Experimental and simulated results detailing the sensitivity of natural gas hcci engines to fuel composition

Natural gas quality, in terms of the volume fraction of higher hydrocarbons, strongly affects the auto-ignition characteristics of the air-fuel mixture, the engine performance and its controllability. The influence of natural gas composition on engine operation has been investigated both experimentally and through chemical kinetic based cycle simulation. A range of two component gas mixtures has been tested with methane as the base fuel. The equivalence ratio (0.3), the compression ratio (19.8), and the engine speed (1000 rpm) were held constant in order to isolate the impact of fuel autoignition chemistry. For each fuel mixture, the start of combustion was phased near top dead center (TDC) and then the inlet mixture temperature was reduced. These experimental results have been utilized as a source of data for the validation of a chemical kinetic based full-cycle simulation. Results reported here clearly demonstrate the ability of a thermo-kinetic, single-zone model to capture the fuel composition effects seen in the experiments. The uncertainty that exists in both the experiment and simulation is discussed in light of the model predictions. This uncertainty is used to quantify what reasonable level of accuracy can be expected between a model and experiment under HCCI operation. Finally, the simulation has been further exercised to compute the sensitivity of ignition timing to changes in hydrocarbon composition outside what has been experimentally tested.