On Wednesday, 6 June 2018 03:35:48 UTC+1, bill....@ieee.org wrote:> On Wednesday, June 6, 2018 at 9:09:35 AM UTC+10, Joerg wrote:> > Looking for a SPICE model that mimics a spark plug, ideally with and > > without fuel. Does anyone know where to find one? > > > > So far I found: > > > > > > .subckt spark_gap 1 4 > > R_off 1 2 1e7 ; dark resistance (affects breakdown voltage) > > R_ion 1 2 R=10/V(ion)**.75 ; dynamic ionization resistance > > Dfall 2 3 10V ; bidirectional cathode fall voltage > > Cdfall 2 3 50p Rser=100 ; for convergence > > V_ion 3 4 0 ; current sense for behavioral sources > > B_ion 0 ion I=I(V_ion)**2 ; measure of channel ionization > > C_ion ion 0 5u Rpar=1 ; ionization time constant > > .model 10V d(Vfwd=10 Vrev=10 Ron=1) > > .ends spark_gap > > > > > > However, the spark occurs at a few hundred volts and changing parameters > > doesn't do much. > > A spark plug breaks over at about 20kV. It's an avalanche breakdown in compressed gas, so you have to have a free charge carrier show up to initiate the the avalanche. Car cylinders are dirty places, so it might be a chunk of soot. > > The currents involved in the established avalanche would be high enough to sustain an arc if it went on for long enough, but you have an initial glow discharge with a voltage drop of a hundred volts or so for perhaps a microsecond before the ion bombardment gets one electrode surface hot enough to allow the arc mechanism to take over - which is to say to let the surface get hot enough into distort under the influence of the applied electric field to create lots of atomically sharp spikes that emit electrons by "warm" field emission. > > Best of luck modelling that in Spice. > > The presence and absence of fuel make a difference to the multiplication process that forms the initial spark, so the initial breakdown voltage is going to be different, and it influences the glow discharge period when the discharge moves from a glow to an arc. Once the arc is established the fuel content doesn't make any difference. > > A friend of mine set up a laser system for looking at the gas flows inside a single cylinder test engine for Shell in the later 1970's, but he was more worried about the combustion initiated by the spark than the spark itself.One car I had with points & coil produced around 6kV for sparkplugs IIRC, nothing like 20kV NT
SPICE model for a spark plug?
Started by ●June 5, 2018
Reply by ●June 6, 20182018-06-06
Reply by ●June 6, 20182018-06-06
> > Now I've got to take care of a production line stop situation. Those are > always fun. Grumble. > > -- > Regards, Joerg > > http://www.analogconsultants.com/the interesting real life behavior of spark plugs is... if you have a "fouled" plug" that the car cannot fire.... sometimes adding another spark gap in series with the fouled plug will allow the car to fire the fouled plug. It seems that if the coil is connected directly to the fouled plug, it can never develop enough voltage to fire. But if a second gap is inserted in series, then the coil CAN develop the voltage and when it fires, both gaps will arc. I discovered this quite by accident. Back in the late 60's I had a car that was mis firing on one cylinder. The standard troubleshooting procedure called for removing the wire from one plug one at a time and the one that makes no difference is the bad one. I noticed as I was putting the wire back on, when I held the wire close to but not attached, an arc would jump and the car would run better. I latter found they actually made small inline gaps just for that purpose. Nothing is ever simple. Mark
Reply by ●June 6, 20182018-06-06
On Wed, 6 Jun 2018 11:08:36 -0700 (PDT), tabbypurr@gmail.com wrote:>On Wednesday, 6 June 2018 03:35:48 UTC+1, bill....@ieee.org wrote: >> On Wednesday, June 6, 2018 at 9:09:35 AM UTC+10, Joerg wrote: > >> > Looking for a SPICE model that mimics a spark plug, ideally with and >> > without fuel. Does anyone know where to find one? >> > >> > So far I found: >> > >> > >> > .subckt spark_gap 1 4 >> > R_off 1 2 1e7 ; dark resistance (affects breakdown voltage) >> > R_ion 1 2 R=10/V(ion)**.75 ; dynamic ionization resistance >> > Dfall 2 3 10V ; bidirectional cathode fall voltage >> > Cdfall 2 3 50p Rser=100 ; for convergence >> > V_ion 3 4 0 ; current sense for behavioral sources >> > B_ion 0 ion I=I(V_ion)**2 ; measure of channel ionization >> > C_ion ion 0 5u Rpar=1 ; ionization time constant >> > .model 10V d(Vfwd=10 Vrev=10 Ron=1) >> > .ends spark_gap >> > >> > >> > However, the spark occurs at a few hundred volts and changing parameters >> > doesn't do much. >> >> A spark plug breaks over at about 20kV. It's an avalanche breakdown in compressed gas, so you have to have a free charge carrier show up to initiate the the avalanche. Car cylinders are dirty places, so it might be a chunk of soot. >> >> The currents involved in the established avalanche would be high enough to sustain an arc if it went on for long enough, but you have an initial glow discharge with a voltage drop of a hundred volts or so for perhaps a microsecond before the ion bombardment gets one electrode surface hot enough to allow the arc mechanism to take over - which is to say to let the surface get hot enough into distort under the influence of the applied electric field to create lots of atomically sharp spikes that emit electrons by "warm" field emission. >> >> Best of luck modelling that in Spice. >> >> The presence and absence of fuel make a difference to the multiplication process that forms the initial spark, so the initial breakdown voltage is going to be different, and it influences the glow discharge period when the discharge moves from a glow to an arc. Once the arc is established the fuel content doesn't make any difference. >> >> A friend of mine set up a laser system for looking at the gas flows inside a single cylinder test engine for Shell in the later 1970's, but he was more worried about the combustion initiated by the spark than the spark itself. > >One car I had with points & coil produced around 6kV for sparkplugs IIRC, nothing like 20kV > > >NTWhat brand? In air, or under compression? ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Thinking outside the box... producing elegant solutions, by understanding what nature is hiding. "It is not in doing what you like, but in liking what you do that is the secret of happiness." -James Barrie
Reply by ●June 6, 20182018-06-06
On Wednesday, 6 June 2018 19:19:17 UTC+1, Jim Thompson wrote:> On Wed, 6 Jun 2018 11:08:36 -0700 (PDT), tabbypurr wrote: > >On Wednesday, 6 June 2018 03:35:48 UTC+1, bill....@ieee.org wrote: > >> On Wednesday, June 6, 2018 at 9:09:35 AM UTC+10, Joerg wrote: > > > >> > Looking for a SPICE model that mimics a spark plug, ideally with and > >> > without fuel. Does anyone know where to find one? > >> > > >> > So far I found: > >> > > >> > > >> > .subckt spark_gap 1 4 > >> > R_off 1 2 1e7 ; dark resistance (affects breakdown voltage) > >> > R_ion 1 2 R=10/V(ion)**.75 ; dynamic ionization resistance > >> > Dfall 2 3 10V ; bidirectional cathode fall voltage > >> > Cdfall 2 3 50p Rser=100 ; for convergence > >> > V_ion 3 4 0 ; current sense for behavioral sources > >> > B_ion 0 ion I=I(V_ion)**2 ; measure of channel ionization > >> > C_ion ion 0 5u Rpar=1 ; ionization time constant > >> > .model 10V d(Vfwd=10 Vrev=10 Ron=1) > >> > .ends spark_gap > >> > > >> > > >> > However, the spark occurs at a few hundred volts and changing parameters > >> > doesn't do much. > >> > >> A spark plug breaks over at about 20kV. It's an avalanche breakdown in compressed gas, so you have to have a free charge carrier show up to initiate the the avalanche. Car cylinders are dirty places, so it might be a chunk of soot. > >> > >> The currents involved in the established avalanche would be high enough to sustain an arc if it went on for long enough, but you have an initial glow discharge with a voltage drop of a hundred volts or so for perhaps a microsecond before the ion bombardment gets one electrode surface hot enough to allow the arc mechanism to take over - which is to say to let the surface get hot enough into distort under the influence of the applied electric field to create lots of atomically sharp spikes that emit electrons by "warm" field emission. > >> > >> Best of luck modelling that in Spice. > >> > >> The presence and absence of fuel make a difference to the multiplication process that forms the initial spark, so the initial breakdown voltage is going to be different, and it influences the glow discharge period when the discharge moves from a glow to an arc. Once the arc is established the fuel content doesn't make any difference. > >> > >> A friend of mine set up a laser system for looking at the gas flows inside a single cylinder test engine for Shell in the later 1970's, but he was more worried about the combustion initiated by the spark than the spark itself. > > > >One car I had with points & coil produced around 6kV for sparkplugs IIRC, nothing like 20kV > > > > > >NT > > What brand? In air, or under compression? > > ...Jim ThompsonLada, late 1960s design. 6-7kV at idle. AIUI figures like 20kV are more associated with electronic ignition, but it's not an area of expertise for me. Measured by an adjustable spark gap in open air, that was measuring the max V_out the coil could produce. So it can't have delivered more to the compressed cylinder content - must have dlivered less in fact. NT
Reply by ●June 6, 20182018-06-06
onsdag den 6. juni 2018 kl. 20.19.17 UTC+2 skrev Jim Thompson:> On Wed, 6 Jun 2018 11:08:36 -0700 (PDT), tabbypurr@gmail.com wrote: > > >On Wednesday, 6 June 2018 03:35:48 UTC+1, bill....@ieee.org wrote: > >> On Wednesday, June 6, 2018 at 9:09:35 AM UTC+10, Joerg wrote: > > > >> > Looking for a SPICE model that mimics a spark plug, ideally with and > >> > without fuel. Does anyone know where to find one? > >> > > >> > So far I found: > >> > > >> > > >> > .subckt spark_gap 1 4 > >> > R_off 1 2 1e7 ; dark resistance (affects breakdown voltage) > >> > R_ion 1 2 R=10/V(ion)**.75 ; dynamic ionization resistance > >> > Dfall 2 3 10V ; bidirectional cathode fall voltage > >> > Cdfall 2 3 50p Rser=100 ; for convergence > >> > V_ion 3 4 0 ; current sense for behavioral sources > >> > B_ion 0 ion I=I(V_ion)**2 ; measure of channel ionization > >> > C_ion ion 0 5u Rpar=1 ; ionization time constant > >> > .model 10V d(Vfwd=10 Vrev=10 Ron=1) > >> > .ends spark_gap > >> > > >> > > >> > However, the spark occurs at a few hundred volts and changing parameters > >> > doesn't do much. > >> > >> A spark plug breaks over at about 20kV. It's an avalanche breakdown in compressed gas, so you have to have a free charge carrier show up to initiate the the avalanche. Car cylinders are dirty places, so it might be a chunk of soot. > >> > >> The currents involved in the established avalanche would be high enough to sustain an arc if it went on for long enough, but you have an initial glow discharge with a voltage drop of a hundred volts or so for perhaps a microsecond before the ion bombardment gets one electrode surface hot enough to allow the arc mechanism to take over - which is to say to let the surface get hot enough into distort under the influence of the applied electric field to create lots of atomically sharp spikes that emit electrons by "warm" field emission. > >> > >> Best of luck modelling that in Spice. > >> > >> The presence and absence of fuel make a difference to the multiplication process that forms the initial spark, so the initial breakdown voltage is going to be different, and it influences the glow discharge period when the discharge moves from a glow to an arc. Once the arc is established the fuel content doesn't make any difference. > >> > >> A friend of mine set up a laser system for looking at the gas flows inside a single cylinder test engine for Shell in the later 1970's, but he was more worried about the combustion initiated by the spark than the spark itself. > > > >One car I had with points & coil produced around 6kV for sparkplugs IIRC, nothing like 20kV > > > > > >NT > > What brand? In air, or under compression? >at idle and low loads there isn't much pressure
Reply by ●June 6, 20182018-06-06
onsdag den 6. juni 2018 kl. 20.09.01 UTC+2 skrev mako...@yahoo.com:> > > > Now I've got to take care of a production line stop situation. Those are > > always fun. Grumble. > > > > -- > > Regards, Joerg > > > > http://www.analogconsultants.com/ > > the interesting real life behavior of spark plugs is... > > if you have a "fouled" plug" that the car cannot fire.... > > sometimes adding another spark gap in series with the fouled plug will > allow the car to fire the fouled plug. > > It seems that if the coil is connected directly to the fouled plug, it can never develop enough voltage to fire. > > But if a second gap is inserted in series, then the coil CAN develop the voltage and when it fires, both gaps will arc. > > I discovered this quite by accident. Back in the late 60's I had a car that was mis firing on one cylinder. The standard troubleshooting procedure called for removing the wire from one plug one at a time and the one that makes no difference is the bad one. I noticed as I was putting the wire back on, when I held the wire close to but not attached, an arc would jump and the car would run better. I latter found they actually made small inline gaps just for that purpose. >many cars run wasted spark with two plugs in series
Reply by ●June 6, 20182018-06-06
On 2018-06-06 11:08, makolber@yahoo.com wrote:> >> >> Now I've got to take care of a production line stop situation. >> Those are always fun. Grumble. >> >> -- Regards, Joerg >> >> http://www.analogconsultants.com/ > > the interesting real life behavior of spark plugs is... > > if you have a "fouled" plug" that the car cannot fire.... > > sometimes adding another spark gap in series with the fouled plug > will allow the car to fire the fouled plug. > > It seems that if the coil is connected directly to the fouled plug, > it can never develop enough voltage to fire. > > But if a second gap is inserted in series, then the coil CAN develop > the voltage and when it fires, both gaps will arc. > > I discovered this quite by accident. Back in the late 60's I had a > car that was mis firing on one cylinder. The standard > troubleshooting procedure called for removing the wire from one plug > one at a time and the one that makes no difference is the bad one. I > noticed as I was putting the wire back on, when I held the wire close > to but not attached, an arc would jump and the car would run better. > I latter found they actually made small inline gaps just for that > purpose. > > Nothing is ever simple. >The redneck solution would have been to strap a piece of wood across the area and lash that one plug connector to it so that it just fires, and call it a day. "Hey look, I fixed it!". -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●June 6, 20182018-06-06
On Wed, 06 Jun 2018 11:34:09 -0700, Lasse Langwadt Christensen wrote:> onsdag den 6. juni 2018 kl. 20.09.01 UTC+2 skrev mako...@yahoo.com: >> > >> > Now I've got to take care of a production line stop situation. Those >> > are always fun. Grumble. >> > >> > -- >> > Regards, Joerg >> > >> > http://www.analogconsultants.com/ >> >> the interesting real life behavior of spark plugs is... >> >> if you have a "fouled" plug" that the car cannot fire.... >> >> sometimes adding another spark gap in series with the fouled plug will >> allow the car to fire the fouled plug. >> >> It seems that if the coil is connected directly to the fouled plug, it >> can never develop enough voltage to fire. >> >> But if a second gap is inserted in series, then the coil CAN develop >> the voltage and when it fires, both gaps will arc. >> >> I discovered this quite by accident. Back in the late 60's I had a car >> that was mis firing on one cylinder. The standard troubleshooting >> procedure called for removing the wire from one plug one at a time and >> the one that makes no difference is the bad one. I noticed as I was >> putting the wire back on, when I held the wire close to but not >> attached, an arc would jump and the car would run better. I latter >> found they actually made small inline gaps just for that purpose. >> >> > many cars run wasted spark with two plugs in seriesThat's purely a trick to use a special ignition coil to serve two cylinders from a single CB wire using a floating HT winding that effectively puts the two spark plug gaps in series. It works best when the waste spark occurs on the exhaust stroke (on a 360 deg crank twin cylinder 4 stroke engine for example). The effect with old fashioned Kettering ignition (whether transistorised or not) on fouled plugs is merely an unexpected bonus. If you want a more foulproof system, the obvious way is to remove the dependence on coil inductance as the HT generating mechanism (flyback pulse mode) and use the coil purely as a step up transformer to the instant application of a 400v charge from a capacitor connected in series with the LT winding across a quenchable dc-dc converter which can be briefly shorted out via a thyristor which arrangement allows one full cycle of ac energy to be applied to produce some 30 to 40 kilovolts from the bare coil, reduced by the actual cylinder pressure at the spark plug points (circa 6KV at tickover to 20 or so KV at full throttle maximum torque revs). There isn't a flyback pulse mechanism for fouling induced leakage resistance to interfere with since the coil is just used as a voltage step up transformer in this case. The leakage due to plug fouling may knock a few kilovolts off the 40KV unloaded coil output but this won't stop the plug sparking at the lower breakdown voltage circa 20KV or so required to ignite the air fuel mixture. The importance of the circuit topology, capacitor charged via the coil's LT winding by the output of a quenchable dc-dc converter which is shorted out by the thyristor, is that it allows the current in the capacitor to reverse via the converter's output rectifier bridge after it hits the positive peak, allowing for a negative voltage peak on the 2nd half of the full cycle which recharges the capacitor up to somewhere in the region of 70 to 80 percent of its initial voltage by which time the thyristor has unlatched and the converter restarts to top up the capacitor in plenty of time for the next sparking pulse. Replacing the function of the CB points in the old Kettering setup with a high voltage switching transistor is so last century (and, oh so shit). -- Johnny B Good
Reply by ●June 6, 20182018-06-06
Lasse Langwadt Christensen <langwadt@fonz.dk> wrote:> at idle and low loads there isn't much pressureQ: Why should there be any difference? The compression ratio doesn't change. When you measure the cylinder compression, it is a static measurement at low rpm. The engine is cranked over by the starter. Variations between cylinders indicates leakage from intake or exhaust valves or worn rings, or a blown head gasket. High loads means more fuel and air enters the cylinders. If the cylinder pressure increased, it would start acting as a diesel. This is called knock and can be very destructive. Most cars have a knock sensor to prevent damage. Also, diesel engines idle fine. This means the cylinder pressure is adequate to ignite the fuel. Why should it change at operating rpm?
Reply by ●June 6, 20182018-06-06
onsdag den 6. juni 2018 kl. 21.38.54 UTC+2 skrev Steve Wilson:> Lasse Langwadt Christensen <langwadt@fonz.dk> wrote: > > > at idle and low loads there isn't much pressure > > Q: Why should there be any difference? The compression ratio doesn't change. > When you measure the cylinder compression, it is a static measurement at low > rpm. The engine is cranked over by the starter. Variations between cylinders > indicates leakage from intake or exhaust valves or worn rings, or a blown > head gasket.because the throttle is closed so the manifold is at vacuum. When doing compression test you need the throttle wide open> > High loads means more fuel and air enters the cylinders. If the cylinder > pressure increased, it would start acting as a diesel. This is called knock > and can be very destructive. Most cars have a knock sensor to prevent damage. > > Also, diesel engines idle fine. This means the cylinder pressure is adequate > to ignite the fuel. Why should it change at operating rpm?diesel engines don't throttle the air they just meter the fuel
