666 on March 14, 2012, 01:08:39 AM IMO the charge density (load) and turbulence have much more effect on flame speed than lambda richer than stoic. If we see the map dzwola max correction is 3°. Also I guess the bore and the placement of spark plug are more important considerations than distance from the spark plug to the top edge of the piston top when it is TDC. I always consider ignition angle BTDC + 16° for all my calculation as our aim is to get the peak cylinder pressure at approx. 16° Atdc.
Title: Re: Few questions about ignition Post by: masterj on March 14, 2012, 02:06:53 AM IMO the charge density (load) and turbulence have much more effect on flame speed than lambda richer than stoic. If we see the map dzwola max correction is 3°. Also I guess the bore and the placement of spark plug are more important considerations than distance from the spark plug to the top edge of the piston top when it is TDC. I always consider ignition angle BTDC + 16° for all my calculation as our aim is to get the peak cylinder pressure at approx. 16° Atdc. load goes into calculation after WOT ignition is calculated... Well, atleast in my theory. I really need the distance from the spark plug to the top edge of the piston top to finish it. Title: Re: Few questions about ignition Post by: masterj on March 14, 2012, 02:12:57 AM not sure if i am answering the correct question, but in Banish's book, he states that most gasoline engines have "effective flame propagation speed of 706 to 985 in/s (18 to 25 m/s). This means that a flame starting from a central spark plug in a 4.00 inch bore engine can reach the cylinder wall in about 2.5 milliseconds...." p.57-58. Thanks, maybe you have Autodata or ETKA that has info on distance from the spark plug to the top edge of the piston top? If we know speed of the flame and the distance we can calculate time... Title: Re: Few questions about ignition Post by: Rick on March 14, 2012, 03:35:26 AM Ignition angle generators are a disaster waiting to happen.
Title: Re: Few questions about ignition Post by: rob.mwpropane on March 14, 2012, 06:29:09 AM Here it's been done/attempted;
http://www.ecuconnections.com/forum/viewtopic.php?f=2&t=81 You have to log in to read it. A good read none the less. Sorry, can't help with the distance from spark to cylinder wall. Title: Re: Few questions about ignition Post by: masterj on March 14, 2012, 01:08:19 PM Here it's been done/attempted; http://www.ecuconnections.com/forum/viewtopic.php?f=2&t=81 You have to log in to read it. A good read none the less. Sorry, can't help with the distance from spark to cylinder wall. Thank you Rob! I'm going to analyze MIDAS solution and update my wizzard :) Title: Re: Few questions about ignition Post by: robin on March 14, 2012, 01:43:40 PM I don't think there is a good 'wizard' method to generate this kind of data. At any kind of power level over stock, you need proper det cans and a load-bearing dyno to find MBT...
Title: Re: Few questions about ignition Post by: masterj on March 14, 2012, 01:54:12 PM I don't think there is a good 'wizard' method to generate this kind of data. At any kind of power level over stock, you need proper det cans and a load-bearing dyno to find MBT... Yes, but your starting point can be calculated... after that you'd just change few degrees here and there... Title: Re: Few questions about ignition Post by: carlossus on March 15, 2012, 12:20:01 AM I would bet a substantial sum that your calculated starting point will not be withing a few degrees of the oem curve. Trouble awaits.
Title: Re: Few questions about ignition Post by: silentbob on March 15, 2012, 04:05:06 AM IMO the charge density (load) and turbulence have much more effect on flame speed than lambda richer than stoic. If we see the map dzwola max correction is 3°. Also I guess the bore and the placement of spark plug are more important considerations than distance from the spark plug to the top edge of the piston top when it is TDC. I always consider ignition angle BTDC + 16° for all my calculation as our aim is to get the peak cylinder pressure at approx. 16° Atdc. 16° ATDC is to late. Best power is usually 50% heat release @8° ATDC what roughly correlates with peak pressure @13-14°ATDC. "Calculating ignition" will not work. No real option for a dyno here (beside cylinder pressure sensors). Title: Re: Few questions about ignition Post by: masterj on March 15, 2012, 06:43:54 AM Hm... Could someone explain to me why ignition angle is advanced so much at idle and low charges? I can't understand it, because all the logic is saying that if rpm is low there should be very small advancement to reach peak power at ATDC 8dgrs. If we advance ignition let's say to 30 degress at idle doesn't it mean that flame will be burning way to early (not 8dgrs ATDC)?
Title: Re: Few questions about ignition Post by: silentbob on March 15, 2012, 07:09:54 AM A lot of effects influence flame speed. The major are charge motion, residual gas content, AFR, dynamic compression ratio and temp.
Idle usually has a lot of residual gas with poor mixture preparation and low dynamic compression ratio resulting in "advanced optimal ignition". What you see in the car is a ignition angle that is the result of a torque reserve for idle speed control. |