Study of the performance and exhaust emissions of a spark-ignited engine operating on syngas fuel

Abstract

To resolve the problem of depletion of petroleum based liquid fuels, various solutions have been proposed. One of them is the use of gaseous fuels that are generated from the gasification of woods, namely syngas or wood-gas fuels, as full supplement fuels in spark ignition internal combustion (IC) engines. This fuel consists of nearly 40% combustible gases, mainly hydrogen and carbon monoxide (CO), while the rest is non-combustible gases. In the present work, a comparison between experimental and computed results is presented for a conventional natural gas, spark-ignited engine, fuelled with syngas instead of natural gas fuel. For the theoretical investigation, a computer model is developed that simulates the syngas combustion processes in a conventional natural gas, spark-ignited engine. The combustion model is a two-zone one, where the combustion rate of syngas fuel depends on the velocity of the flame front that forms around the area of the burning zone and then spreads inside the combustion chamber. The flame front development takes into account the history of pressure and temperature inside the chamber and the local composition, in order to estimate the flame velocity. An equilibrium model is used to determine the concentration of the chemical species involved, the extended Zeldovich mechanism is used to determine the concentration of nitric oxide (NO) and a CO kinetics scheme is used to estimate the CO emission. To validate the predictive ability of the model, experimental measurements are used from the operation of a multi-cylinder, four-stroke, turbocharged, spark-ignited engine fuelled with syngas fuel, with the measurements corresponding to various values of the air to fuel ratio (load). The experimental results are found to be in good agreement with the respective computed ones obtained from the computer model. Comparing the computed results when operating the engine with natural gas as against syngas fuel, a serious effect of the syngas operation on the cylinder pressure diagrams and the engine brake efficiency is revealed, for all test cases examined. Moreover, as far as pollutant emissions are concerned, the use of natural gas instead of syngas has a positive effect on both NO and CO emissions (reduction).