A series of experiments were performed to investigate the effect of ignition energy (E_ig) and hydrogen addition on the laminar burning velocity (S_u⁰), ignition delay time (t_delay), and flame rising time (t_rising) of lean methane−air mixtures. The mixtures at three different equivalence ratios (ϕ) of 0.6, 0.7, and 0.8 with varying hydrogen volume fractions from 0 to 50% were centrally ignited in a constant volume combustion chamber by a pair of pin-to-pin electrodes at a spark gap of 2.0 mm. In situ ignition energy (E_ig ∼2.4 mJ ÷ 58 mJ) was calculated by integration of the product of current and voltage between positive and negative electrodes. The result revealed that the S_u⁰ value increases non-linearly with increasing hydrogen fraction at three equivalence ratios of 0.6, 0.7, and 0.8, by which the increasing slope of S_u⁰ changes from gradual to drastic when the hydrogen fraction is greater than 20%. t_delay and t_rising decrease quickly with increasing hydrogen fraction; however, t_rising drops faster than t_delay at ϕ = 0.6 and 0.7, and the reverse is true at ϕ = 0.8. Furthermore, t_delay transition is observed when E_ig > E_ig,critical, by which t_delay drastically drops in the pre-transition and gradually decreases in the post-transition. These results may be relevant to spark ignition engines operated under lean-burn conditions.

The use of syngas derived from biomass gasification as fuel for internal combustion engines presents significant challenges due to the presence of harmful impurities. However, syngas combustion offers an effective heat supply solution for external combustion engines, such as Stirling engines. This report details the design, fabrication, and testing of a gasifier-stirling engine system using rice husk-derived RDF as fuel. Rice husks are compressed into honeycomb-shaped pellets to improve biomass storage and enhance gasification efficiency. The Stirling engine can be heated directly by the combustion of RDF pellets or indirectly by syngas produced through the gasification of RDF in the gasifier. Initial results indicate that the difference between the simulated and experimental combustion temperatures of RDF is approximately 13%. The gasifier-Stirling engine system has been fully designed and manufactured, ready for testing in the next phase of experimentation.