The need for reduction of harmful emissions in engines has lead to research of new combustion models. One of those models is Dual-fuel which uses natural gas and diesel fuel. Dual-fuel works similarly as conventional Diesel engine which uses self-ignition to start combustion of fuel and air, but the main difference between Dual-fuel and conventional Diesel engine is that the Dual-fuel can use natural gas as a fuel. Natural gas is ignited by the use of small amount of diesel fuel which is injected into the cylinder to start the ignition and combustion of the natural gas and air mixture. Advantage of Dual-Fuel engine is reduction of harmful emissions and rise in efficiency at higher loads which parallels the efficiency of conventional Diesel engine. Main disadvantage is the obvious drop in efficiency at lower loads. The Chair for Engines and Motor Vehicles has been researching the Dual-fuel combustion in their laboratory on the modified experimental engine. Measurements were made on the engine using sensors for many different parameters which differently effect dual fuel combustion. From many measuring points, 16 of them were chosen for further analysis using simulations. The simulations of those points need to be validated which means that the deviation between the simulation and the real Dual-fuel, which was measured, is low so that there are no discrepancies, or they are minimised. Then further analysis can be conducted. The energy loss will be analysed and accoriding to them conclusions will be made. The impact of energy loss on Dual-fuel efficency is observed.