Spark Ignition - Searching for the Optimal Spark Profile

The impact of different spark designs on the ignition and combustion stability is studied using a 13-liter CNG fueled heavy duty spark ignited engine to search for the “optimal” spark design. Experimental results show that robust ignition can be achieved using a significantly shorter spark duration and lower energy than expected. A capacitive discharge ignition (CDI) system enabled to separately control the available spark voltage, current and duration (FlexiSpark® CDI) was compared to a standard CDI system without spark control and an inductive discharge (IDI) ignition system. Typically, a robust ignition can be provided using only 5% of the spark duration and 17% of the spark energy compared to that required by an IDI system to accomplish an equivalent ignition and combustion stability. By applying control of the spark, a robust ignition can be provided which is optimized for the fuel, the engine design, the engine operating condition, and the condition of the spark plugs. This offers a potential to significantly reduce the spark-plug wear and the total cost of ownership without compromising engine performance. The results are especially interesting in the view of hydrogen fueled SI-ICE, where the required available spark voltage is high, but the required spark energy is low. It is desirable to use a spark design with just enough voltage and power to initiate a sustainable combustion, but with minimal energy not to excessively wear and heat the spark plug electrodes to avoid preignition.