Effects of Hydroxy Gas Addition on the Performance and Emission Characteristics of Liquefied Petroleum Gas-Powered Lean-Operated Spark-Ignition Engine

The effect of hydroxy (HHO) gas or Brown gas addition as a secondary fuel on the performance, exhaust emissions, and lean operation limit of a spark-ignition (SI) engine was experimentally investigated in this study. The tests were performed on a single-cylinder liquefied petroleum gas (LPG)-fueled four-stroke lean-operated SI engine. HHO gas was obtained by electrolysis using an electric current to dissociate the water molecules. The generated HHO gas was directly sent into the cylinder by mixing with the fresh air in the intake manifold without any modification and the need for storage tanks. The results showed that HHO gas addition increased the brake thermal efficiency (BTE) by 12.97% and decreased the brake-specific fuel consumption (BSFC) by 11.17%. The exhaust emission results showed that HHO gas enrichment caused an 8.72% reduction in carbon monoxide (CO) and a 21% reduction in unburned hydrocarbon (HC), while a 6.42% increment in nitrogen oxides (NO_x). The results indicated that the addition of HHO gas also increased LPG’s lean operation limit and extended the relative air-to-fuel ratio from 1.35 to 1.56. On the other hand, it was determined that the power consumed to split water (H₂O) into HHO is greater than the power gained from the combustion of the HHO in the cylinder. However, HHO gas can play a significant role in reducing exhaust emissions despite its high energy expenditure.