Advanced automotive ignition systems

Spark ignition engines utilize ignition systems that can develop up to about 30 kV for breakdown of the spark plug gap and typically deliver current levels in the range of 30 to 100 mA. Measurement and analysis of these systems show that the energy transfer efficiency is very low, typically in the order of one percent (1%) or less. This operating level is adequate for older and most modern engines, but will not meet the needs of future lean burn and some alternate fuel engines that require higher energy discharges to effectively ignite the air/fuel mixtures. To meet the requirements for increased ignition power and energy, ignition systems will have to be designed to operate at higher transfer efficiencies. There are two basic approaches to increasing the electrical efficiency of ignition systems. The first is to utilize peaking capacitors across the spark plug. The second is to design and utilize a more efficient discharge circuit in combination with a low resistance spark coil. A third alternative would be to utilize a combination of both. By the first method, transfer efficiency can be increased to nearly fifty percent (50%). By the third, transfer efficiency can be seventy-five percent (75%) or more. This paper summarizes the results of high power ignition experiments and related analyses, for so-called "breakdown ignition" conditions. The paper includes descriptions of both conventional system up-grades and a new higher energy system that features multiple drivers and an energy recovery circuit. It does not include analyses or experiments for arc or glow discharge conditions.