Advanced Plasma and Variable Spark Ignition System IAV 2 nd Ignition Converence , Berlin , November ’ 14

Stable ignition in internal combustion engines under lean or high EGR (exhaust gas recycling) is difficult to achieve with current spark ignition systems. North-West University has developed a novel ignition system to improve ignition by generating a high energy plasma over a larger volume. The plasma is either generated by a corona discharge only, called the Advanced Plasma Ignition (API), or with both a corona and spark discharge, called Variable Spark Ignition (VSI). Although corona ignition systems are not new, API and VSI make use of several novel, patented components to achieve a compact, inexpensive and reliable system. The system consists of three main components, a novel corona plug, a compact high voltage transformer and a robust drive circuit. It is designed to have a similar size, weight and material cost as conventional pencil coils. The high voltage transformer is driven at its resonance frequency to generate a high output voltage (up to 40 kV) of several MHz. The output voltage first generates a corona inside a ceramic cavity. Thereafter the corona plasma is further heated and ejected into the combustion chamber away from the corona plug. Depending on the configuration of the ground electrode, the corona will either continue to grow away from the corona-plug (API) or towards the ground electrode forming a spark (VSI). The corona plug has no sharp metal points exposed in the combustion chamber and no electrodes that obstruct the flame front. The system actively controls the amount of power that is delivered to the plasma depending on the plasma resistance within less than a micro second. For corona ignition (API), sparking is undesired and the system is configured to temporarily suspend power transfer the moment a spark is formed and then resumes again when the conduction channel disappears. To operate the system, 200 V DC power and a digital enabled signal has to be supplied. The system is able to generate several short (<100us) corona or spark discharges per ignition cycle or to grow and sustain one or several corona discharges or sparks for several milliseconds, as determined by the enabled signal. To minimise costs, the high-voltage transformer has only a few metres of copper wire wound on a non-magnetic core and relatively inexpensive components are used in the drive circuit. For reliability, a simple, analogue, self-oscillating drive circuit is used, which make use of a novel, patented technique to protect the semiconductors. The complete system has a diameter of 20 mm, length of 24 cm and can deliver up to 1 J into a 100 kΩ plasma, with more than 50% efficiency. 1. System Description The Advanced Plasma Ignition (API) consists of a corona plug, transformer and drive circuit PCB, as shown in Figure 1. Figure 1: Photo of API prototype and its main components. 200 V DC power is supplied on the power input and a digital signal on the Enabled input switch the system on and off. When in the on state, the drive circuit drives the primary winding of the transformer at a resonance frequency. A high voltage of several MHz is generated on the secondary side which is connected to the inner electrode of the corona plug. The corona plug is configured such that a high electric field is generated at the tip of the inner electrode. A corona discharge from the inner electrode into the combustion chamber then takes place. The corona is sustained for the duration of the enable pulse, which may range from a few microseconds to several milliseconds. Multiple corona discharges can also be performed in a single ignition cycle by giving more than one enable pulse. The system makes use of five novel concepts: A corona plug (patent pending) which generate the corona inside a ceramic cavity and then ejects the warm plasma into the combustion chamber A resonant drive [1] that drive the primary winding at a resonance frequency of the secondary winding in order to achieve a high voltage using a weakly coupled transformer. A push-pull drive circuit [2] where inexpensive transistors can be driven reliably at high frequencies. A spark quenching mechanism (patent pending) where power transfer is immediately suspended when a spark occurs. A segmented-core transformer [3] to achieve a low-loss, compact coil with a large energy density when the system is adapted for a conventional sparkplug.