The fossil fuel reserves are decreasing due to increase in consumption of diesel, hence there is a need to develop alternative fuel. Hydrogen is considered as one of the best alternative fuels for internal combustion engines because of unique combustion properties. For Compression Ignition (CI) engines, it is impossible to get hydrogen to its auto-ignition temperature by compression alone. Hence, an attempt is made using hydrogen as an air enriched medium with diesel as main fuel. Experiments are conducted to study the effect of piston geometry on the emission characteristics of diesel engine enriched with hydrogen at different flow rates such as 2 litres per minute ( lpm), 4 lpm and 6 lpm on four stroke single cylinder diesel engine at constant speed of 1500 rpm for different loads. Knocking tendency is observed for flow rates above 6 lpm at all loads due to raise in temperature and peak pressures with addition of hydrogen. The emissions for diesel engine enriched with hydrogen are reduced to 27.1%, 37.5% and 18.8% of Unburnt Hydro Carbons (UHC), Carbon Monoxide (CO) and smoke density respectively. However, there is 14.9% increase in Oxides of Nitrogen (NOx) emission due to high combustion temperatures by hydrogen induction. Further, the experiments are conducted with toroidal piston bowl geometry for different flow rates of hydrogen without change in compression ratio. The effect of this change on emission parameters is further reduced to 6.9%, 13.6%, 11.6% and 3% in UHC, CO, smoke density and NOx respectively.