-In the present study, a variable compression single cylinder diesel engine was used to study the effects of oxygen enrichment on the performance of engine at different compression ratios (C.R.) from 16.5 to 19.5 at different loads and compared to the amount of additional oxygen in four different rates from 1L/min to 4L/min. Oxygen cylinders were connected to intake manifold with throttle valve to supply additional oxygen. Enrichment of oxygen favours combustion in many performance parameters so the tests were carried out for the brake power (B.P.), Mean effective pressure, (P mef ), specific fuel consumption (S.F.C.), Mechanical efficiency (η mecheff ) and exhaust gas temperature (E.G.T.). The purpose of this study is to deal with the major technological characteristic of enriched oxygen used in variable compression ratio single cylinder diesel engine for best possible values of secure engine limits. The test results show that the combustion performances were enhanced as there was increase in B.P., P mef and decrease in S.F.C. and increase in rate of oxygen in intake air increases the charge burning rates and flame combustibility resulting higher exhaust gas temperature. Overall mechanical efficiency in lower compression ratio was high but for higher compression ratios there was a drop in mechanical efficiency. Keywords -Oxygen Enrichment, Variable Compression Ratio, Brake Power, Specific Fuel Consumption, Exhaust Gas Temperature.I. INTRODUCTION In diesel engine combustion, ratio of fuel varies according to load requirements, so principle of using air in diesel engines says that excess air improves mixing rates but at the time of exhaust, it also carry heat at higher rates which affect the thermal efficiency of each cycle. In the mixture of fuel and air in small diesel engines mixing rates depend on many designs and operating variables and those variables will affect the performance of any engine. According to research under the subject of oxygen enrichment, it results that a certain level of oxygenation can improve the mixing rates to increase the performance and reduce the certain amount of emissions [1] [5] .The investigation and research in this field are very vast and conclusive in many respects. All results show a considerable increase in oxides of nitrogen and decrease in smoke, carbon monoxides and unburned hydrocarbons as the ratio of oxygen increases. Reduction in engine noise due to elevated oxygen level in induced air is also concluded by researchers [4] . Higher oxygen concentrations increase the mixtures' burning rate at the same compression ratio and low quality fuel can also be used in engines without much affecting the performance. The main drawback of oxygen enrichment is higher level of oxides of nitrogen in exhaust due to increased maximum pressure in combustion chamber. The efforts of many researchers conclude a range of percentage of maximum concentration of oxygen in intake is 30% by volume in which both particulate matters and oxides of nitrogen can be reduced for a fixed geome...