This paper discusses the results of combustion duration and performance characteristics of a hydrogen-ethanol dual fueled engine. The tests were conducted on a compression ignition engine (modified to run on spark ignition mode) fueled with hydrogen-ethanol dual fuel combination with different percentage substitutions of hydrogen (0-80% by volume with an increment of 20%) at a constant speed of 1500 rpm and a load of 100% in kW by adjusting the loading switches. The various engine operating parameters like compression ratio, equivalence ratio, spark timing, and engine's performance parameters like brake power, brake specific fuel consumption, brake mean effective pressure, andbrake thermal efficiency effect on combustion duration were studied. The best operating conditions were obtained at a compression ratio of 11:1 and the optimum fuel combination was found to be 60-80% hydrogen substitution to ethanol.For better performance in terms of power and economy, it was found from the present study that the combustion duration has to be in between 35 to 42 0 .