<p>Utilisation of biofuels in internal combustion engines is a promising method to resolve environmental pollution. In this context, an experimental investigation was carried out on an ethanol (E100) fueled single-cylinder, four-stroke spark ignition engine to find out efficiency improvement and emissions reduction avenues using increased compression ratio and oxygen-enriched air for combustion. Tests were conducted at a base compression ratio (CR) of 9.8 and an increased CR of 10.6, with results compared against baseline gasoline operation. The air was enriched by 30% (by mass) by injecting oxygen into the intake manifold of the engine. The results indicate that with oxygen-enriched air, the maximum in-cylinder pressure increased significantly and the heat release rate increased by more than 27% at both compression ratios. With oxygen enrichment at the high compression ratio, cycle-to-cycle variation with COV_IMEP was 1.55%, and the combustion duration decreased significantly (more than 9%) with E100. The brake thermal efficiency of the engine increased to 21.7% with E100, which was 16% with base gasoline. Carbon monoxide and hydrocarbon emissions were reduced to ultra-low levels with oxygen enrichment, while nitric oxide emissions increased by more than 50% due to elevated in-cylinder temperatures. These findings demonstrate the potential of combining ethanol fuel, oxygen-enriched combustion, and higher compression ratios to improve engine efficiency and reduce most harmful emissions.</p>