Controlling Onset of Heat Release by Assisted Spark Ignition in Hydrogen HCCI Engine Supported by DME Supplement

The results of our previous study showed that applying hydrogen (H₂) to homogeneous charge compression ignition (HCCI) combustion with the assist of di-methyl ether (DME) as a supplement improved thermal efficiency compared with homogeneous hydrogen-fueled spark ignition (SI) combustion [1, 2]. As a general characteristic of HCCI combustion, however, stable engine operation is limited to a narrow region by the occurrence of misfiring and abrupt combustion like knocking. The onset of heat release is still not sufficiently controllable to achieve optimum engine performance.

The objective of this study is to control the onset of the main heat release of hydrogen-fueled HCCI combustion by adopting spark ignition to assist autoignition. The results showed that improved thermal efficiency and reduced combustion fluctuation were achieved by attaining MBT operation with the support of spark ignition. Spark-assisted hydrogen-fueled HCCI combustion displayed stable operation under a leaner mixture condition and knocking-free operation under a richer mixture condition by reducing the DME mixing rate. As a result, the stable operating range was expanded with improved output power. In short, improved thermal efficiency, increased output power and an expanded stable operating range were simultaneously achieved through the assistance of spark ignition in a hydrogen-fueled HCCI engine with a DME supplement.