The Effect of Hydrogen Addition on Ignition Delays and Flame Propagation in Spark Ignition Engines

Abstract

The results of an experimental investigation of the effect of supplemental hydrogen (up to 30 percent of the total fuel energy) on the combustion process in a CFR engine are reported. The hydrogen was added under otherwise constant conditions so that chemical properties were varied under constant hydrodynamic conditions. Calibrated cylinder pressure traces, averaged over many cycles, were incorporated into a two-zone thermodynamic analysis to determine the mass fraction burned as a function of crankangle. The techniques employed enabled changes in the induction period and combustion duration of the order of 0.1 ms to be resolved. The added hydrogen resulted in significant reductions in ignition delay or induction times, especially in lean mixtures. Reductions were greater with increased fractions of hydrogen. Once a turbulent flame was well established, the hydrogen had a relatively small effect on the burning rate. The results are consistent with a description of the combustion process which includes an induction period dominated by chemical dynamic effects and a turbulent burning period dominated by turbulent transport effects. Added hydrogen also led to improved efficiency and less cycle-to-cycle pressure variations.