When a switch opens, a current drops to zero, but not a voltage.
The voltage across the switch is known to be zero only when the
switch is closed.
The automobile spark coil has switch, battery, and primary
(solenoid) winding which are in series. When the switch is
closed, the battery is in series with the solenoid (and maybe
a ballast resistor, but that's a minor detail). That puts
a voltage across the solenoid, which causes a rising electric
current. At this time, the secondary (solenoid #2) carries
no current, but that is about to change. The primary current
magnetizes the iron core of the 'transformer' which is
the spark coil. Magnetization of the iron stores up energy,
just as charge in a battery does.
When the switch is opened, the CURRENT in the primary winding
goes to zero, and the magnetized iron in the coil starts to
demagnetize. Magnetization rising caused about +12V across
the primary, and magnetization dropping causes about -12... then
-120... then -300V on the primary. Meanwhile, the secondary
is just as much an induction winding on the core as the primary
was, and it gets its own (rather higher) voltage, up to
-40,000 V, because it has more turns around the core (of finer
wire) than the primary did.
Then another switch closes. The 'other switch' is the least-insulated metal-to-ground part of the secondary circuit, and
it only closes in the sense that it ceases to block current.
There's now a small lightning-bolt, and a conductive blob
of ionized gas, in a small gap between the spark plug electrodes.
Now, the voltage on the secondary drops as the current
flows in the direction that demagnetizes that iron core,
and when there's no longer enough voltage to keep the
gap filled with ionized (conducting) gas, the spark winks out.
would a diode in circuit 1 prevent the Lenz current?
Yes, a diode in the primary circuit WOULD prevent the spark
current, by being a switch that closes at much lower voltage
(about -1V on the primary, when perhaps 130V is across the
secondary). The diode could be either across
the primary of the coil, or from the primary to the battery
(i.e. across the switch); the battery voltage is only a small
difference from ground.
With the diode acting as clamp, the primary voltage swings from
+12V to -1V, the secondary ranges from +1500 to -130, and
the spark plug doesn't fire. Without the diode, the secondary
would see +1500 to -40,000V, and a spark is born.