Determination of the influence of the fuel in use on engine parameters, efficiency, exhaust emissions, injection system functionality, etc. Tests of injector nozzle clogging, comparisons of fuels and additives (for engine clean-up or higher performance) and durability tests are performed. Depending on the test type, suitable specialist apparatus is used; for example, a fuel consumption meter together with a fuel conditioning system, exhaust analyzers or opacimeters. Engine dynos are equipped with lines supplying the engine with liquid and gaseous fuels. When needed, there is the possibility of combining fuels or additives in order to achieve the desired mixture. Analyses of the chemical composition of fuels, fuel mixtures or sediments formed during the fuel combustion process are performed on site, greatly improve the analysis of results and the testing process.