Prasetya, Theodorus Rendy, et al. “Performance of Four Step Engine Generator Set With Oxy-Hydrogen (HHO) Fuel from Water Electrolysis Process Using Vacuum Valve Carburator”. Journal of Renewable Energy and Mechanics, vol. 5, no. 02, Sept. 2022, pp. 76-87, doi:10.25299/rem.2022.10058.