Six-stroke spark-ignition engine fuelled with high-hydrogen content fuel: a theoretical thermodynamic analysis

This work presents a thermodynamic analysis of a six-stroke cycle implemented in Spark-Ignition (SI) engines. The cycle configuration comprises two distinct combustion phases: (1) initial combustion of a methane-hydrogen mixture under fuel-lean conditions (λ > 1), yielding exhaust gases containing residual oxygen, followed by (2) secondary hydrogen injection during the expansion phase to facilitate complete utilization of the remaining oxidizer. The investigation evaluates the system's thermodynamic performance through parametric variation of both the fuel composition (methane/hydrogen, CH₄/H₂ = 3.0 showed the highest cycle efficiency at 50.73%, indicating the best performance among all cases. According to the data, better performance can be achieved by optimizing cycle parameters such as regeneration, intercooling, pressure ratios, and component efficiencies in addition to raising the maximum temperature. In conclusion, better outcomes are not always guaranteed by higher temperatures. Increasing thermal input alone is not as important as designing and optimizing cycles efficiently.lratio) and the equivalence ratio during primary combustion. The results obtained indicate that the changes in the peak temperature of the second part of the cycle are small, up to 60 K relative to the mean value. The fuel mixture with.