COP Ignition System

My past ignition systems use the waste fire approach.  Waste fire is direct fire eliminating the distributor from the spark path.  The waste fire system fires two plugs in series, one to ignite the cylinder on combustion stroke, the other on exhaust stroke.

A COP or "coil on plug" ignition is also direct fire, but has one coil per plug.  The advantage is correct spark polarity on all plugs, and reduced high tension plug wire lengths.  The specially designed coil with magnetic bias reduces the coil size and weight.  The low coil inductance results in less charge time, so multi-spark is possible at low RPM.

Development started with the purchase of eight coils.  A test system was quickly developed in an afternoon, to evaluate the coils by making sparks.

The part on the left is the plug boot, the spring is the internal connector between the coil and plug.  In some applications a short spark plug cable will connect the coil to plug, where it is not readily possible to directly mount coil on plug.  The circuit on the right is a micro controller board used for test purposes to drive the coil and make a complete ignition system, along with additional components.

To test a coil, a circuit with an IGBT was constructed on a heat sink.  The Nano controller was programmed to deliver timed pulses to the plug, with settings for time intervals via USB serial connection on Netbook.  A 13.8V lab supply powered the system.  At the left is the plug and coil.

The scope shows the current ramp, that resembles an incline in yellow, the blue is the coil primary voltage.  The scope was used to measure the ramp time to desired peak current.

Next the test circuit was expanded for multi-strike capability. When the ignition period is reduced by recharging the coil, the coil has stored energy, so the next charge takes less time. Show is a 3-strike waveform.

A distributor was modified by replacing a variable reluctance sensing coil and reluctor, with a shutter wheel and optical sensor.  Code was written to decode the shutter and use the signal for timing reference. Additional code was written for electronic spark advance control.  The control is RPM and MAP based, with real-time user adjustable tables.

Seven of the eight ignition events are shown, the bottom trace is the distributor reference signal.  The RPM is increasing from low to high at a fast rate.

Below is an example of low RPM multi-spark drive signals.

Top side with wires installed.

Finished prototype.